HomeMy WebLinkAboutAPA3417J. . SUSITNA
HYDROELECTR .. IC PROJECT
FEDEti.AL ENERGY REGUt~ATORV COMM.ISSION.c
PRGJE.CT No. 7114
DOWNSTREAM AQUATIC
IMPACT ASSESSMENT R·EPORT
PREPARED BY
ENTRIX,INC.
UNDER CONTRACT TO
lW~).:~?£~~~~~~~@
SlJSilN,A JOINT VENTURE
DRAFT REPORT
FEBRUARY 1986
DOCUMENT No. 3417
...__ ___ Alask~'fl Power Authority -,, .. -------
NOTICE
ANY QOBSTIONS OR COMMENTS CONCERNING
THIS RBPORT. SHOULD BB DIRECTED TO
THE ALASKA POWER AOTBORI'l'Y
SUSITRA PROJECT OP~ICB
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2.0
3.0
TABLE OF CONTENTS
INTRODUCl'ION-•••••••• ~--., •.•.•••.••••• _ •••• ~ ••• e •• ~ ••• ·e ••••••••••••.•• (i ~ •• • • •
1 • 1 Backgroun.d •.••••••••••••••••••••••••••••••• • ••• • • • • • • • • • • •· Q • • • • • •
1. 2 Project Are.a, .................................................. ~ .• , •••••
1·.3 Organization ............... ; •••.• !'· ••••••••••••••••••••••••••••••••
PROJECT DESCRIPTION AND SCHEDULE ••••••••• ; •••••.•••.••• ~ .......... • • • • ..
2.1 Stage I -Watana Initial Reservoir ....... · ........................ .
2 .. 1.1
2 .. 1.2
2 .. 1.3
2.1.4
2.2 Stage
2.2.1
2.2.2
2. 2 .• 3
2.2.4
2.3 Stage
2.3.1
Construction ••••.•••••••••••• ~······················~····
F1111og~··•••~••••••••••••••••••••••••••••c••••••••••···~
Testing and, Conwn1~si oni ng ................. ., ................. .
Operation .• •: -o •••• ~ ••••• , •••••••• Cl ~ •• ~ ........... .,. .... o ••••.•••
I I -Devil Canyon ................................ !» •••••••••••
Construction ••••••••.••.•••••• ·'• ........................... .
Filling ••••••• G;······~·····~····~·········~····~········ Testing and Co11111issioning •••••••••••• ., •.•••••••••••••••••
Operation· •• t.: ............. , •••••• ~ ••••••• ,~ ••• c ••.•••• It ••••••••
III-Watana High Reservoir •.•••••••••••••••••••••••• ~····
Construction •••••• ~···································~·· 2.3.2 Filling •••••••••••••.•••••••••••••••••••••••••••••• ~·····
2.3.3 Testing and Conmissioning ...................... ., •••••••••••
2.3.4 Operation ................................................ .
2.4 Project Schedule •••••• ~ ••••••••••••••••••• , ••••••••••••••••• ~···
EVALUATION SPECIES •••••• • $ e • • •· e a ~ e e • e G e ~ e 9 ~ • e .• • • ~ • e ~ e ·• • e • ~ e ~ e A ~ e • • e •
Se 1 ect ion. •. • • • • • • • • • ....................... ~ .•••... ~ •••••• ~ ~ ••• --~ •
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6
7
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9
10
14
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18
20
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21
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24
27
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28
29
32
3.1
3.2 l:labitat Utilization~.'! Evaluation Species .••••••••••••••••••••••
3~2.1 Mainstem and Si~~ Channel Habitats •••••••••••••••• ~······
3~2~2 Side Slough and Upland Slough Habitats •••••••••••• ~ ••••••
36
36
39
41
47
52 3.~.3 Tributary and Tributary Mouth Habitats ............ :., ........ G.
4. 0 PHYSICAL t~HANGES RESULTING FROM. THE PROJECT •.••••••.•• ~ ............ •"·. 58
4.1 Flows and Water Levels ••••••• w •••••••••••••••••••••••••••••••••• 58
4.1.1 Mean Monthly Flows and Water Levels ••••• ~··~·····: ••••••• 59
4.1.2 Floods ••••••••• ~··············o·······~·················· 71 4.1.3 Flow Variability .......................................... 79
4.2· River .Morphology ••••••••••.•••••••••••••••••••.•••••.••.••••••••• 88
4.2.1 Watana to Devil Canyon ...................................... 88
4 .. 2.2 Devil Canyon to Talkeetna (Middle River) .......... ~.,·."~-···· 90
4.3 Water Quality ............ ·'· •• ., ••• o ••••••••••••••••••••••• ,. : ......... 95
4. 3.1 Water Temperature ......... ~ • • • • • . • • • • • • • • • • • • • • • • • • • • • • • • • 95
4 • 3 .• 2 Ice ••••••••• ~ ••••••••••••••••• _ ............................ -112
4.3~3 Suspended Sediments/Turbidity/Vertical Illumination •••••• 122
4.3.4 Dissolved Oxygen .......................................... l34
4.3.5 Total Dissolved G~s ••••••••• ~~···························l39
4.3.6 Nutrients and Organ·lcs. t• .................................... 144
4.3.7 Total Dissolved Solids, Conductivity, Significant
Ions, Alkalinity, and Metals ••• H••••n·········•••o'•••••147
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TABLE OF CONJ~NTS (Continued)
4.4 Groundwater Conditions.~~~~ ••••••••••••••••••••••••••••••••••• -, •••• 151
4. 4 .1 Watana to De vi 1 Ci.inycn ...................... o •••••••• ·~·· •••• 152
4. 4. 2 De vi 1 Canyon to T~,11 keetna ••••••••••••••••••••••••• o ....... 153
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IMPA:C1~-·ANALYS'IS ................................ , ............ ~ .................. 159
5 .. 1 Altered Flow Regime· ................................................ 159
. 5 .. 1.l Su11111ary of Physical Changes ...... ~ •• n ••••••••••••••••••••• 159
s,.l. 2 Effects on Species Habitats ................................. 162
5. 2. · River Morph·o 1 ogy .................. , .................................. 407
5. 2 .J Su~~~nary of Physical. Changes ••••••••••••••••• ~} ••••••••••• 407 ,1 5.2.2 Effects in Species \:'iabitats .••• · ............... : •............ 407 1
5. 3 Water Qua 1 i ty ................. ·•-• ., ••••••••••••••••••••••••••••••.•• 407 it
5.3 .. 1 Altered Temperature Regime ................................ 407
5.3.2 Ice ••••••• ~··············~·······························439
5.3.3 Suspended Sediments/Turbidity/Vertical Illumination •••..•. 448 _
5.3.4 Dissolved' Oxygen •. .,. ............................................ 455
5.3.5 Total Dissolved Gas Concentratjon ••••• -•.•• : .•••••••••••. 455
5 •. 3.6 Nutrients and Organics ••••• c ...................... ., .......... 455
5 .. 3.1 Total Dissolved Solids, Conductivity, Significant Ions,
A 1 ka 1 in i ty, and Meta.l s •••• ~-••••••• e ....................... 456
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Table 1.
-Table 2 ..
Table 3.
Table 4.
Table 5.
Table 6,
Table 7.
Table 8.
Table 9.
LIST OF TABLES
(S.ection 5 to be added)
Page
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Alaska Power l\uthority Susitna Hydroelectric Project Aquatic
Issues list, March 6, 1984 ••• ~·········7····-······~·········· 2
location of information pertaining to :aquatic issues within
the Aquatic Impacts and Mitigation Report Series ............. ~. • . 3
Flow constraints for environmental flow requirement
Case E-VI ••••••••••••••••••••••• ~~···························· 12
Estimated sa]mon escapements by species and locations in
the Susitna River, 1981-1984 ................................... 40
Natural and project mean monthly flows at Gold Creek~········· 64
Flood frequency at Watana during Qperation ...................... 73
Flood frequency and discharge (cfs) at Go1d Creek during
• + . t. 7.1 proJec-. opera 1 on ................................................ .
Downstream tributaries potentially impacted by pro!ect
opera't ion. ~..0 ••• ~ .••..••••••••••••••• ~ •••.••••.••••••••.••••••••••• .o· .• 92
Influence of ma i nstem flow and wate.r qua 1 i ty on
characteristics ••••••••••••• ~ ••••••••••••••••••••• .-• • • • • .. • • .• • • 93
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:~/LIST OF FIGURES
(Section 5 to be added)
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, /--:Figure 1. -The proposed sites o.f the Watana and De vi 1 Canyon dams. • • • • • • . 4
Figure 2. . lieograph 1 cal section~ fo the Sus i tna River ••••••• ~ • • • • • • • • .. • • • 5
f " .
Figure 3. E:nvi ronmenta 1 flow requirement~; ••••••••.•••• ". " .••..•• ~ c • • • • • • • • 13 • r-Figure 4. Watan~ Stage l construction schedule •••••••••.••• ~" ••.•••. ·:. 33
Figure 5. D1evil Canyon Stage Il construct1ion schedule .•.•••••••••••••••. 34
J;--, Figure 6.. Watana Stage III construction sc:hedule ••••••• , .................. 35
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Figure 7. Me.a1n weekly natural and Stage I discharges exceeded 90%, soi,.,, and 101 of the time.. • • • • • • .. • . • • • .. • . • . • • • • • • • • • • • • • • • . . • • 63
Figure 8. Me1an monthly water 1 evel s ............................. ~ • • • . • . • • • 65
Figure 9. Mean weekly natural and Stage II discharge~ exceeded 901,
50%, and 1~ of the time •.••••••••••••••.•••.•••••••.••••••••• 67
Figure 10. Mean weekly natural and early Stage Ill discharges
exceeded 9~, 50%, and 1~ of the time •••.•••••••••••.•••••.•. 69
Figure 11. Mean week.ly natural and late Stage III discharges exceeded
90%, 5~, and 10% of the time ....... ! .......................... ~. 70
Figure 12. F1ow variability at Gold Creek during Watana filling •••••••••• 75
IF i gure 13. Di schargu! and percent change of natura 1 ai•d Stage I
mean weekly flows ••••••• s~~··································· 83
Figure 14. Discharge and percent change of natural and Stage II
mean weekly flows ••••..•••.•••.••••.• '" . • • . • • • • • • • • • • • • • • • • • .. . . • 85
Figure 15. Discharge and percent change of natura] ~nd early Stage III
mean weekly flows ••. ~ ••••••••••••••••••••••••••••••••••••••••• 86
Figure 16. Discharge and percent change of natural and late Stage III
'mean week.l y flows •••••••••••••••.•••••••••••••••• " ••••••••• a • • 87
Figure 17. Natural and Stage I temperatures ••.••••.•••••.• a•e••••••······l02
Figure .. ~
.10. Natural and Stage I temperatures at RM 130 .••••••••••••••••••• 104
Figure 19 .. Natur"1 and Sta~e ... II temperatures ••••••.••••.••••••••••••••••• l06
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LIST Of FIGURES (Continued)
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Figure 20. Natural and StageD I I I temperatures .............................. 110
. Figure 21 .. · Natural and Stage I river ice conditions .......... •:-· ••••. ~~· •••• 115
Figure 22. Natura-l and Stage I I river 1 ce cond it 1 ons •••• 2 •••••••••••••••• 119
Figure 23. Natural and Stage III river ice ·conditions • .c •••••••• /i ••••••••• 121
.
Figur~:;, 24. t~aturally o~,~curring turbidity vs .. suspended-sediment .
1l · concentration for rivers and lakes in Alaska ••••••.•.••• " •••••• l24
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Figure 25 .. Suspended sediment rating-curve at USGS gaging station
Susitna River near Cantwell, Alaska ••• , •..•.••.••••.•••.•••.••. l25
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1.0 INTROOUCTIOB
· 1.1 Backqroung
"sirtce the \original License Application for the proposed Susitna Hydroelectric
Project was filed before the FERC in February 1983, the, APA has engaged in
extensive consultation with interested agencies wittf the common goal of
identifying the project's environmental impacts, i.mproving project design and
operation, and cooperatively resolving as many issuris-as possible. By March
1984, the APA, i.n. conjunction with the state, fed era 1 and 1 oca 1 resource
agencies, identified 56 is~ues ranging from minor concerns to signifi.cant
resource utilization issues. These issues have provided a mechanism for the
APA, appropriate resources agencies and concerned citizens to focus nn
environmental impact analyses and mitigation planning.
Twelve of ths 56 issues are related to fisheries concerns or other effects on
aquatic resources (Table 1). These 12 aquatic issues are addressed in a four
volume Aquatic Impact and Mitigation Report Series. The location of specifi~
volume coverage fo~ each issue is provided in Tab1e 2. As indicated in Table
2, this report addresses issues related to physical changes downstream from
the proposed dams. Downstream issues are further defined within the report.
1.2 Project Are~
The Susitna River is a large, glacial-fed river located within the northern
portion of Southcentral Alaska. The sites of the proposed Watana and Devil
Canyon dams ara located in the upper Susitna River basin., The basin is
bounded by the Talkeetna Mountains to the southeast and the ,Alaska Range to
the north and west (Figure 1) . The Watana dam wi 11 be sited betw~een river
mile (RM) 184 and !tM 185; the Devil Canyon dam will be built 32 miles
downstream at approximately RM 152. Geographical designations for sections of
the Susitna River that would be affected by the project include the
impoundment zone, middle Susitna River, and lower Susitna River (Figure 2).
The impoundment zone includes those portions of the Susitna River that would
be inundated following construction of each of the clams. The middle Susitna
River refers to the reach of the Susitna River between Devil Canyon and its
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Ta~le I. Alaska Power Authority Susitna Hydroelectric Project Aquatic Issues
List, March 6, 1984.
F-1. Significance of altered flow regime on salmon and resident fish
habitats and populations downstream of the dams, including effects on
migration/access, spawning, and rearing during summer months, and
effects on incubation and rearing during winter months.
F-2. Significance of changes in water quality para'Jieters {turbidity, pH,
heavy metals, dissolved nitrogen, tel\11perature, nutrients} on salmon and
resident fish habitats and popul atior:.1s downstream of the. dams,.
F-3. Signifi'cance of altered ice processes on sa1rnuil and resident fish
habitats and populations downstream of the dams, including effects on
fish access and changes due to staging. -
F-4. Significance of changes in stream morphology on salmon and resident
fish habitats and populations dowk,stream of the dams.
F-5. Significance of impoundment effects on resident fish habitat and
populations upstream of the dams.
F-6. Significance of physical effects of access corridors on fish habitats.
.
F-7. Significance of physical effe~ts of transmission line corridors on fish
habitats ..
F-8. Significance of water quality and quantity effects of construction camp
and permanent village on fish habitat~.
F-9. Significance of water quality and stream morphology effects of borrow
and spoil areas on fish habitats.
F-10. Significance of disturbance effects of human instream activities tln
fish.
F-11. Feasibility and desirability of specific mitigation options, including
structural modifications, flow allocation, physical habitat
modification, hatcheries, and management options.
F-12. Formulation and implementation of post-construction plan to monitor
significant impacts and the efficacy of specific mitigation measures.
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Table 2. Location of information pertaining to aquatic issues within the Aq•.~atic
Impacts and Miti~ation Report Series.
Report No. 1
Access,
Construction
and Transmission
Issue Line Impacts
··' No. and Mi ti gati on
F-1
Report No. 2
Impoundment
Area Impacts
and MitigatiQn
./
Report No. 3 Downstream
Impacts and Mitigation
Flow River Water
Alteration Morphology Quality
*
Report No. 4
Aquatic
Monitoring
Plan
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F-3
F-4
F-5
F-6
F-7
F-8
F-9
F-10
F-11
F-12
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THE PROPOSED SITES OF THE WATANA AND
DEVIL · ~NYON DAMS
SOURCE: APA l985a
AlASKA POWER AUTHORITY
SUSITNA HYDROELECTRtC PROJECT:
L HAAZA·EBASCO
• __________ F_IG_u_R_E _l_._ ___ e_N_T __ R-_•x_,_I_N_c_. __ ..._s_u_s_,_r N--AJ_o_' _,.,_r _v_e_N_r_u_R_e-t =
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.--------...-----~"""""""''""""'~~t-o-~~~ .. ;~~~~ .
N
1
• DEVIL CANYON DAMSITE
• WATANA DAMS ITE
~. LOWER SUSITNA RIVER
~~~ MIDDLE SUSITNA RIVER
•
DEVll CANYON IMPOUNDMENT ZONE
WATANA
IMPOUNDMENT ZONE
GEOGRAPHICAL SECTIONS
OF THE SUSITNA RIVER
ALASKA POWER AUTHORITY
FIGURE 2
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC.
5
HARZA·E BASCO
SUSJTNA JOINT VENTURE
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confluence with the Ta 1 keetna and Cht~l i tna rivers whi 1 e the 1 ower Sus i tna
River indicates the reach below the confluence with the Talkeetna and Chulitna
rivers to Cook Inlet {Figure 2).
The aquatic resources of the Susitn~ River include resident and anadromous
fish which utilize a diverse range of mainstem-associated habitats for
migration, spawning, incubation, rearing and overwintering. The upstream
extent of anadromous ffsh use is generally con.si dered to be De vi 1 Canyon
although a few chinook salmon migrate beyond this point to spawn in streams
tributary to the Susitna River. The high velocities and turbulent conditions
in Devil Canyon likely block the upstream passage of other fish species.
1~3 Organization
The Downstream Fish Impact Assessment and Mitigation Plan report is divided
into two parts. Part I of the document discusses the potential impacts to the
aquatic resources in the mi ddi e Sus i tna .~ i ver and presents an appropriate
mitigation plan. It also includes discussions of project-related effects on
the reach of river between Watana and De vi 1 Canyon prior to inundation.
Impacts and mitigation for the lower Susitna River are addressed in Part II.
Within Part I~ Section 2 presents a description of the proposed three s~age
project, with emph1si s given to features that may affect downstream aquatic
resources. Potential impacts to aquatic resources, identified by linking the
haPitat utilization by each of the ~valuation species {Section 3) to the
predicted physical changes during each stage of the proposed project (Section
4), are described in Section 5. Section 6 presents the mitigation plan for
these potential impacts.. Data and figures supporting summary information
presented in the text ~re provided in the appendices.
The organization of Part II of this report is outlined in the introduction to
that document.
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2.0 PROJeCT DESCRIPTION ANP SCHEDULZ
,.I
The propl:.sed Susitna Hydroelectric Proje\ct is .1 ocated in the southcentra 1
region 'Of Alaskaio apprilximately 120 miles, north-northeast of Anchorage ar11d 145
miles south-southwest of Fairbanks. The two proposed dams, Watana and Devil
Canyon} are to be built at RM 184 and 152, respectively, on the Susitna River,
the sixth largest river in Alaska.
The project involves construction in three distinct stages at the two sites.
The 'Stage I construction at the ~Jatana site is described in Section 2.1.
Stag1e I I at the De vi 1 Canyon site is presented in Section 2. 2. The Stage I I I
corH~truction at the-Watana site is summnrized in Section 2.3. The project
schE~dule is presented in Section 2.4. Additional details are available in
Exhibit A of the FERC License Application Amendment {APA 1985a).
2.1 Stage I -Watana Initial ReservoiJ:
The Watana Sta-ge I dam wi 11 be 1 ocated at mi 1 e 184 above the mouth of the
Susitna River, in a broad U-shaped valley approximately 2.5 miles upstream of
the Tsusena Creek confluence. ·The dam will be an earth and rockfill
embankment consisting of an impervious core protected by fine and coarse
fi 1 ters upstream and downstream. The upstream and downstream outer she 11 s
will consist of rockfill.
The Watana dam will be built to a nominal crest elevation of 2t025 ft with a
ma~imum height of approximately 700 ft above the foundation and a crest length
of 2,700 ft. The maximum water surface elevation during flood conditions w111
be 2~017 ft.~ At the normal maximum operating level of 2,000 ft, a reservoir
approximately 39 miles long with a maximum width of Gpproximately two miles
will be created. The minimum operating level of the reservoir will be
1,850 ft resulting in a maximum drawdown of 150 ft.
" ~~-
The two power i nt&ke structures wi 11 be 1 ocated on the north 'bank ~!-l:h an
approach channe 1 from the reservoir excavated in rock.. The excavated rock
will be used in the construction of the dam and would Minimize or eliminate
the need for opening a quarry site during Stage I. The ; ntakes will be
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concrete structures with multi-level gates capable of op~rating over the full
150-ft drawdown range. From the intake structures, two 24-ft diameter
concrete-lined power conduits and shafts will lead to an underground .
powerhouse comp 1 ex, housing four generating units with Fra\'~ is type turbines
"; .
and,: synchronous generators.. Turbine discharge .wi 11 f1 ow through four draft
"' tube tunne 1 s to a surge chamber downstream from the ptlwerhouse. The surg·e
chamber will discharge to the river through a 34-ft modi fi ed-horses·hoe
concrete-lined tailrace tunnel.
The underground powerhouse complex will be accessed by an unlined access
tunne 1 connecting to a road 1 ocated on the downstream toe of the dam.
Overhead transmission lines will transport electricity from the powerhouse
switching station.
An outlet facility with a capacity of approximately 24,000 cfs will also be
1 ocated on. the north bank and wi 11 consist of a gate structure, pressure
tunnel, and an energy dissipation and control structure housing located
beneath the spillway flip bucket. The primary functioti of the outlet facility
will be to discharge floods with recurrence frequencies of up to once in 50
years after they have been routed through the Watana reservoir o A flood
storage pool is provided between el. 2,000 and el. 2,014 ft. In combination
\~ith the average powerhouse flow of 9,200 cfs, the 50-year flood can be stored
and re 1 eased without raising the poo 1 1 eve 1 above e 1 • 2, 014 ft and without
requiring use of the s~illway. The structure will accommodate six fixed-cone
valves which will discharge into the river 105 ft below. The use of
fixed-cone discharge valves will ensure that downstream erosion will be
minimal and the dissolved nitrogen content in the discharges will be reduced
sufficiently to avoid harmful effects on the downstream fish population. A
secondary function will be to provide the capability to rapidly draw down the
reservoir during an extreme emergency situation.
The spill way 1 ocated on the north bank wi 11 consist of an upstream agee
control structure with thr~e radial gates, an inclined concrete chute, and a
flip bucket designed to pass a maximum discharge of 278,300 cfs with a
corresponding reservoir elevation of 2,014 fto This spillway, together with
the outlet facilities, Will be capable of discharging the estimated Probable
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Maximum Flood (PMF) of 326,000 cfs, while maintaining eight feet of freeboard
on the dam. Emergency release facilities will be located in one c,f the
diversion tunnels after closure to allow lowering of the reservoir over a
period of time for emergency inspection or repair of impoundment structures.
2.1.1 Construction
During construction~ the river will be diverted into two 36-ft diameter
circular diversion tunnelse The tunnels will be concrete-lined and
located on the north bank of the river. The tunnels will have an average
1 ength of 3, 700 ft.
Flows through the tunnels during construction will be essentially .
uncontro 11 ed. The tunne 1 s are designed to pass a flood with a return
frequency of 1:50 years, equi va 1 ent to a peak inflow of 89,500 cfs.
Routing effects are expected to be sma 11, and thus at peak flow the
tunnels will discharge 77,000 cfs. The estimated maximum water surface
elevation upstream from the cofferdam for this discharge will be
1,532 ft. Downstream flows will be essentially the same as under natural
conditions. The upper tunnel will be converted to the permanent
emergency outlet after construction (Section 2.1.2} ..
Cofferdams wi 11 be constructed upstream and downstream of the dams i te.
The upstream cofferdam will be founded on the diversion dike. The
diversion dike will be constructed to el. 1,480 ft, and will consist of
finer material on the upstt·eam side grading to coarser material on the
downstream side. Seepage wi 11 be contra 11 ed by constl"Uct i (i9 a s 1 urry
trench cutoff through the rivet"' bed a 11 uvi urn to bedrock. The upstream
cofferdam w·ill consist of an impervious core, fine and coarse upstream
and downstream filters, and rock and/or gravel supporting shell zones
with slope protection on the upstream face to resist ice action. This
cofferdam will be constructed to el. 1,550 ft and provide an 18-ft
freeboard for wave run-up and ice protection. The downstream cofferdam
wi 11 be a zoned earth and rockfi 11 embankment. The cofferdam wi 11 be
raised to crest e 1 evat ion of 1, 495 ft to a 11 ow dewatering of the river
reach between the cofferdams.
9
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2 ~ 1 . 2 fill i ng
As construction on the dam nears completion~ the upper diversion tunnel
will be converted to a low-level outlet or emergency rele.ase facility.
It is estimated that one year will be required to construct and install
the permanent low-level outlet in the existing tunnel. During the
construction .of the low-level outlet, the intake gates in the upper
tunnel (No. 1} will be closed. This will require that the lower tunnel
(No. 2} pass all flows during this period. The main dam will, at this
time, be at an elevation sufficient to allow a 100-year recurrence
interval flood (99,000 cfs) to pass through Tunnel No. 2. A flood of
this magnitude will result in a reservoir elevation of approximately
1,618 ft.
Upon commencing operation of the low-level outlet, the lower tunnel
(No. 2} will be closed with a permanent plug and filling of the reservoir
will commence. When the lower tunnel (No. 2) is closed, the main dam
crest will have reached an e 1 evat ion st,ffi ci ent to start fi 11 i ng the
reservoir and still have adequate storage available to store a 250-year
recurrence period flood.
The filling of the Watana reservoir, Stage I, is scheduled to commence in
May 1998 .. During the filling operation, the low-level outlet is expected
to pass summer flows of approximately 12,000 cfs,. In case of a large
flood occurring during the filling operation, the low-level outlet would
be opened to its maximum capacity of 30,000 cfs to maintain the reservoir
pool at a safe level.
It will take only one summer to fill the reservoir to a level sufficient
to operate the units. If a dry sequence of flows were to occur in the
first summer of filling, the reservoir water level would not be high
enough to operate the mid-level (cone valve) outlet works and non-power
releases would be made from the low-level outlet works. If an average or
wet sequence were to occur, winter non-power releases may be made through
the mi d-1 eve 1 outlet works instead of the 1 ow-l eve 1 out 1 et works. The
res~rvoir would be filled to its normal maximum level during the second
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summer. Testing and cormlissioning of the units is scheduled'-to begin
during July 1998 (Section 2.1.3). Unit one is planned to become operable
in October 1998 and unit two in January 1999.. .During filling, downstream
flow requirements wi 11 be met and a flood storage safety factor wi 11 be
maintained.
{a} Minimum Flows
The Case E-·VI flow requ·irementz will be maintained during the summer
of filling. Case E-VI flow r~equirements are designed to reduce
downstream aquatic impacts while maintaining economical project
operation. M·inimum target flows at Gold Creek wi'll be attained by
releasing that flow necessary from the Watana impoundment which,
when added to the fi cw contribution from the intervening drainage
area between Watana and Gold Creek, will equal the minimum Gold
Creek target flow. During fi 11 i ng ~ flows at Go 1 d Creek wi 11 be
monitored and the flow at Watana adjusted as necessary to provide
the required Gold Creek flow.
In the winter months {November-March), the maximum flow requirement
of 16,000 cfs at Gold Creek is intended to provide a level of
protection to aquatic habitat. The winter minimum flow requirement
of 2,000 cfs is established to prevent dewatering of aquatic habitat
and represents a high mean natural winter flo"'. Minimum summer flow
requirements are established to maintain aquatic habitat and provide
greater flow stability. The 9,000 cfs minimum flow requirement from
June to early September may be reduced to 8, 000 cfs during June,
July, and August during dry years (one in ten year low flow). Flows
during the transitional periods between summer and winter are also
constrained as shown in Table 3 and Figure 3.
Flow will he released from the reservoir to meet the requirements at
Gold Cr·eek.. Excess water will be stored in the reservoir. If a dry
year should occur during filling, the 8,000 cfs flow requirement for
the months of June through early September will allow filling of the
11
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Table 3.. Fl~w constraints for environmental flow requirement Case E-VI.
Water
Week
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29.
30
31
32
33
34
35
36
37
38
39
Gold Cree~ Flow (cfs)
Minimum Maximum
2,000
2,000
2,000
2,000
2,000
2,000
2,000
2}000
2,000
2,000
2,000
2,000
2,000
2,000
2,000
2,000
2,000
2,000
4,000
6,000
6,000
6,000
9,000 *
9,000 *
9,000 *
9,000 *
16,000
16,000
16,000
16,000
16,000
16,000
16,000
16,000
16,000
16,000
16,000
16,000
16,000
16,000
16,000
16,000
16,000
16,000
16~000
16,000
16,000
16,000
35,000
35,000
35,000
35,000
.
·Water
Week
40
41
42
43
44
45
46
47
48
49
50
51
52
1
2
3
4
5
6
7
8
9
10
11
12
13
Gold Creek Flow (cfs)
Minimum Maximum
9,000 *
9,,000' *
9 000 * ' 9,000 *
9,000 *
9,000 *
9,i000 *
9,000 *
9,000 *
8,000
7,000
6,000
6,000
6,000
6,000
5,000
4,000
3,000
3,000
3,000
3,000
3,000
2,000
2,000
2,000
2,000
35,000
35,000
3.5,000
35,000
35,000
35,000
35,000
35,000
35,000
35,000
35,000
35,000
35,000
18,000
17,000
16,000
16,000
16,000
16,000
16,000
16,000
16,000
16,000
16,000
16,,000
16,000
* Minimum summer flows are 9,000 cfs except in dry years when the minimum will
be S,iJOO cfs. A dry year is defined by the one-in-ten year 'low flow.
Source: APA 1985c
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NOTE
1 .. DISCHARGE FOR 8USJTNA RIVER AT
GOLD CREEK
40.000 --~----1----1----+---+----t---t----t
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U.N vr..-FEB UAR APR UAY JUN
ENVIRONMENTAL FLOW REQUIREMENTS
CASE E Jll
SOURCE: APA l985c FIGURE 3
JUL AUG SEP OCT NOV DEC
AlASKA POWE.R AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC. HARZA·E BASCO
SUSITNA JOINT VENTURE
reservoir to a level of sufficient for test·ing and commis.sioning of
the first unit and commercia 1 power operation in the fo 11 owing
winter.
During the winter after the summer of fflling, the minimum flow
requirement will be natural flows. This means that the Watana
reservoir water 1 eve 1 would not be a 11 o~ted ~~a rise during the
winter. Minimum requirements will be maint~lined by releases through
the powerhouse supp 1 emented, if necessary, by re 1 eases from the
low-level or mid-level outlet works dependilng on the height of the
water level.
(b) Flood Storage Protection
Sufficient reservoir storage will be made available during the
fi 11 i ng sequence so that flood volumes for a'11 floods up to the
250-year recurrence interval flood can be temporarily stored in the
reservoir and discharged through the low-level outlet works without
endangering the main dam. When floods occur and use part of this
storage capacity, discharge from the Watana reservoir will be
increased up to the maxi mum capacity of the out 1 et to 1 ower the
reservoir level.
2 .. 1.3 Testing and Commissioning
Testing and commissi,oning of the powerhouse units will commence as
reservoir fi 11 i ng nears comp 1 et ion and the reservoir 1 eve 1 is above the
minimum drawdown elevation {el. 1,850 ft) ..
Testing of units is scheduled to begin in July 1998 with additional units
tested at three month i nterva 1 s. The process of testing and
commissioning each unit may take several months and will require a number
of tests. I~ will be carried out in a manner to maintain downstream flow
stability.
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The largest fluctuations in powerhouse flow could occur during the
full-load-to-off or off-to-full-load tests when the flow through the
turbine being tested wil'l be quickly reduced from approximate1y·3,500 cfs
to 0 or increased from 0 to 3,500 cfs, respectively. This will be
compensated for by opening or closing the outlet facility gates or other
units which have previously been tested to stabilize flow downstream and
to prevent sudden changes in downstream flows. When testing is done
during su11111er, the Case E-VI requirements w·i11 be maintained and this
will also help to stabilize the flow.
If testing occurs in winter and flow is less than the test flow through
the unit at Watana, flow will be gradually increased to that level over a
one day period prior to the testing and maintained at that level through
the testing period. If testing is temporarily halted, flow will be
gradually reduced.
2.1.4 Ooeration -
This sect1on describes the project during the period from the summer of
1999, when all fciUr powerhouse units are planned to be operational, to
the construction and filling of Stage II.
Watana will be operated in a storage-and-release mode, so that st "Mler
flows will be stored for release in winter. Generai1y, the W"i;t'ana
'··-··es~rvoir will be at or near its r.ormal maximum operat1ng level of el.
2, 000 ft each year at the end of September. The reservoir wi 11 then be
drawn down gradually to·meet winter energy demand. The flow during this
period wi 11 be governed by environmental flow constraints, the winter
energy demand, the water 1 eve 1 in the reservoir, and the powerhouse
characteristics. The turbine characteristics will allow a maximum
powerhouse flow of approximately 14,000 cfs at full gate. Normal
powerhouse discharges are simulated to range from approximately 2,700 cfs
to 12,000 cfs.
In early May, the reservoir will reach its minimum annual level of
approximately el. 1,870 ft and then begin to refill with the spring
15
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runoff. Flow in excess of both the downstream flow requirements and
power needs; wi 11 be stored during the summer until the reservoir reaches
the normal maximum operating level of el. 2,000 ft. If the reservoir
reaches e l. 2, 000 ft and inflows exceed en vi ronmenta 1· and energy
re~qui rements, excess fl CIW will be re 1 eased to prevent encroachment on dam
safety requjrements.
During prnJ!!ct operation the Case E-VI environmental flow requirements
wfll be maintained. Minimum requirements will be met by releases from
tht~ powerho;use and, if nece!ssary, the out 1 et works. Da i 1 y ~~·i '}Charge
would be a.llowed to vary between 90 percent and 110 percen~, ~f the
ave~ rage weekly discharges. The corresponding expected range of stage
fluctuations in the middle river would be from Og2 ft to 0.7 ft.
The operation of the project during floods will focus on dam safety. If
the Watana reservoir 1 eve 1 E~xceeds the norma 1 maxi mum operating 1 eve 1 ,
dam safety ct~i teri ~ wfll sup•~rsede both weekly flow constraints and flow
stability constraints. Envi-ronmental considerations are built into the
dam safety criteria as: disc:ussed herein. Project operation at Wgtana
will be similar for both Watana operating alone and Watana operating witlh
Devil Canyon once the Watana reservoir reaches or exceeds the norma·.l
ma.ximum operating level.
If the water 1 evel in i;he Watana I reservoir reaches el. 2, 000 ft and
con'tir.ues to rise, Watana discharge will be increased by releasing water
thr1ough the 1:>utl et work:s. Because the intake to the outlet works is
applroximately 80 ft below the water surface, operation of the outlet
~torks results: in reduced downstream water temperatures. In order to
pro vi de for a.s gradua 1 a change in \"later temperature as poss; b 1 e, the
following guidelines will apply:
• Supply as much enel .. gy as possible from the Watana powerhouse
within the constraints of the system energy demand, other
generation, and Watana powerhouse capacity.
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• Increase the outlet works discharge at the estimated minimum
rate required to prevent the water 1 eve 1 from exceeding el .
2,000.5 ft. If the inflow to the reservoir is more than
~
24,000 cfs greater than the powerhouse can discharge, then the
release from the outlet works will be 24,000 cfs when the water
level reaches el. 2,000.5 ft.
If the outlet works are not releasing water at full capacity and the
water' level rises above e~. 2,000.5 ft, the outlet works will be opened
immediately to full capacity. If the full capacity of the outlet works
and powerhouse flow are not sufficient to discharge all the inflow the
water level will continue to rise.
If the water level exceeds el. 2,000.5 ft but does not reach .el.
2,014.0 ft then the Watana discharge will remain relatively constant
unti 1 the water 1 eve 1 decreases to e 1 . 2, 000 .. 5 ft. 1 f the water 1 eve 1
starts to decrease below el. 2,000.5 ft then the outlet works will be
closed in a grad'Jol manner as they were opened. The rate of closure will
be that estimated to cause the water 1 evel to reach el·. 2, 000.0 ft when
the oHtl et works di.scharge reaches zero. The outlet works wi 11 be
completely closed before the water level is allo\f,\ed to decrease below el.
2,000.0 ft.
The outlet works capacity and flood surcharge level have been planned to
store and release the 50-year flood without operating the spillway&
Thus, there is less than a 1 in 50 chance that in any one year the water
level will continue to rise to el. 2,014.0 ft. If the water level
reaches el. 2,014.0 ft and continues to increase, the spillway will be
opened. Since spillway operation may increase gas concentrations in the
river downstream, the spi 11 way wi 11 a 1 so be opened up as gradually as
possible, consistent with providing sufficient freeboard on the dam to
meet safety requirem~nts. The powerhouse and outlet works releases will
continue as before~ and the spi 11 way wi 11 be opened at the estimated
minimum rate required to prevent the water level from exceeding el.
2,014.3 ft. If the water level reaches el. 2,014.3 ft and continues to
rise, the spillway gates Will be opened as much as needed to prevent the
17
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water level from increasing any further. As explained in Exhibit F of
the FERC License Application Amendment (APA 1985b), the spillway has the
capac·ity to pass the 10,000-year flood at a reservoir level of el.
2,014.3 ft. Thus, there is less than a one in 10,000 chance in any year
that the water level would exceed el. 2,014o3 ft.
If the reservoir water level reaches el~ 2,014.3 ft and the fuliy opened
spillway, outlet works antf powerhouse are· insufficient to pass the
inflow, the water level will increase uncontrolled. The spillway is
designed to pass the Probable Maximum Flood {PMF). The water ltvel would
reach approximately el. 2,017 ft, eight feet below the dam crest during a
PMF. Watana discharge would not be controlled again until the watev·
level decreased to el. 2,014.3 ft. When this occurs, the spillway will
be closed gradually in a manner estimated for the water level to reach
el. 2,014.0 ft when the spillway discharge is zero. The spillway gates
will be completely ~lased before the water level is allowed to decrease
below el. 2,014.0 ft.
In emergency situations, if powerhouse operation is not possible, outlet
facilities will be operated to meet the flow requirements.
Correspondingly, if another part of the energy generation system is
temporarily 1ost, Watana may be operated to make up the deficit. The
resulting discharge variation may exceed the maximum variation rate of 10
percent, and discharge may reach the maximum flow constraint. However,
the discharge at Gold Creek will not be allowed to exceed the maximum
weekly flow requirement and the rate of change of discharge wi 11 be
constrained by ~he rates established for Case E-VI.
2.2 Stage II -Devil Canyon
The Stage II Devil Canyon development will be located at mile 152 in a narrow
canyon 32 mi 1 es downstream of the Watana deve 1 opment. A reservo; r
approximately 26 miles long with a maximum width of 0.5 miles will be created.
The dam wi 11 be a doub 1 e curvature thin arch concrete dam with a crest
f 1 elevation of 1,463 ft (not including a 3-ft parapet) and maximum height of w
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646 ft. The dam wi 11 be supported by mass concrete thrust blocks on each
abutment. On the south bank, the 1 ower bedrock surface wi 11 require the
construction of a substantial thrust block. Adjacent to this thrust block, a
saddle dam will provide closure to the south bank. The saddle dam will be an
earth and rockfill embankment generally similar in cross section to th~ Watana
dam. The dam will have a nominal crest elevation of 1,470 ft and a maximum
height above foundation level of approximately 245 ft. During normal
01peration, the reservoir ievel will reach a maximum elevation of 1,455 ft.
lrhe minimum operating level will be 1,405 ft providing a drawdown of 50 fta
The maximum water surface elevation during the design PMF flood conditions
will be 1,466 ft (APA 1985b).
A power intake on the north bank will consist of an approach channel excavated
in rock leading to a reinfor~ed concrete gate structure. From the intake gate
structure, four 20-ft diameter concrete-1 i ned penstock tunne'J s wi 11 1 ead to an
underground powerhouse complex housing four units with Francis turbines and
synchronous generators. The turbines will discharge to the river by means of
a single 38-ft diameter tailrace tunnel leading from a surge chamber
downstream from the powerhouse cavern. Access to the powerhouse complex will
be by means of an unlined access tunnel approximately 3,200 ft long as well as
by a 950-ft deep vertical access shaft. A cable shaft will connect to the
switchyard at the surface. From the switchyard, electricity produced at the
Devil Canyon powerhouse will be transported by overhead transmission lines.
Outlet facilities consisting of seven individual outlet conduits will be
1 ocated in the 1 ower part of the main dam. These wi 11 be des; gned to
discharge all flood flows of up to the estimated 50-year flood with Watana in
place.. Each outlet conduit will have a fixed cone valve similar t.o those
provided at Watana to dissipate energy and min1mize undesirable nitrogen
supersaturation in the flows downstream.
An overflow spillway will also be located on the north bank. As at Watana,
this spillway will consist of an upstream ogee control structure with three
vertical fixed-wheel gates, an inclined concrete chute, and flip bucket. This
spillway, together with the outlet facilities, will be capcble of discharging
the routed PMF from Watana without overtopping the dam.
19
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2.2.1 Construction
During construction, the river will be diverted by means of a single
35.5-ft diameter concrete-lined diversion tunnel on the south bank of the
river~ The Devil Canyon diversion tunnel is scheduled to be completed in
1999 and construction on the main dam will begin in that year. The
tunnel will have a horseshoe-shaped cross section with a major dime~sion
of 35.5 ft. It will be 1,490 ft in length.· The tunnel is designed to
pass a flood with a return frequency of 1:25 years routed through the
Watana reservoir. The peak flow that the tunnel will discharg~ will be
approximately 43,000 cfs. The maximum water surface elevation upstream
of the cofferdam will be el. 944ft.
Cofferdams will be constructed upstream and downstream of the damsite is
a manner simi 1 ar to the cofferdams constructed during Sta!~e I. Tha
cofferdams will be zoned embankments consisting of an impervious core,
fine and coarse upstream and downstream fi 1 ters, and ·tock she 11 s with
larger stone. Slurry wall cutoffs ~i11 minimize seepage into the main
dam excavation.
The flow regime during construction wi 11 be regula ted by the Stage I
Watana dam. Under the proposed schedule, the Watana development will be
operational during construction of the Stage II Devil Canyon dam. Little
storage of flow is expected due to the diversion tunne1 and flows will be
essentially controlled by the operation of the Watana development
(Section 2. L.4).
2.2.2 Filling
Upon completion of the Devil Canyon dam to a heilght sufficient to allow
ponding to a level above the outlet facilities, the intake gates will be
partially closed allowing for a discharge of minimum envir~nmental (Case
E-VI) flows while raising the upstream water level. This first phase of
the filling process will require from. 1 to 4 weeks depending on time of
year and Watana powerhouse flows when filling is begun. Once the level
rises above the lower level of discharge valves, the diversion tunnel
20
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will be permanently closed and discharge will be through the 90-inch
diameter fixsd-~one valves in the darn. The diversion tunnel will be
p 1 ugged with concrete and curtain grouting performed around the P 1 ug ~· .
Construction will take approximately 1 year. During this time the
reservoir will not be allowed to rise above el. 1,135 ft unless a flood
exceeding the outlet works capacity occurso In this case the water leve'11
will be allowed to rise as needed to store the flood.
Filling of the reservoir to its normal operating le\'e1 of el. 1)455 fft
will be accomplished as quick.ly as possible following the completion CJif
construction. Case E-VI flow requirements will be maintained downstre1m
of the reservoir.
The Devil Canyon reservoir will be filled from the normal Watana release,
for power generation and flood releases while maintaining the instream
flow requirements. During the filling period, the Watana powerhouse will
be operated to supply as much of the total railbelt energy demand as
possible so that the Devil Canyon reservoir can be filled in a timely
manner. The flow from the Watana reservoir in excess of the Case E-VI
requirement will be used to fill the Devil Canyon reservoir. The rate of
filling will also be dependent on the need to monitor dam and foundation
performance during filling to assure a safe structure.
2.2.3 Testing and Commissioning
Testing and commissioning is scheduled to begin in October 2004. Each
powe:" generating unit will be tested individually. The testing and
commissioning of the units involves many sequences of bringing the unit
on-line and taking it off-line. These will be carried out in a manner to
minimize impacts to flow stability., To compensate for flow passing
through the units during testing, the flow through the outlet works will
be reduced by a comparab 1 e amount as discussed for the testing and
commissioning of the Watana Stage I units (Section 2.1.3)e
21
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2.2.4 Operation
After De vi 1 Canyon comes an 1 i ne, Watana Stage I wi 11 be operated as a
peaking plant and Devil ·canyon will re-regulate Watan~ flows. Advantage
will be taken of the two-reservoir system to optimize energy production
with the constraint that the Case E-VI downstream flow requirements will
be met. Devi 1 Canyon discharges may vary between 90 percent and 110
percent of the average weekly flow.. The Case E-VI environmental flow
requirements will be maintained by releases from the powerhouse and, if
necessary, the outlet works.
Tha Devil Canyon reservoir will normally be at its maximum water level,
el. 1,455 ft, between January and May. In dry years Devil Canyon wirl be
drawn down below maximum level between May and December reaching its
minimum level of el. 1,405 ft in August. In average flow years, the
reservoir will be drawn down below maximum level between June and August
reaching a minimum of approximately el. 1,435 ft in July. Average weekly
Devil Canyon powerhouse flows will be similar to Watana, but slightly
higher due to add it i ona 1 i nf1 ow in the intervening area between the two
dams.
With Devil Canyon on line, Watana will still be operated in a storage-
and-releas,~ mode similar to Stage I, so that summer flows will be stored
for release in winter. Generally, the Watana reservoir wi 11 be at or
near its normal maximum operating level of ele 2,000 ft each year at the
end of September. The reservoir wi 11 gradually be drawn down to meet
winter energy demand. The flow during this period wi 11 be governed by
winter energy demand, water level in the reservoir, and powerhouse .
characteristics. The turbine characteristics will allow a maximum
powerhouse flow of approximately 14,000 cfs at full gate. Normal Watana
average weekly powerhouse discharges will range froffi approximately
3,000 cfs to 8,500 cfs~
In early May, the Watana ~eservoir will reach its annual minimum level of
approximately el. 1,870 ft and then begin to reffll with the spring
runoff. Flow in excess of both the downstream flow requ; rernents and
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power needs will be stored during summer until the reservoir reaches the
normal maximum operating level of el. 2,000 ft. If the reservoir reaches
el-: 2,000 ft, and inflo\'~ exceeds energy and instream flew requirements,
excess flow wftl be released to maintain dam safety requirements.
Dam safety'criteria at Watana with both Watana and Devil Canyon operating
will be similar to Watana only operation when the water level in Watana
reservoir exceeds e1. 2,000.0 ft, especially·in the early years of Devil
Canyon operation. However, while while Watana reservoir is filling in
the spring, and before the water level reaches el. 2,000.0 ft! the Devil
Canyon powerhouse wi 11 be used to generate most of the system energy
demand. Watana still must generate a portion of the energy in order to
meet peak energy demands. This policy was adopted to minimize downstream
temperature effects resu1 t i ng from the use of the De vi 1 Canyon outlet
works*' When the Watana water 1 eve 1 reaches e 1 . 2, 000. 0 ft, it is
necessary to switch energy generation from Devil Canyon to Watana 1 n
order to pass the 50-year flood through Watana without using the
spi 11 way. The change from the De vi 1 Canyon to the Watana powerhouse
would be made in a gradual manner, but in no case would the Watana water
level be allowed to r:se above e1., 2,000.5 ft without the Watana
powerhouse supplying available system energy demands and the Watana
outlet works releasing at 24,000: cfs. After the system load is
transferred from Devil Canyon to Wat~na, the operation at Watana would be
identical to that for Watana only operation.
When the Watana water level reaches el. 2,000.0 ft, the Devil Canyon
reservoir will be allowed to fill while minimum flow requirements ar~
· being met. The Watana and Devi 1 Canyon outlet works and ope rat in~
policies have been plan ned so that whi 1 e the De vi 1 Canyon reservoir ; s
filling, the outlet works will be opened up in a gradual manner estimated
to prevent the water level from exceeding el. 1,455.0 ft. When the water
level reaches el. 1,455.0 ft, the otJtlet works will be opened as much as
necessary to keep the water 1 evel stable. In this period, De vi 1 Canyon
will operate as ess~ntially a run-of-river project, passing Watana
outflows and intervening flows. The rates of change of Devil Canyon
23
discharge will be similar to t.hf:lse for Watana with small modifications
resulting from variations in inte,.'·ening flow.
Devil Canyon can pass all of the Watana outflows and all in~ervening
flows through its out'iet works without using its spillway unless the
Watana spillway is operating. The 50-year flood inflow may exceed the
capact ty of the De vi 1 Canyon outlet works (APA 1985b). Therefore,
surcharge stor'age is provided to store the flow in excess of the outlet
works capacity. During floods, the Devi 1 Canyon water. 1 evel wi 11 be
maintained at el. 1,455.0 ft until the outlet works are discharging at
full capacity. If the inflow exceeds the capacity, the water level will
be allowed to increase to el. 1,456.0 ft.. In this manner the 50-year
flood can be stored and released without operating the spillway. If the
water 1 eve 1 cant i nues to rise above e 1 . 1, 456.0 ft, the De vi 1 Canyon
spillway must be opened to maintain freeboard on the dam. The chance the
spillway would be operated in any one year is less than 1 in 50. The
spillway ~ates will be opened at whatever rate is necessary to keep the
pool at this level. The spillway has the capacity to pass the 10,000-
year flood with the r~servoir at el: 1,456.0 ft (APA 1985b}. Thus, there
is less than a 1 in 10,000 chanLe that the Devil Canyon water level would
exceed this level in any one year. If the spillway gates were opened
completely and the reservoir level continued to rise, discharge from
Devil Canyon would be uncontrolled. The Devil Canyon spillway is
designed to pass the PMF. The maxi mum water 1 eve 1 obtai ned during
routing of the PMF is e 1 • 1, 465. 6 ft, which is 0. 4 ft be 1 ow the top of
the concrete parapet and 4. 4 ft be 1 ow the crest of the rockffll sections
of the dam. Control would not he regained until the water level receded
to el. 1,455.0 ft. When the water level decreases to el. 1,455.0 ft the
spillway and outlet wo;--ks will be closed in a manner to keep the water
level at el. 1,455.0 ft.
2. 3 Stage I I I -Wata~•a High Reservoir
Stage III involves raising the Watana dam 180 ft to el. 2,205 ft; at the
maximum normal reservoir el. of 2,185 ft, a reservoir approximately 48 miles
1 ong with a maxi mum width of approximate 1 y 5 mi 1 es wi 11 be created. The
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maximum water surface e 1 evat ion during flood conditions wi 11 be 2, 199.3 ft.
The minimum normal operating level of the reservoir will be el. 2,065 ft,
providing a normal drawdown of 120 ft.
The Stage I internal zoning will be maintained. in raising the dam. Some
excavation at the top of the Stage I dam will be necessary to ensure
cent i nui ty of the zones. The nomina 1 crest e 1 evat ion of the dam wi 11 be
2,205 ft, with a maxim~m height of 885 ft above ·the foundation and a crest
length of 4,100 ft. The embankment crest will initially be cambered to el.
2,210 ft to allow for ~otential settlement. The total volume of fill material
placed in the dam during Stage III construction will be 26,363,000 cubic
yards, bringing the total volume of the dam to 58,470,000 cubic yards.
A new power i ntcrke wi 11 be constructed adjacent to the existing two intakes.
The existing intake concrete superstructure will be raised to accommodate the
higher reservoir level. Simultaneously, the concrete superstructure for the
outlet facilities will also be raised. The approach channel constructed
during Stage I wi 11 be adequate for the efficient flow of water to a 11
intakes. There will be no change to the outlet facilities downstream of the
intake structure.
Additional power capacity will be achieved by the increased head on the Stage
I generating units, which were designed for this reservoir r"aising, and the
two additional generating units installed during this stage. This
installation will require an extension of the powerhouse chamber to the south
of the service bay. Simi 1 ar extensions wi 11 be required to the south of the
transformer gallery and surge chamber.
A third power shaft and tunnel bifurcating into penstocks to supply water to
the two generating units will be excavated and 1 ined with concrete from the
new intake structure. The power conduit wi 11 have an ·; nterna 1 diameter of
24 ft.
The penstocks will be stee 1-l i ned for a distance of 200 ft upst\~eam of th1e
powerhouse.. The steel-'iined section will have a diameter of 15 ft. The
remaining penstock reach to the bifurcation will be 18 ft in diameter.
25
The surge chamber extension will be hydraulically joined to the powerhouse
cavern by two draft tube tunnels. The turbine discharges will flow from the
south end of the surge chamber by a secnnd 34-ft diameter C(lncrete-1 i ned
modified~horseshoe tunnel. This tunnel will intersect the Number 2 diversion
tunne 1 (Section 2.1}, wh 1 ch wi 11 be used to camp 1 ete the tunne 1 ta i 1 race
system, and discharge to the river downstream of the dam. The transformer
ga 11 ery extension wi'~ 1 house the added transformers serving the two
genera~ors.
The spillway control structures, however, w~lll require substantial
modification. The bridge wi 11 be removed, and the p,i ers and abutment wa 11
concrete wi 11 be raised. This wi 11 be fo 11 owed by raising th~ overf1 ow
spillway to a crest elevation of 2,135 ft.. The Stage I radial gates and
hydraulic hoists will be re-installed. The ogee section will, in effect, be a
gravity dam section with its downstream face forming the upper reach of the
spillway chute prior to joining the lower reach which was constructed during
Stage I. The spillway will still have the capacity to pass the PMF without
overtopping the dam. The emergency release facilities constructed in
·diversion tunnel No. 1 will still be available for lowering of the reservoir
over a period of time to permit emergency inspection or repair to the
impoundment structures.
Work on raising the Watana dam to its Stage III crest level of el. 2,205 ft is
currently scheduled to begin in 2006, follow·ing the completion of the Devil
Canyon dim. Filling of Watana Stage III will occur at the same time the dam
crest level is being raised. Therefore, construction and filling of Stage III
are not distinct phases. As addressed in the following section, the
construction phase wi 11 refar to the period between the year 2006 and the
beginning of fi 11 i ng of Watana Stage I I I. This phase wi 11 end when the dam
crest is high enough that the water 1 eve 1 can be raised without adverse 1 y
affecting the safety of the structure. It is current 1 y p 1 an ned that the dam
crest can be raised to el. 2,100 ft by the year 2010. Work on raising the
power intake and spillway ogee crest levels will begin in 2008 and 2010,
respectively. Filling of the Stage III reservoir will begin in 2011 even
though construction is not scheduled to be completed until 2012~
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The Stage III operational period refers 'to the period after the normal maximum
water level has reached el. 2,185 ft, which may be between two and six years
after the beginning of filling, depending on the reservoir inflow and energy
production. Stage III operation is anticipated to begin in 2016.
2.3.1 Co~struction
Passage of river flows during Stage III will ·be accomplished by in-place
Stage I project features~ Stage III diversion will involve
reconstructing the downstream cofferdam over the in-place slurry trench
cutoff, and dewatering the area between the Stage I dam and the cofferdam
by pumping.. The construction on the dam will be accomplished in the dry
during the seasona 1 (lrawdown when the Stage I reservoir e 1 evat ion is
below 1,925 ft. The placement of the fill on the downstream face of the
Watana dam and raising of the crest elevation prior to filling will not
affect power generati~m or flows as described in Section 2.2.4.
2.3.2 Filling
Filling of the Stage III reservoir from a normal maximum water level of
el. 2,000 ft to a fliormal maximum level of el. 2,185 may take between
three and seven year:s depending on inflow to the project, energy demands
and progress in construction of the dam, powerhouse intake and spillway.
Flood flows Which would normally be released through the outlet works in
Stage II will be utilized to fill the res~rvoir. This will result in a
decrease in July-September flows and a stabilization of r·iver flows
during the period of fi 11 i ng. Fi 11 i ng wi 11 take place in a gradua 1
manner as the dam crest, spi 11 w;1y agee crests, and intake tower are
raised. Since portions 01e the spillway crest will be constructed during
this period, storage will be provided in the reservoir so the remaining
spillway capacity will be sufficient to ensure the safety of the dam.
This will be one limit on the rate that the reservoir water level can be
raised. A second 1 imit on the water level will be the amount of flow
incomi.1g to the reservoir and the power gener~.r-ed by the project during
this period. A third constraint \~f:: b~ the environmental flow
requirements of Case E-VI.
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During ''ormal operation of Stage II, between zero and 2,000,000 acre-feet
of water wi 11 be passed through th1e outlet works in the July-September
period every year to maintain dam freeboard requirements and ensure the
safety of the structures.. During Stage I I I fi 11 i ng, this water wi 11 be
used to raise ttie normal maximum w:ater level. Power generation will be
maintained at Watana during the filling process and water levels in the
reservoir will vary in the same mafilner as for normal operation. That is,
they will reach their highest point in ·September and be reduced
throughout the winter. Beginning! in May, water levels will start to
rise~ Water levels will generally continue to rise through July9 August,
and September, provided that sufficient flood storage is avai 1 able to
compensat~; for reduced spillway capacity during spillway constr·uction and
provided t\~e multi-level intake tower has been raised. The maximum water
1 eve 1 attained in September wi 11 increase from year to year unti 1 the
normal maximum level of ~1. 2,185 ft is reached.
During the fill1ny process the Case E-VI flow requirements will be
maintained. Since excess July-September flows will be stored in Watana
the flows at Gold Creek will be reduced from normal operational flows in
July through September. The flow~ will generally be near the minimum
flow requirements during the summer.
Flood flows downstream will be reduced since these will be stored in the
reservoir. As noted before, sufficient storage will be maintained so
that the structure is not endangered by floods.
2.3.3 Testing and Commissioning
The fifth unit at Watana and the fir~t unit to be installed in Stage III
is scheduled to be tested and commissioned in spring of 2012. The second
unit will be tested and commissioned in the summer of 2012. The testing
of th.e units requires several set:!uences of bringing the units on-1 ine and
taking them off-line. These will be accomplished in a manner to minimize
the effects on flow stability. This can be done in several ways, any of
which may be selected. One method would be to reduce flows through the
outlet works or other units by amounts compat'ab1 e to the test flow
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through the unit. A second method would be to store the test flow at
Devil Canyon Reservoir w1thout releasing it downstream.
2e3.4 Operation
After Stage III comes on line, Watana will be operated as a peaking plant
and Devil Canyon as a baseloaded plant subject to discharge fluctuation
constraints between 90 percent and 110 percent of the weekly average.
Advantage wi 11 be taken of the two-reservoir system to optimize energy
production with the constraint that the Case E-VI downstream flow
requirements will be met. Minimum requirements will be met by releases
from the powerhouse and, if necessary, the outlet works.
Devil Canyon Reservoir will re-regulate peak disc~arges from Watana. The
Devil Canyon Reservoir will normally be at its maximum water leve1 7 el.
1, 455 ft, between November and May. In dry years De vi 1 Canyon wi 11 be
drawn down between May and November reaching its minimum level of el.
1, 405 ft in August. In average flow years, the reservoir wi 11 be drawn
down between June and August reaching a minimum of approximately el.
1,440 ft in July.
Watana will still be operated in a storage-and-release mode similar to
Stage II, so that summer flows will be stored for release in winter.
Generally, the Watana Reservoir will be at or near its normal maximum
operating 1 eve 1 of e 1 . 2,185 ft each year at the end of September.
Gradually, the reservoir wil1 be drawn down to meet winter energy demand.
The flow during this period wi 11 be governed by winter energy demand,
water level in the reservoir, and powerhouse characteristicso The
turbine characteristics will allow a maximum powerhouse flow of
approximately 22,000 cfs.
In early May, the Watana reservoir will reach its annual minimum level of
between approximately el. 2,080 ft and 2,130 ft, depending on energy
demand and inflow, and then begin to refill with the spring runoff~ Flow
in excess of both the downstream flow requirements and power needs will
be stored during the summer until the reservoir reaches the normal
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maxi mum operating 1 eve 1 o1~ ·a 1 . 2 11 185 ft. If the r~servo i r reaches e 1 .
2,185 ft, and inflow exceeds energy and environmental flow requi\~ements,
excess flow will be released and the reservoir water level will rise as
the flood is being stored.
Project operation for dam safety criteria at Watana with both Watana and
Devil Canyon operating in Stage III will be similar to Stage II .
operations. However, the normal maximum water level in Watana Reservoir
will be el. 2,185 ft and the flood surcharge level will be el. 2,193 ft ..
Whi 1 e Watana reservoir is fi 11 i ng in the spring, and before the water
level reaches el. 2,185.0 ft, the Devil Canyon powerhouse will be used to
meet system energy demand~. Watana must st i 11 generate a por.·t ion of the
energy in order to meet peak system energy demands. Wlhen the Watana
water level reaches el. 2,185.0 ft, it is necessary to switch enE~rgy
generation from Devil Canyon to Watana in order to pass the 50-year f"lood
without using the spillway. The change from Devil Canyon to Watana would
be made in a gradual manner, but in no case would the Watana water level
be a 11 owed t.o rise above e 1 . 2, 185.5 ft without the Watana powerhouse
supplying all available system energy demands and the Watana outlet works
releasing at 24,000 cfs. AftAr the system load is transferred from Devil
Canyon to Watana, the operation at Watana would be identical to that for
Watana only operation.
When the Watana water level reaches el. 2,185 ft, Devil Canyon reservoir
will be allowed to fill while minimum flow requirements are being met.
While the Devil Canyon reservoir is filling, thr~ outlet works will be
opened up in a gradual manner estimated to prevent the water level from
exceeding e 1 . 1 ~ 455 ~ 0 ft. When the water 1 eve 1 reaches el . 1, 455.0 ft
the outlet works wi 11 be opened as much as necessary to keep the water
level stable. In this per1od, Devil Canyon will operate as essentially a
run-of-river project, passing Watana outflows and intervening flows. The
rates of change of Devil Canyon discharge will be similar to those for
W&tana with small modifications resulting from variations in intervening
flow.
30
Devi'I Canyon can pass all of the Watana outflows and all intervening
flows through its outlet works without using its spillway unless the
Watan~ s;p~llt~ay is operating. The 50-year flaod inflow may exceed the
capacity of the Devil Canyon outlet works (APA 1985b). Therefore, a
surcharge storage is prov1d,~d to store the flow in excess of the cutlet
works capacity. During f1 oods the ~~~vi 1 Canyon water 1 eve 1 ~; 11 be
maintained at el. 1,455.0 ft until the outlet works 4re discharging at
their fr~ll capacity. If the inflow exceeds the capacity., the water level
will be allowed to increase to e·l. 1,456.0 ft. In this manner, the
50-year flood can be stored and released without operating th~ spillway.
If the water level continues to t"ise above el. 1,456.0 ft, the Devil
Canyon spillway gates must be opened to maintain freeboard on the dam.
The chance the spillway would,be operated in any one year is less than 1
in 50. The spillway gates will be opened at whatever rate is necessary
to keep the pool at this level. The spillway has the capacity to pass
the 10,000-year flood with the reservoir water level at el. 1,456.0 ft
(APA 1985b). Thus, there is less than 1 in 10,000 ~chance that the Devil
Canyon water 1 eve 1 waul d exceed this 1 eve 1 in any one year. If the
spillway gates were opened completely and the reservoir level continued
to rise, discharge from Devil Canyon would be uncontrolled. The Devil
Canyon spillway is designed to pass the PMF. The maximum water level
obtained during a routing of the PMF was el. 1,453.1 ft which is 2~9 ft
be 1 ow the crest of the concrete parapet wa 11 and 7 ft be 1 ow the top of
the rockfill dam sections. Control would not be regained until the water
1 eve 1 receded to e 1 . 1, 455 o 0 ft. When the water 1 eve 1 decreases to e 1 .
1,455.0 ft the spillway and outlet works will be closed in a manner to
keep the water level at el. 1,455.0 ft.
When system energy demand increases, the oper-ation to pass floods would
differ slightly from the early years of Devil Canyon operatic~. If the
water level at Watana were to rise above el. 2,185.0 ft it would not be
necessary to switch all the energy generation to Watana. Only that
generation would be switched which would be necessary to keep the Watana
water level from exceeding el.· 2~193~0 ft for the 50-year flood. It is
estimated that this requires a Watana powerhouse discharge of 7,000 cfs ..
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Additionally, the increased -Jnergy demand means that Devil Canyon would
have the capacity to discharge some flow fr()m its p'owea"house before it
becomes necessary to open the outlet works. The additional Devil Canyon
powerhouse flow waul d make it possible to pass the 50-year flood :.without
surcharging the reservoir.
Overall, operation of the two dams with greater system energy demands
Wi'~l result in more gradua 1 changes in discharge and 1 ess chance of
outlet works or spillway operation than in the first years of Stage III
operation. In an emergency situation where part of the energy generation
system is temporarily out of operation, Watana and/or Devil Canyon may be
operated tQ provide the nee~ed power as described in Section 2.1.4.
2.4 Project Schedule
The proposed schedules for each stage of the Project are presented in Figures
4 through 6. Access construction for Stage I I wi 11 overlap the construct·i on
on the Stage I Watana dam. Construction of Stage III wiil be initiated
·following completion of Stage II construction"
32
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l'lliCAIPTlON ,,,._
Ot
02 INITIAL ACCESS (1987)
03 -04 MAIN ACCESS
05
08 MAIN SITE fACILITIES -07
08 DIVERSION TUNNELS
09
10 COFFERDAMS
u
12 DAM EMBANKMENT
13
14 RELICT CliANNEL
t5
16 SPILLWAY EXCAV.
17
18 SPILLWAY CONCRETe
1i
20 OUTlET FACIU~
' 21 _,
22 POWER INTt.l<f
23
24 POWER. TUNt~ElS
25
28 POWeRHOUSE
27
28 <RANSFORMER GAllARY/CABtE SHAFTS
29
~ T AILRACE/SURQE CHA~13ER
31 -32 TURBINE/GENERATORS
33
34 MEvH.IELECT. SYSTEMS
35
31 SWITCHVARD/CONTROL BLOO,
37
38 TRANSMISSION LINES
3~
40 IMPOUNDMENT .. , ..
41 TEST AND COMMISSION
43 ...
'vVATANA STAGE I
CON.STRUCTION SCHEDULE
SOURCE: APA 1985a
I
, ... , .. , 111:1 1tU
.., ~~
,..,.., ............. ...... tl 1 --
K Itt ll m V
'
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'
LIGINt -ACCESS/FACILITif.S -£XCAVATION/FOUNUA110t~ TAt:ATMENT
.. '"''''' filL -~Ut4CRETE ........ Mft..HM41t;Alii:L EC TfUCAl
-IU .. uUNUMt.Nl
FIGURE
"'"' , ... , ... .. ., .. .. ....
01
02
03
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05
01
07
01
*UIVC.Hl'ilON ot
' ,,,,,,,,,,, to
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................ ..,,,J ·''''''"'~ ......... ,y,.,,,,.: ,,y,.~'''' 12
13 ---...
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17 ,,. ..
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22
23 -24
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33 .. ....... ,..
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UNITS l ! 10NLtHl .. ,
4.2
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ALASKA POWER AUTHORITY
.SVSITNA HYDROELECTRIC PROJECT
ENTRIX, INC. HARZA·E BASCO
4 SUSITNA IOINT VENTURE
-..
/;
011\CIIIPTlOM ,. .. , ... uer Ull ,, .. 1000
01
02 UAIN ACCESS
03
04 SITE fACILITIES
OS
06 DIVERSION tUNNELS . ~ ....
07 . ~DIVI:H:>IUN
oa COFFERDAMS ,,,,,,,,,,,,,
09
~
to UAIN DAU --11
12 SADDLE OAU
13
" , .. OUTLET FACILITIES
15
16 SPILLWAY
t7
18
19 ..
20 POWER INTAKE
21
22 POWER TUNNELS
l3 ACCESS V~
24 POWERHOUSE
2S
.zt lRAkSFOAMER GALLERY /CABLE SHAFTS
n
l6 TAILRACE/SURGE CHAMBER -~
2'
30 TUJII81NES/OENERATORS
ll ..
32 MECH.IELECT~ ~\'STEMS
33
34 SWITCtftARO/CONTAOL SLOG
3S
' lS TRANSMISSION LINES I
J7 ,_._
l. IMPOUNDMENT -39
40 TEST & COr.lMISSION --.. , -.
•z
<13
u
1. ......
-ACCESS/fACILITIES
DEVIL CANYON STAGE II -EXCA\IATION/fOUNDATION l'AEATWE~T
·'"''"" fiLL
CONSTRUCTION SCHEDULE -CONCRETE
_.__ MfCHANICAL/EL£CTRICAL
-IMii'OUNOi.;S:NT • SOURCE: APA 1985a FIGURE 5
•'
lOOt 1001 1001 ..... •••• .....
.l .
-DIVERSION PLU<
•
:
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PH CRANES ! .......... --··-·· ..... ·--STRUCTURES/I I"\ I ..,...._..,,,,,, .. .......... , I
i -..... ,... ... t -· .1. EL • 1455 !
l.
UNITS .. ,.., ' .. a ll .... 'nN.IIt.tl'
.
ALASKA POWER AUTHORITY
SUSITN,t, HYDROELECTRIC PROJE.CT
HARZA-EBASCO ENTRIX, INC • SUSITN~. JOINT VENTURE
01
02
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04
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FIGURE 6 SUSITNA JOINT VENTURE ' I
3. 0 EVALUAJIOtLSPEC1ES
3.1 ,S..e.1 ect ion
Various species and 11ife stages have different critical 1 ife requirements and
respond differently to habitat alterations. A change in habitat conditions
that benefits one species or 1 ife stage may 1dversely affect another.
Moreover, project impacts on the habitats of certain sensitive fish species
are of greater concern th~n changes in di stri but ion and abundance of 1 ess
sensitive species. Sensitivity can be related to high human use value as well
as susceptibility to change because of project impacts. Statewide policies
and management approaches of resource agencies suggest that concern for fish
and wildlife spet·ies wi-::.h tomtr.ercia1, subsi$tence, or othfH" consumptive uses
is greater than for species -withcJUt .such value. These species are often
numerous, and utilize a wide range of habitats, as well as having high human
use value. ~~~~h characteristics nften result .! t these species being se"'Jected
for careful evaluation when thelr habitats are sub.jected to alternative uses ..
By avoiding or minimizing alterations to habitats utilized by these species,
the impacts to other less sensit~'~e species that utilize similar habitats may
a 1 so be avoided or reduced. Therefore, the criteria used in th~ eva 1 uat ion
species selection process were:
o High human use value;
o Dominance in the ecosystem; and
o Sensftivity to project impactse
The e'Jaluation species for the middle Susitna River were selected after
initial baseline studies and impact assessments had identified the important
species and potential impacts on ava71able habitats throughout the year.
Sfnce the greatest changes in downstream ha~itats are expected in the reach
between Devil Canyon and Talkeetna) f·ish using that portion of the river 'f!ere
considered to be the most sensitive to project effects. Because of differ-
ences in their seasonal habitat requirements, not all species would be equally
affected by the proposed project .. Of the species in the middle Susitna RiVf!r,
chum and sockeye salmon appear to be the most vulnerable because of their
depaqdence on slough habitats for spawning, incubation and early rearing. Of
36
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these two, chum salmon are the dominant species. Chinook. and coho salmon are
less likely to be impacted by the project because two critical life stages,
spawning and i\:icubation, occur· 'in habitats that are not 1 ikely to be altered,
by the project. Similarly, while some pink salmon spawn in slough habitats in
the reach between Ilevil Canyon and Talkeetna, most of these fish utilize
tributary habitats. Project effects on the rearing 1 i fe stage of ju~en i 1 e
salmon, particularly chinook salmon, are also of concern~ The chinook juve-
niles rear in the river for up to two years and coho salmon juveniles for up
to 3 years prior to outmigrationa Much of the coho rearing apparently occurs
in clear water areas, such as in sloughs and tributary mouths, with the more
abundant chinook rearing in turbid side channels as well as clear water areas.
Maintenance of chinook rearing habitat should provide sufficient habitat for
less numerous resident species with similar lif~ s~age requirements.
In summary, the primary and secondary evaluation species and 1 i fe stages
selected for the Susitna Hydroelectric Project in the Devil Canyon to
Talkeetna Reach are:
);
PRIMARY
Chinook Salmon
-Rearing/overwintering juveniles
Chum Salmon
-Spawning adult~
-Embryos and pt"e~-emergent fry
SECONDARY
Chinook Salmon
-Returning adults
-Outmigrant juveniles
Chum Salrnon
-Retur~ing adults
Rearing juveniles
-Outmigrant juveniles
37
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Sockeye Salmon
-Returning adults
Spawning adults
Embryos and pre-emergent fry
-Rearingioverwintering juveniles
Qutmigrant juvenilei
Coho Salmon
-Returning adults
-Rearing/overwintering juveniles
Outmigrant juveniles
Pink Salmon
Returning adults
-Spawning adults
-Embryos and pre-emergent
-Outmigrant juveniles
Rainbow Trout
-Adults
-Juveniles
Arctic Grayling
"" Adults
-J'tveni l es
Burbot
-Adults
-Juveniles
Dolly Vard~n
-P~dults
38
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3.2 Habitat Utilization by Evaluation Species
Twenty species of fish have been observed in the Susitna River (WCC 1985a).
Of the twenty species, nine were chosen ?~ evaluation species for the
assessment of project effects on fish in the middle reach of the Susitna River
(Section 3.1). The e~valuatiort species include chinook, chum, sockeye, coho,
and pink salmon, rainbow trout, Arctic grayling, burbot, and Dolly Varden. A
detailed discussion of species. biology and utili;~ation of the various habitat
types in the middle Susitna River is found in WCC (1985a)e
Fishery resources of the Sl~sitna River comprise a major-portion of the Cook
Inlet commercial salmon harvests and !}rovide sport fishing opportunities for
anglers. Five species of Pacific salmon form the base of the commercial and
sport fisheries. The annual escapements of the five salmon species to various
locations in the Susitna River for 1981 th~ough 1984 are presented in Table 4.
.Based on escapements to Curry Station (RM 120) for 1981 through 1984, the
middle reach of the Susitna River provides habitat for annual escapements of
approximately 13,000 chinook; 28,200 chum; 2,400 sockeye; 1,600 coho; 87,900
even-year pink; and 3,300 odd-year pink (Table 4). Chinook and ~oho salmon
spawn in tributary streams and tributary mouths in the middle Susitna River,
pink salmon primarily in tributary streams and tributary mouths (with a small
number utilizing slough habitats), chum salmon in tributary streams, sloughs,
and tributary mouths, and sockeye almost exclusively in sloughs {ADF&G 1985a).
Relatively few salmon spawn in the mainstem and side channels in the middle
Susitna River. Of those which do, chum salmon predominate (ADF&G 1985a).
Four of the five salmon species present use middle Susitna River habitats for
rearing (APF&G 1984a) .. From May to September, juvenile chinook salmott rear in
tributarir .: ~ tributary mouths, and side channels.; coho mostly rear in
tributaries, tributary mouths, and upland sloughs; and sockeye move from natal
side sloughs to upland sloughs for rearing. From May to July raaring chum
salmon are distributed in tributaries, side sloughs, and side channels. Pink
salmon juveniles move downstream to Cook Inlet shortly after emergence and do
not rear in the middle Susitna River (ADF&G 1984a).
39
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Table 4. Estimated salmon escapements by species a11d locations in the Susitna
River, 1981-1984.
Sampling Escagement!l
SockeyeY Coho Total Location Year Chinook Pink ·Chum
Flathorn 1984 11 605,800 3,629,900 812,700 190.,100 5,238,500
Station
Yentna 1981 !/ 139,4CIO 36,100 19,800 17'' 000 212,300
Station 1982 113,800 447,300 27,800 34,100 623,000
1983 104,400 60,700 10,800 8,900 184,800
1984 149,41)0 369,300 26,500 18,200 563,400
Sunshine 1981 y 133,51JO 49,500 262,900 19,800 465,7no
Station 1982 52,900 151,500 443,200 430,400 45,700 1,123,700
1983 90,100 71,500 40,500 265,800 15,200 483,100
1984 121,700 130,100 1k017,000 765,000 94,700 2,128,500
Talkeetna 1981 y 4,800 2,300 20,800 -3,300 31,200
Station 1982 10,900 3,100 73,000 49,100 5,100 141,200
1983 14,400 4' 20l') 9,500 50,400 2,400 80,·900
1984 24,800 13, 10tl 177,900 98,200 11,800 325,800
Curry 1981 y 2,800 1,000 13,100 1,100 18,000
Station 1982 11,.300 1,300 58,800 29,400 2,400 103;200
1983 9,700 1,900 5,500 21,.100 800 39,000
1984 18,000 3}600 116,90.0 49,300 2,200 19·tJ,OOO
.lJ Escapement estimates were derived from tag/recapture population estimates
except Yentna Statiou escapements which w~re obtained using side scan
sonar.
Y Second l,un sockeye .>almon escapements only.
Y Chinook salmon were not monitored for escapement.
Y Yentna Station side scan sonar equipment was not operational on the dates
required to estimate the total Yentna River chinook salmon escapements
for 1931-84 ..
Source: ADF&G 1985a.
40
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Rainbow trout, Arctic grayling, and Dolly Varden spawn in tributaries of the
middle reacb of the Susitr~a Rtver. Juvenile and adult rainbow trout, Arctic
grayling, ~~nd Dolly Varden rear in tributaries, tributat'Y mouths, and to a
1 esser exttant. sloughs. Most fish of these three species apparently move from
tributari~s to the mainstem to overwinter (ADF&G l984a, 1985b).
Estimates of the rainbow trout population si~e in the middle Susitna River
range from 1,000 to 5,000 fish (ADF&G 1984a, 1985b}. The Arctic grayling
population size in the middle Susitna River is estimated to range from 2,500
to 7,000 fish {ADF&G 1985b). Dollv Varden are not abundant in the middle
Susitna River, with insufficient numbers of fish caught to estimate population
s,ize.
From May to September in the middle Susitna River, juvenile and adult burbot
are found in turbid mainstem-influenced areas, typically in low-velocity,
deep-water areas of the mainstem and slough mouths. Burbot also spawn and
overwinter in mainstem areas. Burbot densities in the middle Susitna River
were estimated to be 15 fish per mile in 1983 (ADF&G 1984a).
To facilitate the assessment of project effects on fish in the middle Susitna
Rive~ .. , a summary of the habitat utilization of the primary and s-t~condary
evaluation species and life stages is p~esented in the following sections. A
detai1~d discussion of the habitat types and their response to changes in flow
can be found in EWT&A and wee (1985).
3.2.1 Mainstem and Side Channel Habitats
The mainstem of the middle Susitna River has both single and split
channel configurations. Single channel reaches are generally stable with
non..,erodible banks controlled by valley wallst bedrock, or an a,.mor layer
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cor;;1isting of graval and cobbles. The channel is either straight or f'
meandering. In straight channel reaches, the thalweg often meanders
across the channe 1 • Sp 1 it channel configurations are character; zed by
moderately stable channels with a gravel/ctlbble substrate. There are
usually no more than two channels in a given reach. Channels are
separated by well established vegetated islands.
41
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Side ch~linels are generally located in peripheral areas of th~ mainstem
corridor. Side channels have a diverse morphology with some having broad
channels while others are narrow and deep. Side channels are highly
influenced by mainstem discharge and water quality. In general, a side
channe 1 habitat conveys 1 ess than 10 percent of the total discharge in
the rive·r, but conveys mainstem discharge more than 50 percent of the
time during the summer high flow months (EWT&A 1984, 1985}. Side
channels normally breach, i.e. convey mainstem water, at ma'instem
discharges less than 20,00t1 cfs {EWT&A and AEIDC 1985). Side channels
have relatively low ve·locity (less than 3-4 ft/sec), shallow depths, anu
convey turbid water during the summer. When mainstem discharge decreases
in the late fetll and winter, side channels may become complete·fy
dewatered or may convey water derived from local runoff, tributaries, or
upwelling groundwater.
The utilization of the mainstem and side channels by the primary and
secondary evaluation species and life stages is summarized below.
{a) Primary Evaluation Species
{i) Chinook Salmon -rearing/overwintering juveniles .
Some rearing juvenile chinook salmon move into the mainstem
from natal tributaries as part of their downstream
redistribution to rearing areas in the middle Susitna ~iver or
the lower Susitna River. Thust the mainstem serves as a
migrational corridor for rearing juvenile chinook salmon. The
movement of rearing juvenile chinook through the mainstem to
rearing areas usually commences in May or June and cant i nues
through September (ADF&G 1984a). Juvenile chinook also use the
mainstem as a migrational corridor from September through
November1 when moving from .~aring areas to ove~wintering
areas.
Side channels pro vi de habitat for the 1 argest proportion of
rearing juvenile chinook salmon in the middle Susitna River,
42
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excluding tributaries. Approximately 23 percent of the catch
per un·it effort for juveni 1 e chi nook salmon was from side
channels in 1983 (AOF&G 1984a}. Rearing juvenile chinook
ut·llize side channels from late May or ~arly June to October
(ADF&G 1984a}. It appears that most juvenile chinook move out
of side channels in September and October and move tQ
over\t~i nteri ng areas in s 1 ou.ghs.
( i i) Q)um Sa 1 mon -spawning_ adults, embryos,__ and pre-emergent fry
Chum salmon spawning adults utilize the mainstem and side
chann~ls in the middle Susitna River. In 1984, when a
concerted effort was made to locata mainstem spawning areas,
approximately 3,800 adult chum salmon (8 percent of the
estim~ted chum escapement to Cur·ry Stati~·n) spawned in the
mainstem and side channels {ADF&G 1985a}. Most spawning
activity occurred in areas o·f upwelling groundwater during
September and October. Chum salmor embryos and pre-emer~ant
fry remain in spawning sites until emergence in March or April.
(b) Secondary Evaluation Spec~es
{1) Chinook Salmon-returninq adults, outmigrant,juveniles
Chinook salmon returning adults utilize the mainstem, and to a
lesser extent sid~ channels, as migrational corridors to
spawning areas in tributaries. Based on estimated escapements
at Curry Station for 1981 through 1984, approximately 13,000
· chinook salmon armu&lly utilize the mainstem , ~r upstream
movements. Migrational timing of adult chinook ~dlmon in the
middle Susitna River extends from June through July (ADF&G
198Sa). The mainstem and side channels also serve as
migrationai corridors for outm·igrant juvenile chinook salmon.
Juvenile chinook salmon utilize the mainstem and side channels
for outmigration from May through September i.n the middle
Susitna River (AOF&G 1984a}.
43
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(ii) Chum Salmon -returning adults, rearing :luveniles, outmigrant
Juveniles
Chum salmon returning adults use the mainstem and side channels
for Movement to spawning areas in the middle Sus i tna .~i ver.
Based on estimated escapements at Curry Station for 1981
through 1984, approximately 28,200 thum salmon annually migrate
into the mi.ddle Susitna River (AD.F&G 1985a). The adult chum
migratiJn 1 asts from mid-July through mid-September in the
middle-Susitna River.
Rearing juvenile churu salmon utilize side channels during May
and June. Side channels and the mainstem are also important
migrational corridors for outmigrant juvenile chum salmon. The
juvenile chum salmon ,outmigration lasts from May to ea,~ly July
in the middle Susitna River (AGF&G 1984a).
{iii) Sockeye Salmon -returning aQ..y.Jts, spawning adults, embryos and
---....
pre-emergent fry, rearing/overwintering juveni 1 es ,_putmigrant
juveniles
Sockeye s~\mon returning adults and outmigrant juven~1as
utilize the mainstem and side channels primarily as migrationat
corridors. Returning adults migrate through the mainstem, and
to a 1 esser extent side channels, from July through
mid-September to spawning areas in side sloughs {ADF&G 1985a}.
Based on estimated escapements to Curry Station for 1981
through 1984, approximately 2, 400 sockeye annua 11 y uti 1 i ze the
mainstem fo~ upstream migration to spawning areas~
Juvenile sockeye utilize the mains tern and side channels for
movements to other areas for rearing, overwintering, and
outmigration. The outmigration timing of juvenile sockeye
salmon extends from May throu~h September in the middle Susitna
River {ADF&G 1984a).
44
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(iv)
Sockeye spawning adults rarely utilize the mainstem or side
channels. H~~nce, embryos and pre-emergent fry also o~cur
infrequently in these areas. Rearing and overwintering
juvenile sockeye primarily utilize sloughs and rar'ely use the
mainstem or side channels.
Coho Salmon returning adults, rearing/ov~rwintering
juveniles, outmigrant juveniles
Coho salmon returning a'Jults and outmig,..ant juveniles utilize
the mainstem and side channels primarily as migrational
corridors. Returning adults migrate through the mainstem, and
to a lesser extent side channels, from mid-July to
mid-September to sp~wning areas in tributaries. Based on
estimated escapements at Curry Station for 1981 through 1984,
approximately 1,600 coho annually utilize the mainstem for
upstream migration to spawning areas (ADF&G 1985a}.
Juvenile coho salmon utilize the mainstem and side channels for
movements from nata 1 tributaries
ove:rwi nteri ng, and outmi grat ion.
main stem and side cha.nnel s occur
September (ADF&G 1984a).
to other areas for rearing,
These movements thrnugh the
primarily during Ma~ through
Rearing and overwintering juvenile coho rarely use the mainstem
or side channels.
Coho salmon outmigrant juveniles utilize the mainstem and side
channels for downstream movements from May through September
{ADF&G 1984a}.
(v} Pink. Salmon -returning adults, spawning adults, embryos and
pre-emergent fry, outmigrant juveniles
Pink salmon returning adults utilize the mainstem and side
channels primarily as migrational corridors. Returning adults
45
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(vi)
migrate through the mainstem, and: to a lesser extent side
channels, from mid-July through August to .spawning areas in
tributaries and sloughs. Based on estimated escapements at
Curry Station for 1981 through 1984, approximately 87,900
even-year and 3,300 odd-year pink s.almon annually utilize the
mainstem for upstream migration to spawning areas {ADF&G
1985a).
Pink salmon spawning adults rarely use the mainstem or side
channels. Hence, few embryos and pre-emergent fry are in the
mainstem or side channels.
Pink salmon outmigrant juveniles utilize the mainstem and side
channels for downstream movements from M~y to mid-July {ADF&.G
1984a).
Rainbow Trout -adults, juvenile..s.
Rainbow trout adults move into the mainstem for overwl\"tering
{ADF&G 1984a, 1985b). The movement of adult rainbow trout into
the mainstem occurs from October to December. Rainbow trout
l!tilize. the mainstem for overwintering until April or May, when
they move into tributaries to spawn.
Rainbow trout adults and juveniles also utilize the mainstem
and side channels as migrational co7'ridors from natal
tributaries to rearing areas in sloughs. The movement of
rainbow trout into sloughs usually coincides with the timing of
salmon spawning {August and Septerr~ber) {ADF&G 1984a),
{vii) Arctic Grayling -adults, juvenile!
Arctic grayling adults move into the mainstem for overwintering
{ADF&G 1984a). Arctic grayling move into the mainstQm in the
fall, reside primarily downstr&am of natal tributaries, and
46
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move from the mainstem into tributaries to spawn in late April
and May (ADF&G 1984a).
Arctic grayling adults and juveniles also utilize the mainstem,
and to a lesser extent side channels~ as migrational corridors
from natal tributaries to rearing areas in sloughs. The use of
sloughs by Arctic grayling adults and juveniles appears to be
limited {ADF&G 1983a).
{viii) Burb9t -adults, juveniles
( ix}
Burbot adults and juveniles utilize the mainstem throughout the
year (ADF&G 1983a, 1984a). Side channels are also utilized
during the summer high-flow season. All life stages of burbot
(spawning, incubation, rearing, and overwintering) occur in the
rnainstem. Spawning adults utilize the mainstem in late
December to Febtuary. Incubating embryos are in the mains~em
from mid-winter until MaYch to June.
Dolly Vurden -adults
Dolly Varden adults move into the mainstem from tributaries
presumably in October and November (ADF&G 1983a, 1984a). Dolly
Varden overwinter in the mainstem until April or May, when they
move into tributaries to rear (ADF&G 19S4a).
3. 2. 2 Side Sl otJ~h and Y.P.J.and Sl oug~h Habitats
Side sloughs are morphologically similar to side channels a.nd
distinctions between side sloughs and side channels are somewhat
arbitrary {EWT&A 19~35). Side sloughs may be distinguished fti3m side
channels by the mainstem discharges required to breach the upstream ends-
A mainstem discharge of approximately.20,000 cfs was selected (EWT&A and
AEIDC 1985). Hence., side sloughs convey mainstem water less than
approximately 50 percent of the time during the summer high flow months.
47
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Upland sloughs are analogous to sma11 tributaries (EWT&A 1984).
Discharge in upland sloughs is derived from local runoff, smill
tributaries~ and groundwater upwe~1ing. Many of the upland sloughs are
inhabited by beavers. The upstream ends of upland sloughs are often
separated from the rdainstem by vegetatt:., areas indicating that breaching
of the upstream end occurs only at extremely high .mainstem discharge.
The utilization of side sloughs and upland· sloughs by the primary and
secondary evalu~tion species and life stages is summarized below.
{a) Primary Evaluation Species
( i) Chinook s,lmon -rearing/overwintering juveniles
Rearing juvenile chinook salmon utilize side sloughs and upland
sloughs, but the proportion of the catch per unit effort in
side sloughs and upland sloughs was only 16 percent in 1983
{ADF&G 1984a). Rearing juvenile chinook utilize side sloughs
and upland sloughs throughout the summer (May through
September). Juvenile chinook salmon also use side sloughs and
upland sloughs fer overwintering (ADF&G 1985c).
( i i) ,khum Sa 1 mon.-spawning adults 3..~rt1bryos and j)re ... emergent fry
Chum salmon spawning adults utilize side sloughs, and
occasionally upland sloughs. Side sloughs are important areas
for spawning chum sa~mon in the middle Susitna River. In 1984,
about 50 percent of the ~stimated chum salmon spawning i~ the
middle Susitna River occurred in side sloughs (ADF&G 1985a) ~
Incubating embryos and pre-emergent fry are present in side
sloughs through the winter until emergence in March and April.
48
: ,-.~
(b) Secondary Evaluation Species
(i) Chinook Salmon -returning adults. outmigrant juveniles
Chinook salmon returning adults and outmigrant juveniles rarely
utilize side slough or upland slough habitats.
(ii) Chum Salmon • returning adults, rearing juveniles, outmigrant
iuveniles
Adult chum salmon in sloughs are considered spawning adults
[Section 3.2.2(a)].
Chum salmon rearing juveniles utilize natal sloughs for rearing
for one to two months after emergence (ADF&G 1984a).
Outmigrant juvenile chum move out of sloughs from May to July
(ADF&G 1984a}.
{iii) Sockeye Salmon -returning adults, spawning adults, embryos and
pre-emergent fry, reari ng/overwi nteri ng ;i uven i 1 es, outmi grant
juveniles
In the middle Susitna River, a;most all sockeye salmon spawning
adults utilize side sloughs. Based on slough escape~t~ent
surveys during 1981 through 1985, over 95 percent of the adult
sockeye 1n the middle Susitna River spawned in side sloughs
(ADF&G 1985a, 1985}. Hence, most sockeye incubating embryos
and pre-emergent f~' in the middle Susit~a River are present in
side sloughs.
After fry emergence, juvenile sockeye rear in side sloughs for
a short time before outmigrating in July and August (ADF&G
l984a). Outmigrant juvenile sockeye either move to upland
sloughs to rear and overwinter or move downstream to the lower
Susitna River or Cook Inlet (ADF&G 1984a!.
49
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n 1· I 1 l
j \
L i _,
(iv} ~ho Salmon returning adults. rearin9/overwintertng
Juveniles, outmigrant juveniles
Coho salmon returning adu1ts rarely utilize sloughs.
Some rearing juvenile coho salmon move out of natal tribu~aries
and into sloughs for rearing. From May through November 1983,
the proportion of the coho catch per unit effort was about 35
percent in upland sloughs and approximately 10 percent in side
sloughs {ADF&G 1984a}. Juve~ile coho salmon also use upland
sloughs to overwinter.
Outmi grant juveni 1 e coho move downstream out of sloughs ov·
tributaries to other rearing or overwintering areas throughout
the summer (May to September) (ADF&G 1984a). Some juvenile'
coho outmi grants move into the 1 ower Sus i tna River or Cook
Inlet.
(v) Pink Salmon -returning adults, spawning adults, embryos and
pre-emergent fry, outmigrant juveniles
Some pink salmon spawning adults utilize sloughs in the middle
Susitna River. The use of sloughs by s:pawning pink salmon is
dependent on run size. During even years, the use of side
sloughs for spawning is higher than during odd years .. Overall,
the utilization of sloughs by spawning adult pink salmon is a
small proportion of the estimated pink salmon escapement to
Curry Station {ADF&G 1985a). Hence, incubating pink embr'yos
and pre-emergent fry are present in sloughs, but not abundant.
Juvenile pink salmon move out of natal areas almost immediately
after emergence {ADF&G 1984a}. Thus, most pink salmon
outmigrants move out of sloughs in April and May.
50
.,
(vi) Rainbow Trout -~dults, juveniles
Some rainbow trout adults and juveniles use sloughs in the
middle Susi tna for rearing and overwintering. The use of
sioughs by rearing rainbow trout occurs primarily during the
salmon-spawning period (August and September).. Rainbow trout
apparently feed on salmon eggs that are dislodged from spawning
areas {ADF&G 1984a).
Rainbow trout utilize slo.ughs in the middle Susitna River to a
limited extent for overwinte&"ing (ADF&G 1983a). The mainstem
and tributaries appear to be the preferred habitats in the
middle Susitna River for overwintering rainbow trout.
{vii) Arctic Grayling -adults, juvenilas
The use of sloughs in the middle Susitna River by Arctic
grayling adults and juveniles appears to be limited {ADF&G
1983a).
(viii} Burbot -adults, juvenile~
The use of sloughs in the midd:le Susitna River by burbot
appears to be limited. Juvenil~ burbot have been found in
sloughs and adults are thought to use the deep, backwater areas
in slough mouths (ADF&G 1983a, 1984a)~ However, the population
size of burbot in the middle Susitna River appears to be low
and few burbot have been caught in sloughs.
{ ix) Doll v Varden -adulli
Sloughs are rarely utilized by Dolly Varden in the middle
Susitna River.
51
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3.2.3 Tributary and Tributary Mouth Habitclil
Tributaries that flow into the middle Sus i tna River a 11 convey c 1 ear
water into the river. Tributary streamflowt sediment, and thermal
regimes reflect the integration of the hydrology, geology, and climate of
the tributary drainage. Hence, the physical attributes of tributaries
are not dependent on mainstem conditions. The two major tributaries of
the middle Susitna River are Indian River (RM 138.6) and Portage Creek
{RM 148.8), . each of which have an annual average discharge of
approximately 500 cfs.
Tr~ butary mouth habitat extends from upstream in the tributary, at '~he
point where backwater effects from the rna i nstem are observed, into the
mainstem where mainstem water mixes with the tributary water. The
downstream extent of tributary habitat is obvious during the summer when
the mainstem water is turbid and the tributary water is clear. The size
and the lat~ral location of the available tributary mouth habitat varies
with mainstem discharge and discharge from the tributary itself. At high
mainstem discharge, the habitat tends to be near the bank vegetation at
the mouth of the tributary, whereas at 1 o'l.r mai nstem discharge, the
habitat is further away from the bank vegetation.
The utilization of tributary and tributary mouth habitats by the primary
and secondary evaluation species and life stages is summarized below.
{a) Primary Evaluation Species
( i) Chi nook Sa 1 mon -reari ng/c·verwi nteri ng j uven i 1 es
Rearing juvenile chinook salmon utilize natal tributaries
throughout the summer. From May through November in 19R3,
~ approximately 61 percent of the catch per unit effort of
juveni 1 e chi nook was from tributaries (ADF&G l984a). Thus,
tributaries arn important rearing areas for juvenile chinook in
' the middle Susitna River.
52
a
{.
' I)
..
Soll'Je juvenile chinook salmon remain in tributaries throughout
tbe winter (ADF&G 1985c). Juvenile chinook that overwinter in
tr'ibutaries move out of tributaries in May, June, and July
(/~DF&G 1984a).
Tributary mouths are utilized by rearing juvenile chinook
salmon during summer. In August and September juvenile chinook
move! tu tributary mouths to feed on sa 1 mon eggs dis 1 odged from
the spawning areas of adult salmon {ADF&G 1984a, 1985c}.
{ii) Chum Salmon -spawning adults, embryos and pre-em~rqent fry
Tributaries are important spawning areas for chum salmon in the
middl'e Susitna River. In most years approximat.ely 50 percent
or more of thE! chum salmon spawning in the midd'le Susitna River
occurs in tributaries (ADF&G 1984b, 1985a). Hence, chum
embryos and pr'e-emergent fry are abundant in tributaries.
Tributary mouths in the middle Susitna River are also utilized
by churn spawning adults {ADF&G 1985a}. Thus, chum embryos and
pre-emergent fry occur in tributary mouths. Tne use of
tributary mouth.s is a relatively small J,.roportion of the total
chum salmon spawning in the middle Susitna River.
{b) Secondary Evaluation Species
(i} Chinook Salmon -returning adults, outmigrant juveniles
Chinook salmon v·eturning adults utilize tributary mouths as
migrational corridors to spawning habitats in tributaries"
Almost all spawning chinook salmon in the middle Susitna River
ut·il ize tributaries (a few spawn in tributary mouths) {ADF&G
1984b, 1985a)~ Hence, nearly all returning chinook salmon in
the middle Susi.tna River move through tributary mouths to spawn
in tributarie!). The utilization of these areas by chinook
salmon occurs in late June and July (ADF&G 1985a).
53
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Outmigrant juveni ie chinook salmon begin moving out of natal
tributaries in June. T~e downstream redistribution of juvenile
. chinook continues throughout the sum1~er. Thus, outmigrant
juveni 1 es move out of tributaries into tributary mouths or
other areas from June through SeptembP.r (ADF&G 1984a).
{ii) Chum Salmon
juveniles
returning adults, rearing juveniles, outmigrant
Chum salmon returning adults utilize tributary mouths as
migrational corridors to spawning areas in tributaries. Chum
salmon move into tributaries in late July through mid-September
in the middle Susitna River (ADF&G 1984b, 1985a). The
utilization of tributaries and tributary mouths by spawning
chum salmon was discussed in Section 3.2.3{a).
Rearing juvenile chum salmon use natal tributa~ies for one to
three months after fry emergence (ADF&G 1984a). In 1983 about
one-third of the catch per unit effort for juvenile cht~m salmon
was in tributaries (ADF&G 1984a}. Outmigrant juvenile chum
salmon move out of tributaries in May, June, and early July.
By mid-July most juvenile chum salmon have moved\ downstream of
Talkeetna (ADF&G 1984a).
(iii) Sockeye Salmon -returning adults, spawning adults, embryos and
pre-emergent fry, rearing/overwintering juveniles, outmiqrant
juveniles
Sockeye salmon rarely utilize tributaries and tributary mouths
in the middle Susitna River.
(iv) Coho ~almon returning adults, rearing/overwintering
juveniles, outmigrant Juveniles
Almost all spawning coho salmon in the middle Susitna River'
utilize tributarie.·s {ADF&G 1984b, 1985a). Thu~, coho salmon
54
returning adults utilize tl"ibutary mouths ·as migrational
r.:,ar\ridors to spawning areas in tributaries4 The migrational
t'imi ng of coho sa 1 mon into tributaries extends from August into
September (ADF&G 1984b}.
Following· the emergence of fry, many rearing juvenile coho
salmon remain in tributaries. From May through November in
1983, over 50 percent of the catch·per unit effort of juvenile
coho salmon was in tributaries {ADF&G 1984a). Tributaries also
provide overwintering habitat for juvenile coho salmon.
Some juvenile coho salmon move downstream to rear in tributary
mouths.. The greatest abun9ance of juvenile echo salmon in
tributary mouths occurs in August and September during the
salmon-spawning period. Presumably, the juveniles inhabit
tributary mouths to feed on salmon eggs dislodgeld from spa~n1ng
areas or drifting aquatic invertebrates {ADF&G 1984a). No
overwintering juvenile salmon have been observed in tributary
mouths.
Coho salmon outmigrant juveniles move out of natal tributaries
to other rsari ng or overwintering areas, or to the 1 ower
Susitna River and Cook Inlet, from May through September (ADF&G
1984a).
(v) Pin~ Salmon -returning adults, spawning adults, embryos and
pre-~~ergent fry, outmigrant juveniles
Most pink salmon in the middle Susitna River spawn in
tributaries {ADF&G 1984b, 1985a). Thus, returning adults move
through tributary mouths and into tributaries to spawn. The
migrational timing of pink salmon into tributaries is from
mid-July through August. Some pink salmon spawn in tributary
mouths, but the use of these areas by spawning pink salmon
comprises a relatively small proportion of the total pink
salmon spawning in the middle Susitna River. Embryos and
55
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pre-emergent fry are present in tributaries and tributary
mouths 1 n · direct proportion to the re 1 at i ve abundance of
spawning adults~
Pink salmon outmigrant juveniles move out of natal tributaries
and tributary mouths soon after fry emergence. Most juvenile
pink salmon move downstream from natal areas· in May and June,
and by mid-July almost all juvenile pink have moved downstream
of Talkeetna (ADF&G 1984a).
(vi) Rainbow Trout -adults, Juveniles
A 11 of the known rai nbo·w t·rout spawning in the middle Sus i tna
River occurs in tributaries (AOF&G 1984a, 1985b). Rainbow .
trout move from the mainstem into tributaries {through
tributary mouths) during May and June to spawn. Hence, rainbow
trout embryns are present in tributaries.
Tributaries are important rearing areas for juvenile and adult
rainbow trout throughout the summer. In early fall (August and
September) juvenile and adult rainbow trout move downstream to
tributary mouths to feed on salmon eggs (ADF&G 1984a}.
Most adult rainbow trout move out of tributaries and tributary
mouths into the mainstem to overwinter {ADF&G l984a}. Rainbow
trout usually move into the mainstem by late November or earJy
December. Some adult and juvenile tainbow trout may remain in
tributaries during winter.
(Vii) ~rctic Grayling -adults, juveniles
In the middle Susitna River, J\rctic grayling spawn in
tributaries in May and early Jun:e (ADF&G 1984a, 1985b). Prior
to spawning, there is a migration from overwintering
the mainstem to spawning areas in tributaries.
embryos are present in tributaries.
56
areas in
Grayling
Tri butariGs are 'important area~; for juveni 1 e and adult Arctic
grayling rt~ari ng (ADF&G 1984:a) . Most grayling adults and
·juveniles rear in tributaries throughout the summer. In the
'' fall (August and September) some adult a11d juvenile gra.Yling
move downstream to tributary mouths. Most. grayling move into
the mainstem to overwinter, although it appear~ that some
grayl i ng may remain in tri butatri es to ovetwi nter.
(vii) Burbot -adults, juveniles
Burbot adults and juveniles are rarely found in tributaries in
the mi dd'J e · Su;i i till a River. Burbot uti 1 i ze tributary mouths in
the middle Susitna River, but the use of these areas also.
app~r.trs to be limited {ADF&G 1984a).
(viii) Dolly Varden -adults
Dolly Varden adults move intcJ tributaries in May and ear·ly June
in the middle Susitna River. They remain in tributaries
throughout the summer to rear. Dolly Varden adults are thought
to spawn in tributaries du'ring fall (October) (ADF&G l984a).
After spawning, it appears that must adult Oo11y Varden move
from tributaries to t.he mainstem for overwintering. The
movement of Dolly Varden into the mainstem from tributaries
likely occurs in November.
57
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4.0 PHYSICAL CHANGES RESULTING FROM THE PROJECT
The physical changes in the middle Susitna River resulting from the proposed
Susitna Hydroelectric Project as compared to natural conditions include
variations in flows and water 1 eve 1 s, river morpho 1 ogy, water qua 1 i ty, and
groundwater conditions. Details of project operations which would cause these
changes are presented in the project description and schedule (APA 1985b).
Flows and water levels in the middle Susitna River·will generally be increased
in winter and decreased in summer during project operation.. The morphology of
the middle Susitna River is expected to· adjust slightly to the altered flow
and ~ediment regimes~ Changes in water quality include variations in
temper~ture, ice conditions, suspended sediment concentrations, and turbidity
levels in the middle Susitna River. Water temperatures during project
operation are expected to be generally warmer in the winter and cooler in tha
summer than during natura 1 conditions. Ice is anticipated to deve 1 op 1 ater
and break up earlier, and the upstream edge of the ice front is expected to be
located downstream of the ice front under natural conditions. Suspended
sediment concentrations and turbidii~ levels are expected to be substantially
1 ess than natural 1 evels during summer and sl ight1y gre~ter than natural
during winter. The water quality in the middle Susitna River is not expected
to be affected by the use of fuel and hazardous materials or the production of
concrete at the damsites, as potential contamination from these sources will
be avoided or minimized as described in the Access Corridor, Construction
Zone, and Transmission Corridor Impact Assessment and Mitigation Plan (Entrix
1985a).
4.1 Flows and Water Levels
The proposed Susitna Hydroelectric Project would regulate the river and alter
water levels downstream from the damsites. summer flows, generally high under
natural conditions, will be reduced as water is stored in the r·eservoirs.
Higher than natural winter flows would result from increased power generation
during the winter. The flows would be less variable under project conditions
compared with natural flows. Water levels during the open-water season would
be lower in summer and higher in fall than natural 1evels. In winter, the
water lt!vels upstream of the ice front would be similar Ol" lower than
58
natural}y occurring ice-staged\ ·:water levels. Oowns;treagt of the ice front,
water levels wo,uld be increased from natural ice staged water levels. Flood
frequency would be reduced and! flood occurrences ~tould be shifted fr·om the
natural flood period of May to June to the July to September period.
4.1.1 Mean Monthly Flows and Water Leve;t
In general, with-project flows will be reduced during the sunun~.r and
' I'
I
I
I
increased cluring the winter from natur'al flows. Water levels in the I
summer will also be r.educed from natu\~•11 conditions. However, water
levels in the winter will not reach the low levels which occur naturally
prior to ice staging in the fa 11 • Water 1 eve 1 s wi 11 depend upon the
location of the ice front; water levels upstream of the ice front will be
simi 1 ar or 1 ower and water 1 eve 1 s downstream of the ice front wi 11 be
higher than natural staged water levels. As the project progresses from
Stage I to Stage III, flows and water levels wf~l become increasingly
uniform throughout the year.
(a) Watana to Devil Canvon -
(i) Stage I
-Constructiort
Mean monthly flows and water levels between Watana and Devil
Canyon will be minimally affected during Stage I
construction. There vill be no significant change ·in flows
and ~later 1 eve ls during construction of the two diversion
tunnelsfl Upon completion of the diversion facilities,
closure of the upstream cofferdam will be completed and flow
will be diverted through the lower of the two diversion
tunnels. Although the mean monthly flows and water levels
downstream of the dam wi 11 not be a 1 tered, a 0. 6 mi 1 e
section of the Susitna River will be dewatered in the
construction zone. The resulting impacts are discussed in
the construction zone impact assessment (Entrix 1985a).
59
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-Filling
Mean monthly flows and water 1 evel s during May through
September ( 1998) wi 11 be reduced from natura 1 conditions
CJUring filling. Flows will be relatively steady and close
to the Case E-VI criteria summarized in Section 2.1.2.
During the winter fo 11 owing the one summer of fi 11 i ng, the
minimum flow. requirement will be natural flows. The Watana
reservoir water level is expected to be sufficiently high to
begin testing and commissioning the first unit in July 1986;
testing and commissioning other units would follow on
three-month i nterva 1 s. Flows wi 11 be greater than winter
minimum flows while testing and commissioning the powerhouse
units. It is expected that the first two units would become
operational in the 1998-1999 winter. The reservoir water
level in the following spring (May) will likely be above the
minimum operation level.
Operation
ln general, the downstream flow rate will be more stable
than under natural conditions. Summer flows will be reduced
and winter flows increased from natura 1 discharge rates.
lowest flows occur in early May and October since the energy
demands in these months are 1 ess than for other months.
During most years of Stage I operation, discharges would
likely be greater than the minimum flows experienced during
the year of filling.
The reservoir normally begins'to fill in May and the reser-
voir operating policy is to try to fill the reservoir by
early September to ensure adequate ~nergy production in the
winter. Thus, May and June releases from the reservoir are
penerally lower than in July and August. In average and wet
years the reservoir may fi 11 before September. Re 1 eases
60
would then · be made in excess of power and en vi ronmenta 1
requirements.
(ii) Stages II and III
During construction of the Stage II dam, mean monthly flows and
water levels in the Watana to Devil Canyon reach will remain
unchanged from thQ$e during Stage r operation. Ouri ng fi 11 i ng
of Stage I I, the reach wi 11 be inundated. Impacts to this
reach of river during filling and operation of Stage II and all
phases of Stage I I I are discussed in the impoundment impact
assessment (Entrix 1985b).
{b) Devil Canyon to Talkeetna (Middle River)
(i} Stage I
-Construction
No noticable changes in mean monthly flows or water levels
in the middle Susitna River are expected during Stage I
construction.
Filling
Flows and water levels will be reduced from natural levels
during the summer of filling i:, a manner similar to that
described for the Watana to Oevil Canyon reach. Flows
during the following winter will be maintained at natural
levels except during testing and commissioning of the
powerhouse units, when the flows will exceed the natural
flows.
61
-Operation
Although mean annual flow will remain the same, f1ow will be
redistributed from the summet" months to the winter months to
meet energy demands. Mean weekly streamflows for 10, 50,
and 90 percent exceedance 1 eve 1 s are shown in Figure 7.
Stage l mean monthly flows at Gold Creek are compared to
natural flows in Table 5. Mean monthly water levels at
three locations within the middle Susitna River are compared
graphically for natural and Stage I conditions in Figure 8.
(ii) Stage II
-Construction
Downstream flows and water 1 eve 1 s during Stage I I
construction will continue to be those described for Stage I
operation.
-Fi 11 ing
Devil Canyon reservoir will be filled in two distinct
filling periods. The first will last one to four weeks and
will take place during the construction phase, while the,
second wi 11 complete the fi 11 i ng at the conclusion of the
dam construction. The tot a 1 fi 11 i ng time fo·r the De vi 1
Canyon reservo ·1 r wi 11 be short {5-8 weeks) • During both
filling periods, flows will be reduced below Stage I
operation levels at Gold Creek to near minimum requirements.
-Operation
After Devil Canyon comes on line, Watana Stage I will be
operated as a peaking p 1 ant and De vi 1 Canyon wi 11
re-regul ate Watana flows. Devi 1 Canyon di schar•ges may vary
between 90 percent and 110 percent of the average weekly
62
•
5oooo...-I~-----------_-_-_-_-_-_-_-_-_-_-_-_-_-_-~---_-_-_-_-_-_-_-_-_-_:=-========:======;~·\,~·.~
45000
35000
_.....
~ 30000 -
t!1
0::
(..)
25000
~ 20000
(!)
15000
10000
5000
0
.. .. ..
" ..
"
NATURAL
----·-STAGE I
CASE E-VI MAXIMUM
---... ,..,...,..,.,.,. .. -.z-.r.r.,..., .. .....
. ' .. ---------------, ' ....... " ' ..... -~ ... ~~..... --....... . -., .,_..,__~_ ... ----
CASE E-VI MINtMUti--...-..-.. -,'
JAN
~-I I I
JUN JUL
MONTH
MEAN WEEKLY NATURAL AND STAGE I DISCHARGES
I
I f I I I ' I I I A . I I I • I ' I I I I I I
AUG SEP OCT NOV DEC
SOURCE: APA 1985c
AlASKA POWER AUTHORlTY
S U S I T N A H Y 0 R 0 E L .E C T R I C P R 0 I E C T
EXCEEDED9C%,50%,AND10%0FTHETIME ~-~~~~~~~~~~~~~.A~R~ZA--E-O_A_K_O~~~
FIGIJRE 7 ENTRIX, INC<! SUSITNA JOINT VfNTURE L----------------... ..---a. ....... --...... --.~.._ ____ _.,,
-
.. 1 •J
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! l q
t -
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'':? ~ ·, t
. --··, 1 t
Stage III
Stage III
Percsnt Percent Month Natural Early Change Late Change January 1,500 8,300 +450 10,300 +590 February 1,300 8,100 +520 10,100 +680 March 1,200 7,300 +510 9,100 +660 April 1,400 6,600 +370 8,100 +480
:.::. May 13,500 7,600 -40 9,000 -30 June 27,800 9,200 -70 10,400 -60 July 14,400 13,200 -50 9,400 -60 August 21,900 18,500 -20 10,700 -50 September 13,500 13,400 0 10,800 -20 October ,5,800 7,700 +30 8,600 +50 November 2,600 8,200 +220 9,500 +270
--~ December 1,800 9,000 +400 11,000 +510
64
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MEAN
~ee
see
~e-4
.... ._.. ..
~e.:s ~ ...
~ :S82 ~ ~ e~1 L...o...l
~eo
e?sa t e.? a
MEAN
eo?
eoe
eo:s
== S0-4
·~. eo~
~ 502
801
eoo
eQsa
MONTHLY \/VATER L .. EVELS AT RM
L.P.:OENC
1 27.1
-,
\
\
\ ~
\ .. ... -~ ... / ,.:;-............ ·•····· .......... ....... /. .... 1............. . ~······· . .... . ..... ,. ... ,.... .... ...,..-:-. .-,_,., ... """'-~-........... -~ , .. ...-::::::-. ....... --~· ···-· ~ ...... /
\/
..J Gr"l .... l:lo Mor" Apr" Moy ..Jwrt .J ... I Aw9 Sep Oct1: Nev Cleo
MONT ....
Stc:~.ge I
Sto•• II
s~~•• 111 (eo.-ty)
Stave 111 (Ia,•>
MONTHLY \/VATER LEVELS AT RM
L.E:GENO
1 .29.3
-,
\
\
\ .. ~
\ ~?~ ~
• ••• ·-·. ;-· • II. .. ·., \ .•'/ ~ ~< ··.. I····.J!. ................. ~ ··..... ·· .... .,\ ........... /' ········· ·-.~--......... ...~-...... .......... \ ........ .-:-::·T ...... , .... /
\/
.Jot'! JPeb Mar" ....... ,. Mey .JUI"'' .J..,I A'-'9 Se .. Oca' No~ Cl•o
MONTH
S'tac;;e t
stav• II
s'aca• 111 C•a,.ty)
Stao• Ill Cleat•)
MEAN MONTHLY WATER LEVELS AT RM 136.68
-= --~ ·~
eee T
51!17
588
5ee
5e•
5e~J
5e:z
881
5eo
L.EOENO --
S-tav• 1
St""q-II
Stac;;-Ill C•ol"ty)
S'tca.g• Ill Cia~•)
..aa,., ..... Mar" Apr" May.Jw" .Jwl Au.g S•p Oa1: Nov Cl•o
MONT ....
MEAN MONTHLY
WATER LEVELS
FIGURE 8
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
SUSITNA JOINT VENTURE
HARZA·E BASCO ENTRIX, INC.
65
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flow. A more detailed discussion of Stage II operation is
included in Section 2.2.4.
The increase in hydraulic head and generating capacity when
De vi 1 Canyon becomes operat i ana 1 wi 11 a 11 ow winter energy
demands to be met with 1 ass flow than in Stage I. Thus,
less water is needed to meet mid-winter (December-February}
demands and more water can be used irn October, March, April,
and May, thereby making Stage I I winter flows more uniform
than in Stage I. Since summer energy demands also require
1 ess flow, Watana storage is fi 11 ed earlier in the summer
and non-power releases are necessar·y earlier than i·n St;l.ge
I. This accounts for higher July-September flows with Stage
I I than for Stage I.. Stage I I mean monthly flows .at Go 1 d
Creek are compared to natural flows in Table 5.
Although mean annual flow will remain the same, flow will be
redistributed from the summer months to the winter months to
meet energy demands. Flows at 10, sa,, and 90 percent
exceedance levels at Gold Creek during Stage II opera~ion
are shown in c,'tnpari son to natura 1 flows in Figure 9.
Wat~r surface elevations corresponding to Gold Creek flows
with 10, 50, and 90 percent exceedance levels for selected
weeks during May through September are illustrated in Figure
8 for three mai nstem 1 ocat ions between Portage Creek and
Talkeetna--The figure illustrates the water level change
expected as a result of Stage I I operation. In genera 1 ,
there is a decrease in water 1 eve 1 from natura 1 1 eve 1 s to
Stage II operation levels in the summer and an increase in
stages in winter.
66
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50000~-----------------------------------------------------------------------------,
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40000
35000
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25000
§ 20000
(.!)
15000
10000
5000
NATURAL
STAGE II
CASE E-VJ MAXIMUM
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-...... , ,.._.,.--I .... -------'---------~~'""'
• • • '
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SOURCE: APA ::gasc
MEAN WEEKLY NATURAL AND STAGE II DISCHARGES
EXCEEDED 90~~ .. 50%, AND 10% OF THE TIME
ALASKA POWER AUTHORITY
SUSITNA HYDROElECTRIC PROJECT
FiGURE 9 ENTRIX, INC.
,, -..
HARZA·E BASCO
SUSlTNA JOINT VENTURE
.. -
{iii) Stage III
-Construction
No change from Stage II operation flows will occur.
-Filling,
Fi 11 i ng of Stage I I I wi 11 occur at the same time the dam .
crest is being raised, so construction and filling are not
distinct phases. Since excess July-September flows will be
stored in Watina, the flows at Gold Creek will be reduced
from norma 1 operation a 1 flows in July through September.
Filling will take between three and seven years, beginning
in 2011. The flows will generally be near the minimum flow
requirements during the summer. Testing and commissioning
of the last two units is scheduled to take place in 2012.
-Operation
Minimum flow requirements will be met by releases from the
powerhouse and, if necessary, the outlet works. In general,
operation results in higher than natural winter flows and
lowe·r than natural summer flows {Figures 10 and 11). Lowest
flows occur in early May and October.
The flow regime during the early years of Stage III is
simi 1 ar to Stage I I except in September and October of dry
years when the early Stage III flows would be less than
Stage II. As energy demand increases, the flow regime would
become more uniform, and in average years during late Stage
III, the flow wou'{d be very uniform throughout the year. In
dry y~ars there would be decreased flows in September and
October and in wet years increased flows in August and
September.
68
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50000~--------------------------------------------------------~--~----------~
45000
40000
35000
-~. 30000 ___..
3r.: ~ lli 25000
0:.:
(_)
~ 20000
(!)
15000
10000
5000
NATURAL
EARLY STAGE Ill
CASE E-Vil M/ ... XIMUM
• • I
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50"
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4 , ..
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-"t-":'"1 ........... -......... ... -c-._.. ••. , . .. .... ---.. -.--...... -------· .... ..
o~~~~1-~~-r+•~•~•~1~•~•~•~• +1~•-r•~•~+l~l-rr+l~l-ri+t~•~l~•~•~•~+-~~~~~~~~~~~
JAN .,_.AR APR MAY JUN JYL AUG
MEAN WEEKLY NATURAL AND
EARLY STAGE Ill DISCHARGES
EXCEEDED 90%, 50%, AND 10%
OF THE TIME
-
MONTH
FIGURE 10
..
SOURCE: APA 1985c
ALASKA POWER AUTHORITY
SUS!TNA HYDROELECTRIC PROJECT
ENTRIX, INC.
-..
HARZA·E BASCO
SUSITNA JOINT VfNTURf
.. --rv~-:~··,---.... 1
' ' ' ..... -·~···'·'"
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45000
40000
35000
~ ~ 30000 -~ iH 25000
a:::
(..)
§ 20000
(!)
15000
10000
5000
NATURAL
LATE STAGE Ill
CASE E.-VI MAXJMUM
------·1 0"----..
-·50"·--------.... --..
' ..... _ --------.... -----.. QQ"'.-----... ------.... .... --.. ----~--
CASE E-Vi MINIMUM
MEAN WEEKLY NATURAL
AND LATE STAGE Iii DISCHARGES
EXCEE·DED 90%, 50%, AND 10% OF THE TIME
10"
• , -~ '
... '' -: ____ ., .... ,,_ .. -~--# ....
'
..-·· .. ....
,-.... ,... 411 ,_ ,' .. -", ·------··::--..... ---... ...... .. ....
SOURCE: APA 1985c
ALASKA .POWER AUTHORITY
SUSITNA HYDROElECTRIC PROJECT
I FIGURE 11 ENTRIX, INC. HAil.ZA-EDASCO
SUSITNA JOINT VENTURE
,·
With-project mean monthly flows at Gold Creek are compared
to natural flows in Table 5.
· 'Water surface elevations corresponding to flows at 10,. 50,
and 90 percent exceedance levels at Gold Creek for selected
weeks during May through September at three mainstem
locations between Portage Creek and Talkeetna are
illustrated in Figure 8 for early and late Stage III
conditions. The figu~e illustrates the water level change
expected as a result of operation of Stage III. In general,
there is a d2crease in water level from natul"al to
with-project levels in the summer.
4.lo2 Floods
Flood peaks are expected to be reduced and flood durations would be
extended compared to natura 1 conditions. Floods would be expected to
occur during the July to September period a~:: a result of reservoir
storage instead of the May to J ... me period f11lr most natura 1 floods.
Floods would become less likely as the project progresses from Stage I to
Stage III due to the increasing volume of the reservoirs resulting in
increasing flood storage capability.
{a} Watana to Devil Canyon
{i) Stage I
-Construction
The two aiversion tunnels are designed to pass the 50-year
recurrence interval flood of 89,500 cfs with a maximum water
surface elevation of 1,532 ft and a maximum outflow of
77,000 cfs. For flows up to the SO~year flood event, water
levels and velocities downstream of the diversion tunneis
will be almost the same as pre-project levels.
71
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Floods greater than the 50-year event could overtop the
Watana cofferdams and cause failure of the cofferdams. If a
flood event of a magnitude 1 arge enough to overtop the
cofferdam did occur, the area that would be affected ,the
greatest is the main dam construction site. If the dam
height is less than the cofferdam when overtopping occurs,
significant losses would occur. However, if the main dam is
somewhat higher than the cofferd~m when overtopping occurs~
no damage is anticipated. Although damage could occur
further downstream, the relatively small volume of the head
pond and the attenuation of the flood wave as it moves
downstream would significantly reduce the potential for
downstream flooding.
-Filling
The filling criteria dictate that the reservoir must be
capable of storing the flood volume of a 250-year flood less
the flow which can be discharged through the outlet
facilities during the flood event. The maximum discharge of
the outlet facilities at Watana is 30,000 cfs, which
represents a substantial f1ood peak reduction. After a
flood event, the outlet facility will continue to discharge
at its maximum capacity until the storage volume criterion
is reestablished. This will cause the flood to be extended
beyond its normal duration although at a greatly reduced
discharge.
-Operation
Tab 1 e 6 presents the computed spring, summer, and annua 1
flood frequencies at Watana. During a wet year, the Watana
reser·voir can be filled by July or August, after which time
inflow will equal outflow. Consequently, with-project
July-September discharges will be higher than May-June
discharges, when the reser'voi r is recharging. Annua 1 Stage
72
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Table 6. Flood frequency at Watana during operatiQn
Stage I
Period Mal:-June Jul~-Segtember Annual
JYears). Natural Stage I Natural Stage I Natural Stage I
2 39,000 5,900 34,200 31,100 43,500 Similar
5 51,500 5,900 45,700 33,200 57,400 to July-
10 60,000 5,900 54,500 33,200 67,000 September
25 73,800 5,900 67,200 33,200 79,800 Series
50 84,400 5,900 77,800 33,200 89,500
Stages II and III
Watana to Devil Canyon reach is inundated
73
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1 flood dischargt·s would nearly always occur in. the
July-September period in contrast to '-naturally occurring
annual floods, which typically occur in~the May-June period.
(ii) Stages II and III
During construction of the Stage II dam, floods in the Watana
to Devil Canyon reach will remain similar to those during Stage
I operation. During filling of Stage II, the reach will be
inundated. Impacts to this reach of ~i ver during fi 11 i ng and
operation of Stage II and all phases of Stage III are discussed
in the impoundment impact assessment (Entrix 1985b).
(b) Devil Cafli'_Q!Lto Talkeetna (Middle River)
{i) Staae I
-ConstructiQD.
No changes to river flooding chara~teristics in the middle
Susitna River are expec~ed during Stage I construction.
-Filling
Floods in the middle Susitna River will be damped due to the
controlled Watana discharge. Using discharges measured
during a typica1 August as an example (Figure 12), the daily
natural and simulated with-project flows would be
significantly different under normal operation. The amount
of difference is dependent upon the reservoir level at the
time of the flood, with the greatest difference associated
wit~ the lowest reservoir level.
In filling Sequence {1) in Figure 12, the reservoir is
initially nearly full. While the peak of the flood is
reduced by allowing the flood to surcharge the reservoir,
74
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LEGEND:
AU(iUST 19~8 FlDWS
Q5 FfWHG SEQlENQ: I, AUGUST 19SS
Fl.OWS-WATANA MINIMUM STORAGE
CRITERtA VIOLATED
_(j;,_-FILUNG SEQJENC! 2, AU.GUST 19~8
Fl..OWS<Ja WATANA CAPABLE \1
ABSORSffG HYOROGRAPH
FLOW VARIABIUTY
AT GOLD CREEK
DURING WAIANA FILUNG
FIGURE 12
AuGUsr
NOTES:
L WAT.lNA FLOW ASSUMED TO SE 84 o/o OF
GOLD CREEK f'l.OW. .
2e R£SERV1'JIR FilUNG CRITERIA EXCE£0ED
WITH SEQUENC£0
3. NEGUGlS,LE CHANGE IN OAM HEIGHT
DURING FlOOD EVENT
4. MAXf,t.tUM RELEASE AT WAT»>A 3 I, 000 CFS
(COMBWED POWERHOUSE AND 0Ul1..£T FACn.~rry CISCHARGE).
SOURCE: APA 1985c
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC.
75
HARZ.A·E BASCO
SUSITNA JOINT VENTURE =
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outflow is greater than inflow on the receding limb of the
hydr·ograph in order to reestablish the reservoir stor•age
volume criterion. Hence, during this time period, the Gold
Creek. flow is greater than the natural flow.
In filling Sequence (2) illustrated in Figure 12, the
reservoir level is near the minimum level and able to absorb
the entire flood hydrograph. ·The Gold Creek flow would
remain constant at 9,000 cfs as excess flows are stored in
the reservoir*
-Operation
For the area upstream of the confluence of the Chulitna,
Talkeetna, and Susitna Rivers, the largest annual floods
genf~rally occur' in June as a result of snowmelt and
ra i nfa 11-runoff. Thus tin-natura 1 May-June series floods
are larger than for the July-September series (Table 7}.
The project will delay flood peaks until later in the year
as a result of storage. Project floods upstream of the
confluence will also be reduced in magnitude from natur~l
(Table 7).
(ii) $tage II
-Construction and Filling
The flood magnitude and frequency downstream of Devil Canyon
will b~ the same as that described for Stage I operation.
-Operation
Flood flows will be less than for natural conditions in the
middle reach due to Watana storage capacity. A small
decrease in flood magnitude is expected for spring floods
during Stage II operation as compared with Stage I
76
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Table 7. Flood frequency and d~scharge (cfs) at Gold Creek during project
operation.
Return Ma~-June Ser.i es
Period Stage III
(Years) Natural Stage I Stage II Early Late
2 42,500 19,800 17,300 18,000 19,700
5 56,200 26,800 24,300 25,000 26,700
10 66,300 30,600 28,100 28,800 30,500
25 80,500 33,900 31,400 32,100 33,800
50 92,100 37,900 35,400 ~;6, 100 37,800
Return Jul~-Seutember Series
Period Stage II!
(Years) Natural Stage I Stage II Early Late
2 37,300 36,500 36,500 35,500 15,700
5 49,800 43,100 43,100 43,100 21,300
10 59,400 44,000 45,000 45,000 24,000
25 73,200 44,000 45,000 45,000 26,500
50 84,800 46,600 47,000 47,300 29,500
Return Annual Series
Period Stage III
(Years} Natural Stage I Stage II Early late
2 48,000 Similar to July-September Series shown above
5 63,300
10 73,700
25 87,300
50 97,700
77
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o~eration. No significant change is expected for late
summer floods {Table 7). ·Under natural conditions, the
highest annual floods at Gold Creek generali'.t occur in June.
With Stage II operation, the annual flood peaks will
generally occur in the July-September period rather than
June (Table 7).
With Devil Canyon operational,· a sm.all amo~nt of flood
storage will be provided to prevent spillway releases during
floods with return periods of less than 50 years. This will
cause the maximum outflow for these events to be less than
or equal to 42,000 cfs, the outlet works capacity.
Spring floods downstream of the project wi 11 be reduced by
the discharged stored in Watana Reservoir. De vi 1 Canyon
Reservoir will generally be full during this period and
would not provide any flood storage. Peak flows will
generally be passed through De vi 1 Canyon Reservoir without
attenuation.
(iii) Stage Ill
-Constrc:tion and Filling
The discussion of flood flows for Stage II operation is
applicable to the Stage III construction period before
filling starts. Filling of Stage III will occur at the same
tirne the dam crest is being raised, so construction and
filling are not distinct phases.
Flood flows downstream will be only slightly reduced from
Stage II operation levels due to increased storage in the
reservoir. Sufficient storage will be maintained so that
the structure is not endangered by floods.
78
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Ooeratjon
Spring floods downstream of the project wi 11 be reduced by
the discharge stored jn Watana Reservoir by a magnitude
similar to those during Stage II operation (lable 7). Devil
Canyon Reservoir will generally be full during this period
and will not provide any flood storage. Peak flows will
generally be passed through Devil Canyon Reservoir without
attenuation. late in Stage III, July-September flood flows
become sma 11 er than May-June flood f1 ows as energy
generation at Watana is increased, and flood storage
capacity increases accordingly.
4 .. 1 .. 3 Flow_Variabilit;t
Flow variability downstream of the damsites will be reduced from natural
conditions following dam construction~ Flow variations occurring
upstream of Watana will be impounded in the reservoir, allowing a
relatively steady flow to continue downst~eam. Variations in flow will
become greater downstream because of natura 1 inflow fr·om tributaries. As
the project progresses from Stage I to Stage III, flows will increase in
stability as the reservoirs become more regulated to produce more
constant powerhouse flows.
{a) Watana to Devil Canvon
(i) Stage I
-Construction
No changes to downstream flows are expected as a result of
Stage I construction.
79
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-Filling
Under normal hydrologic conditions, flow from the Watana
development Will be totally regulated. The downstream flow
will be controlled by the following criteria: downstream
environmental flow requirements, minimum power demand, and
reservoir operating rule curve. However, there can be
significant variations in project discharge from one season
to the next and for the same month from one year to the
next.
Substanti~l changes in flow, which can occur daily under
natural conditions, will be reduced during the filling
process. Flow variations occurring upstream of Watana will
be impounded in the reservoir, allowing a relatively steady·
flow to continue immediately downstream. Further
downstream, the relative contribution of tributary and
runoff flow increases such that flow variations become
progressively more prominent.
-Ooeration
The Stage I discharge from Watana may be allowed to vary by
ten percent above and bel ow the mean weekly flow. The
maximum variation in the mean weekly flow from one week to
the next will be 20 percent.
Monthly flow duration curves have been prepared and
presented in Chapter 2 of the FERC License App 1 i cation
Amendment {APA 1985c) to illustrate the variation in
with-project flows as compared to natura 1 variation. The
Watana flows show little variability because of the high
degree of reservoir regulation and the relatively constant
powerhouse flow.
80
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(ii) Stages II and III
During construction of the Stage I I dam, flow vari abi 1 i ty in
the Watana to De vi 1 Canyon reach wi 11 remain unchanged from
that during Stage I operation. During filling of Stage II, the
reach will be inundated. Impacts to this reach of river during
filling and operation of Stage II and all phases of Stage III
are discussed in the impoundment· impact assessment (Entrix
1985b).
(b) Devil Canyon to Talkeetna (Middle River}
(i) Stage I
Construction
No changes in flows in the middle Susitna River are expected
during Stage I construction.
-Filling
Stage I flow releases will provide a relatively steady flow
immediately downstream of Watana. Large changes in the
outflow rates at Watana will be virtually eliminated during
filling. With increasing downstream distance, flow
variations will become greater as tributary inflows provide
a la~ger percentage of the mainstem discharge.
-Operation
Vari~tions in flow at Gold Creek are greater than at Watana
because of natura 1 inflow in the reach between. This is
graphically illustrated in the flow-duration curves
presented in Chapter 2 of the FERC Application (APA 1985c);
these curves show a diminishing difference between natural
and witho(project flow durations with increasing downstream
81
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distance. Another approach to illust~ating the flow
vai'.,iability under natural and project flow regimes is to
show the 10, 50, and 90 percent exceedance values of the
percent cha.nge in discharge from one week to the next
(Figure 13}.
For the normal range of powerhouse discharges during Stage
I, the expected range of stage ·fluctuations in the nri ddl e
Susitna River for a daily change in discharge of 20 percent
(10 percent +) would be from Oo2 to Oo7 ft.
(i i) Stage II
-Construction
During the Devil Canyon construction phase, most differences
in the flow variability from the natural conditions will be
the result of the presence and operation of the Watana
facility. Therefore, the conditions for Stage I operation
will be applicable.
F.ill ing
Changes in flo~ during the short duration of Stage II
filling will be similar to or slightly more stable than
Stage I changes.
-Operation
Stage II operation out}lows will have little variability
because of the high degree of reservoir regulation and the
relatively constant powerhouse flow. Gold Creek flows
exhibit more variation because of the variability in local
inflow .. Flow duration curves ~how a diminished natural and
with-project difference with distance downstream from Devil
Canyon.
82
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NATURAL
1~000
STAGE I
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""" i -sooo u
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""" '"" :a
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DISCHARGE AND PERCENT
CHANGE OF NATURAL AND
STAGE I MEAN WEEKLY
'10'1
-.
DI:C
ALASKA POWER AUTHORITY
5USITNA HVDROELECTRIC PROJECT
FLOWS
FIGURE 13 ENTRIX, INC. HARZA-EBASCO
._----------------------------~~------------------JL--~S~U~SITNAJOINTVENTURE
83
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A series of charts of flow duration and variability at
several middle Susitna River locati:'lns illustrate the
improvement in flow stability for project conditions as
compared to natural conditions (APA 1985c}" Graphs of
percent change in flow from one week to the next also
illustrate the relative stability of project flows (Figure
14). Stage II flows are expected to be less stable in July
and August as the reservoir becomes full and 1 ess storage
capacity for floods is available.
(iii) Stage III
-Construction and Filling
The discussion of flows and water 1 eve 1 s for Stage I I
operation is applicable to the Stage III construction period
before filling starts. Filling will occur simultaneously
with raising the crest. Flow variations will be bracketed
by Case E~VI requirements (minimum} and flood control
filling criteria (maximum). Flow variations immediately
below Devil Canyon will be minimized by controlled reservoir
re 1 eases. Tributary inflow wi 11 contribute more to flow
variability as downstream distance increases.
-Operation
While project flows will show little variability at the
Devil Canyon dam, Gold Creek flows exhibit more variability
because of local inflow between the dam and the Gold Creek
gage site. Flow variability at Gold Creek for natural and
Stage III operation is shown in the form of 10, 50, and 90
percent exceedance values for the percent change in weekly
average discharge in Figures 15 and 16~
84
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"'ONTH
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NATURAl..
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a&:
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a&: w
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DISCHARGE AND PERCENT ALASKA POWER AUTHORITY
cHANGE oF NATUnAL AND sustTNA HvoRo,eLecrRlc PROJEcT
STAGE II MEAN WEEKLY ~------------T---~--~~--~ FLOWS
FIGURE 14 ENTRIX, INC.
85
HARZA·E BASCO
SUSITNA JOINT VENTURE
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1:5000 ....... EARL.Y STAG£
w
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300
EARL.Y STAGE Ill
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DISCHARGE AND PERCENT r-------........ -------1 CHANGE OF NATURAL AN ALASKA POWER AUTHORITY EARLY ·STAGE Ill MEAN
\AJEE~<L Y FLOWS SUSITNA HYDROELECTRIC PROJECT
FIGURE 15 ENTRIX, INC.
86
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DISCHARGE AND PERCEN1T
CHANGE OF NATURAL Ar\10
LATE STAGE Ill MEAN
WEEKLY FLOWS
FIGURE 16
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ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC.
87
HARZA·E BASCO
SUSITNA JOINT VENTURE
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4.2 River Morphology
Changes in river morphology characteristics are expected to occur as a result
of project operation. Summer flows and water levels during project operation
are less than natural. Tributaries will downcut their beds to new equilibrium
positions eorresponding to the lower Susitna level, and vegetation will
encroach on sloughs, on side channels, and on the narrower mainstem upstream
of the ice front and to a 1 esser extent downstream of the ice front.
Overtopping of slough berms will occur less frequently and for shorter
• duration during spring and summer. Sediment trapping in the reservoirs will
decrease the downstream sediment suspended and bed loads, allowing the
mainstem to e~ode the existing bed. Consequently, the river will narrow and
deepen slightly, and the percentage of coarse material in the bed will
increase as fines are picked up and carried downstream. Details of these
changes are presented below and in Chapter 2 of the FERC License Application
Amendment (APA 1985c).
4.2.1 Watana to Devil Canyon
{a) Stage I
(i) Construction
Since changes in flow will be negligilJle during Watana Stage I
construction, impacts on morphology of the Susitna River will
be confined to the dam and borrow sites. Borrow Site .E wi 11
become a deep pond adjacent to the river~
( i i) Fi 11 i ng
The morphology of the river downstream wi 11 begin to change
during filling of the Stage I reservoir due to changes in the
sediment transport characteristics. Since filling the
reservoir will require only one summer, changes in channel
morphology will not become significant~
88
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During filling, most flows in excess of the Case E-VI
downstream requirements will be store<i in the reservoir. At
the end of the summer of fi 11 i ng, approximate 1 y 75 to 85
percent of the incoming sediment {particles larger than 5 to 10
microns) will be trapped. The reduced discharge volume,
combined with the sediment trapping within the reservoir, will
result in smaller downstream sediment loads than under natural
conditions. Some d.egradat ion may· occur, but it wi 11 not be
significant bec~use of the small discharge and the short period
' requir6d to fill the reservoir. Reduced downstream water
levels in the Susitna River during filling may also allow
aggradation at the out 1 ets of some downstream tributaries.
Delta aggradation will also be minimal, however, because of the
short filling period.
(iii) Operation
{b)
Duri.ng operation of Watana Stage I, virtually all the bedload
ente···ing th~ reservoir would be trapped. Suspended sediments
of about 0.004 mm and less will remain in suspension and pass
through the reservoir (HE 1985, PND 1982). This sediment would
be small enough in volume and particle size that it would not
be deposited downstream. The river downstream of the dam will
probably erode some bed material and therefore cause 1 owering
of the streambed elevation {degradation) and possible
coarsening of riverbed material {Section 4.2.2).
Reservoir operatioq will moderate downstream discharges. Peak
flood flows will be reduced along with the volume and size of
bed materia 1 transpor-ted dur·i ng those flows, i ncl udi ng that
contributed to the mainstem by tributaries.
Stage II and Stage III
During construction of the Stage II dam, river morphology tn the
Watana to De vi 1 Canyon reach wi 11 remain unchanged from Stage I
89
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operation. During filling of Stage II, the reach will be inundated&
Impacts to this reach of river during filling and operation of Stage
II and all phases of Stage III are discussed in the impoundment
impact assessment (Entrix 1985b).
4~2.2 Devil Canyon to Talkeetna (Middle River}
{a) Stage I
{i) Construction and Filling
( i i)
Change::; in river morpho 1 ogy ar,e not expecttd during Stage I
construction and filling. Some bed degradation will occur
during filling since dam releases will contain little sediment,
allowing the flow to erode more of the existing bed. Tributary
delta aggradation will begin a:s mainstem flows decrease. Both
bed degradation and delta aggradation will be minimal, however,
because of the short filling time.
Operation
It is anticipated that the Sus1tna River between Devil Canyon
and the confluence of the Susitna and Chulitna rivers would
tend to become more defined with a narrower channel witt, the
reduced Stage I opev~ati on sununer flows. The main channel river
pattern will strive for a tighter, better defined meander
pattern within the existing banks. A trend of channel width
reduction by encroachment of vegetation and sediment deposition
near the banks is expected, especially upstream of the ice
front. The tendency of the main channel to degrade and to be
confined may cause the channel to recede from the heads of some
sloughs and side channels.
The estimated bed degradation in the middle Susitna River may
be as great as 0.8 to 1.3 ft during Stage I. Degradation tends
to be greatest immediately downstream of the dam and to
90
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decrease further downstream although the amount of degradation
at each site depends upon site-specific characteristics such as
channel slope and bed material {Harza-Ebasco l985a). Actual
degradation in the mainstem is expected to be less than tt:1.1
estimated values as additional sediment will be contributed to
the system from tributaries and bank erosion-'" {Harza-Ebasco
1985a). In addition, sedifnents eroded upstream are likely to
be redeposited downstream {R&M Consultants and WCC 1985). The
rate of degradation may not allow equilibrium to become
established during the scheduled period of Stage I operation.
Because of reduction in flow ve 1 oci t i ~s in the rna in river,
tributary streams, including Portage Creek, Indian River, Gold
Creek, and Fourth of July Creek, may extend their alluvial fans
into the river. Tributaries will either downcut their beds or
remain perched above the Susitna (APA 1985c). If the tributary
remains perched due to the presence of an erosion-resistant
layer preventing downcutting, fish access to the tributary from
the mainstem may be \ .. educed. Ho~·ever, most of the tributaries
wi 11 adjust to a new flow regime t4i thout detrimenta 1 effects to
fish access, bridges, or the ra fl road bed. Depending on the
hydrau1 ic and sediment transport characteristics at the mouth
of the tributaries, the adjustment may occur over a period of
'
one wet season tw· a number of years (Trihey 1983, Harza~·Ebasco
1985a, R&M Consultants 1~\82). Potential changes to specific
tributaries are 1 i sted in Tab 1 e 8. The re 1 at i ve amounts of
change to physical characteristics in the Susitna drainage are
shown in Table 9.
Overflow into most of the side channe 1 s and s 1 oughs wi 11 be
1 ess frequent and of shorter duration during spring and summer
as high flows wi11 be attenuated by the reservoir. The effects
of. backwater from the mainstem to the sloughs also will be less
during spring and summer because water levels in the mainstem
will be lower. Thus, there will likely be some encroachment of
vegetation to the upstre~m reach and periphery of some sloughs.
91
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T~ble 8. Downstream tributaries potentially impacted by project operationll
Name
River Bank of Reason Type ofy
Mile Susitna21 for Concern Assessment 3
Portage Crt!ek 148 .. 9 RB fish access 2
Jack Long Creek 144.8 LB fish access 1
Indian River 138.5 RB fish access 2
Gold Creek 136.7 LB fish access 2
unnamed 13240 LB Railroad {RR) 1
4th of July Creek 131 .. 0 RB fish access 2
Sherman Creek 130.9 LB RR/fish access 2
unnamed 128.5 LB Railroad 1
unnamea 127.3 LB Railroad 1
Skull Creek 124.7 LB Railroad 2
unnamed 123.9 RB fish access 1
Deadhorse Creek 121.0 LB fish access 2
Little Portage Creek 117.8 LB Railroad 2
Gash Creek 111.7 LB RR/fi sh access 1
unnamed 110.1 LB Railroad 1
Whi.skers Creek 101.2 RB fish access 1
!/ Source: APA 1985c Zf Referenced by facing downstream (LB • left bank, RB = right bank)
Y Type of Assessment: 1) Visual -bed material size not available
Potent_!jl
Impact
1
3
2
1
6
1
2
6
5
7
3
1
6
6,4
5
4
2) Comparison of transportable size vs. bed material
size.
!/ Potential Impact
1. Potential fish access problems less likely than rot categQry 2 since
tributary bed material smaller than size transportable by mainstem.
2. Potentia 1 fish access problems more 1 ike 1 v than for category 1 unt i 1
tributary adjusts. ·Tributary bed material larger-than size
transportable by mainstem.
3.. N·o data on tributary bed material. Visual assessment indicates
potentia 1 for fish access prob 1 em for a period unt fl tributary
adjusts.
4. No data on tributary bed material. Visual ass~ssment indicates no
potential for fish access problem.
5. Visual assessment indicates potential for limited scour at RR bridge,
potentially limited by geologic features. Depth of RR foundation may
~xceed scour depthi
Vi sua 1 assessment indicates no potentia 1 for scour endangering RR
bridge.
Comparison of tributary bed material size to transportable size by
mainstem indicates potential for limited scour at bridge.
92
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Table 9. Influence of main stem flow and
of aquatic hatitat types.;11
Habitat Type Hydr·aul ic2/ Hydrologic
Mainstem (MSj 4
Side Channel (SC) 3
Tributary Mouth {TM) 3
Side Slough {SS) 2
Upland Slough (US} 1
Tributary {T) 0
Lake (L) 0
0 -no influence
1 -small, limited influence
2 -moderate, occasional influence
3 -moderate, frequent influence
4 -direct, extensive iufluence
ll Source; APA 1985c
4
4
3
2
1
0
0
Y Depth, velocity, wetted area, etc.
93
water quality on characteristics
, .
Temperature Turbidity Ice Total
4 4 4 20
4 3 4 18
2 2 3 13
2 2 2 10
0 0 0 2
0 0 0 0
0 0 0 0
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(b)
Sediment will deposit at the confluence of the Susitna,
Chulitna, and Talkeetna rivers because of the 1 arge sediment
discharge from th~ Chulitna River and the reduction in the peak
flows of the Susitna River.
Stage II
( i) Construction and Filling
Since tJperation of Watana Stage I will not be significantly
affected by the construction or fi 11 i ng of the De vi 1 Canyon
Dam, the morphological processes discussed previously will
continue to occur except at the Devil Canyon damsite. No
impacts to the morphology of the Susitna River are anticipated
fr0m borrowing of construction materials because no borrow site
is located within the river.
(ii) Operation
The mean of the annual maximum weekly discharges expected at
Gold Creek during Stage II operation will be about 28,000 cfs. -.
Resulting riverbed degradation may be ~s much as 1.0 to 1.5 ft
(Harza-Ebasco l985a). As described for Stage I operation,
actua 1 degradation may not be as great as estimated and may
occur over a longer period of time. The extent of degradation
will decrease to near zero at the confluence of the Susitna and
Chulitna rivers due to aggradation at that 1 a cation.
Vegetation encroachment and tributary delta building in the
reach will continue toward new equilibrium positions.
{c) Stage III
(i) Construction
Impacts on Susitna River morphology will be the same as those
for Stage II operation.
94
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(ii) Filling
(iii}
The fi 11 i ng of Watana Reservoir for Stage I I I operation may
take about five years under average flow conditions.
The impoundment will reduce the frequency of discharging large
floods downstream; the additional impact on downstream
morphology would be negligible. The potential for additional
bed degradation from that described for Stage II will be
insignificant.
Operation
Re 1 ease of 1 arge flows in excess of meeting the energy and
downstream requirement will be less frequent in Stage III than
in Stage I I. Reservoir operation studies indicate that the
mean of the annua 1 maximum weekly flows wi 11 be sma 11 er than
the mean of the annual maximum flows during Stage II operation.
Therefore, the probability of further degradation (lowering of
the bed level} beyond that under Stage II operating conditions
will be reduced.
Sediment deposition near the confluence of the Susitna,
Chulitna, and Talkeetna rivers will continue but the river will
gradually stabilize with a better ~efined, narrower channel.
4.3 ~ater Qualit~
4.3.1 Water Temperature
River temperatures will be similar to but lag about 2 weeks behind
natural conditions during Stage I operation. Winter temperatures between
the upstre~m ice edge and the dam wi 11 be 0-2°C, whereas the natura 1
temperature in this reach is 0°C. Water temperatures greater than o0 c
wi 11 persist downstream 1 anger into winter and arrive earl; er ; n the ...
spring than under natural flow conditions due to warmer project outflows.
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Varying the depth of water wi thdrawa 1 from the reservoir waul d have no
significant impact on downstream river ~Pmperatureso
During Stage I I, temperatures relative to Stage I are coo 1 er from June
through early August, warmer from mid-August to mid-April, and sirnila("
from mid-Apri 1 thrO\.tgh 1 ate May. Stage I I summer temperatures 1 ag
natural conditions by one month. The use of a high-level intake to the
Devil Canyon outlet works will increase the average river temperature at
r~ver mile 130 by 1 to 2°C from natural condition!;.
Summer temperatures simulated for Stage III are generally coo1er than
those during Stage II. Winter temperatures are somewhat warmer.
Temperatures would lag behind natural conditions by approximately one
month.
The procedures for developing downstream temperature regimes for project
conditions is described in detail in other reports by the Applicant (APA
1985a, Harza-Ebasco 1985b, AEIDC 1983, 1984a, 1984b, 1984c, 1985).
Briefly, the Watana reservoir outflow temperatures, which were simulated
lfS i ng DYRESM were input to the program SNTEMP to eva 1 uate downstream
water temperatures.
Temperature simulations using SNTEMP were carried out for open water
reaches of the river between the dams and the Sunshine stream gaging
station (RM 84). In .sununer, the entire reach was simulated. In winter,
only the reach from the dams to the location of 0°C was simulated.
Temperatures for the three stage project were only simulated for the
period May 1985 through September 1982. This represents a wet summer
fo 11 owed by an average temperature winter fo 11 owed by an average flow
summer ..
Simulations for the three stage project were limited to the cases
discussed above, in order to show the similarity between simulated
temperatures for the original two stage and the proposed three stage
project. Because the simulated temperatures for the three-stage project
are similar to those for the two-stage project the simulations which have
96
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been made for the two stage project (APA 1984, Harza-Ebasco 1985c} may be
used to determine the sensitivity of the river temperatures to various
other hydrologic and meteorologic conditions. Simulations are also
presented in other reports (AEIDC 1983, 1984a, 1984b, 1984c, 1985).
The simulation results presented below were developed using the policy of
withdrawing water from the reservoir which has as close a temperature to
natural as possfble. This policy is known as 11 inf1ow temperature
matching." Additional simulations have been carried out to evaluate
whether other policies of multi-level intake operation would
significantly affect temperatures. The policies considered were:
o warmest water -draw warmest W4ter from the reservoir all year using
the proposed multi-level intake
0 1 owest 1 eve 1 -use 1 owest 1 eve 1 of proposed intake in summer and
winter regardless of outflow temperature to preserve reservoir heat
in summer for use in winter
o warmest water with other possible intakes at el. 1636 ft and el.
1800 ft -draw warmest water from the reservoir a 11 year but with
the addition of intakes at el. 1636 ft and el. 1800 ft.
The effect of the various operating policies on summer river temperatures
at RM 130 is minimal,. The inclusion of intakes at el.. 1636 and el.
1800 ft on the Watana outlet works does not appear to affect summer
temperatures.. The use of a high-level intake to the Devil Canyon outlet
works has a noticable effect on river temperatures, generally increasing
average temperatures during outlet works operation by 1°C to 2°c.
Slough and side channel surface water temperatures are generally
dependent on the temperature of groundwater upwelling, climate conditions
and the temperature of mainstem flow wh~n tt~ upstream berm is
overtopped. Si nee the frequgncy of overtopp,i ~ •( •tf ~h~ upstream berm wi 11
be reduced due to lower summer flows the ~lu\.il~il and side channel surface
water temperature will be more often solt;:y a function of groundwater
97
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temperatures and climate, and thus independent of project stage. It has
been determined that the temperature of the groundwater component of
s 1 ough flow is ge~iera lly equa 1 to the mean annua 1 temperature of the
river. Since thfs will not change significantly during project
operation, the only change in surface water temperatures in sloughs and
side channels will be a function of the frequency of overtopping of the
upstream berm.
When habitat areas in s 1 oughs and side channe 1 s are not overtopped in
summer their surface water temperatures are genera 11 y 1 ess than the
mainstem roflecting the groundwater temperature and the climatic
conditions. Therefore, a reduction in overtopping of habitat berms will
generally cause slough surface water temperature in summer to be somewhat
lower, on the average, t'han natural conditions, but higher than the
groundwater temperature. The variation in surface water temperature
resulting from intermittent overtopping of the berms wi 11 be reduced.
Side channels will be affected less than sloughs because summer
discharges during project operation will keep most side channel areas
overtopped.
Surface water temperatures in tributary habitat areas are genera 11 y a
function of tributary temperature and will not be affected by the
project. The extent of the effect of the tributary temperature on the
mainstem may change as a result of decreased summer mainstem flows.
{a} Watana to Devil Canyon
{i} Stage I
-Construction
Since operation of the diversion structure will essentially
be run-of-river, no impact on the temperature regime will
occur downstream from the tunnel exit.
98
-Filling
.. The reservoir outlet temperatures during the first summer of
filling should be similar to natural temperatures with short
lags of about two weeks, bein~J slightly cooler in May and
June a_nd slightly warmer in September (APA 198Sc, APA 1984}.
During the filling period, water temperatures at Watana Dam
wi 11 be as much as 7°C co·o 1 er than norma 1 during June,
whereas in July and August outflow temperatures wi 11 be
similar to the reservoir inflow temperatures. Downstream
river temperatures during the summer of filling Watana Stage
I are expected to be similar in magnitude to natural
conditions with a similar lag time. Because river flows
will be less than natural, heat exchange with the atmosphere
and the river water will proceed more rapidly than under
natural cQnditions and temperatures down~tream are expected
to be clos~r to natural than at the darn.
·ouri ng the first winter after fi 11 i ng, the project wi 11
become operational when units one and two begin generating
in October and January, respective 1 y. The temperature of
the water discharged from the dam will range from 2-4°C
depending upon which i ntaks-port is used to withdraw water
from the reservoir ·and the air temperatures. Outflows are
expected to be taken from near the surface of the reservoir,
and since the reservoir will be stratified at this time,
releases will have temperatures similar to operational
conditions in later years. Since winter reservoir outflows
would average 2,500 cfs to 3,500 cfs, the river water will
cool down toward 0°C more rapidly than when more units are
operating. During this period, instream water temperature
is expected to decrease rapidly from 2-4°C at the Watana Dam
to 0°C in Devil Canyon because of the small volume of water
to be discharged~
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Ooeration
The Stage I intake ports are located at five levels, and the
discharge temperatures can be controlled to approximate the
natural ir;;tream temperatures. The discharge temperatures
would range from approximately 5°C to 12°C in the summer and
approximately 0.5°C to 3°C in the winter depending on the
meteoro 1 ogi cal co~d 1 t 1 on, and energy demand 1 eve 1 • In the
summer, the inf~tows are. more responsive to variations in the
meteorologica?-conditions than the reservoir due to the
shallowness Jf the river. The river inflow warms up in the
early summer and cools down in the late summer more rapidly
than does the reservoir. Hence, the reservoir discharge
water wor.ld be colder in the early summer and warmer in the
early f?,11 than the natural river conditions. However, in
most o~1 the summer months the discharge temperatures could
be re~ulated to approximate inflow temperatures. During the
wi nt,;~r months, discharge from the Watana Rest1r'voi r wi 11 be
considerably greater under Stage I of the project than under
natura 1 conditions. At the dam, temperature of the water
will be between 1°C and 3°C depending upon the water surface
elevation in the reservoir re 1 at i ve to the port in the
intake structure being utilized at the time. As the water
surface is dr~wn down through the winter, discharge
temperature will gradually decrease. However, when the
water surface e1evation is low enough to require use of the
next lower intake port, the temperature of the discharge
water will increase by approximately I°C followed by another
gradual decline.
Once the water is released from the reservoir, water
temperature will decline to 0°C at a rate dependent upon the
air temperatures. The water temperature is not expected to
reach 0°C within the Watana to Devil Canyon reach.
200
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{ii} ~tg_q.~s II and III
During construction of the Stage II dam, water temperatures in
the Watanc1: to Dev i 1 Canyon re~ch wi 11 remain unchanged from
those dur·ing Stage 1 operation. Ot.iring filling. of StagE! II,
the reach will be i rtundated g Impacts to this reach of river
during fi 11 i ng and operation of Stage I I and a 11 phases of
Stage Ill are discussed in the impoundment impact assessrr.ant
{Entrix 1985b).
(b) Devil Canyon to Talkeetna
{i) Stage I
-,C,Q,nstruction
No changes in river temperature fro~ natural conditions are
exi)ected from Devil Canyon to Watana during Stage I
construction.
-Fi 11 ing
Downstream river temperatures during summer of filling Stage
1 are expected to be similar in magnitude to natural condi-
tions with a short lag of about two weeks. During the first
winter after fi 11 i ng, the operation of two units with 1 ow
flows will cause downstream river temperatures to be similar
to but cooler than normal Stage I operating temperatures.
-Operation
Average weekly temperatures (natural and Stage I ~imulated)
at RM 150, RM 130 and RM 100 are shown in Figur~ 17. Summer
Stage I river temperatures exhibit a lag behind natural
conditions of approximately 2 weeks. River temperature
simulations were made at river mile 130 (between Devil
101
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tif~TES:.
1, CliMATOLOGICAl. AND
HYOROLOGtCAl OAT A
Pf:AIOO MAY 1a11-SEJtT.
... 2
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INflOW TEMPERA TORE
MA TCIUNG POLICY FOR
MULTI-LEVEl ~TAK~
STAGE I OF 3 STAGE
PAOJiCT
AVERAGE WEEKLY VAL~S
!-VI FlOW REQUIREM'SNTS
TE~PERATURES S'MUL.~TED
IY SNTEMP fOR PERIOD
NOVEM8EA.~APA1l SHOUlD
liE USED WUH CAUTION Aa
AN ICt: COVER MAY EXIST
ON AlYEA AND SNTEMP
DOES NOT SlMULA TE
TEMPERATURES UNDER AN
ICE COVER (SEt; RiVER ICE
SIMULATiONS}
lEGEND
SIMUlATED NATURAl
TEMPERA TLIAES
SIMUU7ED TEJ.IPERAT\MES
Pt;•SE 1 OF TWO ST AQE
PROJECT (FOfl COMPARISON
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2
SIMUlATED Tf.WERATUAES
STAGE I Of PftafiOSED
PAO.JEGT
a
0
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R c ~ E s
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1981
NATURA.L AND STAGE I
TEMPERATURES
FIGURE 17
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RM 130
RM ISO
19!2
SOURCE: APA 1985c
ALASKA POWER AUTHORITY
SUSITNA HYOR()ELECTRIC PROJECT
ENTRIX, INC.
'---~--------~-.... ------11:&·~-.... -~p-------... HARZA·E BASCO
SUSITNA JOINT VENTURE
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Canyon and Talkeetna); the results are ge·nerally applicable
to the Watana to Devil Canyon reach during Stage I
operation. Simulated temperatures at river mile 130 are
generally near 4°C in early May, peak at near 10°C in late
\Junre.: through early August and decrease t!" 0°C by
mid-November. At RM 130, the water temperatures will be 2
to 3°C cooler in May and June, 0.3 to 0.9°C cooler in
summer~ and up to 3°C warmer in· September through October
compared to natural conditions. The mean annual temperature
{time weighted) at river mile 130 ha.s been calculated for
the period May 1981 to April 1982 to be 3.7°C for natural
conditions and 4°C for with-project conditions.
In wet years the reservoir fi 11 s by early July and thus the
outlet works must be o~erated to pass flow. Because the
outlet works draw from a lower elevation in the reservoir,
its flows are generally cooier. This can cause a clrop in
river temperatures in early July {APA 1985c). The effect of
annual flow variability on temperatures at River Mile 130 is
shown for natural conditions and for simulated Stage I
operation in Figure 18.
The temperature of the mainstem will remain above 0°C longer
into the winter because of the warmer reservoir outf1 ows.
The temperature in the spring will warm up above 0°C sooner
for the same reason~ Between the upstream end of the ice
cover and the dams the river temperature will generally be
between 0°C and 2°C to 3°C, whereas the natural temperature
in this reach is 0°C.
(ii) Stage II
-Construction and f)1ling
There will be little or no difference in water temperatures
in the Dev·i 1 Canyon to Ta 1 keetna reach during Stage I I
103
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WEATHER CONDITIONS~
---1182 AVERAGE Ff..OW
-• .._.-1111 HIGH FLOW
----1174 LOW FLOW
-··-··-1171 AVERAGE FLOW
Noll.
IMAATIOHI WEill MADI ,011 NATURAL
COHOITIONI AND AAI PAEIENTI!D TO
LLUITRA !I TEa.tPERA TURE o•FERENCEI
fOR WET, DRY AND AVERAGE fLOW
CONOITIONI A 1' RIVE" tAILE 1 :SO
JU!..Y AUG I
I I I I 1 SEPT 1
' I I I . I I
OCT I • 1 1 r-.. o .. a
WATER WEEK
60 1
WEATHER CONOITIOHS:
----1a12 AVERAGE FLOW
-·-·-1811 HIGH fl.QW
---1874 LOW ~'1W
-··-··-1171 AVERA(.&I! FLOW
NOTE
SIMULATIONS WERE MADil fOR FJAST
STAGE Of TWO STAGE PROJECT FOR
STAGE I ENERGY DEMANDS
AND ARE PRESENTED TO ILbUSl'RATE
TEMPERATURE oaFFERENCES FOR
WET, DRY AND AVERAGE fLOW
cor~~rr~Ns
SOURCE:
NATURAL AND STAGE I
TEMPERATURES AT . RM 130
AlASKA POWER AUTHORITY
SUSITNA HYDROELECTRiC PROJECT
FIGURE IS
''
ENTRIX, iNC.
104
HARZA·E BASCO
SUSITNA JOINT VENTURE
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construction and filling as compared to these of Stage I
operation.
-9_g_gration
Differences betw:.en wat~r temperatures under natural
conditions and under Stage ~I project operation conditions
are more pronounced than under Stage I operation at a 11
locations within the middle Susitna River. Summe"' Stage II
river temperatur~~s exhibit a lag behind natural conditions
of approximately one month. Simulated tempe~atures at RM
130 are generally near 4°C in early May, range from 6 tl 8°C
during the summer, peak ·at near l0°C in '!ate August thrvt~gh
1 ate September, and decrea,se to 0°C by 1 ate December (Figure
19). Closer to the dam (RM 150} temperature effects of the
reservoir releases are more pronounced, while downstream {RM
100} temperatures are close to natural (Figure 19}.
In winter, the temperature of the mainstem will remain above
0°C longer than natural because uf the warmer uutflows from
the projett. The temperature in the spring will warm up
above o·i)C sooner for the same r·eason o Between the upstream
end of the ice cover and the dams the river temperature will
generally be between 0°C anj 2°C to 3°C, whereas the rtatura1
temperature in this reach is 0°C. This change in winter
temperatures is reflected in ice simulations discussed
later.
From May through August, Stage I I operation wi 11 l~esul t in
wateY temperatures 2 to 4°C cJoler than natural at RM 130 ..
Fall watar temperatures would be 2 to 6°C warmer. Through
th~ winter, water temperatures are expect~d to be less than
1°C most of the time with occasional periods of 0°C
temperatures. During Stage II operation, an ica cover may
occasionally form at RM 130 (Section 4.4.2}.
105
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~~~~~~~~~~~~~~~~~
~81 1982
RM 100
MOTES:
1. CLIMATOLOGICAL Afo·')
HYDHO'-OOICA~ OA 1'.4
ltERIOO WAY ti11-~I,.Y.
, .. 2
1. IFJ.,ri.OW TEMPERATURE
MAiCHING POLICY FOR
M~$1. TJ-l£VEI., INTAKE
'· Sl'~,QE 2 OF 3 STAGE
ltftOJECT
4, AYE .. AGI! WEEKI.Y VAlU!S
!. E-VI FLgW AEOUIR(;MENTS
1., TE~?~F,A TUAt:~ SIMULATED
IV SM\'2WP' FOR PERIOD
NOVEMBER-MARCH SnOIJlD
B.e USED WITH CAUTIO~ AS
"t.l lCE ;~~VEA MAY' \'EXIS7
ON fiiVER A!i!O SHaMP
C:OES NOT SIMULA n:
TEMPE~AT!JRSS UNDER AN
ICE COVER (SEE RIVER ICE
$Jl.~ULATIONS)
1.. UaYil CAf•WOt~ ORA WOOW~
0~ 50 FEEt-7 .NELS OF
SHUTTERS
LEO!;NC
SIMULATED N~T\1!ltA&.
TEMPERATURES
--•• eNOlA TED TEMP£AA l\JAES
PHASE 2 OF TWO STAGE
IIROJECT (FOft COMP~ONJ
SM.Jl.ATEt'll ei.IP£RI'~S
ST AO.: 2 OF PROPOSEG
PROJECT
RM 130
RM 150
SOURCE: APA l985c
NATURAL AND STAGE H
TEMPERPiTURES ALASKA POWER AUTHORITY
SUSlTNA HYIJROELECTRIC PROJECT
FIGURE 19 ENTRIX, INC.
'-------~~-~.--.-------~--------MD~~-------------~. 106
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In wet years the reservoir fills by early July and thus the
outlet works must be operated tc pass flow. Because the
outlet works draw from a lower elevation in the reservoir,
its flows are generally cooler. This will cause a drop in
river temperatures in July in wet years.
Based on the simulations of natural conditions and project
operation, the mean annual temperature (time weighted) at RM
130 for the period May 1981 to April 1982 was calculated to
be 3.7°C fo!" natural conditions and 4.2°C for Stage II
project conditions. Simulations of other hydrological and
meteoro 1 ogi ca 1 conditions for other flow requirements a 1 so
indicated that the mean annual temperature with-project
would be similar to natural conditions.
The simulated Stage II operation results in a drawdown of
Devil Canyon Reservoir in mid-June. This drawdown may be up
to 50 feet in some years,, When the water 1 eve 1 decreases
below the upper of the two levels, the lower level intake is
opened. This intake, being relatively deeper in the
reservoir, draws coldar water for a short period until the
water level decreases further. Thus, there is a simulated
decrease in river temperatures in mid-June to early July
dependin~ on the year simulated. The effect of this drop is
most noticeable near the dam, and because of climatic
conditions, is not noticeable at RM 100. Two simulations
were carried out with ~odifications to the operating policy
of Devil Canyon and to the multi-level intake to attempt to
improve temperatures. Because the effeacts of these two
modifications on temperatures were minor, the Applicant
maintained the Devil Canyon drawdown of 50 ft and the two
level intake. The modifications which the Applicant
considered are dis~ussed below.
The first of these modifications was to hold the water level
at Devi 1 Canyon above the upper 1 evel intake which 1 imi ts
107
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the drawdo"'" at Devi 1 Canyon to nine feet. This reduces
project energy production somewhat since minimum flow
requirement!; must be met from Watana storage rather than
Devil Canyono This modification policy generally eliminates
the drop in temperatures resulting from 1 owe red watel'
levels. However, it also results in a noticeable increase
in temperatures in mid-June and larger temperature decreases
when the outlet work:-:: operate than for the 50-ft drawdo:wn
policy.
The second modification tested was to include a third level
of ports between the two existing 1 eve 1 s of ports at. the
Devil Canyon multi-level intake. This policy also
el im·inated the drop in temperatures resulting from lowered
Devil Canyon water levels, and provides a smaller decrease
when the outlet works operate and generally more uniform
temperatures in June and July than the other two policies.
(iii) Stage III
-Construction
No change from Stage II operation is anticipated.
-Filling
During the filling of Stage III Watana Reservoir, the
capacity to select the water temperature to be discharged
will be increased as more ports in the intake become
available for use. The increased flexibi-lity to select
water temperature Pnd the increased volume of water
available at higher elevations will enable the release of
water with temperatures more closely matched to the inflow
temperature early and late in the summer months.
lOS
..
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L
Outlet works releases during the July-September period of
filling will be reduced. The intake to the outlet works is
located in the hypolimnion and releases through t-t1e outlet
works are generally co 1 der than those through the
powerhouse. Therefo~e, the reduction in these releases will
result in temperatures in the river downstream of the dam
being warmer than normal operation. Additionally, the
reduced river flow in this per:iod will result in greater
river surface area per unit discharge and more heat transfer
between the river and the atmo::>phere causing an increased
rat.e of warming toward natural temperatures.. Therefore ..
during the fi 11 i ng period, river temperatures are expected
to be closer to natural than for normal operation of the
project as described for Stages II and III.
Ooeration
Stage III temperatures were simulated for early and 1 ate
project energy demands. Summer temperatures simulated for
early Stage III are generally cooler than for Stage II of
the three-stage project. Thus, when Stage III begins
operating; summer temperatures may be the same or decline
slightly from those of Stage llo Summer temperatures will
probably be below those experienced during stage III
filling, since outlet works releases during Stage III
fi 11 i ng wi 11 be mini rna 1 • As energy demands increase, the
outlet works re 1 eases wi 11 decrease and summer temperatures
will increase toward maximum energy demand levels.
Stage III temperatures for late project energy demands are
generally warmer than early Stage I I I tamperatures in May
through July or ear1y August and cooler than early Stage III
temperatures from August through October (Figure 20).
Summer Stage III (late) simulated temperatures are closer to
natural tha~ Stage II or early Stage III.
109
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RH 100
NOTES:
t. CLIMATOlOGICAl AHD
HYDROLOGICAL DATA
PERIOD MAY ttet-.SEPT. •••z
2. INFLOW TEMPERATURE
I.IA TCHING f'Ol.ICY FOR
UUL. TI-LE VEl. INT AI<E
3. STAGE 3 OF 3 STAGE
PROJECT
... DEVIL. CANYON DAAWOOWN
OF 50 FEET-2 lEVEt.S OF
SHUTTEAS
L T'HE TWO SN.l.AllONS SHOMI
lfAOYIX: IIO'.H>S ON TEJoi'£JIIAlUIES
WHI04 CAN ll fXP!CTED DUING
STAGE a. AS ENEAQY OEt.IAHD AIG
PROJECT EJE:\GY PROOUC110H
INCREASES TEIM'EAATlRS WU.
lfAOGRESS FROM THOSE SHOWN FOI'
EAAl.Y STAGE I OEt.IANOS TO lliOSE
SHOWN F~ LATE STAGE • OEWfoCS
L.EOEND
-St.liJlATED NA'T\JRAL
Ta.APERA T\JAIES
------lATE STAGE I
---EAfl.Y STAGE I
RM 130
RM 150
~~~~~~~~~~~~~~~~~
1981 1982
NATURAL AND STAGE Ill
TEMPERATURES
FIGURE 20
SOURCE: APA. 1985c
---------~~,T,'·--------------------..
AlASKA POWER AUTHORITY
SUS~TNA HYDROELECTRIC PROJECT
t-w-------~-~~,-------------~--m.----------------------~
ENTRIX, INC.
110
HARZA·E BASCO
SUSITNA JOINT VENTURE
0
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For 1 ate project .energy demands, summer with-project river
temperatures wou7,d exhibit a lag behind natural conditions
of approximately; one month. Simult!ted ternperatut·es at lt'1
130 are close to 4°C in early May, peak near 10°C between
July and August, and decrease to 1°C by late November. In
wet years the reservoir fills by early August; thus, the
outlet works must be operated to pass flow. Because the
outlet works draw from a lower elevation in the reservoir,
these flows are generally cooler. Outlet works releases due
to a full reservoir causes the drop in simulated river
t~mperatures in July 1981 and July 1982.
The open water temperatures in winter should not change much
throughout Stage I l I. This is i 11 ustrated by river ice
simulations undertaken for early and late Stage IJ1 energy
demands {HE 1985b) \.rhich showed little difference in ice
cover between these two energy demands. Open water
temperatures in winter for all of Stage III are warmer than
Stage II.. Winter open water temperatures will increase
gradually from Stage II operation through Stage III filling
to Stage III operation ..
In winter, the temperature of the mainstem will remain above
0°C 1 onger than natura 1 because of the warming outflows fl"Om
the project. The temperatur~ in th~ spring will exceed o0 c
sooner than natura 1 for the same reason. Bet·r~een the
upstream end of the ice cover and the dams, the river
temperature will be between 0°C and 2°C to 3°C, whereas the
natural temperature in this reach is 0°C.
The mean annual (time weighted) temperature at RM 130 has
been calculated for the period May 1981 through April 1982
to be 3.7°C for natural conditions and 4.7°C for late Stage
III conditions. Simulations of natural and with-project
conditions for other meteorological and hydrological
conditions for other flow requirements also indicates that
111
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mean annual w·ith-pro.ject temperatures may be slightly
greater than natural mean annual temperatures. Mean annual
temperatures in dry year with-project simulations are
generally closer to natural conditions than in wet years.
River ice conditions between Watana and Talkeetna during operation of the
~toject were simulated with th& !CECAL river ice model (HE 1985b). The
I
primary objective of the ICECAL model is to simulate the timing and
magnitude of river stage fluctuations resulting from ice processes.
(a} Watana to Devil Canyon
(i) St&ge I,
-ConstructiQD.
No downstream impacts on river ice are expected as a result
of Stage I construction. The diversion tunnels are large
enough to pass the 1 ar.gest ice floes that have been
observed, so that no significant downstream effect during
breakup is anticipated. During freezeup, some additional
frazil ice may be formed in the diversion tunnels due to the
high velocities and associated turbulence. The volume of
frazil ice formed is not expected to affect downstream ice
formation.
,.. ... , . -r 11 1 ng
During the winte~ after filling of the Stage I W tana
Res~rvoi r, reservoir re 1 eases waul d be warmer than natura 1
and would, therefore, delay frazil ice generation and ice
cover formation, compared to natural conditions. River ice
conditions durina the winter following the summer of filling
are expected to be similar to the fil~ing simulations
112
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(ii)
presented in the ".Instream Ice Simulation Study" (HE 1985b).
Frazil ica g~neration and border ice growth would typically
begin between 5 and 40 miles downstream of the dam, varying
with weather conditi~ns, being closer to the dam during
colder periods and further downstream in warmer periods. In
the reach approximately 30 miles immediately downstream of
the dam, an ice cover is not expected to form.
River ice thicknesses and ice-induced stages would be
' somewhat less than those of natural conditions. Breakup of
the ice cover would typically occur in May, similar in
tirning to natural breakup. Breakup is expected to be
somewhat milder than natural, due to the warmer than natural
reservoir releases which melt and weaken the ice covero
-Operation
Based on the average winter weather conditions of 1981-82,
the Case E-Vl flow requirements, and the projected Stage I
energy demand, frazil ice generation would begin downstream
of the Watana to De vi 1 Canyon reach. The ice front wi 11
advance a few miles upstream of RM 140 during a cold winter,
but ~~ not expected to extend to the Watana to Devil Canyon
reach. Upstr-eam of the ice cover, the ri v~j" wou 1 d remain
open with some border ice and anchor i ee expected within
approximately 10 miles upstream of the cover. Depending on
climate, during relatively cold periods a greater length of
river would have br"'der and anchor ice than in a warmer
period. Maxi mum l"i ver stages upstream of the ice cover
would be equivalent to or lower than those of natural
conditions with an ice cover.
Stages II and III
DuriP!:I construction or the Stage I! dam, ice ,conditions in the
Watana to De vi 1 Canyon reach wi 1 'l remain unchanged from those
1 .. .,..,
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during Stage I operation. During fi 11 i ng of Stage I I, the
reach will be inundated. Impacts to this reach of river during
filling and operation of Stage II and all phases of Stage III
are discussed in the impoundment impact assessment (Entrix
1985b).
(b) Devil Canyon to Talkeet,!l!
-Construction -·
No tmpacts on i~e regime are expected to occur during Stage
I construction.
-Filling
During filling, the ice front is expected to advance
upstream to RM 140 during an average winter, gOd upstream or
downstream a few miles during cold and warm winters,
respectively. River ice thicknessrs and ice-induced stages
will ba slightly less than those of natural conditions.
·· Operation
River ice model ~esults during Stage I Watana operation are
shown in Figure 21 based on the average winter weather
conditions of 1981-82, and the Case E~VI flow requirements.
For these conditions, f)"azil ice generation would begin
where stream temperatures have cooled to 0°C, typically 35
to 6~ miles dO\·mstream of the dam {RM 150 to 120) and would
vary with daily weather conditions and reservoir release
temparatures. Ice cover progr~ss ion upstream of Ta 1 keetna
is expected to begin in mid-December, approximately 3 weeks
later than for natural conditions. Progression of the ice
cover would reach a maximum extent near RM 140 in 1 ate
114
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1~~~~-------------T~hn~nr.~·--+·----~~~--------------------~ 0°C ISOTHERM FOR I • •
!
~-130
8~
-':'i .... a: 120
!~ ~!. 110
w y -
100
w 14
0 12 ~ en 10 CIC w-a >J--'II a:w 8
STAGE I~ : : : e • e .., I I ..... : .. , ()..,... : .: ....
I I 1 I ,.-I "-: • .,.·=~·~ ll I I I I I ... ~. ~· I •• I I
I Q 1 I Je lela -.~ I • : :
I I I IIIII I 'II II ~ 1 1
I I 1 I • 1 0 e ··.. I 1 I I 1 I ....
.... I I I _, II.,, II I•~
I 1 l'l II I ~··· : r· . . ~-··:~ I I II~~ .. . •,.
I I If I •, ..
11 ·-!. • • • "-l!.. ~ ~ ~~~
••••• ••• . ~~
il • • • •
I \•
i '~~ I ~ •
-r----N-O-V--~----O-E-C--~-----JA-N--~~--F-e-8----~---M-A-=R~~.~---A-PR--~~
REFERENCE LINE· r 3000 cfs OPEI'w WATER SURFACe PROFILE 'JJ
I _;9~ !
' ~· ' . I
~· -, . ..._ ...
~·' \ ~I ~
I ·~~.l / -......... " ·, ~~ ~ ,I \
~~
:::) 4 ~
__ _..., ..... ---~v " VI • ~ l/ ~ ~ .. /
' iJII"' l't ~ ~ ---
X 2 .c
~ 0 ~
I
100 110
w (.,) -10 -J-...J~ 8 Cu.. .... _ J 6 etg
:& w .. . ~'
:::)' z ::E~ 2 -·-~--·-·-·-· -•• ~-r--'"'
X~ 0 <t-~ I
110 100
NOTES: f. -STAGE 1 SIMULATION BASED ON CASE E-VI
FLOWS. STAGE I ENERGY DEMAND. INFLOW
MATCHING TEMPERATURE: POLICY.
2~ NATURAL. CONDiTIONS NOT S1MULATEO
UPSTReAM OF RM 140.
3 3000 cfs REPRESENTS TYPICAl. WINTER
FLOW UNOER NATURAl.. CONDITIONS
AT FREE~!: UP.
NATURAL AND STAGE I
RIVER ICE CONDITIONS
FIGURE 21
120
R.IVER MtLE
·'~ ·" r\..' .. ,/
/. -~~
.
120
RIVER MILE
LEGEND:
" ~
I
130
} ~ , " j' ~
I \ I -,
'--•• •
I
130
--..• NATURAL CONOITlONS
·-...,-STAGE I OPERATING
·~ -~ v
r
I
140
' ·~ --
i
140
• NAnJRAL SLOUGH BERM ELEVATION
I!
SOURCE: APA 1985c
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, lf\IC.
115
HARZA~E BASCO
SUSITNA JOlNT VENTURE
i s
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January. Maximum expected ice cover thicknesses range from
3 ft to 9 ft along the river, and are similar to those of
natural conditions. Maximum river stages within the
ice-covered reach (downstream of RM 140) would often be 2 to
6 ft higher than those of natural conditions (Figure 8) and
a greater' number of s 1 oughs would be overtopped in this
reach. ,A fiel1 program in the fall of 1985 collected
topographic data along the perimeters of sloughs SA, 9, 9A,
11, and 21. The topographic data were compared to the
maximum ice stages predicted by the ice simulation {HE
19S5b). The comparison suggests that the heads of sloughs
SA, 9, 9A~ at'!~ 11 waul d be overtopped; a separate analysis
of overtc;;ping of sloughs under winter conditions in the
FERC 1 icense application amendment (APA 1985c) confirmed
these results. However, the i sl a.nds separating the s 1 oughs
from the mainstem are not expected to be inundated under
average winter weather conditions.
Flow in sloughs caused by overtopping may cause scouring in
the sloughs. However, because of the increased backwater at
the slough mouths due to mainstem staging, velocities at the
downstream ends of the sl<Jugh~ should be reduced, thereby
reduc1ng the chances of scouring in the lower reaches of the
sloughs. Velocities upstream of the backwater effects may
be as high as 3 fps {0.9 m/sec) unde!' the ice cover, which
are sufficient to cause erosion of finer materia 1 such as
sands or small gravel. Currently, the bed material in the
sloughs becomes coarser with distance upstream and 1 s more
resistant to flow, thus minimizing the potential flr
erosion.
Upstream of the ice cover, the river would remain open with
some border ice and anchor ice expected within approximately
10 miles upstream of the cover. During relatively cola
periods a g;~eater 1 ength of river would have border and
anchor ice than in a warmer period. Maximum river stages
116
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upstream of the ice cover would be equivalent to or lower
than those of natural conditions with an ice cover. Slough
21 and Side Channel 21 are not expected. to be overtopped
(APA 1985c).
Colder winters will move the ice cover upstream and increase
ice thicknesses up to 2 to 3 ft. A field program in 1S85
collected topographic data along "the islands between sloughs
SA, 9, 9A, 11 and 21 and the. mainstem. These are cons·idered .
to be the major salmon-spawning sloughs of the middle
Susitna River (ADF&G !985a). The topographic data were
compared to the simulated maximum ice stages; the island at
Slough,9A appears likely to be inundated under cold weather
conditions. Conversely, during warm winters the ice cover
will remain further downstream and ice thicknesses will be
reduced by a few feet.
The ice cover upstream of Talkeetna is expected to
substantial'ly melt in place by the end of April. Mechanical
break-up of the ice cover, which occurs during natural
spring flow increases and results in ice jaffis and slough
overtoppings, is expected to be substanti-a11y reduced or
eliminated upstream of Talkeetna with Watana Stage I
operating.
{ii) Stage II
-Construction and Fillina
lee processes wi 11 be unchanged from those discussed for
Stage I operation.
-Operation
Frazil ice generation would be limited to the reach
downstream of RM 135 and would vary with daily weather
117
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1-' i
C,
I
I }
I
I
I
I
I
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I
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I
I
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~
tr~l
f,r l
tJ
,1 I
I
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I
r
conditions and reservoir release temperatures. At times, no
frazil would be produced upstream of Talkeetna.
Ice cover progression at Talkeetna is expected to bP~in in
1 ate December and waul d reach a maxi mum extent near RM 133
in late J~:1uary. This is approximately six miles downstream
of the simulated Stage I maximum ice extent. Expected Stage
II ice conditions are shown in ~igure 22. Maximum expected
ice cover thicknesses would range from 2 ft to 6 ft and
would be generally similar to or less than those of natural
conditions. Maximum river stages within the ice-covered
reach would often be 1 ft to 4 ft higher than those of
natural conditions (Figure 8} :u1d greater overtopping of
sloughs would therefore be expected in this reach if the
mitigation measure of berm construction were not
imp 1 emented. In genera 1, river st<\ges waul d be 1 ess than
those during Stage I operation. Upstream of the ice cover,
the river would remain open and maximum river stages would
be equivalent to o·r slightly less than during natural
conditions.
The ice cover upstream of Talkeetna is expected to
substantially melt in-place by late March. Mechanical
breakup and res~lting ice jams and flooding events are
expected to be substantially reduced compared to natura 1
condit.ions.
With Stage II operating, the river ice effects of the
alternative power intake designs and operating policies are
expected to be less evident than those discussed for Stage
I. Relative to the "inflow-matching" policy, the 11 warmest
water" policy has ~s$entially no effect on the simulated
river ice conditions with both dams operating. Simulations
for the final stage of the three stage project show that the
simulated maximum extents of the ice front for both policies
are within one mile of each other and maximum water leve1s
118
...
...... · ... ~
J '
1!KJ--.-----·-..._ ___________ . ___ ........, ____________ .,
I 140 -
0°C ISOTHERM FOR
·~
I
STAGE II ~ .. , ··.··~--~~ : __ .. _.,.,. ····· • • • , •• , --• ..!t8 .... . ~ . . ~. . ,. . . . ,_ .........
• ~ ' : I '•'•
: &. ' •• • •• \ . . .. :. . • J • ., ••• . . . . \,_ : 1.· ~ ~. : ... "-. . . .. , • • • : I ···~ • G • • .. .__. I ·~\
• • •
100
I
I
I
~-+--------~--------~---------~------~~-----------------~ NOV oec JAN FEB MAR APR I
s
R~FERENCE LINE: r3ooo cfs OPEN WATER SURFACE PROFJLE 1/
w 14 I
<:J 12 ~ en 10 cz: ""-8 J ...... _,. .....
>I-.--·-'1 X ;, ........ ""'' -w 1-j~ a:w 8 -·--I
2~ .,..-•7 IJV ' ....._... ~ .·~ r, ~ ~ • :l 4 2 ['~~ -~ , lL ·-""' • ·' )( 2 ~ ' ~
2 0 I I I -
I
I
I
100 110 120 13f' 140 \
RIVER MILE
w <.l -10 ! . f ' ~ _,_
..J "' 8 ~~ ~'· o-8 J :'\..
.... t~ ......... ~ "· .L. .~, .... ~~ I 21el 4 ~----·-'· ·' ~ ~-l :)z i 2~ , ~· : .....
-~ 2 "" )(::: <t-0 I l l 2
100 110 120 130 140
NOTES: RlV~R MILE
. 1. STAGE II SIMULATION BASED ON CASE .
• .~ .. ...... \.
.~ r' r~-
I
I
11
E-Vl FLOWS. STAGE Jr ENERGY LEGE NO:
DEMAND, INFLOW MATCHING NATURAL CONDITIONS TEMPERATURE POLJCY
2. NATURAL CONOITlONS NOT SIMULATED -·-·STAGE II OPERATJNG
P1 lJ
UFSTREAM OF RM 140. • NATURAL SLOUGH B!:RM ELEVATI0~4
3. 3000 cfs REPRESENTS TYPICAL WINTER SOURCE~ APA 1985c FLOW UNOER NATURAl.. CONOITIONS
AT FREEZE UP' .
Jl tl . !
L..J
ALASKA POWER AUTHORITY
NATURAL AND STAGE II SUSITNA HYDROELECTRIC PROJECT
RIVER ICE CONDITIONS
ENTRIX~ INC. HARZA·E BASCO
FIGURC 22 SUSITNA JOINT VENTURE
!19
•
\'
L,,
are within one foot of each othero The similarities between
ice conditions for the two policies would be the same for
Stage II as Stage III. Simulations with alternative low
level intake ports showed only slight reductions in
simulated river ice conditions.
For Stage 11 operation the maximum simulated ice
thicknesses, river stages arid ice front extent are
substantially less than those for Stage I Watana operation~
Slough overtopping events during Stage II operation are
therefore expected to be milder and less frequent than those
of Stage I operation.
(iii) Stage III
-Construction and Filling
The discussion of ice for Stage II operation is applicable
to Stage I I I construction before fi 11 i ng commences.
Conditions will gradually apprcach those discussed below for
Stage III operation as the reservoir is being filled.
Operation
Frazil ice generation would be limited to the reach
downstream of RM 115 and would vary with daily weather
conditions and reservoir release temperatures. For much of
November and December, no frazil ice would be generated
Upitream of Talkeetna.
Ice cover progression at Talkeetna during Stage III
operation is expected to begin in t1arly January and would
reach a maximum extent near RM 114 in late January9 Maximum
ice cover thicknesses of two feet are expected and would be
several feet less than those of natural conditions {Figure
23). Maximum river stages within the ice .. ·covered reach
120
t
I ~/
(.
0
''
"'
\,,
L
l.
t •..
-.. ,. .... -:-~·":.. .... -~~,..~-· ~~ --:: ......,,.~. _...,..,-~~
·-·-'"'~--~·-•. , •.•• ,,~, ,.._,_,_ .... ,. __ ..... '"'-·-+~>·•"--.....;.'"'"
1~~~------------------------------------------~-------------
140 -·-ICE FRONT z
0
~-130
•• • • OCC ISOTHERM
8~
~2
... CIC 120
Zu,a
0> CIC-•
v... ~ 110
.-, __ ,-~, -.. L
t • --'\ :'·--~-.,. EARLY STAGE Ill ,.,.. , \, ,_
I .• \' ,, . . " : J r:--'' •I ':, I ; -~• ·~: •·•1 \' ~ .... ~ • '' • I I' •t : e •• .. \ t _,, •• g _.-\, \ "
"' u -100
I •• • \' ~ • • \~• !.' '• I:···J I ··:: ·~, 'V.J ~.-r--L4TE STAGE Ill
I• : • ~\ ' .: I ··~ ·= ' \. ...•
~-r--~~--~~~--,-------~--------r-------~------~ NOV DEC JAN FEB MAR APR
"' 14
C) 12 <
I
... en 10 CIC ""-8 > ... -w IJ:u,a 8 2~ :::> 4 :i -X 2 < 2 0
tOO
"" (,) -10 .......
.~: 8 <· ,... ... o-8 ,_~
2w 4 :;,Z 2~ 2 -!: x::
4( ... 0 2
100
NOTES:
.--REFERENCE LJNE:
' 3000cfs OPEN WATER SURFACE PROFILe: 31
I ---I I
·-.,LATE STA
~ 1
~. -1..-..-.--.i.---__ ....
......
T -· 1
I
110
:il ID
.J ~
1-'"· '~
!" "'
I ..
/
... ,/ -r--
,,~ , ......
lJ • ~:
' -·-
120
RIVER MILE
~'
...... --
EARl :y ~TA pE Ill
"" J~ "' VI • ~
'Oil.~ ...
"'""" ·-
l
130
i'-.. "-..
' I ~
" ~' ~-··-·· ~ ,., ... ........ ------·-·-·-t
110
·-... , ~ ...
120
RIVER MILE
-' ... ;"' ....
l
130
1. STAGE m S1MU\.AT10N BASED ON CASE lEGEND:
l/ ~
~ !-""'""'
i"
~ ", L~ ,...
~P-
'
E-VI Ft.OWS. LATE STAGe II ENERGY DEMAND,
1NF1.0W MATCHING TEMPERATU~E POUCY ---NATURAL CONDITIONS
_.,_.,LATE STAGE R1 OP£RATING
'-~ . -~ ·-· ~· ~~~--
T
I
140
I
140
2. NATURAL CONOIT10NS NOT SIMULATED
UPSTREAM or: RM 140.
• NATURAL SLOUGH BERM ELEVATION -·s-EARLY STAGE Ill OPERATING
~f-t
3. J000 cfs REPRESENTS TYPICAL. WINTER
FlOW UNOER NATURAL CONOITIONS
AT FREEZE UP. SOURCE: APA l385c
NATURAL AND STAG,E Ill
RIVER ICE CONDITIONS
FIGURE 23
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC.
121
HARZA·E BASCO
SUSITNA JOINT VENTURE
i
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,,
would be approximately two feet higher than those of natural
conditions {Figure 8} causing somewhat greater than natural
slough overtoppings in this reach. Overtopping would not be
expected where berms are elevated as a mitigation measure.
Upstream of the ice cover, maximum river stages would often
be 1 to 3 ft lower than those of natural conditions with an
ice cover, and fewer than natura 1 s 1 ough overtoppi ngs are
expected.
The ice cover upstream of Talkeetna with Stage III operation
is expected to be melted out by early March. As discussed
for Stage I and Stage I I, the ice c :wer is expected to
substantially melt in place without major ice jamming or
associated flooding.
The effects of differing winter weather conditions on river
ice are expected to be generally similar to the trends
discussed for Stage II operation. Relative to the river {ce
conditions for the average 1981-82 winter, ice front
progression for other weather ccmtjitions may occur a few
weeks earlier or later and may reach a maximum extent a few
mi 1 es further upstream or down~tream. Maximum ice cover
thicknesses and river stages would also be expected to vary
by a few feet among the various weather conditionso
The effects on Stage III river ice conditions due to
alternative designs and operating policies for the
multi-level power intakes is expected to be similar to that
discussed for Stage II. The alternative designs and
operating policies are not expected to substantially affect
the river ice conditions.
4.3~3 Suspended Sediments/Turbidity/Vertical Illumination
Previous studies indicate that, with the projectt there will be an
overall reduction in the suspended sediment load of 80 to 90 percent from
122
0
:o
...
natural conditions. Turbidity levels will be measurably reduced from
natural conditions in the summer (May through September) and increased in
the winter (October through April).
Turbidity is a water quality parameter important to the fishery
resources.
the water.
It is a measure of the light transmitting characteristics of
Low values of turbidity indicate high light transmittance and
vice-versa. Turbidity is influenced by the size, concentration ~ ,,d
mineralogy of material suspended in the water including sediment, dyes,
and other organic and inorganic material. In the Susitna River the
turbidity levels are. chiefly influ~nced by 1tne concentrations and grain
size of suspended sediment; the ratio of turbidity to suspended sediments
apprcpri ate for quiescent water bodies such as the reservoir is 2: 1
{Fi~ure 24). Vertical illumination is proportional to turbidity.
The DYRESM model was used to simulate the suspended S\diments in the
Watana Res~rvoir and in tne proj~~ct outflows {APA 1985c). Case E-VI flow
requirements and 1970 and 19~1-82 meteorological conditions were
considered. Data on the suspencled sediment concentration and size
distribution in the Susitna River ~ere available from USGS. Figure 25
shows the esti~~ted relationship between discharge and suspended sediment
load at the USGS gaging station on the Susitna River near Cantwell.
{a) Watana to Devil.Canvon
{i) Stage I
-Construction
During construction, suspended sediment concentrations and
turbidity levels are expected to increase within the
impoundment area and for some distance downstreamo This
will result from the necessary construction activities
within and immediately adjace1nt to the river as described in
123
I
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~
~
: ,/
s
~ -
LAICIS .UG UNTlC S'YSTtiiS--'
MTU/TSS ::wz.o
• • • • •
• • •
• 1...._ .................................. ......_.....w....w.~o..-..-~--.. ................ ...._ ....... _....,.w,w..._ .............. ~ ...
• 1 1 10 100 lJOO . 10,000
SUSPENDED SEDIMENT CONCENTRATION
, .. /liter)
NATURALLY C·CCURlRING TURBIDITY
vs. SUSPENDED SEDIMENT CONCENTRATION I
FOR RIVERS AND LAKES IN ALASKA
ft
;(
if
lr
(Mt'JDIFIED AFTER LLOYD 1985)
FIGURE 24
SOURCE: APA 1985c
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC.
124
HARZA-E BASCO
.SUSITNA JOINT VENTURE
..
•
t-IOO,OOO....-.-.,..--.,_,_....-r II"Y" ,..-r--, ' I I I Q 8 I I I I I I I I I I I I I I I ' I I I I I I • •
~ v . ~ ~-
t-"' _, ~~ • ~~~o~------4---~----------~--~----------4----+----------+----+V~----~~t----t?,4--1 , -1-v
/ , ,'
t--,' ,' ~ l , , ~
..., ,,v' b.4~ ,·, , , , ~ ,, i • ,' ,
-
-
--. . .
--
-
I I j Jltl
llf 100 iO 1410 ----~J--~·~·~LJLlJ~I~---._1_._1~1~~·~·~··~~-._I_LI.~ ~~ I I I
" IU 10 iJO 5000 10, ~0 ~UIJ I.JU "" ~·"'
I J I I
IUIPIHDID IIDIMIHT Dll:tH.AIOI YONi/0~'4
SUSPENDED SEDIMENT RATING CURVE
AT USGS GAGING STATION
SOURCE: APA 1985c
SUSITNA RIVER NEAR CANTWELL~~ ALASKA ALASKA POWER AUTHORITY
SUSITNA H'JOROELECTRIC PROJECT
HARZA·f BASCO
• SUSITNA lOINT V~NTURf ENTRIX, INC. FIGURE 25
-.. ---.. -----
the Access Corridor, Construction Zone, and Transmissi~R
Corridor Impact Assessment and Mitigation Plan (Entrix
1985a}.
The excavation of the diversion tunnels and construction of
the first diversion cofferdam may cause temporary increases
in suspended sediment and turbidity. Cofferdams will be
constructed upstream and downstream of the diversion tunnels
to enable tunnel construction. Material ex~avated from the
tunnels will generally be confined within the cofferdams
prior to disposal. Thi$ wi11 minimize increases in
suspended sediment and turbidity. The first diversion
cofferdam will be located in the river. It will be
constructed by dumping rock material into the river to
divert flow to the diversion tunnels. During perigds when
roct is being placed, some sediment will be washed
downstream. The amount of materia 1 introduced into the
river in this manner is not expected to cause significant
increases in sediment concentration si nee the tot a 1 amount
of m~terial in the cJosure cofferdam is small relative to
the existing river sediment load.
Summer flows wi 11 be passed through the diversion tunne 1
with no impoundment. Hence, little settling of
naturally-occurring suspended sedime~cs is expected to
occur. Pending is not expected upstream of the diversion
tunnels in the winter, and so normally low winter sediment
and turbidity levels will not be changed.
-Filling
In general, the suspended sediment concentration in the
Watana to De vi 1 Canyon reach wi 11 be reduced from natura 1
conditioh3 during summer and increased during winter.
126
\ ~
As the reservoir begins to fill, water velocities in the
river will be reduced and deposition of the larger suspended
sediment particles ~ill occur. Initially, all but the
larger particles will pass through the reservoir but as more
water is impounded, smaller diameter particles will settle
before reaching the reservoir outlet. As the reservoir
approaches normal operating levels, the percentage of
particles settling will be similar to that occurring during
norma 1 reservoir operation. During the summer of fi 11 i ng,
water wi 11 be passed through the 1 ow-l eve 1 out 1 et. As a
consequence, 1 arger part i c 1 es are expected to pass through
the reservoir during the summer of filling than during
operation. This wi 11 result in concentrations of sediment
higher than those during operation. Maximum suspended
particulate sizes passing downstream through the project
area will decrease from about 500 microns during pre-project
conditions to between 5 and 10 microns when the project
becomes operation a 1 .. During the winter fo 11 owing fi 11 i ng,
concentrations would be similar to operation since units one
and two wi 11 be on-11 ne and re1 eases wi 11 bs through the
multi-level intake. Maximum suspended sediment
concentrations would occur during wet years with high
suspended load influent to the reservoir. l.inimum suspended
sediment c;:oncentrati ons waul d occur during dry yaars with
1 ower suspended 1 oad inflow. Because of the c 1 ear water
tributary inflow in the Watana to Ta 1 keetna reach, further
dilution of the suspended sediment concentration may occur
as the flow moves downstream.
During periods of high tributary flow, the same amount of
suspended sediment will be added to the river by the tribu-
taries as for natural conditions. Ta'lus slides along the
mainstem will also continue to contribute suspended sediment
to the flow downstream from Watana. However, erosion of
slide areas along the river should decrease due to increased
flow stability and dec~eased flood frequencies and flows.
127
~'
~,, .. ,,
"'
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' t.
!
f
)
Summer turbidity levels will be reduced from natural levels
ranging between 60 and 3,010 mg/1 to an estimated value of
100-300 NTU. These values will persist until December and
wi 11 decrease during winter to a mini mum of between 20 and
40 NTU in early May prior to breakup. Because of the
reduced turbidity in summer, the vertical illumination will
be enhanced. Winter vert i ca 1 i 11 umi nation wi 11 be reduced
from natural.
-Operation
Outflow suspended sediment concentration and turbidity level
wi 11 be more uniform throughout the entire year than for
natural conditions. The summer suspended sediment 1 evel
will be decreased from about 60-3,010 mg/1 tc about
50-150 mg/1 and the winter suspended sediment level will be
increased from about 1-80 mg/1 to about 20-100 mg/1,
reaching a minimum between 10 mg/1 and 40 mg/1 in early May.
Turbidities will average approximately 200 NTU from June
through December and decrease to minimum values of 20-40 NTU
by early May. Because of the reduced turbidity in summer,
the vertical illumination will be enhanced while winter
vertical illumination will be reduced.
The susp~mded sediment concentrations and hence the
turbidity in the reach between Watana and Devil Canyon will
be controlled by the concentration in the reservoir release,
and any contribution from the reach. The contribution from
the reac' is not expected to be significant since the
tributaries contain generally clear water and there is very
lit~;·e fine sediment or glacial flour present in the
streambed or on the banks which might be entrained in the
flow. During summer flood periods the contribution from the
intervening areas may increase concentrations in the
mainstem river as a result of erosion and bank sloughing.
Talus slides along the mainstem may continue to contribute
128
suspended sediment to the flow downstream from Watana as
discussed for filling conditions.
{ii} Stages II and Ill
During construction of the Stage II da~, suspended sediments,
turbidity, and vertical illumination in the Watana to Devil
Canyon reach wi 11 remain unchanged· from those during Stage I
operationa During filling of Stage II, the reach will be
inundated. Impacts to this reach of river during filling and
operation of Stage II and all phases of Stage III are discussed
in the impoundment impact assessment {Entrix 1985b}.
(b) Devil Canyon to Talkeetna
(i} Stage I
-Construction
Increases in suspended sediment concentrations in this reach
during constrt!ction will be quite small. Proper sediment
control at the construction site will minimize additional
sediment inputs. Any changes occurring during the summer
are expet:ted to be within the natural range of variation.
Suspended sediment con~entrations may be slightly increased
during wet, warm winters.
-Filling
The trends will be the same as those in the Watana to Devil
Canyon reach during Stage I fi 1 1 i ng {Section 4. 3. 3 (a) { i ) ) .
Suspended sediment concentrations will be reduced from
natural conditions during summer and increased during
winter. Maximum and minimum concentrations will occur in
wet years and dry years, respectively. Turbidity will be
129
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I
I
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I
'i
• .... #141£ ZJJ..Z .:z.*--,:-~L-~
reduced to 100-300 NTU during summer and increased from
natural conditions to 20-4·0 NTU by winter's end.
.. Operation
In genera 1, the trends described for the Watana to De vi 1
Canyon reach during Stage I operation in Section 4.3.3(a}(i}
are applicable. Summer concentrations of downstream
suspended sediments will decrease from natural conditions of
60-2000 mg/1 to project conditions of 60-150 mg/1.
Converse 1 y, TSS concentrations during winter wi 11 increase
from 1-80 mg/1 to 20-100 mg/1. Turbidity will
correspondingly in,crease and decrease in proportion with
TSS, while verti1cal illumination will vary inversely.
Turbidity wi 11 average 200 NTU from June to December, then
decrease to minimum values of 20-40 NTU by early May.
(i.i} Stage II
Construction
Construction of the De vi 1 Canyon faci 1 i ty is expected to
cause increased siltation and turbidity similar to increases
anticipated during Watana construction, but of a sma 11 er
magnitude. Details of physical changes at the construction
site are presented in the Access Corridor, Construction
Zone, and Transmission Corridor Impact Assessment and
Mitigation Plan (Entrix 1985a}.
During winter, essentiaily all the suspended sediment
concentrations and turbidity levels released from Watana are
expected to pass downstream of the Devil Canyon construction
site without significant chang~.
130
""' ;<,_.o,.
-Filling
As reservoir filling progresses, the Devil Canyon reservoir
will provide sett1ing capabflity in addition to the trapping
of sediments by the Watana reservoire The net result will
be a slight decrease in suspended sediment and turbidity and
a corresponding slight increase in vertical i~1umination
downstream from Devil Canyon.
-Operation
As in the case of Watana Stage I reservoir outflows, the
Devil Canyon reservoir outflow suspended sediment
concentration and turbidity levels will be more uniform
throughout the entire year than under the natura 1 river
conditions. As with Watana Stage I, the average summer
suspended sediments concentration (90 mg/1} and turbidity
level will be measurably reduced from natural conditions.
The outflow. suspended sediment concentration from Devil
Canyon wi 11 reach its 1 owest 1 eve 1 of about 20-30 mg/1 in
Apri 1 or May and increase toward a maxi mum of about 130 to
150 mg/1 in late July or early August.. The corresponding
turbidity level may vary from about 40 to 60 NTU in spring
to a maximum of about 250 to 300 NTU in late July or early
August.
During Stage I! operation some of the suspended material in
the Watana outflow waul d be trapped in the De vi 1 Canyon
reservoir. Simulations show that during Stage II the
outflow concentration of suspended sediment from Devil
Canyon would be about 10-20 percent less than in the outflow
from Watana. Additionally, tne Devil Canyon reservoir will
tend to regulate the concentrations so that the abrupt
changes in concentration resulting from changing multi-level
intake port operations at Watana would not be apparent
downstream of Devil Canyon. With Stagca I I the average
131
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July~December outflow concentration would be approximately
80·100 mg/1. The maximym occurs in late July and would be
about 150 mg/1, but the concentration would be relatively
constant between July and December.
Between January and early May the concentration generally
decreases to approximately 20-30 mg/1. For Stage II,
su::,:snded sediment concentrations were only simulated for an
average year {1982). Based on the results for Stage I, low
sediment {1970) and high sediment {1981) years would result
in concentrations approximately 10-lO percent less and 10-20
percent greater than for an average year, respectively •
The suspended sediment concentration between Devi 1 Canyon
and the Chulitna-Susitna confluence will be similar to that
in the outflow from the dam. Some sediment may be injected
by tributaries during floods. However, the contribution
from tributaries will normally be minimal. Thus the
· turbidity in the Devil Canyon to Chulitna confluence reach
is expected to be slightly less than in Stage I or about
160-200 NTU on the average, between July and
decreasing to a minimum of 50 NTU in May.
illumination will be increased slightly from
conditions in the middle reach of the Susitna River.
(iii) ~age It!
-Construction
December
Vertical
Stage I
Fluctuations in TSS downstream of Devil Canyon are not
expected to change from Stage II operation. Additional
impacts on TSS, turbidity, and vertical illumination due to
Stage III construction will not be noticeable downstream of
Devil Canyon dam. Sediment input will be minimized using
best management practices developed for the project {APA
132
• •
I
1985). Most sediment that does enter the watercourse
between Watana and Devil Canyon will settle in the I
reservoir.
-Fi 11 ing
Downstream river flows during this period will be less than
during normal operation of the project in the July-September
period because normal excess releases will be used to raise
the water level. Thus, the ability of the downstream flow
to pick~ up additional sediment will be reduced from normal
operation.
The outflow concentrations of suspended sediment would
gradually change from those described for Stages I axad I I
normal operation to that described for Stage III normal
operation; therefore, the suspended
sediment/turbidity/vertical illumination conditions may be
similar to the conditions described for those stages.
-Operation
As indicated in the Stage II studies, the Devil Canyon
outflow suspended sediment concentration and turbidity level
are expected to be more uniform throughout the entire year
thar: the natural river condition. The outflow (suspended
sediment concentration of the Watana Reservoir in Stage III
in July and August would be less than for the Watana
Reservoir in Stages I and II. The reduction in
concentration may be up to about 50 mg/1. This reduction is
due to t. e 1 arger and deeper Watana Reservai r formed in
Stage Ill (retention time increases from 9 months to 20
months). The outflow suspended sediment concentration from
Devil Canyon Reservoir is correspondingly less in Stage III
than in Stage II.
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The outflow suspended sediment concentration from Devil
Canyon wou 1 d reach its 1 owest 1 eve 1 of about 10 to 20 mg/1
in ~pri 1 or May and approach a maximum of about 90 to
100 ~~/1 in July or August. The average concentration
between August and January would be about 70 mgjl.
Tu.rbidity levels in this reach would be less than Stage I
and II because of the reduced· suspended concentrationse
Turbidity in the summer would be reduced from natural
conditions because of the irapping of material in the
reservoir. Willter turbidity levels will be higher than
natural because of the fine material which remains suspended
in the reservoir. Summer turbidity levels are simulated to
increase from values of 20-40 NTU in early May to maximums
of 200 NTU in 1 ate· July and to decrease to approximately
100 NTU by September. Turbidity would be relatively
constant at 100-140 NTU through December and decrease to
minimum levels in early May.
Vertical illumination would be greater than in Stages I or
II.
4.3.4 Dissolved Oxygen
Dissolved oxygen conc~ntrations downstream of the damsites are not
expected to be substantially affected by the proposed project. Susitna
River flow will likel~' remain high in dissolved oxygen concentrations.
{a) Watana to Devil Canyon
(i) Stage I
-Construction
Changes in dissolved oxygen concentration are not·
anticipated during construction of Stage I.
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-Filling
During the filling of Stage !5 stratification of dissolved
oxygen concentrations will begin to occur. Water will
likely be released from water near the reservoir bottom and
would likely contain lower dissolved oxygen levels than are
normally found in the middle Susitna River. However, the
oxygen deficit of the water near. the bottom of the reservoir
in Stage I is not expected to be high due to the small size
I
of the reservoir, the volume of freshwater inflow, mixing
effects caused by the 1 ow 1 eve 1 out 1 et works, wind and
waves, and the weaker stratification during filling than
during normal operation. Moreover, additional reoxygenation
of this water will occur naturally as it passes downstream
through the turbulent rapids in the upper reaches of Devil
Canyon.
Operation
Susitna River flow from the reservoir during Stage I
operation will continue to have both high dissolved oxygen
concentrations and high percentage saturations. Dissolved
oxygen changes are not anticipated since water will be drawn
from the upper layer of the reservoir. The oxygen demand of
the water entering the reservoir will be low.
A 1 ayer of Qrgani c matter at the reservoir bottom wi 11 be
present and cou1 d create some 1 oca 1 i zed oxygen dep 1 et; on
a 1 ong the reservoir floor. However, the · process of
decomposition will be very slow because of the cold
temperatures near the bottom. Any waters with low dissolved
oxygen will be diluted by the larg:e reservoir volume of
water with relatively high dissolved oxygen content.
The stratification that is anticipated in the reservoir may
limit the oxygen replenishment in the hypolimnion. The
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spring turnover, with its large inflow of freshwater
containing relatively high concentrations of dissolved
oxygen, will cause mixing; however, the depth to which this
mixing will occur is unknown. It is anticipated that the
upper 200 feet {60 :n} of the impoundment should maintain
high dissolved oxygen concentrations.
{ii) Stages II and III
The reach between Watana and De vi 1 Canyon wi 11 be inundated
fo 11 owing construction of the Stage I I De vi 1 Can,yon dam.
Dissolved oxygen conditions will remain similar to Stage I
operation until inundation (Entrix 1985b).
{b) Devil Canyon to Talkeetna
{i} Stage I
Downstream iissolved oxygen conditions will remain similar to
natura 1 cor. 'ii. t ions as desC;';"i bed for the Watana to De vi 1 Canyon
reach.
-Construction
Construction of t~;e Stage II dam is not expected to affect
the dissolved o~ygen concentration downstream.
-Fi 11 ing
Prior to filling, all large standing vegetation in the
reservoir area will be selectively harvested or cleared and
burned, the·reby eliminating some of the oxygen demand due to
the long-term decomposition of vegetation following
reservoir filling.
136
Because ·of the extremely short residence time, 0(1
hypolimnet·lc oxygen depletion is expected to develop either
during tha one year that the reservoir is held at el. 1,135
ft, or during the final period of r-eservoir filling.
-Operation
Within the uppell layet's (epirimnion) of the reservoir,
dissolved oxygen concentrations will remain high. 'inflow
water to the impoundment will continue to have a high
dissolved oxygen content and low BOD. Since water for 1
energy generation is drawn from the upper 1 ayers of the
reservoir, no adverse effects to downstream dissolved oxygen
levels are expected~
Reduction of dissolved oxygen concentrations can occur in
the lower levels of deep reservoirs. Stratification and the
slow biochemical decomposition of organic matter will
p-.. omote 1 ower oxygen 1 eve 1 s near the De vi 1 Canyon Reservoir
bottom over time. However, all large vegetation will have
been selectively cleared and burned or buried prior to
inundation thereby reducing the potential oxygen demand
decomposition process. No estimates of the extent of oxygen
depletion can be calculated.
Ouri ng periods of re 1 ease through the De vi 1 Canyon outlet
facilities, water with somewhat reduced oxygen levels may be
di schlarged. Given the dynamic nature of the rive~, these
reduced concentrations should quickly return to saturation
levels. Quantitative estimates of these reduced oxygen
levels are not possible.
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(iii) Stage III
-Construction
The Devil Canyon reservoir will act as a buffer to stabilize
any decreases in dissolved oxygen concentrations. No
changes in downstream oxygen concentration are expected
during Stage III construction.
Filling
During the Stage III filling period, the reservoir
stratification will be similar to that described for normal
operation of Stages I, II and. III. A significant
biochemical oxygen demand is not anticipated. The timber in
the reservoir area between the Stage II clearing level and
the Stage 1 I I c 1 eari ng 1 eve 1 wi 11 be se 1 ect i ve 1 y c 1 eared
thereby eliminating some of the associated oxygen demand
that would be created by the inundation and decomposition of
vegetation. Further, the chemica 1 oxygen demand of the
Susitna River is low.
-.Qoer.at ion
Dissolved oxygen levels in Stage III would be similar to
Stage I I. In genera 1 , di sso 1 ved oxygen is expected to be
similar to natural conditions because water will generally
be withdrawn from near the reservoir surface. During
periods when the Devil Canyon outlet works are operating,
some water with lower than natural dissolved oxygen rr-;ay be
released from the reservoir. This wate~ will be released as
a diffused spray which Will tend to increase its dissolved
oxygen content. Additionally, exposure to the atmosphere
and mixing with water re 1 eased through the powerhouse wi 11
increase dissolved oxygen levels downstream. Continual
operation of the Devil Canyon outlet works will cause
138
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replacement of water near the bottom of the Devi 1 Canyon
reservoir with water from near the surface of Watana. Thus,
after a period of releases with potentially lower dissolved
oxygen 1 evel s, the cor·cnntrat ion in the water re 1 eased
· through the o·ut 1 et works ·is expected to increase.
4~3.5 Total Dissolved~Gas
Total dissolved gas concentrations are expected to r~main similar to
natural concentrations as the outlet works wo~Jld be designed to minimize
gas supersaturation. A flip bucket would be installed on the low-level
outlet works and fixed-vone valves would control flow from the outlet
works at Watana.
The Devil Canyon rapids naturally entrain
of dissolved gas immediately downstream.
with-project are not expected to
concentrations.
{a) Watana to Devil Canyon
(i} Stage I
-Construction
air and cause supersaturation
Dissolved gas concentrations
exceed naturally occurring
No changes to the total dissolved gas concentration is
expected to be caused by Stage I construction.
Filling
Changes in the concentration of total dissolved gas are not
anticipated in the Watana to Devil Canyon reach. Water that
is released during the filling of the reservoir to meet
environmental flow requirements will pass through the
low-level outlet. A flip bucket is provided on the
low-level outlet works to disperse the flow and to prevent a
139
hydraulic jump in order to minimize the potential for gas
supersaturation. Gas concentrations in the river are
expected to be similar to natural.
Operation
Supersaturated dissolved gas (nitrogen) conditions can occur
belo~ high head dams as a result ~f flow releases. However,
fixed-cone valves are planned to control flow from the
outlet works at the Watana dam and wi 11 be used during
project operation to release floods with return periods of
less than 50 years. The amount of supersaturation in the
Watana release is expected to remain constant between 100
and 105 percent for up to the 50-year event.
(ii) Stages II and III
During construction of the Stage II dam, dissolved gas
concentrations wi 11 be unchanged from concentrations during
Stage I operation. The reach between Watana and Devil Canyon
will subsequently be inundated (Entrix 1985b).
(b) Devil C~nyon to Talkeetna
(i) Stage I
-Construction
Construction activities are not expected to change dissolved
gas concentrations downstream of Devil Canyon.
-Filling
Supersaturated dissolved gas conditions currently exist in
the Susitna River below the Devil Canyon rapids due to the
entrainment of air and pressurization due to the plunging
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action as the river flows through this reach. Filling will
cause reduced downstream flows and result in 1 ower s~mmet"
dissolved gas concentrations below the Devil Canyon rapids.
However, dissolved gas concentrations will be similar to
concentrations occurring naturally at a similar flow. Based
on observed pre-project conditions~ August flows of
12,000 cfs at Gold Creek should result in total dissolved
gas saturation levels of approxi~ately IDS percent or less.
Operation
During operation, dissolved gas concentrations downstream o~
Devil Canyon are expected to be similar to natural
conditions under low fall flowso
As flows increase, flow in Devil Canyon would become more
turbulent. The amount of supersaturation in De vi 1 Canyon
waul d increase so that the tot a 1 gas concentration
downstream of Devil Canyon would be approximately 115 to 125
percent for the 50-year flood. Gas concentrations have not
been measured for natura 1 conditions for flows exceeding
35,000 cfs, and a direct comparison nf with~project and
natural conditions is not possible for these floods.
However, if the relation between flow and gas concentration
developed for flows less than 35,000 cfs were extrapolated,
gas concentrations for floods greater than the mean annual
event for natural conditions would be higher than for
with-project conditions.
Although no measurements of dissolved gas levels exist for
the winter period for natural conditions, it is anticipated
that average with-project flows (5,000 to 10,000 cfs) will
cause levels of dissolved gas below Devil Canyon which
exceed saturation. Concentrations are not expected to
exceed the water quality standard of 110 percent (18 AAC
70.020) based upon the available natural condition
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measurements taken at slightly higher discharge conditions
and higher ambient air temperatures.
(ii} Stage II
Canst ruction
During c_onstruction, dissolved gas concentrations will be
similar to those occurring during Stage I operation.
-Filling
Dissolved gas supersaturation will not be a concern during
the filling of the Devil Canyon reservoir. As the reservoir
is filled, the rapids between the mouth of Devil Creek and
the Devil Canyon damsite will be inundated and the
turbulence that presently causes the supersaturation wi 11
thus be eliminated. Thus, dissolved gas concentrations in
the reservoir area wi 11 be 1 ess than those for Stage I
operat ·ion.
-Operation
Fixed-cone valves have been included in the design for the
Devil Canyon dam. This will minimize the potential for gas
supersaturation to exceed naturally occurring levels during
floods with return per-i ads of 1 ess than 50 years.
Additionally, the inundation of the Devil Canyon rapids will
eliminate a natural source of gas supersaturation. Gas
concentrations downstream of Devil Canyon dam are expected
to range from approximately 102 to 107 percent of
saturation. This assumes that supersaturation occurring at
Watana will not be reduced in Devil Canyon reservoir. The
level of supersaturation will decrease downstream of Devil
Canyon.
142
(iii) Stage III
During construction of Stage III, the Devil Canyon dam
operation will CChrtrol the dissolved gas concentrations
downstream.
-Filling
During filling of Watana Stage III the water normally
released through the outlet works for flood control and dam
safety purposes will be stared in the reservoir to raise the .
water level. Therefore, Watana outlet works use will be
minimized during this period. Some water may be released
through the Devil Canyon outlet works to meet environmental
flow requirements and as a result of floods in the area
between Watana and De vi 1 Canyon. However, there is 1 ess
likelihood that the outlet works or spillway will be used
during this period than at any other time during project
operation. Therefore, super-saturated gas concentrations
ar~ expected to be minimized during this periode
-Operation
As discussed for Stages I and II, the project operating
policy and project design are planned to minimize the
potential for downstream gas concentrations to exceed
naturally occurring levels. Dissolved gas concentrations
during Stage III operation would be similar to Stage II
operation. Fixed cone va 1 ves are provided in th~ outlet
works to disperse releases and minimize dissolved gas
concentrations downstream. Floods with recurrence intervals
of less than 50 years would be released without operating
the spillway. Immediately downstream of the Devil Canyon
dam, dissolved gas concentrations would not exceed 105
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percent to 110 percent. Furth~r downstream, g~s
concentrations would be reduced. Gas (;Oncentrations are
expected to be 1 ess than natural for some.· floods with return
periods of greater than 50 years also, due to the inundation
of the Devil Canyon rapids and mixing of spillwi!y, outlet
works and powerhouse flows.
4.3.6 Nutrients and Organics
Concentrations of nutrients and organic compounds are expected to remain
similar to natural concentrations. Initially, a slight increase in
concentration may be caused by the leaching of minerals in the reservoir
areas. However, the settling of sediments would 1 ikely precipitate
nutrients from the water co 1 umn. The magnitude of the net change is
unknown, but concentrations are not expected t~ change substantially from
natural levels.
{a) Watana to Devil Canyon
{i) Stage I
-Construction
Potential increases in concentrations of nutrients and
organic compounds in the river from construction activities
will be minimized as described in the report describing
potential impacts in the construction zone {Entrix 1985a).
Concentrations of waterborne nutrients and orga;jic compounds
downstream of the Watana damsite may be slightly increased
from natural levels during construction {Entrix 1985a). A
retvrn to natural nutrient and organic compound levels is
likely to occur within one summer {Entrix 1985a).
144
Filling
Initial filling of Watana will likely cause an increase in
nutrient concentrations due to leaching processes. However,
this increase in nutrient concentration would be offset by
the precipitation of the nutrients from the water column by
settling of sediments transported into the impoundment. The
magnitude of net change is unknown, but it is likely that
nutrient concentrations will increase, especially in
proximity to the reservoir floor for at least a short time
during filling. Similarly the concentratiohs in release
waters would be sxpected to increase.
-Operation
Concentrations of nutrients and organic compounds in the
resetvoir discharge are expected to be below natural levels.
Within the reservoir, sedimentation will remove some of
these constituents from the water column, making them
unavailable for downstream use. Settling of suspended
sediments within the reservoir will continue during project
operation an1 will result in a sediment blanket that will
reduce leaching and biological cycling of macro and micro
nutrients, primary and secondary productivity, and organic
detritus oxydation {Wetzel 1975, Campbell et al. 1975,
Crawford and Rosenberg 1984, Wiens and Rosenburg 1984, Hicky
and McCo 11 ough 1984) • Deve 1 opment of sma 11 , 1 ow density
biological communities in the. reser·,oir is expected to
occur. The anticipated trophic status of the Watana
Reservoir has been develCJped in part by Peterson and Nichols
{1982).. The t .. ate of removal is unknown, although it is
expected to be small relative to the flow rate through the
reservoir.
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( i i ) Stages ll and I 1 I
During construction of the Stage II dam, nutrients and organics
in the Watana to Devil Canyon reach will remain unchanged from
those during Stage I operation. During fi 11 i ng of Stage I I ,
the reach wi 11 be inundated. Impacts to 'this reach of river
during fi 11 i ng and operation of Stage I I and a 11 phases of
Stage III are discussed in the impoundment impact assessment
(Entrix 1985b).
(b) Devil Canyon to Talkeetna
{i) StagFLl
-Construction, Filling, Operation
The impacts on nutrient levels are similar to those in the
reach from Watana to Devil Canyon, although they will be
less distinct due to input from local tributary discharges.
{ii) Stage II
-Construction, Filling
During Stage II construction, nutrients and organics in the
Devil Canyon to Talkeetna reach will remain unchanged from
the levels described for Stage I operation. Also similar to
Watana Stage I, two opposing factors wi 11 affect nutrient
concentrations during the filling process. First, initial
inundation will likely cause an increase in nutrient
concentrations due to leaching. Second, sedimentation will
remove some nutrients from the water column. Again, the
magnitude of the net change in nutrient concentrations will
increase in proximity to the reservoir floor during the
filling process.
146
-Operation
Nutrient l:vels downstream will be slightly reduced due to
sedimentation in the Devil Canyon reservoir.
(iii) Stage III
-Construction, Filling, Operation·
Impacts wi 11 be simi 1 ar to those for Stage I I Operation.
The Cldd1t ion a 1 impoundment in the Watana Reservoir is not
expected to change the downstream nutrient and organic
compound concentrations measurably.
4.3.7 Total Dissolved Solids, Conductivity, Significant Ions,
Alkalinity, and Metals
Changes in the water quality in the Susitna River downstream of the
damsite are expected to include slight increases in sediment, metal, and
salt ion concentrations resulting from construction disturbances and from
leaching of soil and rock in the reservoirs. The water quality should
not be substantially changed from natural conditions.
{a) Watana to Devil Canyon
(i) ,S.tage I
-Construction
The sma 11 increases in the concentration of trace meta 1;,;
resulting from construction disturbances to soi 1 s and rock
on ths river bank and in the riverbed are 11ut e.:xp~,.:ted to
create adverse conditions in the ecosystem as thte
concentrations of many metals currently exceed establishe:d
water quality criteria (APA 1985b) ..
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-Fi 11 ing
The initial filling of the reservoir will inundate rocks and
soi 1 s in the reservoir that cause short-term i ncteases in
dissolved solids, conductivity, and most of the major ions
by leaching processes (Peterson and Nichols 1982). Balke
and Wad de 11 { 1975) found the highest concentration:> of a 11
major ions~ except magnesium, occurred immediately after dam
closure. Symons (1969), also identified similar increases
of alkalinity, iron, and manganese. These findings were all
attributed to the initial inundation and leaching of rocks
and soils in the reservoir. The magnitude of the expected
changes cannot be quantified, but should not be significant
(Peterson and Nichols 1982). Furthermore, Baxter and Glaude
(1980) have found such effects are temporary and diminish
with time.
The effects of leaching will diminish for two reasons.
First, the most soluble elements will dissolve into the
water rather quickly and the rate of 1 each ate production
will correspondingly decrease with time. Second, much of
the inorganic sediment carried by the Susitna River will
deposit in the Watana reservoir; the formation of an
inorganic sediment blanket on the reservoir bed will retard
the leaching process (Peterson and Nichols 1982).
Concentrations of leaching products will be highest near the
reservoir bottom, but may be re-entra i ned into the upper
levels during overturns, The products of leaching are not
anticipated to be abundant enough to affect more than a
small layer of water near the reservoir bottom (Peterson and
Nichols 1982). Some leaching products may be distributed
throughout the reservoir during the fall overturn following
the summer of filling. Dilution by the large reservoir
volume would make th~ resulting concentrations biologically
insignificant. Since the power intakes are located in the
148
upper 1 eve 1 s of the reservoir, water re 1 eased thrcagh the
turbines should not be affected by leaching products.
During the summer of fi.ll i ng, re 1 eases from the 1 ow-l eve 1
outlets could i ncr~ase downstream concentrations of the
previously mentioned parameters but detr.:imental effects on
freshwater aquatic organisms are not expected.
-Operation
During operation, the leaching process may result in
slightly elevated concentrations of water quality
parameters, especially near the reservoir bottom. As
described far filling, leaching effects are expected to
decrease over time.
Di sso 1 ved su 1 ids concentrations near the reserve i r surface
may also increase slightly due to evaporation in the summer
months and rejection from freezing ice in the winter months.
At no time, however, are these increases expected to be
biologically significant in the reservoir. Changes in
downstream water quality are not expected even during
overflow spil1way operation as the overflow spillway will
not be operated except during a major flood {Section 2.1.4)
when all other outlet facilities will also be in operation.
Surface water will thus be diluted considerably and
increases in concentration are expected to be be 1 ow the
detection limit.
Metal concentrations within the reservoir and consequently
in the discharge may be reduced by metal precipitation.
Metals have been observed to precipitate in reservoirs,
particularly those which are oligotrophic with high pH and
dissolved salt concentrations (APA 1985c). Although neither
pH nor dissolved salts have excessively high concentrations
in ·the Susitna River, the reservoir is expected to be
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oligotrophic (APA 1985c); a slight decrease in .metal
concentrations may nccur.
(ii} Stages II and III
As the reach between Watana and Devil Canyon will be inundated
following completion of the Devil Canyon dam~ further physical
changes in water quality are addressed within the impoundment
impact assessment {Entrix 1985b).
(b) Devil Canynn to Talkeetna
{i} Stage I
-Construction
Disturbances to soil ~nd rock adjacent to the river during
Watana construction will increase dissolved and suspended
materials in the river as described for the Watana to Devil
Canyon reach. Although slightly elevated metal levels may
result from construction activities, water quality should
not be significantly changed.
-Filling and Operation
Chan0es in water quality are expected to be similar to those
described for the Watana to Devil Canyon reach.
(ii} Stage II
-Construction, Filling, and Operation
Changes in water quality resulting from Stage !I will be
similar to those identified for Stage I. Leaching may occur
over an extended period of time in the Devil Canyon
reservoir as a blanket of glacial sediments will develop
150
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slower than in the Watana reservoir. However, changes in
water quality due to the leaching process are expected to be
diluted by the large volume of water in the reservoir and
significant changes in downstream water quality are not
expected.
Stage III
-Construction, Filling, and Operation
Water quality changes will be similar to those described for
Stage II operation. The Devil Canyon reservoir will act as
a construction buffer capturing increased trace metal
concentrations, salts~ or sediments releas~d during Watana
Stage III construction. The water quality released during
filling and operation of Watana Stage III dam will be
similar to the water quality during Stage II operation.
4.4 Ground~ater Conditions
Changes in the groundw.ater conditions between Watana and De vi 1 Canyon
will be primarily limited to the floodplain of the Susitna River.
Following construction of Stage I, the groundwater level adjacent to the
rna i nstem is expected to decrease in the sununer and increasE! during the
winter in comparison to natural levels. The filling of the Devil Canyon
reservoir will inundate the reach between Watana and Devil Canyon.
Project changes in the middle Susitna River affecting groundwater
conditions will primarily consist of increases and decreases in
groundwater levels adjacent to the mainstem. During the winter,
groundwater 1 eve 1 s and upwe 11 i ng upstream of the ice front w·i 11 be
decreased from natural mid-winter conditions. Groundwater levels and
upwelling downstream of the ice front will be increased. In the summer,
groundwater levels at the streambank will be decreased about 2 ft from
natural levels as described for the Watana to ilevil Canyon reach.
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4.4.1 Watana to Devil Canyon
(a) Stage I
(i) Construction
~1ostantial changes in groundwater conditions are not expected
during construction of the dam as ·there wi 11 be no change in
mainstem discharge or water level other than in the localized
area of the project. In the immediate construction area, minor
groundwater changes will likely result from the construction of
the slurry cut-off trenches and the dewatering of the
construction area (Section 2el.l).
(ii} Filling
During the summer of fi 11 i ng, groundwater 1 eve 1 s adjacent to
the mainstem are expected to be reduced. Decreased summer
flows will cause a decrease in the water levels in the mainstem
of the river which will cause a reduction in groundwater levels
in the river fl oodp 1 a in area. The average change in
groundwater level during this period will be a reduction of
about 2 ft near the streambank with less change occurring with
increasing distance away from the river.
Winter groundwater levels are expected to be similar to natural
leve 1 s as ice staging during the first winter fo 11 owing the
summer of filling will be similar to natural conditions.
(iii) Operation
Groundwater changes during summer operation are 1 i kely to be
similar to impacts during filling and will generally include a
1 oweri ng of the groundwater 1 eve 1 s in the fl oodp 1 ai n. The
river flows in the summer will be increased slightly from
152
fi 11 tng flows and wi 11 result in groundwater 1 eve 1 s c 1 oser to
but less than natural levels.
In the winter, ice staging will not occur between Watana and
De vi 1 Canyon as the flow wi 11 have warm temperatures.
Groundwater levels are thus expected to be similar to the
levels occurring under natural conditions in the early fall
when natural river flows are approximately 10,000 cfs.
(b) Stage II and III
Following construction of the Devil Canyon dam, the reach between
Watana and Devil Canyon will be inundated. Resulting changes in
water levels are discussed in the Impoundment Zone Impact Assessment
and Mitigation Plan {Entrix 1985b).
4.4.2 Devil Canyon to Talkeetna
{a) Sj:age I
{i) Construction
No changes to groundwater conditions in the middle Susitna
River reach are expected as ~ result of Stage I construction.
{ i i ) F i 11 i ng
-Mainstem
Changes in groundwater conditions of the middle Susitna
River during filling will be similar to the changes
described for the Watana to Devil Canyon reach.
-Sloughs and Peri phera 1 _Habi ~at
Lower groundwater levels in the river floodplain during the
summer of filling will result in a dewatering of some of the
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seep areas in the sloughs, mainly in the higher, upstream
portions. The reduced sununer mainstPm flows and resulting
1 ower water 1 eve 1 s wi 11 cause changes in the groundwater
levels in various sloughs. Flows have been investigated in
three sloughs (Sloughs SA, 9, and 11), and equations derived
that link mainstem stage to slough flow (APA 1985c), Based
on these equations, a 2-ft reduction in mainstem stage will
result in a reduction of 0.6 to 1.2 cfs in slough flows ..
This loss will mainly occur in the summer. The groundwater
flow from the mai nstem to other s 1 ough and side channe 1
habitat areas will be affected in the same manner.
Groundwater recharge of slough aquifers wi 11 probably be
reduced as overtopping of slough berms wi 11 occur 1 ess
frequently due to reduced summer flows during filling.
Ice staging during the winter of filling will be similar to
natural conditions and thus groundwater flow in sloughs will
be similar to natural.
{iii} Operation
-Mainstem
Groundwater changes between Devil Canyon and Talkeetna
during surmter Stage I operation will be similar to those
changes described between Watana and De vi 1 Canyon. During
winter, increased ice staging will occur during freeze-up
and hence groundwater 1 eve 1 wi 11 be increased from natura 1
1 eve 1 s a 1 ong ice covered ~ect ions of the ma i nstem.
Groundwater leve 1 s upstre: • .~ the ice front wi 11 be 1 ess
than those occurring in mi~~inter under natural conditions.
However, groundwater levels will be greater than the minimum
natural levels which occur in the fall prior to ice-staging.
154
-Sloughs and Peripheral Habitat
During winter in the Devil Canyon to ·Talkeetna reach,
groundwater flow wi 11 be increased in s 1 oughs and side
channels downstream of Gold Creek adjacent to an ice-covered
section of the river (Figure 8). As an ice cover forms at
the project operation flows of about 9, 000 cfs, the river
will stage. The associated water level will be a few feet
above normal winter water levels and will cause an increase
in the groundwater table and thus an increase in groundwater
flow.
Sloughs upstream of Gold Creek may be adjacent to open water
sections of the river. Because monthly average flows will
be between approximately 4,000 and 9,000 cfs in winter, the
unstaged water 1 eve 1 during project operation wi 11 be 1 ess
than water levels during natural ice-staged conditions.
Sloughs in this area may experience a decrease in
groundwater flow in the· winter compared to natura 1
conditions. However, water levels upstream of the ice front
wi 11 fluctuate 1 ess· on an al'nua1 basis than during natura 1
conditions, resulting in groundwater flows wh•1ch will be
more stable all year than for natural conditions.
In addition, the groundwater upwelling under project
operation will be greater than the minimum natural upwelling
rates which occur in the fall prior to ice-staging. Natural
flows generally decline during the fall to near 5,000 cfs
before an ice cover forms. This is the period of lowest
groundwater flow. As Stage I discharges and water levels
will remain higher than natural during this period, the
minimum groundwater flow will be increased.
During summer, the mainst&m-slough groundwater interaction
will be similar to that during impoundment with the
('xcept ion that the summer operation a 1 flows wi 11 be greater
155
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than the downstream flows during filling. Summer
groundwater levels will thus be increased from filling
levels.
{b) Stage II
{i} Construction
The construction of Devil Canyon will not modify the Watana
operation or flows, and the groundwater conditir,;: discussed
under Watana operation will remain relevant during tnis period.
Some local changes in groundwater levels in the immediate
vicinity of the Devil Canyon damsite may occur due to
dewatering of open and underground excavations.
(ii) Filling
No major groundwater changes are anticipated during the filling
of the Devil Canyon reservoir; conditions are expected to
remain similar to those identified for the filling of the
Watana reservoir.
(iii) Operation
-Mainstem
Groundwater levels adjacent to the mainstem during Stage II
operation will generally be less stable than for Stage I in
summer (June through September), but more stable the rest of
the year. During Stage II, higher mainstem flows will cause
increased groundwater levels in late July to early September
and 1 ate February to mid May. Groundwater 1 eve 1 increases
due to ice staging will not extend as far upstream as during
Stage I as the river ice cover will form further downstream
with Stage I I. Groundwater 1 eve 1 s adjacent to the ice-
156
covered mainstem will also be slightly lower than for Stage
I as winter flow releases will be less during Stage \1.
-Sloughs and Peri ph era 1 Habitat :.l\reas
Groundwater flows to s 1 oughs and other peri phera 1 habitat
areas would reflect the flows and water 1 eve 1 s in the
mainstem as discussed for Stage ·I. Groundwater flow during
the period when natura 1 groundwater flow is the 1 owest .
{October) will generally be higher than Stage I and higher
than natura 1 (Figure 8). Winter ice cover wi 11 not extend
as far upstream as in Stage I nor result in as high water
1 eve 1 s. Therefore, groundwater f1 ow in s 1 oughs and side
channe 1 s wi 11 be reduced from Stage I, but wi 11 st i 11 be
higher than natural. Upstream of the ice front, the
rna i nstem stage wi 11 be reduced from natura 1 and wi 11 be
simi 1 ar to fa 11 and spring 1 eve 1 s, thus i ncr~ as i ng the
stability of groundwater flows.
(c:) Stage III
{i) Construction
Groundwater changes from construction of Stage I I I wi 11 be
similar to changes identified for Stage II operation as the
mainstem flows for Stage II operation will be continued until
Stage III filling commences.
( i i ) F i 1 1 i ng
-Mainstem
During filling, the groundwater levels along the mainstew
wi 11 be reduced from July to September si nee excess flows
normally released from Watana will be stored in the
reservoir. Groundwater 1 eve 1 s a 1 ong the ma i nstem may be
157
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!'educed by up to 2 .. 5 ft near Gold Creek in August.
Groundwater 1 eve 1 s are expected to be more uniform during
May to November as mainstem flows will be more stable during
filling than during natural conditions.
-Sloughs and Peripheral Habitat Arill,.
The ground·.1ater upwe 11 i ng to s 1 oughs wi 11 fo 11 ow the s arne
general pattern as the groundwater table along the mainstem . .
That is, groundwater upwelling ·Will be more stable in the
May-November period during fi 11 i ng of Stage I I I. Upwe'l 1 i ng
wi 11 be 1 ess than during norma i operation in the
July-September period. Groundwater upwe 11 i ng during this
period may be reduced by an average of 0.5 to 1.3 cfs based
on relationships obtained for Sloughs SA, 9, and 11.
(iii) Operation
Downstream groundwater level changgs will be similar to those
described for Stage I operat 1 on and wi 11 be confined to the
river fl oodp 1 ai n area. During winter 1 the extent of river
covered with ice wi 11 be reduced from Stages I and I I due to
the warmer temperatures of the re 1 eased water. Change.s in
groundwater conditions upst~"'eam and downstream of the ice front
are discussed for Stage I operation.
158
..
S.J IMPACT ANALYSIS
5.1 Altered Flow Regime
5.1.1 Summary of Physical Changes
(a) Stage I
{ i ) F i 11 i n_g
The changes in flow regime due to the fi 11 i ng of the Watana
reservoir, Stage I, is discussed in Sections 2.1.2, 2.1.3,
4.1.1, ancl 4.4; key changes are summarized below:
o Flows at Gold Creek are expected to be at or slightly
above the E-VI minimum flow requirements from May
' through September 1998.
o Minimum flows during the winter following the one summer
of filling will be natural flows; flow levels may exceed
· natural flows during unit testing and commissioning.
(ii) Operation
Watana, Stage I operation and its effect on flow regime is
discussed in Sections 2.1.4 and 4.1.1; major changes in flo\'1
regime are summarized below:
o The Stage I operaticnal flow regime is scheduled to
begin in the summer of 1999 and continue until the Devil
Canyon dam is constr·ucted and filling behind that dam
begins.
o The Stage I operational flow regime will be more stable
than natura 1 flows, with 1 ower flows and water 1 eve 1 s
than natura 1 during summers and higher than natura 1
159
flows (and water le·~els downstream of the ice front)
during winters.
o The Stage I operational flows will normally exceed the
flows during Stage I filling.
(b) ,S_tage II
o Groundwater levels will be higher downstream of the ice
front and similar upstream of the ice front compared to
natura 1 winter 1 eve 1 s and 1 ower than natura 1 summer
levels.
(i) Filling
The changes in flow regime due to the fi 11 i ng of the Devi 1
Canyon reservoir are discussed in Sections 2.2.2, 2.2.3, and
4.1.1; key changes are summariz~d below:
o Filling of the Devil Canyon reservoir will be conducted
in two distinct periods totaling 5 to 8 weeks in length.
o Downstream flows will be at or slightly above the E-VI
minimum flow requirements during filling.
(ii) Operation
The changes in flow regime resulting from operatic" of the
Devil Canyon reservoir are discussed in Sections 2~2.4 4.1.1,
and 4.4; changes which cause impacts to fish resources are
summarized below~
o Watana Sta~e I wi 11 be operated as a peaking p 1 ant and
Devil Canyon operation will re-regulate Watana flows.
160
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o Stage II operation will generally result in higher than
natural winter flows and water levels and lower than
natura 1 summer flows and water 1 eve 1 s; flood peaks wi 11
be considerably reduced.
o Stage II operation flows will be more uniform during the
year than flows during Stage I operation.
o Groundwater levels will be higher in summer than Stage I
a 1 though 1 ower than natura 1 summer 1 eve 1 s; in winter,
groundwater levels will be lower than Stage I and higher
than natural levels downstream of tha ice front.
(c) Stage III
(i) Filling
The changes in flow regime due to the filling of the Stage III
Watana reservoir are discussed in Sections 2.3.1 and 4.1.1;
changes which cause impacts to fish resources are presented
below:
o Filling will take between three and seven years,
beginning in 2011.
o filling flows will generally be neal~ the minimum flow
requirements during the summer.
(ii) Operation
The changes in flow regime due to the Stage III operation are
discussed in Sections 2.3.4, 4.1.1, and 4.4; changes which
cause impacts to fish resources are presented below:
o Watana will operated as a peaking p1ant and Devil Canyon
as a baseloaded plant.
161
o The flow regime during early Stage III operation will be
very similar to Stage II flow regime, with higher than
natura 1 winter flows and water 1 eve 1 s and 1 ower than
natural summer flows and water levels; flood peaks will
be considerably reduced.
o The flow regime will become more uniform as Stage III
progresses.
o Groundwater 1 eve 1 s wi 11 be higher than Stage I I and
lower than natural levels in summer; in winter, the
groundwater levels will be higher than natural levels.
5.1.2 Effects on Species/Habita~
(a) Access and Passage
{i} Sloughs and Side Channell
Access and passage of fish into .sloughs and side channels is
provided through the interaction of channel morphology,
mainstem flow, and local flow. The altered flow regime during
project filling and operation may affect the channel
morphology. Sloughs and side channels may degrade up to
0. 3 ft; potentia 1 rna i nstem degradat i 011 may range between 1 . 0
and 1.5 ft in the middle Susitna River (Harza-Ebasco 1985a}.
This impact assessment has been prepared assuming that bed
degradation will be minor. If the bed does degrade, a
reevaluation will be done at that time as described in Section
5.2.
The project flows wi 11 be 1 ess than natura 1 flows during the
period of upstream migration of salmon adults. Access into
sloughs and side channels will be reduced.
162
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-Primary Evaluation Species
Chum Salmon Soawninq Adults
•
.. ,
Stage I
Detailed analysis of mainstem flows required for
succe3sful passage into the major chum salmon spawning
sloughs have been conducted by ADF&G {Blakely et al.
1985, Sautner et al. 1984). However, a quantitative
assessment of the availability of passage conditiotrs
during reservoir fi 11 i ng using this information is not
possible for average and wet years since the available
flow data and mean monthly flows mask the monthly
variability in flows caused by short-term rainstorm
events that often provide passage. It can be assumed,
however, that. since the mean monthly flo\'JS for filling
are 1 ess than those occurring naturally in August and
SeptemberJ for average and wet weather conditions that
the frequency of successful passage conditions would be
reduced.. In a dry year with 8,000 cfs E-VI minimum
flows during the spawning period and assuming no
precipitation {no variability around the minimum flow
value), passage would be restricted beyond Passage Reach
I in Slough SA, Passage Reach IV in Slough 9A, Passage
Reach I in Slough 11, and Passage Reach VI in Side
Channel 21 .
.. Operation
Passage conditions within sloughs and side channels will
be restricted by the Stage I operation flow regime.
Stage I -1996 project flows during the spawning season
for churu salmon (August 12 -September 15) would be less
163
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than natural flows (Section 4.1.1}. Although the flows
are substantially greater than E-VI minimum constraints,
a reduction in the frequency of occurrence of successful
passage conditions and availability of suitable habitat
within sloughs and sirle channels would occur. The
extent of these reductions for the major chum-producing
sloughs and side channels (sloughs SA, 9, 9A, 11, 21 and
Upper Side Cha~nel 11 and Side Channel 21) were
analyzed. The percent of time successful passage
conditions would be available at the passage reaches of
each slough was estimated for the specified time period
by selecting the exceedance value associated with the
minimum mainstem discharge that provided passage either
through backwater, controlling breaching flows or local
flow from groundwater infiltration {excluding direct
surface runoff). The appendix presents the passage
exceedance eva 1 uat ion for each week and for the entire
period from week 45 to 49 for the major chum producing
sloughs. ThE.\ re~~nts of these analyses are discussed
for individual sloughs below.
••. Slough SA
Relative Utilization
During the 1981-1985 studies, the mean peak count of
chum salmon in Slough SA was 442 {range: 37-917). The
mean estimated total escapements to the slough were
1,029 chum (range: 112-2383). Slough SA mean estimated
total chum escapement comprised 15.7 percent of the mean
estimatei total chu~ escapement {6,552) to all sloughs
in the middle Susitna River.
164
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Impact Mechanism
The frequencies of occurrence of succe5sful passage
conditions at each passage reach of Slough SA under
natural and Stage I flows are graphically depicted for
each week and for a 11 weeks combined of the spawning
period in Figure 26. The mainstem discharges for
passage considering backwater, local flow and breaching
effects and the passage frequency va1ues are listed for
each week and for the entire period in Appendix Tables 1
to 6.
Under natural and Stage I flow regimes, the frequency of
successful passage conditions decreases progressively
with each week of the spawning season as mainstem flows
decline. The differences between natural and Stage I
flows are greatest, a 1 though not substantial, at the
beginning of the spawning season (Week 45) and gradually
narrow by the last week {Week 49). This is attributable
to the passage provided by the relatively high
discharges required for successful passage at Slough SA
whi tch occur at a greater frequency with natura 1 flows
than with project flows early in the season. Later in
the season the frequencies of these flows are at or near
zero for both natural and project flows •
••• Slough 9-98
Relative Utilization
During the 1981-1985 studies, the mean peak count of
chum salmon in Slough 9 (including 98) was 269 {range:
94-423). The mean estimated total escapements to the
slough was 449 chum (range: 118-645). Slough 9 and 98
mean estimated total chum escapement comprised 6.9
165
'.:.·· ll
f L
L
AUG 12-
SEPT 15
AUGUST
12-18
AUGUST
19-25
.A.UG 26-
SEPT 1
SEPT
2-8
SEPT
9-15
100
eo
eo
41-0
20
0
100
eo
eo
40
20
c:::J NATURAL E:3 STAGE 1
0 ~_.--~--~~--~~~~~~~~~~~-L~~~~
100
eo
60
20
0 --~~~~~~~~~~~~~~~~~~~~~~~
100
eo
eo
-40
20
.,00
eo
eo
20
0
100
eo
60
20
0
100
eo
60
40
20
0
100
eo
60
40
20
0 --~.~~--~~--~~~~~--~~~~~~~~~~ 0
100 ~00
eo eo
eo eo
20 20
0 7-_.--~~~~._ .. ~~~~~~~~~~-L~~~~
100 0
., 00
eo eo
eo eo
20 20
0 II Ill IV V VI VII Vtll IX X P SSAGE REACH
PERCENT
OF TIME
PASSAGE
IS
AVAILABLE
Percent of time passage is
possible under natural and
Stage I mainstem discharges
for weeks between August 12
and September 15 at SloJgh SA.
ALASKA POWER AUTHORITY
FIGURE 26 ···
SUSlTNA HYDROEtECTRIC PROJECT
ENTRIX, INC.
166
HARZA·E BASCO
SUSITNA JOINT VENTURE
•
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percent of the mean estimated total chum escapement
(6,552) to all sloughs in the middle Susitna River.
Impact Mechanism
The frequencies of occurrence of successful passa~e
conditions at each passage reach of Slough 9 under
natura 1 and Stage I flows are graph i ca 11 y depicted for
each week and for a11 weeks of the spawning period
combined in Figure 27. The mainstem discharges for
passage and the frequency values are 1 i sted for each
week and for the period in Appendix Tab1es 7 to i2.
In general, the reduction in frequency of passage from
natura 1 to Stage I for each week and for the entire
period would not 1 i kely be sufficient to a 1 ter present
utilization patterns. The frequency of passage thr~ugh
passage reaches IV and V would be decreased sl ight1y
from natural conditions to Stage I conditions •
..• Slough 9A
Relative Utilization
During the 1981-1985 studies, the mean peak count of
chum salmon in Slough 9A was 168 (range: 105-303). The
mean estimated total escapements to the slough were 227
chum (range: 86-528) o Slough 9A mean estimated total
chum escapement comprised 3o5 percent of the mean
estimated total chum escapement (6,552) to a11 sloughs
in the middle Susitna River.
Impact Mechanism
The frequencies of ocCb~~~~ce of successful passage
conditions at each pa~~Jpe reach of Slough 9A under
167
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l
c::J NATURAl... E3 STAGE 1
100
eo
AUG 12-eo
SEPT 15 ~0
20
0
100
eo
AUGUST eo
12-18 40
20
I
0 .L.._,
100
eo
AUGUST eo
19-.... 25 40
20
0
100
eo
AUG 26-eo
SEPT 1 40
20
0
100
eo
SC:PT eo
7:-8 40
20
0
100
eo
SEPT eo
9-15 40
20
0
Percent of time passage is
possible under natural ~nd
Stage I mainstem discharges
for weeks between August 12
and September 15 at Slough 9.
FIGURE 27
II Ill IV V
PASSAGE REACH
100
eo
eo
20
0
100
eo
eo
40
20
0
.,00
so
40
20
0
, oo·
.!SO
60
40
20
0
100
eo
eo
20
0
.,00
eo
eo
20
0
PERCENT
OF TIME
PASSAGE
IS
AVAILABLE
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJE~T
ENTRIX, INC ..
. 168
HARZA·E BASCO
SUSITNA JOINT VENTUf<~
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•••
natural and Stage I flows are graphically depicted for
each week and for all weeks of the spawning period
combined in Figure 28. The mainstem discharges for
passage and frequency va 1 ues are 1 i sted for each week
and for the period in Appendix Tables 13 to 18.
The low breaching flow {13,500 cfs} and low mainstem
discharges that provide the local flow necessary for
passage at most passage reaches account for the slight
and inconsequential reductions in passage frequencies
from the natural to project flows.
Slough 11
Relative Utilization
During the 1981-1985 studies, the mean peak count of
chum salmon in Slough 11 and Upper Side Channel 11 was
660 {range: 238-1,586). The mean estimated total
escapements to the s 1 ough and upper side channel was
1,626 chum {range: 674-3,418). Slough 11 and Upper Side
Channel 11 mean estimated total chum escapement
comprised 24.8 percent of the mean estimated total chum
escapement (6,552) to all sloughs in the middle Susitna
River.
Imoact Mechanism
'ihe frequencies of occurrence of successful passage
conditions at each passage reach of Slough 11 under
natural flows and Stage I flo.ws are graphically depicted
for each week and for all weeks combined of the spawning
period in Figure 29. The mainstem discharges for
passage and frequency va 1 ues are 1 i sted for each week
and fo~ the period in Appendix Tables 19 to 24. ·
169
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r.
t.
t
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L_.
c:::J NATURAL E:3 STAGE 1
100 t 100
eo eo
AUG 12-eo eo
. SEPT 1~ -+O -+0
20 20
. 0 L_~~LCLL~~~~~~~~~~~~~~~
,00 0
,00
eo eo
AUGUST eo eo
12-18 .... o ~0
20 20
0
100 0 PERCENT ,00
eo eo OF TIME
AUGUST
eo tSO PASSAGE
19-25 40 40 IS
20 20 AVAILABLE
0
100 0
100
eo eo
AUG 26-eo so
SEPT 1 40 40
20 2.0
Q 0
100 100
eo eo
SEPT eo
2-8 40 40
20 20
o 1-~~LC~~~~~~~~~~~~~~--~-r
100 t 0
100
eo eo
eo
SEPT eo
9-15 -+O --4-0
20 20
0 l__L~~~~~~~JI~ILLI.lV~~V~~V~t~-V~II~V~1~11~~~~·~~~
PASSAGE REACH
0
Percent of time passage is
possible under natural and
Stage I main stem discharges
for weeks between August 12
and September 15 at Slough 9A.
FIGURE 28
ALASKA POWER AUTHOR~TY
SUSt-rNA HYDROELECTRIC PROJECT
ENTRIX, INC.
170
HARlA·E BASCO
SUSITNA JOtNT VENTLIRE
1{.
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\,..,._,...
L'
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At."J 12-
SEPT 1S
AUGUST
12-18
AUGUST
19-25
AUG 26-
SEPT 1
SEPT
2-8
SEPT
9-1!S
80
eo
.... 0
2.0
~ NATURA~ E3 STAGE 1
100
~0
eo
40
20
~ ~--._--~~~~_._.~_.~-~~~~~~~~~-~
1 oc... ) 0
eo
eo
.... 0
20
eo
so
-+0
20
I 1 oo
·eo
eo
.... o
20
0
100
eo
eo
..... 0
20
0
100
J!SO
eo
40
20
0 L_~~~~~~~~~~_LJ=~~=L~.-~-l 0
1 00 4
eo
eo
.... 0
20
eo
eo
20
II
100
eo
eo
..... 0
20
0
100
eo
eo
..... 0
_j 20
0 VI VII Ill IV V
PASSAGE REACH
ALASKA POWER AUTHORITY
PERCENT
OF TIME
PASSAGE
IS
AVAILABLE
Percent of time passage is
possible under natural and
Stage I mainstem discharges
for weeks between August 12
SUSITNA HYDROELECTRIC PROJECT
and September 15 at Slough 111 ENTRIX, INC. HAR:ZA-EBASCO
._ ________ ..._..::_F)GURE 29 SUSITNA JOINT VENTURE
~--~~1~7~1----~------~~~~~~~~-J
o'
Project flows would reduce the frequency of successful
passage only to a minor degree in Slough 11. The
relatively high breaching discharge at this site
indicates that it contributes infrequently to passage.
The 1 ocal flows required for successful passage occur
more frequently under natural conditions than under
Stage I conditions especially early in the spawning
season {week 45). Frequencies of passage during Stage I
become more similar to natural frequencies later in the
spawning season {week 49}.
..• Upper Side Channel 11
Relative Utilization
(See Slough 11)
Impact Mechanism
The frequencies of occurrence of successful passage
conditions at each passage reach of Upper Side Channel
11 under natural flows and Stage I flow are graphically
di sp 1 ayed for each week and a 11 weeks of the spawning
period in Figure 3rt. Insufficient data were available
to evaluate the influence of mainstem discharge on lccal
flow and backwater effects at Passage Reach II (Appendix
Tab1es 19-2~·).
The difference in the per~ent of time passa~1c 1 s
available under natural and Stage I project flows based
on breaching flows would not 1 ikely affect the
utilization of this site to a large degree.
172
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I.".' f' '
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r
L
AUG 12-
SEPT 1~
AUGUST
12-18
AUGUST
19-25
AUG 26-
SEPT 1
SEPT
2--a
SEPT
9-15
c::J NATURAL.. E3 STAGE 1
100 " 100
eo . . eo
. eo eo
~0 ~ I ~ 40
20 . 20
0 0
100 1-100
eo . . . eo
eo · eo
~ 40
. 20
0
20 OL_ ____ _L __ i=~L__l __ l===L_ ____ J
,00 100
eo ·eo
eo ·
20.
'1 o l_ ________ JL __ _jt====L----L----t====L·---------1
, 00 1-
eo~>
SO F
, 00 .
eo
-4-0 •
0 -, 00 -+
I
eo
eo ·
:.
I l J I F I .
t
-~
0 L_ _______ _L __ ~==~----L---~==~-------1
1 PASSAGE REACH 11
eo
40
20
0
100
eo
eo
40
20
0
'100
~~0
eo
40
20
0
100
eo
eo
40
20
0
PERCENT
OF TIME
PASSAGt:
IS
AVAILABlE
.
Percent of time passage is
possible under n~tural and
Stage 1 mainstem discharges
for weeks between August 12
ALASXA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECt -and September 15 at Upper ENTRIX INC HARL:A·EBAsco
..
..
Side Channel 11. FIGURE 30 · ' • SUSITNA JOINT VENTURE
~-----------~--------~--~~----------~--------~~~~ 173
•
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I,
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l t
·~
l
~·
L.
.... .sJ ough 21
Relative Utilization
During the 1981-1985 studies, the mean peak count of
chum salmon in Slough 21 and Stde Channel 21 were 792
{range:. 274-2,354}. The mean estimated total escapement
to the slough and side channel was 1,612 chum (range:
481-4,245). Slough 21 and Side Channel 21 and Side
Channel 21 mean estimated total chum escapement
comprised 24.6 percent of the mean estimated total chum
escapement {6,552) to all sloughs in the middle Susitna
Rivere
Impact Mechanism
The frequencies of occurrence of successful pa~sage
conditions ctt each passage reach of Slough 21 under
natural flows and Stage I flows are graphically
displayed for each week and for all weeks combined of
the spat~ning period in Figure 31. The mainstem
discharges for passage and the frequency values are
listed for each week and for the period in Appendix
Tables 25 to 30.
Project flows would reduce the frequency of passage
slightly at passage reaches IIIL ak1d IIIR. Passage at
other passage reaches would not be re~uced from natural
conditions due to r~oject flows .
.•. Side Channel 21
Relative Utilization
(See Slough 21)
174
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•
;;
(.
r·
r··
L
r t.
l
r ll
L ..
L.
c:J NATURAL E3 STAGE 4
AUGUST
12-18
eo
so
~·0
20
100
eo
eo
-4-0
20
0
,.00
so
eo
20
0 ~-----~--~--~~~-----~----
f ::0
AUGUST
19-2S
AUG 26-
SEPT 1
SEPT
2-8
SEPT
t'-1!5
,00
eo.
ISO
20
0
100
eo
II!SO
..... 0
20
0
100
eo
eo
•i-0
20
0
100
eo
eo
~·0
20
0
Percent of time passage is
possible under natural and
Stage I mainstem discharges
for weeks between August 12
and September 15 at Slough 21.
FIGURE 31
40 f
eo
-_._ __ ._J. 200 C:-t-:=? .
,00
G.O
40
20
0
'100
eo
cso
eo
.!SO
20
PERCENT
OF TIME
PASSAGE
IS
AVAILABLE
ALASKA POWER Al.'THORITY
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC.
175
HARZA·E BASCO
SUSITNA JOINT VENTURE
•)
' ~
' y
"
ImP.act Mechanism
The frequencies of occurrence of passage conditions at
f~ach passage reach of Side Channe 1 21 under natura 1 flow
and Stage I flows are graphically disrlayed for ea~h
week and for a 11 weeks combi net! of the spawning period
in Figure 32. The mainstem discharges and the frequency
values are also listed for each week and for the period
in Appendix Tables 25 to 30.
Due to the iow breaching f1~w {12,000 cfs} that affects
the n •. Jjority of passage reaches in the side channel,
proj~?.ct r ~ ~,;ws waul d slightly reduce the frequem-::y of
passage at Passage Reach VI a 1 though no other passage
teach waul d be affected by r·--oject flows.
Stage II .. and III
If slough modification measures are imp1ementad under
Stage I, the natural conditions would be altered and
consequently a comparison of the percent of time passage
occurs under natural and Stage II and III flows is not
i·easib1eo The mitigation plan {Section 6e0) addresses
the frequency of passage which would be available
following slough modification.
There is also the possibility that the patterns of
utilization of different habitat types may change during
this time without a net decrease in productivity.
Attempting to assess impacts for Stages II and III based
on current uti 1 i zat ion patterns waul d therefore not be
productiv,. Provision will be made in a long-term
monitoring program to assess changes in productivity of
the evaluation species.
176
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,..._,_,
•
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1
t
l
\.
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AUQ 12·-
SEPT 1 ~.
AUGUS1'
12-18
AUGUST
19-2S
AUG 26-
SEP'Y 1
SC:PT
2-8
SEPT
9-15
I 1 STAGE 1
100
eo
eo
<40
20
0 --~--~~--~----.. ~----~~~~._~~--~~--_. ,00
eo
eo
20
0 ._~_.~~~~----~~~~~~~~~~~~~~--~
100
eo·
eo
40
20
0 ~~-+~~~~~~ .. ~~~L-~-L~~~~~~~--
100
eo
eo
~0
20
0 ~~~~~~~~~ .. ~~~~~~-L~~~~~~~--~
,00
eo
so
20
0 ._~--~~--~----.. ~~~~~-L~~~--~~~--~
100
eo
eo
20
0
II Ill IV V·
PASSAGE · VI VU VIti IX
100
eo
eo
~0
20
0
100
eo
eo
~0
20
0 PERCENT 100
eo OF TIME
eo PASSAGE
40 IS
20 AVAILABLE
0
10C;:-
eo
eo
40
20
0
100
eo
eo
-40
20
0
100
eo
eo
40
20
0
Percent of time passage is
possible under natural and
Stage I mainstem discharges
for weeks between Au~ust lZ
and September 15 at Side
AlASKA POWER AUTHORITY
Channel 21. FIGURE 32
SUSITNA HYDROELECTRIC PROJE':!
ENTRIX, INC.
177
HARZA·E BASCO
SUSITNA JOINT VENTURE
,::;
Chinook Salmon Rearing Juvenile$
•
0
Stage I
?assage into sloughs and side channels is required for
chinook salmon juveniles to access rearing habitat
within the sloughs and side channels. The Case E-VI
minimum flows are expected· to provide adequate depths
and velocities to allow passage of chinook salmon
rearing juveniles.
Stages ll and III
Passage conditions into sloughs and side channels for
chinook sarfmon rearing juveniles during Stages II and
III are expected to remain similar to conditions during
Stage I.
-Secondary Evaluation Species
Chum, Sockeye, Chinook! and Pink Salmon Outmigrant Juveniles
•
..
•
Stage I
Flows during filling and operation would reduce the
frequency and amplitude of spring runoff flows that can
act as stimuli for outmigration for juvenile salmon in
sloughs and side channels. These reduct i.ons are not
expected to impact seaward migration because other
factors such as photoperiod, water temperature, and
physiological condition also stimulate out1r-~tgration.
Stages II and III
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No additional impacts are anticipated for Stages II and
III as the flow regimes will be similar to Stage I. ~
178
--Sockeye and Pink Salmon Soawning Adults
•
•
Stage I
Sockeye and pink salmcn are smaller and generally have
better swimming performances than chum salmon (Bell
1973, Scott and Crossman 1973). Therefore, the analysis
of passage conditions for chum salmon provides a
conservative estimate Gf the passage conditions within
sloughs and side channels for sockeye and pink salmon.
Hence, under similar flow conditions •t is expected that
sockeye and pink salmon will have less difficulty
gaining access to spawning areas in sloughs than chum
salmon.
Stages II and III
Th~ flow regimes imposed by Stages II and III will not
be substantially changed from Stage I. Access
conditions are expected to be similar to those described
for Stage I.
{ii) Tributaries
Access and passage of fish into tributaries is contro1led by
conditions at the confluence of the tributary and the mai.nstem.
The altered flow regime during project filling and operation
wi 11 affect the configurations of the tributary mouths. The
lower· mainstem stage resulting from reduced flows will
initially perch the tributary mouths above the mainstem and
inhibit the passage of fish intQ tributaries (WCC 1985b).
Based on the analyses by R&M Consultants (1982), Trihey (1983)
and Harza-Ebasco {1985a)s most tributaries in the middle
Susitna River will rapidly adjust to the lower mainstem flows
without impeding fish access (WCC 1985b).
179
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-Primarv Evaluation Specie1
Chum Salmon Spawning Adults
0
•
Stage I
Chum salmon access into important spawning areas within
the tributaries may be slightly reduced by the perching
of tributary mouths resulting from the lower than
natural summer flows associa:ed with project filling and
operation. However, tributary mouths are expected to be
down cut rapidly and an equ i 1 i bri um condition wi 11 be
reestablished. The flow regime will be more stable than
previously and promote a rapid readjustment of tributary
mouth configuration. The upstream passage of salmon is
not likely to be restricted under the proposed project
flow regime {Trihey 1983).
S~age II and III
Passage conditions in tributary mouths are expected to
be similar to conditions established during Stage I
following the downcutting of triburary mouths.
-Secondary Evaluation Species
Chinook, Chum: Pink, and Coho Salmon Returning Ad~lts
• Stage!; I, II,Jnd III
Chinook, pink, and coho salmon spawn a1most exclusively
in tributaries. Passage of salmon into tributaries is
not expected to be impeded as the tributary mouth
configurations are likely to adjust rapidly tJ the lower·
mainstem stage as described for chum salmQt.'l.
180
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--Resident Salmonidl
• ~tages I, II, and 111
Arctic grayling, Dolly Varden, and rainbow trout
generally migrate from tributary habitats into rna i nstem
overwintering habitat and return into tributaries in the
spring for sununer rearing and spawning. Access into
tributaries is e~~ected to be provided by naturally
occurring high flow events in the spring. Tributary
mouths will likely r\nwncut rapidly duriilg spring high
flows and passage of resident salmonids is not expected
to be restricted.
Main3tem
Minimum project flows at Gold Creek of 9,000 cfs, or 8,000 cfs
in a dry year (Section 2.1.2}, are expected tQ be sufficient to
maintain fish passage in the mainstem. Under natural
conditions, a discharge of 8,000 cfs occurs in the fall prior
to the minimum natural flow o~ about 5,000 cfs (SeLtion 4.4.1).
A study of water elevations at several middle Susitna River
cross sections found that depths in the mainstem typically
remain in excess of 5 ft at a discharge of 8,000 cfs (R&J~
Consultants 1982).
Primary Evaluation Species
Chum Salmon Spawning Adults
• Stage~ I, II, and III
The proposed minimum summer flows of 9,000 cfs
(8,000 cfs in a dry year) for all stages of the project
are expected to provide depths sufficient for adult chum
salmon to access mainstem spawning areas.
181
--~.!linook Salmon Rearing Juveniles
• ~tages I, I I, and I I I
Passage in the mainstem is important to allow chinook
salmon juveniles to move from natal tributaries
downstream to other rearing or oveniintering areas
throughout the summer. Chinook salmon age l+ juveniles
outmigi~"ate during the spring. Project flows wi 11 be
sufficient in th~~ spring and summer to maintain
downstream passage of juveniles in the mainstem of the
Susitn& River.
-Secondary Evaluation Species
Chinook, Chum, Sockeye, Coho, and Pink Salmon Returning
Adults
• Stage i
Minimum summer flows are not expected to impede the
upstream migration of adult salmon in the mainstem of
the middle Susitna River.
Adult salmon generally do not migrate upstream of the
Devil Canyon rapids {RM 152). However, a few chinook
salmon {approximately 20 spawning pail"S) negotiate the
rapids each year anJ spa\\'n primarily in Che~chakc and
Chinook creeks (ADF&G 1985a). The upstream movement
through the rapids occurs during July.
Based on a comparison of nat~ra l and simulated
with-project flaws at Gold Creek (RM 136.7) it is
expected that the lower than natural with-project flows
during July will facilitate the upstream movement of
chinook salmon through the rapids. In 1982: 1983, and
182
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1984 the mean monthly July flows at Gold Cr~ek were
24,120 cfs, 21,150 cfs, and 23,400 cfs, respectively.
Minimum daily flows in July of 1982, 1983, ~nd 1984 were
16,600 cfs, 16,400 cfs and 18,600 cfs, respectively.
Based on flow records since :951, the average mean
monthly July flow at Gold Creek is 24,390 cfs, with a
minimum monthly flow of 16,100 cfs. In contrast, the
estimated mean monthly July flow during Stage I filling
will be 12,740 cfs, with a minimum flow of 9,000 cfs
(8,000 cfs during dry years). During Stage I operation,
the me~n monthly July flow at Gold Creek ts expected to
be 14,490 cfs, with a minimum flow of 9,000 crs
{8,000 cfs during dry years). Because of the lower·
flows ~1uri ng Stage I fi 11 i ng and operation, ve 1 oc it i es
will also he reduced somewhat. This should increase the
number of chinook salmon able tJ negotiate the rapids.
In addition, it is probable that other salmon species
may gain access to spawning habitats within and upstream
of De vi 1 Canyon. Hence, during Stage I fi 11 i ng and
operation an expansion of the use of spawnt -. ilabitats
upstream of De vi 1 Canyon is expected for a 11 sa 1 mon
species.
Stages II and III
Minimum summer flows are not expected to impede the
upstream movements of adult salmon in the middle Susitna
River. Any gains 'in the amount of spawning hab tat
w~thin and _upstream of Devil Canyon {see prev~nus
section} will be lost due to construction of the Devil
Canyon dam. Additionally, the present util.ization of
spawning habitat by chinook sal~.iJn within and upstream
of Devil Canyon ~ill be blocked by the Devil Canyon dam.
183
•
1984 the mean monthly July flows at Gold Creek were
24,120 cfs, 21,150 cfs, and 23,400 cfs, respectively.
Minimum daily flows in July of 1982, 1983, and 1984 were
16,600 cfs, 16,400 cfs and 18,600 cfs, respectively~
Bas~d on flow records since 1951, the average mean
monthly July flow at Gold Creek is 24,390 cfs~ with a
minimum monthly flow of 16,100 cfs. In contrast, the
estimated mean monthly July flow during Stage I filling
will be 12,740 cfs, with a minimum flow of 9,000 cfs
{8,000 cfs during dry years). During Stage I operation,
the mean monthly July flow at Gold Creek is expected to
be 14,490 cfs, with a minimum flow of 9~000 cfs
{8,000 cfs during dry years), Because of the 1 ow~r
f1 ows during Stage I fi 1.1 i ng and operation, ve 1 oci ties
will also be reduced somewhat~ This should ;ncrease the
number of chinook salmon able ta negotiate the rapids.
In addition, it is probable that other salmon species
may gain access to spawning habitats within anti upstream
of De vi 1 Canyon. Hence, during Stage I fi 11 i ng and ·
operation an expansion of the use of spawning habitats
upstream of De vi 1 Canyon is expected for a 11 salmon
species.
Stages II and III
Minimum summer flows are not expected to impede the
upstream movements of adult salmon in the middle Susitna
River. Any gains in the amount of spawning habitat
within and upstream of Devil Canyon (see previous
section) will be lost due to construction of the Devil
Canyon dam. Additionally, the present utilization of
spawning habitat by chinook salmon within and upst}"eam
of Devil Canyon will be blocked by the Devil Canyon dam.
183
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Chum_,_ Pi n.k, Coho, and Sockeye Sa 1 mon Outmi grant Juven i 1 es
Stages I, II, and III
Project flows will be sufficient to pro vi de passage for
outmigrating juveniles in the mainstem.
Resident Salmonids
• Stages I, II. and III
During overwintering of Arctic grayling, Dolly Varden,
and rainbow trout, in the mainstem, project flows will
be greater than natural winter flows. The higher f1ows
will provide depths greater than those occurring
naturally. Although velocities in the mainstem will be
correspondingly greater, passage is not expected to be
restricted by velocity requirements as the flows will
not exceed natural spring flows when resident salmonids
migrate to tributaries.
Burbot
• Stages I. II, and III
Burbot primarily utilize mainstem and mainstem
asso(iated habitats. Passage within the mainstem is not
expected to be restricted for burbot.
(b) Spawning/Incubati~n
{i) Mainstem
Mainstem habitat is comprised of those portions of the middle
Sus i tna River that norma 11 y convey streamflow throughout the
year. Few salmon spawn in the mainstem. Of those that do,
184
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chum salmon predominate. Mainstem spawning appears to be
1 imited by the armored streambed, high velocities, and
infrequent areas of upwelling.
-Primary Evaluation Species
Chum Salmon Soawning Adults
The amount of available mainstem spawning habitat for chum
salmon remains relatively unchanged over a wide range of
mainstem discharge, except for a slight increase in habitat
at mainstem discharges of approximately 14,000 to 15,000 cfs
(Figure 33). Hence, as so~e areas of spawnine habitat are
lost due to changing mainstem discharges, others are usually
gained.
0
••
$tage I
Filling
The available spawning habitat in mainstem margins for
dry, ewer age, and wet years during Stage I fi 11 i ng is
presented in Table 10. If a dry year occurs during the
fi 11 i ng period, spawning habitat wi 11 be reduced by
aporoxi mate 1 y 50 percent in August an~ 65 percet1t in
September. If an average year occurs during the filling
period, spawning habitat will be increased by about 75
percent in August, but decreased by almost 70 perc~nt in
September. An increase in availarle spawning habitat in
August a~i subsequent decrease in September is expected
if a wet year occurs during filling~
•• Operation
Habitat avai 1 abi 1 i ty in rna i nstam margins under nattJra 1
and Stage I flows is compared in seasonal habitat
185
()
......
co
0\
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•
16 ,.._
+>
4-
o-
(J) 12
-o c
<0
(/)
::l 8 0 ..c.
4-> . -
<C
::::>
3:: 4
.,.,. ... ,..,...--, .. . ....... .., ~--' ,, ' ~ ~-
0 I
0 5 10
Chum s~lmon spawning habitat
response ~urve and percent
contribution to total avail-
able habitat of mainstem areas
in the mir:M1e Susitna River.
15
FLOW
·~ 100
eo
HABITAT z
0 ... _...
X CONTRIB . t-......... .., __ ::J . 60 ro -0::: . 1-z
0
.. 40 (.J
t-z
'" w u
0:::
20 w
Cl.. .
'
..._ ... .. _
""'-·-----~ ..... _
1-----.. ~=~==p·· ----~ 0 ~
20
(thousa
FIGURE 33
I
"\I:" 30 35 40 £~
nd cfs)
I AlASKA POWER AUTHOR~TY
SUSITNA HYOROElECYRIC PROJECT
ENTRIX, INC. HARZA·E BASCO
SUSITNA JOINT VENTURE
~-~------~-------
{
I. t
t
' t
.
Table 10. Estimated change in ~hum spawning habit,..-(WUA} in mainstem margins
due to filling of the Watana -Stage I Reservoiro
Month
Dry Year
August
September
Discharge (cfsj_,_
Natural Filling
17,392
10,422
8,000
5,800
_ Chum Spawn1ng WUA (sg ftl .
Natural Filling -· %Change
12,379
9,171
6,120
3,181
-50.56
-65.31
t Average Year
August
September
Wet Year
August
September
22,228
13,221
25,236
15,124
12,415
6,800
15,505
6,800
187
7,362
14,466
5,207
15,797
12,929
4,484
15,285
4,484
75.62
-69.00
0
• •
duration curves and weekly habitat time series plots
(Figures 34 and 35}. During Stage I operation, a slight
increasl in available spawning habitat will occur
throughout much of the spawrli ng season.
The contribution of mainstem margins to the habitat
availability provided by all groups for natural and
Stage I operation is shown-in Figure 36. A slight
increase in percent contribution is expected during
August, whereas, the range of percent contri but i Oti is
expected to be similar to natural conditions during
September.
Stage II
Filling
Filling flows for Stage II would be of short duration,
consequently habitat availability during this period is
more appropriately discussed under operation.
H Operation
Habitat availability in mainstem margins under. natural
and Stage II flows is compared in seasonal habitat
duration curves and weekly time series plots (Figure 34
and 37). During mid-August a slight increase in
available spawning habitat is expected 50 percent of the
time, whi 1 e in 1 ate August a decrease of up to 40
percent in available spawning habitat is expected.
During the remainder o.f the spawning season, habitat
availability is expected to be similar to natural~
The contribution of mainstem margins to
availability provided by all groups for
Stage II operation is shown in Figure 38.
188
the habitat
natural and
The range of
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,,
\
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-3 ~ -
)C 2 • -. u -
-MMM.
--STAll: t
--STAI:£2
-STAII:l
-lAX STAll: 3
0 ~~--~--------------~--------~ 31 41 Ill ID UIJ
Percent oF Tiee Equaled or Exceeded
-20 ~ ....
'-11
i"
ltz .,
~ -. ..... < ..... --I:D .. ~
-KAlUW..
--STME 1
__ $TAG[ 2
-STitliiE3
-MXSTAGE l
• 100
Percent of T i 11e Equa 1 ed or Exceeded
-aa ~
~
'-II -MllM.
a-., --STMIE1
i t2 --STMiiE 2 .,
~ -STMiiE 3 -. -JIM STIG: 3
..... < .....
(]l .. :s ....
c ~ 41 Ill 1D ~
Percent of Time E~1aled or Exceeded
Flow duration curve {upper)
and seasonal (middle) and
maximum weekly (1 ower) chum
spawning habitat duration
curve for mainstem.
FIGURE 34
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC.
189
HARZA-E BASCO
SUSITNA JOINT VENTURE
J\
•
. ' .r··~
f:
I
' .. ~
' .
fX -'
...
~·
············~············ o•
10 •••••••••·•····~OJI
•
oL------,2-------,.------2-.------2------~.-------
211
f 11
0 en
0 12
~
;:)
0 1 ~ -~ ~ 4 t-.:::-:...:------
.uouST
STAiiiiE 1
_,. ____ ~._. ---!iDI
---
0~------------------~-------
12 1t
Mean weekly discharge (upper),
chum spawning WUA for mainstem
(middle) and percent change in
WUA (lower) exceeded 70, 50,
and 10 percent of the time for
natural and Stage I flows.
AUGUST
19
AUCUSi
FIGURE 35
S!:PY'
10 I
215 2
SEPT
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC.
190
HARZA·E BASCO
SUSITNA JOINT VENTURE
...
I
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)
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a .MAINSTEM
~· -~
G:tl i -- - - - - - - --IGI i" /~~--~-
It! ~~
I~--------
a 1===:=::=========--12 ,. 2• 2 •
AUGUST SI:PT
SIDE SLOUGH
~-~
i ''----~-----101 ~· . --------~
. ~a--------
"
.~--------------------------12 ,. 2 •
AUGUST
Percent contri but 1 on of chui~
spawning habitat in mainst~m,
side channels, side slc~ghs,
and up 1 and s 1 oughs to tot a 1
habitat during Stage I
exceeded 90, 50 and 10 percent
of the time.
SOOT
..
a
,
• UPLAND SLOUGH -=-----..,.
i• ................ -----i ---. ··-----~ ·-----._
[ .
• • 12 ,. at. 2 • AUGUST S~T
SIDE CHANNEL
• ------
·~--------------------~-----,.
AUGUST
ITME1
AlASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC. MARZA·E BASCO
SUSi fNA JOINT VENTURE FIGURE 36
191
·•
, ....
r
f
...
.. .. .. .. .. ..
10 ·····••······· o•
oL------12------,-.------2-.----~a~----~~------
C.l
Ill
0 12 z ~
J
0 • J: t.
~
j • L--~:-.:-
AuousT sc~
STAiiE 2
---
---••· -./-D --/
_________ _,.,.
Q ~--------------+-------------~
t4; :J
?J
~
Ill
0
~ 1
u
~
12 28 2 ;
SEPT
~ ri ~..::::===------::;::;.-------~ I
w a.
Mean weekly discharge (upper),
chum spawning WUA for mainstem
(middle) and percent change in
~UA (lower) exceeded 90, 50,
and 10 percent of the time for
natural and Stage II flows.
Hl
AUGUST
FIGURE 37
2tS 2
SEPT
AlASK.A POWER .4.UTHORITY
SUSITNA HYDROElECTRIC PROJECT
ENTRIX, INC. HARZA·E BASCO
SUSITNA JOINT VENTURE
192
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f
L r-
'>,.,,.,
I ' t.
r
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r
h
' }
~ 0
' ;
i
'-•
MAINSTEM UPLAND SLOUGH -_,.
a• -
~------------·· , _____ --i --~----·----~ -
1: -·~-----------------------12 ,.
AUOUS1'
2 •
SCJIIIT
12 ,.
AUOVST
2 •
S~T
• SIDE SLOUGH SIDE CHANNEL
----, .. -
I . -·----~------=---1:~=-=-=-===·=---=--------------~ 11
~3 -~11 -
~c.
·~-----------------------• 12 2 •
SEPT 12 ,. 2f'r, 2 • AAJGUST SEfOT
ALASKA POWER AUTHORITY
Percent contri but 1 on of chum
spawning habitat in mainstem,
side channels, side sloughs,
and up 1 and s 1 oughs to tot a 1
habitat during Stage I t
exceeded 90, 50 and 10 percent
of the time. SUSITNA HYDROELECTRIC PROJECT
FIGURE 38 ENTRIX, INC(.
193
HARZA-E BASCO
SUSITNA JOINT VENTURE
•
•
• •
percent contribution during Stage II is expected to be
similar to the range of contribution under natural
conditions.
Stage III
Filling
Fi 11 i ng of Watana during Stage I I I would occur over
several years and consequently discussion of habitat
availability relating to this process are more
appropriately addressed under operation.
.. o Opg_rat ion
Habitat availability in mainstem margins under natural,
early Stage III operation, and late Stage III operation
is compared in seasonal habitat duration curves and
weekly time -series plots {Figures 34, 39 and 40).
During early and late Stage III operation there is a 50
percent chance or greater that available spawning
habitat in rna i nstem margins wi 11 be reduced. However,
during much of the spawning season there is a 50 percent
likelihood that available spawning habitat will
increase. Moreover, the percent increase in habitat
peaks during water week 48. This is of particular
importance since water week 48 coincides with the peak
activity of the spawning season. Thus, although
available spawning habitat is likely to be reduced
during most of the spawning season, available spawning
habitat would likely increase above natural during the
peak of the spawning season.
The contribution of mainstem margins to the habitat
availability provided by all groups for natural, early
Stage I I I operation, and 1 ate Stage I I I operat; on ; s
194
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',;,,
:r
~· E~o
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0
1:1 ,. a • AIJC1UST 2;a.T
ST~3
0 ~~-~----------------~----~ 1.
AUCUST
~------·-------~------~----~~ 1~ 28 2 g
•ucuST se:n
Mean weekly discharge (upper),
chum spawning WUA for mainstem
(middle) and percent change in
WUA (lower) exceeded 90, SO,
and 10 percent of the time for
natural and early Stage III
ALASKA POWER AUTHORITY
flows. FIGURE 39
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, IN(~.
195
HARZA·E BASCO
SUSITNA JOINT VENTURE
..
l
i i.
'
Q'
r
[
[
L
L
f
L
...
10
-~.....:·:....··---~-....... ... • 1 Q,. .. ···-········ •• •• .................. 10. ..
-----.5,0'1
------·---·--···-...5~~ ••••••••o•••••••••••••••••t•••••···~·••• .......... a,.
oL------,a------,-.----~2~.----~2~----~.------
0 en
0
! :>
0
J: I c
~
AUOU111' ~
_,. ,.
--'=
~==-=~~----~---D
---a
---------------/s -------------.......... .
~ .. ,--L----
a ~-------,-.----~2~.-------2----~
12 SEJIOT ... UOUST
~
~
~
11.1
" ~ ,
(J
1-z
~ o -su
~ L----------------------------~1
.,mL.--------:2~tS----:t2 ___ 'i.i
12 t~ S~PT AUGUST ""
MAX STAGE 3
Mean weekly discharge {upper),
chum spawning WUA for mainstem
(middle) and percent change in
WUA (lower) exceeded 90, 50,
and 10 p~rcent of the time for
natura 1 and 1 ate Stage 1 I I
ALASKA POWER AUTHORITY
flows. FIGURE 40
SUSITN1\ HYDROELECTRIC PROJECT
ENTRIX, INC"
196
HARZ",·E BASCO
SUSITNA JOINT VENTURE
I
I
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I
I
I I
I
.I
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shown in Figures 41 and 42. In late Stage III
operation, mainstem margins would usually contribute a
higher percentage of available spa\ti:.,ing habitat to the
total available habitat provided by all groups, because
of substantial reductions in available spawning habitat
for other groups.
Chum Salmon Embryos and Pre-Emergent Fry
•
•
Stage I Filling
Flows during the fall and winter after the summer of
filling Stage I are expected to be similar to natural.
Thus, conditions for incubating embryos are expected to
be similar to natural.
Stage I, II, III Operation
Chum embryos in mainstern-influenced areas are subject to
dessication and freezing as a result of reduced
discharge in the river during the October and November
period prior to ice cover formation. Under Stage I
project operation, discharge in the middle river would
be maintained at a considerably greater discharge than
under natural conditions as indicated in Section 4.1.1.
As a result, embryos deposited in the spawning areas are
not expected to be as subject to dessication and
freezing. In fact, water depths and velocities in the
spawning areas will be maintained at higher than natural
levels. This will increase the effective spawning area
over natural conditions. Hence, conditions for
incubation are expected to be maintained or improve
during project operation because of the higher, stab 1 e
flows in the fall and winter.
197
I
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f
[
MAIN STEM a
~--;
a: 11
i IGI
u -· ~ 11 --/
~ /
/
~~ /
/
; ----0
12 ,. :zs 2 • AUGUST sen
SIDE SLOUGH
lS. .... -........ ....
!i .... __ ~ IQI =· ....
~ u
[
I
12 ,. :lS
AUGUST
Percent co11tri but ion of chum
spawning habitat in mainstem,
side channels, side sloughs,
and u~l and s 1 oughs to tot a 1
habit<.t ~'ur'·ing early Stage III
exceeded ~0, 50 and 10 percent
of the time.
a
a
2 • SEPT
UPLAND SLOUGH • ,.
!i• -i --. ~ -~
1:
0
12 ,. :ze 2 • .AUCUST SEPT
SIDE CHANNEL • ---------·· -
~· !Ill -.... . m a:• ! -----• ·-------------------r t!i .
II
12 ,. 2e 2 • AUGUST SEPT
STAGE 3
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
FIGURE 41 ENTRIX, INC. HARZA·E BASCO
SUSITNA JOINT VENTURE
.. ---------------~--------------~--------------------.&----------------~~--~ 198
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r
l
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I
!
t
l
MAIN STEM
_...._------=-:------,,.
---~-
-----------
12 ,. 2 •
AUGUST SU7T
SIDE SLOUGH
~· -i ,,. -. g ---------------... ___ -
.... u ....
[ .... ....
• 12 ,. 2. 2
AUGUST
Percent contribution of chum
spawning habitat in mainstem,
side channels, side sloughs,
and up 1 and s 1 oughs to tot a 1
habitat during late Stage III
exceeded 90, 50 and 10 percent
of the time.
a
• SD'T
UPLAND SLOUGH • ,.
!• -i ·-. ~ -
12 ,. 2 •
AUCUST SEI"T
SIDE CHANNEL
~«< -~
0:»
i ....
[
II
12
--
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
HARZA·E BASCO ENTRIX, INC. FIGURE 42 SUSITNA JOINT VENTURE
199
..
-Secondary Evaluation Species
Bur bot
Stage I Filling
Stage I filling will not affect burbot spawning and
incubationn Filling wi.ll be completed by early fall,
whereas burbot spawn during mid-winter. Thus, project
effects on burbot spawning and incubation are more
appropriately discussed under Stage I operation.
Stage I Operation
Within the middle Susitna River, the population of
burbot is relatively low and because of this, spawning
locations in this reach of river have not be~n
identified. Burbot are thought to inhabit relatively
1 ow-ve 1 oci ty deep-water areas in the mai nstem of the
middle Susitna River during winter.
Stage I operation will substantially increase flows
during winter. Mid-winter mean monthly flows, which
typically range from 750 to 3,000 cfs {mean of
approximately 1,500 cfs), will range from 5,000 to
11,500 cfs with an average of about 8,000 cfs during
Stage I operation. This higher in flow is expected to
increase the amount of 1 ow-velocity, backwater areas.
If this occurs, burbot in the middle Susitna River are
not expected to be adversely affected by the project
flow regime.
Stages II and III
Because the project flow regime during Stages II and III
will be similar to Stage I operation, no significant
200
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I
I
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I
I
effects on spawning burbQt due to the filling or
operation of Stages II and III are expected.
{ii) Side Channels
In general, side channels convey 1 ess than 10. percent of the
total discharge in the river, but ~onvey mainstem discharge
more than 50 percent of the time during the summer high flow
months (EWT&A 1984, 1985}. Relatively few salmon spawn in side
channels of the middle Susitna River. Of those which do, chum
salmon predominate.
-Primary Evaluation Species
Chum Salmon Spawning Adults
The amount of available side channel chum salmon spawning
habitat remains relatively constant at mcdnstem discharges
greater than 20,000 cfs (Figure 43}. As mainstem discharge
falls below 20,000 cfs the available spawning habitat in
side channels decreases substantially. This is primarily a
result of receding backwater effects at the mouths of side
channels.
•
• •
Stage I
Filling
The available spawning habitat in side channels for dry,
average, and wet years during Stage I filling is
presented in Table 11. If a dry year occurs during the
filling period, spawning habitat will be reduced by
approximate 1 y 90 percent in August adn 50 percent in
September. If an average year occurs during the filling
period, spawning habitat will be decreased by about 70
percent in August and by 80 percent in September. A
201
I()
I\.)
0
N
100
12 80 _........ HABITAT :z -a-> 0 4---. X CONTRIB t-o------::J (/) 90 60 m
~ -a e::: c: t-<0 z ([) r'. 0 ~ , ..---\ u 60 ' '"" 0 r ./, ........ , -40 ' .. ..c ' -. ' t-...., I '\ z '~ .......... ' .., __ w • ,_. ... .J ......... __ u < -.... ... _
0::: ...
:::J 30 -...... .,. 20 w "-·· ~ Q..
r 0 0 ~-I·
0 5 10 15 20 25 30 35 ~0
FLOW (thousand cfs)
Chum salmon spiwn1ng habitat
response curve and percent
contr1 but 1 on to tot a 1 ava fl-
able habitat of side channel
ari~as 1n the middle Sus1tna
River.
~--!Ill --
FlGURE 4l
.. ---
;:_; ::")
ALASKA POWER AUTHORITY
SUSITNA HYDROELE.rTRIC PROJECT
Et\ITRIX, INC.
--all -
HARZA·E BASCO
SUSilNA JOINT VENTUR(
---
~
\
!
l .l
l
l
l
I
Table 11. Estimated change in chum spawning habitat (WUA) in side channels due
to filling of the Watana -Stage I Reservoir.
Month
~· Dry Year
August
September
Average Year
August
September
:let Year
August
September
Discharge (cfsl
Natural Filling
17,392
10,422
22,228
13,221
8,000
5,800
15,505
6,800
203
Chum Spawning WUA (sg ft)
Natural Filling % Chaoge
84,027
23,985
160,644
35,486
186,379
46,174
18,869
14,087
33,642
14,600
57,734
14,600
-77.54
-41.27
-79.06
-58.86
-69.02
-68.38
!
n
!
~
.~ L;
~
~
rL. ll~
E
:'
'
' '
~'
{[
k~
~4
i
l
' ' •
decrease in available spawning habitat in August of 40
percent and of 85 percent in September is expected if a
wet year occurs during filling.
. ., Operation
0
0 •
Habitat availability in side channels under natural and
Stage I flows is compared in.a seasonal habitat duration
curve and a weekly habitat time series plot (Figures 44
through 47). During Stage I operation, a reduction in
available spawning of 0 to 80 percent could occur
throughout the spawning season. However, in September
available habitat coul·d increase by up to 60 percent.
The contribution of side channels to the habitat
availability provided by all groups for naturai and
Stage I operation is shown in Figure 36. The range of
percent contribution is expected to be similar to
natural conditions dtiring August and September.
Stage ll
Filling
Filling flows for Stage II would be of short duration,
consequently habitat availability during this period is
more appropriately discussed under operation.
.• Operation
Habitat availability in side channels under natural and
Stage II flows is compared in a seasonal habitat
duration curve and a weekly time series plot (Figures 44
and 46} . During mid-August a decrease of up to SO
percent in available spawning habitat could occur.
204
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. "
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-·liM.
_ .srMt t
-..STMiE 2
-SfM13
-IAIStMEl
o~~--·-----------------------3" ~ • • ~
-~
E -~·
Percent. or T i.., Equa 1 ed or Exceeded
-Ml\M.
·--STACE 1
--STMIE 2
-STACE 3
-MI STAGE 3
0~-+--._~--~~------~-.----~ ~ c m m ~
Percent oF Ti.., Equa 1 ed or Exceeded
....
i~~-----MltiW.
1,
j
-.STMit t
--STAlE Z
-STACE ~ _,
-1M1 STAiit 3
!:< ..... -i•
0 ~------------~------~------~ 211 c m m 1111
Percent of T i 11e Equaled or Ex~
Flow duration curve (upper)
and seasonal (middle) and
maximum weekly (lower) chum
spawning habiiit duration
curve for side channels. ALASKA POWER AUTHORITY
FIGURE 44
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC.
205
HARZA-E BASCO
SUSITNA JOINT VENTURE
•
t I
'
"~ ·IL·
~'
Jiv
~ '
' !
... ...
I.
I
':::u
! .. I i ,.
10
•
.. ..... ···-.. ·····-······-............ -~ ·····-.....
• .... 10.
·········~---·Q····
····-••••• Q • ········-----····-
·-·:::·······--..eo•
oL-----------~,.~--~~~.----~2----~.-----~ 12
AUOUST liD"T
..... ..... ......... ..... ..... '--·---::_:::-D --
'------------------------·----~ . -
12
• o( i •
! •
~.
18
.4UC:UST
20 2 g
SEPT
____ 101
i·~------~--------~11 u.,.
~ ... ..,
~...,
"' 12. -e.J.----~
-··--------:~----2~--~g
12 1Q 28 SEPT AUGUST
No\llJIAI.
51'1;6;£ 1
Mean weekly discharge (upper),
chum spawning WUA for side
channels (middle) and percent
change in WUA (lower) exceeded
VO, SO, and 10 percent of the
t1me for natural and Stage I
ALASKA POWER AUTHORITY
flows. FIGURE 45
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC.
206
HARZA·E BASCO
SUSITNA JOINT VENTURE
I
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('
.[.
~~~ Lt
lr .
.
. l
,_
I
--211 I 1 ..
I,.
.. ······· •••••••••••o•••' .......... ....... .......
···-.... 10.
··~·-·······-······
•••·•······ . ······~---··-··-··
.................. ~9~
••
oL------------,~.-----a~.~--~2~----~.------
12 AUOUST S~
P.-~-~-~-~-~-~~~~~-~---------1m
- - - - - -.... .._ _.;-::::---=-::::...=--=-:-...::-::..::... D
.~----------------------------12
• <( i •
i ..
rl a
1!1
AUCUST
2S 2 sa
SEPT
~ , l--------L.-----:;:: II u.,.
~-Q
11.1
~--Ill
IL -tDl------
-t----------:2~ .. ---~2:-----~Sl
12 '" .. AUCUST SEPT
STAiiE1
Mean weekly discharge (upper),
chum spawning WUA for side
channels (middle) and ~ercent
change in WUA (lower) exceeded
VO, 50, and 10 percent of the
time for natura 1 and Stage I
ALASKA POWER AUTHORITY
flows. FIGURE 45
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC.
206
HARZA-E BASCO
SUSITNA JOINT VENTURE
I
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~
1:
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40
~·
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I • aa+ ·····~-.
! I ao
............
•••• QJII
i ,. ... ... .. .-.. ..
10
········•••••••••• OJIIl
•
0
12 ,.
N.JOUST
~---------------------------,.
12
~· .
~ .
10
~GUST
28 2
SEPT
':1 ~ :I~~
J : ~.,......_ · -------II
u -· ... Q-41 .
0
~-w a. ...
-•---------2:+:,--·--~~"'-----:sa 12 19
AUGUST SEPT
ST-"E 2
Mea~ weakly discharge (uppe~),
chum spawning WUA for side
channels (middle) and percent
change in WUA (lower) exceeded
fO~ 50, and 10 percent of the
time for natural and Stage II
ALASKA POWER AUTHORITY
SUSifNA HYORO:il~C:TRIC PROJECT
ENTR!X, INC. HARZA·E BASCO flows. FIGURE 46
SUSlTNA JOINT VENTURE
207
I :so
I .a.
!20
I i ,.
10
•
-~--------~---~ ..
.. .. ·-~.......
-.-•••• ~ 0111
--c.···
-----'•"··············-----·7'!,..80.!11
oL-----~,2----~,~.----~2.~--~2~-----~.------
.... .... ....
' ' '
AU~ST S~
' ' ' ............ -..__ ____ -::;-:::::-D
.... -
------·-----------~--!IIJI
.~----~------~-----------2 a
K" 12 28
• Ill
j.
~.
~a
~o~----------~r=~-~~
o -z ... ~ ....
u
/
_/ ~-.....
.L----~
-~----~---~------::~--~ 12 ,. 21 2 a
Mean weekly discharge (upper),
chum spawrii ng WUA for side
J.UGl,I$T SCPT
channels (middle) and percent
change in WUA (lower} exce~ded
90, 50, and 10 percent of the
time for naturtl.l and early
ALASKA POWER AUTHORITY
Stage III flows. FIGURE 47
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC.
208
HARZA·E BASCO
SUSITNA JOINT VENTURE
f
f.
I
I_
f
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i
t.
t
r.m
l
L.
[~
L~
t.
L
During the remainder of the spawning season, habitat
availability is expected to be similar to natural.
The contribution of side channels to the habitat
availability provided by al1 groups for natural and
Stage II operation is shown in Figure 38. The range of
percent contribution during Stage I I is expected to be
similar to the_ range of contribution under natural
conditions.
Primary Evaluation Species
Chum Salmon Embryos and Pre-emergent Frv
•
Stage I Filling
Flows during the fa 11 and winter after the summer of
filling Stage I are expected to be similar to natural.
Thus, conditions for incubating embryos are expected to
be similar to natural.
Stage I. II. III Operation
As rnentioned previously, conditi-ons for incubation in
mainstem-influenced areas are expected to be maintained
or improved during project operation because of the
high~r/ stable flows in the fall and winter.
-Secondary Evaluation Species
Side channels in the middle Susitna River do not provide any
known si<]nificant spawning habitat for the secondary
evaluation species.
209
0
.. .
Stage III
Filling
Filling of Watana during Stage III would occur ovar
several years and consequently discussion of habitat
availability relat·ing to this process are more
appropriately ~,ddressed under operation .
•• Ooeration
Habitat availability in side channe·ls under natural,
early Stage III operation, and late Stage III operation
is compared in seasonal habitat duration curves and
weekly time series plots (Figures 44, 47 and 48).
During early Stage III operation there is a 50 percent
chance that available spawning habitat in side channels
wi 11 be reduced by up to 80 percent during the first
ha 1 f of the spawning season. There is a 50 percent ·
chance that available spawning habitat will be reduced
by at 1 ea~~t 50 percent during 1 ate Stage I I I operation.
The contribution of side channels to the habitat
availability provided by all groups for natural, early
Stage I I I operation, and 1 ate Stage I I I operation is
shown in Figures 41 and 42. During early Stage I I I
operation the range of percent contribution will be
similar to natural. Percent contribution would likely
be substantially reduced during late Stage III
operation. Percent contribution would approach natural
conditions at the 1 ower end of the range of
contributions throughout the season and at the higher
end of the range during late September.
210
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L.
.sa
(.so
I
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! 20 i i ,.
•
·~---, '~'-·-"'-----.......--.. .. ,..,.,.,:'~""~'""·'~~..:,...""~~~~~~~-.. --...------., . .
•• ~····· 10. -~,..;;_-..................... . .. ·· ~·•••-a·•·········10• .. ... -----aa.
..... ~---·-···-·--~~ ••••••••••••••••••••••••••t·-···········~-••••• .-o•
oL------,~2 ----~,.~--~2~.----~2~----;.------
AuouST s~
----.... ---... --~=-.... ooc:::~:""----1ar
' ' ' ..... .... taz
--!IJZ ----·--------=-'-~---901 0~-------------------------
• ~ ~ Ill
~ .
Iii 31 ()
18
.t.UGU$1'
28 2 Sl
SEJII'T
~ 0 1-----_..:. ________ 101
(J -31 ... ~ ...
0
G:-4iD Iii
____ !DJ
IL _., t-=========------~ !0 I -trm,~2-----,•.----~2~.~---~2----~.
AUGUST SEPT
IIATUW.
Mean weekly discharge (upper),
chum spawn 1 ng WUA for s 1 de
channels (middle) and percent
change in WUA (lower) exceeded
fO, SO, and 10 percent of the
t1me for natural and late
ALASKA PO\VER AUTHORITY
Stage III flows. FIGURE 48
--
SUSITNA HYDROELECTRIC PROJECT
ENTRBX, INC.
211
HARZA·E BASCO
SUSITNA JOINT VENTU~E
t
r
!
Chum Salmon Embryos ~nd Pre-emergent Fry
•
•
Stage I Filling
Flows during the fa 11 and winter after the summer of
fi 11 i ng Stage I are expected to be simi 1 ar to natura 1 •
Thus, conditions for incubating embryos are expected to
be similar to natural.
Stage I, II, III Operation
As mentioned previously, conditions for incubation in
mainstem-influenced areas are expected to be maintained
or improved during project operation because of the
higher, stable flows in the fall and winter.
-SecondarY Evaluation Species
Sockeye Salmon Spawning Adults
Side channels in the middle Susitna River provide
significant spawning habitat for sockeye salmon. Slough 11
provides habitat for almost 70 percent of the spawning
sockeye in the middle Susitna River.
(iii) Side Sloughs
Side sloughs are morphologically similar to side channels, but
the upstream ends of side sloughs are breached by mai nstem
discharges of 20,000 cfs or greater (EWT&A and AEIDC 1985).
Hence, side sloughs convey mainstem water less than 50 percent
of the time during the summer high flow months. A substantial
portion of the chum spawning and much of the sockeye spawning
in the middle Susitna River occurs in side sloughs. Some pink
salmon use side sloughs for spawning, mostly in even-numbered
years.
212
-Primary Evaluation Species
Chum Salmon Spawning Adults
The amount of side slough spawning habitat for chum salmon
remains relatively unchanged below 20,000 cfs (Figure 49}.
However, spawning habitat in side sloughs substantially
increasas as mainstem discharges ~xceed 20,000 cfs. This is
a result of side channels transforming to side sloughs at
• various discharges above 20,000 cfs&
• Stage I
• • Fi 11 i ng
The availab1P-.spawning habitat in side sloughs for dry,
average, and wet years during Stage I filling is
prasented in l~ble 12. If a dry year occurs during the
filling period, spawning habitat will be reduced by
approximately 30 percent in August and September. If an
average year occurs during the filling period, spawning
habitat will be decreased by about 60 percent in August
and by almost 30 percent in Septembero A decrease in
available spawning habitat of almost 80 percent in
August and 35 percent in September is expected if a wet
year occurs during filling~
•• Operation
Habitat availability in side s.l6ughs under natural and
Stage I flows is compared in seasonal habitat duration
curves and weekly habitat time series plots (Figures 50
and 51). Reductions in available spawning habitat of
between 10 and 60 percent are expected 40 percent of the
time throughout the spawning sEason, while increases of
213
r~
N
J-l
~
r-,:
......-...
-+> 4-
o-
(/)
-o c co
(/)
:::J
0 ..c -+> ..__
<C
:::J
::3:
r~. ::. r-: r-7' ~ r-; ' l
80
40
0
0 5 10
Chum salmon spawning habitat
response curve. and percent
contribution to total avail-
able habitat of side slough
areas in the middle Susitna
River.
r-r-~ tr••'>c> r: ~ ~ !!. " -~ c-•>-->< (~,-_,,.,,
15 20 25 30
r:~
HABITAT
ft"'"JJI!!IW!l c .,,·.~
100
80
X CONTRIB
35
60
40
20
0
40
:z
C> -._
::J
C!J --0:::
t--z
0 u
t-z w u
0:::: w a_
FLOW (thousand cfs)
ALASKA POWER AUTHOP.ITV
SUSITNA HYDROELECTRIC PR0~1 ECT
F!GURE 49
.
SUSITNA JOINT VENTURE
HARZA·E BASCO ENTRIX, INC.
~---~-~~---~~----
(/
tJ
r~ Table 12. Estimated change in chum spawning habitat (WUA) in side sloughs due
¥.--: to fi 11 i ng of the Watana -Stage I Reservoir.
l.' '
.i
Month
lJ Dry Year
L· . .
l
(
r~
Li
l .
August
September
Average Year
August
September
Wet Year
August
September
Discharge (cfs
Natural Filling
17,392
10,422
22,228
13,221
25,236
15,124
8,000
5,800
12,415
6,800
15,505
6,800
215
Chum Spawning WUA (sg ft}
Natural Filling %Change
24,385
18,982
49,721
20,241
100,845
22,547
16,595
13,287
19,559
14,594
22,812
14,594
-31.95
-30.00
-60.66
-27.90
-77.38
-35.27
rJ
l
t
t .. ~
'' ....
L
L
•
-J ~ -
: :r .... u -
-MllM.
--S1'ME1
--S1'ME 2
_srMi£ 3
--SfMi[ 3
o~----.-~--~--~--------------20 c sa m 1aJ
Per-cent. or T i 11e Equa 1 ed or E.leceeded
-Mn.IW.
--STMiE1
__ srMi£ 2
-STMiE l
-IMX sr.-a: l
.. _.i
0 ~----~--~~--.-~~----------~ 20 c m m ~
-< ::)
311: ..
""'" cr .,
~ 2 .,
]
~ -1
!< ..... -~to
Percent aF T i 11e Equa 1 ed or Exceeded
-M'IlM.
--STNiEt
__ sr.: -~
-S1'Mt3
-!lAX STNiE 1
0~--------~----~----------~--~ 2Q 41 6D ll 100
Per-cent. of T i •e Equa 1 ed or Exceeded
Flow duration curve (upper)
and seasonal (middle) and
maximum weekly {1 ower) chum
spawning habitat duration
curve for side sloughs.
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC. FIGURE 50
HARZA-E BASCO
SUSITNA JOH•H VENTURE
216
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r."''·· 'I
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'··-:.11
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-::...J,
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••
.. ····~-.................... 0~
10
•
oL------,a------~,.~--~2~.----~a~----~.------
AUOUST S~
-t
0 ill.
0 t z
~
:l
0 1
:t c
STAQ: 1
a ~----------------~~-------
12
o( ..
:l II ~
~ • w ~ 0
~ II
0 -211 ,.. z_,., w
0
~· w
11. ..
•I
12
1~
AUGUST
HI
AUGUST Mean weekly discharge (upper),
chum spawning WUA for side
slough (middle) and percent
change in WUA (lower) exceeded
10, 50, and 10 percent of the
time for natural and Stage I
flows. FIGURE 51
28 2 g
SEPT
.__ ____ !OX
28 2 g
SEPT
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
HARZA·E BASCO E~~TRIX, INC.
SUSITNA JOINT VENTURE
217
•
between 0 and 30 percent are expected 40 percent of the
time throughout the spawning period.
The contribution of side sloughs to the habitat
availability provided by all groups for natural and
Stage I operation is shown in Figure 36. At the lower
range of contribution, th·e percent contribution during
Stage I operation is expected to be similar to natural
conditions, whereas, at the upper end of the range
percent contribution is expected to slightly decrease
under Stage I operation.
Stage II
• • Fi 11 i ng
Filling flows for Stage II would be of short duration,
consequently habitat availability during this per 1.od is
more appropriately dis~ussed under operation.
.• Operation
Habitat availability in side sloughs under natural and
Stage 11 flows is compared in seasonal habitat duration
curves and weekly time series plots (Figures 50 and 52).
During the first two weeks of the ~pawning season,
available habitat may decrease up to 25 percent.
However, increases of up to 30 percent are expected -in
late August coinciding with the peak spawning activity.
The contribution of side sloughs to the habitat
availability provided by all groups for natural and
Stage II operation is shown in Figure 38. The range of
percent contribution during Stage I I is expected to be
similar to the range of contribution under natural
conditions.
218
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I
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I
I
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•
I
~
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t' ;,
t
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; <'
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f
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i J !
L
' ' f
t '
I .........
I ' .....
=t
.. f ~~o
• :zs
i ··t I , .. . .. .. •••••• 0" ...............
-t
0 en
a z
~
::l
0
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l: 1 ... -
····· ..
I
12
' ' '
,.
AYOUST
' ' '
2
0 J-_______________ _
12
• ~ ~ ID
~ .
~ 2D
Ul
AUGUST
25 2 g
SEPT
~ II I..c:::::::__-.,-----___;:::a,----~~
(J -31 ... ~_..,
~-~~~ w a. ...
-tcmL..----..:::------:2':"5 ___ +;;2--~~
12 1V SEI'"T AUGUST
Mean weekly discharge (upper),
chum spawning WUA for side
slough (middle) and percent
change in WUA (lower) exceeded
VO, 50, and 10 percent of the
time for natural and Stage II
Al.ASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
flows. FIGURE 52 HARZA·E BASCO ENTRIX, INC.
SUSITNA JOINT VENTURE
219
,• .
;
~
,.
""""'
0
0 •
Stage III
Fi 11 ing
Fi 11 i ng of Watana during Stage I I I waul d occur over
several years and consequently discussion of habitat
availability relating to this precess are more
appropriately addressed under operation.
•• Operation
Habitat availability in s·ide sloughs under natural,
early Stage III operation, and late Stage III operation
is compared in seasonal habitat duration curves and
weekly time series plots {Figures S!i 53 and 54).
During early Stage I I I operation, reductions in
available spawning habitat from 0 to almost 50 p~rc~!'!t
could occur early in the spawning season. However,
during the middle and 1 a ter portions of the spawning
period increases of up to 20 or 30 percent could occur.
In late Stage III operation, reductions in available
spawning of up to 50 percent or greater caul d occur
throughout the spawning season.
The contribution of side sloughs to the habitat
availability provided by all groups for natural, early
Stage III operation, and 1 ate Stage III operation . lS
shown . Figures 41 and 42. In late ln Stage III
operation, the range of percent contribution would be
more narrow, particularly early in the spawning season.
220
I
I
I
I
•
I
I
I
I
I
I
.I
I
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I.
I
I
j ..... ,
t '
I ,...,,
t ,
..
.sa
········--·"···········--······ •••• 0'1 .. .. ............... o,.:
•
o~-----,-a------,.-------a.-------a------~.------
..... t:
0 rn
Q 1 z ~
:J
0 t
E.
~
3
--... -
AUOUIIT SU"T
--.....
' ' ' ~
'\.m
-= = =-= = -~--iii - -........... - -= • ~------------+-----~------~
12
~3 ~
~ .
w a
" z ~~~--~-------=~~jl
(,) oCD ...
~-4.)
~--"' G..
tcl"-o--·--------~----.....
Mean weekly discharge (upper),
chum spawning WUA for side
28 ~ .
SEPT
STMiE 3
s 1 ough (middle) and percent
change in WUA (lower) exceeded
70, 50, and 10 percent of the
time for natural and early
A ~. A S K A P 0 W E R A U T H 0 R I T Y
SUSI~fNA HYDROELECTRIC PROJECT
Stage III flows. FIGURE 53 ENTRIX, INC. HARZA·E BASCO
SUSITNA JOINT VENTURE .... ------------------------------~--~~ ~~------~ .. --------~--------------~ 221
.------------------------------------·~·'--~ .. -------------------------,
~· ; ,_
I .u
120 I i ,.
10
•
....
0 eo,.•, • ..,0 ••• tO'I
-.-•• ~ • ...._.__,_ ••••• •• •• • ........... , .........
1
o•, ..
:.:...___.....__ ~
~ .......... ~~ •••••••••••••ue•••••••••••a ..................... ~oJI
oL---~-,2~--~,~.----~2=.~--~2~----;.------
f
0
ln.
0 1
z
iii g,
~
""
AUo~ST ~~
--........ ,.,. ......... .... .... .... ' ............
oL-----~-------------------
~ .
i ..
~ .
w 31 0
~ a
X
u -211
~ ... 1&.1 u a:: ;a w 11.-m
_,
12 19
AUGUST'
28 2 ~
SEPT
~-----------~>-====11 ----
12 2 ~
SEPT Mean weekly discharge (upper),
chum spawning WUA for side
slough {middle) and percent
change in WUA (lower) exceeded
fO, 50, and 10 percent of the
time for natura 1 and late
ALASKA POWER AUTHORITY
S\JSITNA HYDROELECTRIC PROJECT
Stage III flows. FIGURE 54 HARZA·E BASCO EN'TRIX, INC.
SUSITNA JOINT VENTURE
222
..
~'
' '
I
I
I
I
I
I
I
I
I
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I
I
I
I
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If
fj
1':
1.~
I
l,-
1_
I.
~-~
IL
IL
JL
l.
t_
t
i __
lr
'~
l
l
Ch~m Salmon Embryos and Pre~emergent Fry
•
0
Stage I Filling
Flows during the fall and winter after the summer of
filling Stage I are expected to be similar to natural.
Thus, conditions for incubating embryos are expected to
be similar to natural.
Stage I. II. III Operation
As mentioned previously, conditions for incubation in
mainstem-influenced areas are expected to be maintained
or improved during project operation because of the
higher, stable flows in the fall and winter.
Secondary Evaluation Species
Sockeye Salmon Spawning Adults
• Stage I Filling and Operation
In the middle Susitna River, sockeye salmon spawn in
side sloughs, with two side sloughs {SA and 21)
providing habitat for 25 percent of the sockeye
spawni.ng.
The habitat requirements of spawning sockeye salmon are
similar to those of chum salmon. Thus, the habitat
modeling developed for spawning chum salmon (see above)
can be applied to sockeye salmon. The habitat modeling
for chum salmon provides a conservative estimate of
available spawning habitat for sockeye salmon, because
sockeye are able to negotiate more shallow passage
reaches than chum sa 1 mon. Hence, at a se 1 ected flow,
sockeye salmon will likely have access to more spawning
223
•
habitat than the model predicts because of their ability
to negotiate more shallow depths than the minimum depth
criteria for successful chum salmon passage.
Stages II and III
Habitat availability for' sockeye would be similar to
chum salmon.
Pink Salmon Spawning Adults
• Stag@ I Filling and Operation
In the middle Susitna River, pink salmon spawn primarily
in tributaries, and to a lesser extent in sloughs. In
odd years, when the run strength is low, few pink salmon
spawn in sloughs (ADF&G 1985a}. During years of high
pink escapements (even years), pink salmon spawn in
sloughs more frequently. Sloughs SA and 20 were areas
utilized for slough-spawning pink salmon during 1982 and
1984 (ADF&G 1985a)~
Since habitat requirements of spawning pink salmon and
chum sa 1 mon are di ssimi 1 ar (pink sa 1 mon tend to use
areas with higher velocities and smaller substrate), the
analysis of available habitat for spawning chum salmon
cannot be applied to pink salmone
•
(section on pink spawning and incubation to be added
upon completion of IFR secondary species evaluations in
March 1985}
224
I
I
I
I
I
I
I
·I
I
I
I
I
I
I
I
I
I
• Stages II and III
(section on pink spawning and incubation to be added
upon completion of IFR secondary species evaluations in
March 1985)
(iv) Upland Sloughs
Upland sloughs are analogous to small tributaries since their
upstream ends are only breached by mainstem water at extremely
high mainstem discharge (greater than 40,000 cfs). Chum,
sockeye, and pink salmon spawn in upland sloughs, with Slough
11 containing most of the utilization in this habitat type ..
-Primary Evaluation Species
Chum Salmon Spawning Adults
The amount of available upland slough spawning for chum
salmon in the middle Susitna River increases substantially
between mainstem discharges of 12,000 to 20,000 cfs {Figure
55}$ At discharges below 12,000 cfs and above 20,000 cfs
there is little change in the amount of available upland
slough spawning habitat.
• Stage I
•• filling
The available spawning habitat in upland sloughs for
dry, average, and wet years during Stage I fi 11 i ng is
presented in Table 13. If a dry year occurs during the
filling period, spawning habitat will be reduced by
approximately 75 percent in August and 40 percent ; n
September. If an average year occurs during the filling
period, spawning habitat will be reduced by
225
•
N
N
0\
,_.,. ... ___ ::-,
~-· ·-
""'",.,.._ "#' ---. ~ ;...-:; _:_,:t '< -·
'100
1 80 .-.,.. _,.,...,
4-
z
0 ........
HABITAT
o-
(/)
1-
=:J en
~
X CONTRIB
60
-o c
«'
(fJ
:::J
0 ..c
+>
0::
t-z
0
L)
I-z
40
......... w
< ::l
:::1:
u
0:: w
CL 20
0 ~----~~-----+------~------r-~---~·------~1------+•-· _____ _j 0 c 5 1 0 15 20 25 30 35 40
Chum salmon spawning habitat
response curve and percent
corr:tr1but1on to total avail-
. able habitat of upland slough
i'reas in the 11iddle Susitna
River.
FLOW (thousand cfs)
FIGURE 55
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC. HARZA-E BASCO
SUSITNA JOINT VENTURE
},
~ ' i
"'~:
1' r
l
l . j·
j.
f
I
i· l
l:
!:
i
~
~
If~
lJ
Table 13. Estimated change in chum spawning habitat (WUA) in upland sloughs
due to filling of the Watana -Stage I Reservoir.
Month
Discharge (cfs _ Chum Spawning WUA (sg ft)
Natural Filling--%Change Na~ural Filling
tJ Dry Year
f 1 t.J
r;
~~)
c
l :.
..
• J
1
b
w
l :·
~
~
c:
u
August
September
Average Year
August
September
Wet Year
August
September
17,392
10,422
22,228
13,221
25,236
15,124
S,.Q{JO r;,8oo
12,415
6,800
15,505
6i800
227
92,581
16,"755
127,335
50,922
125,723
69,518
10,828
8,798
39,526
9,380
72,374
9,380
~88.30
-47.49
-68~96
-81 .. 58
-42.43
-86.51
' \
\,
approximately 75 percent in August and 40 percent in
September. If an average year occurs during the filling
period, spawning habitat will be decreased by about 75
percent in August and by alm9st 60 percent in September.
A decrease· in available sp4wning habitat of almost 70
percent is expected in both August and September if a
wet year occurs during filling.
... Operation
•
••
Habitat availability in upland sloughs under natural and
Stage I flows is compared in seasonal habitat duration
curves and weekly habitat time series plots (Figures 56
and 57) ~ During August a reduction of up to 70 to 80
percent of the available sp,awning habitat is expected 50
percent of the time. However, in September reductions
in the available habitat will be less and there wou1d be
a 50 percent chance that available habitat would
increase by up to 50 percent. ~
The contribution of upland sloughs to the habitat
availability provided by all groups for natural and
Stage I operation is shown in Figure 36o A slight
decrease in percent contribution is expected during
August, whereas, percent contribution is expected to be
similar to natural conditions during September.
Stage II
Filling
Filling flows for Stage II would be of short duration,
consequently habitat availability during this period is
more appropriately discussed under operation.
228
I
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I
I
I
I
I
I
I
r
\
1_ ·;_"'~_· f ~ '
'i.J
f }
I b.~
{ '
k
,r I
L .:_,;(
-J ~ -
)C z c: u -~t
-M11M. _ ... sr• t
--STMIE 2
-STMIE J
-IAI~ili«J
o~--~.~--~.~--~m~--~m~--~1~
Percent. of T i 11e Equa 1 ed or Exceeded
-MAnM.
--STMIE1
--STMiE 2
-STMIEl
_ IIAl STMiE 3
31 •
Percent of T i.e Equa 1 ed or E.~ceeded
-, ~
-M'NW.
--STMIE 1
--STMiiE 2
-STMiE 3
_MXSTMi£3
o ~~--a~--~~c~~~m~--~m~~~,~
Pereent. of Ti • Equa 1 ed or Exceeded
Fl ow d urat1 on curve (upper)
and seasonal (middle} and
maximum weekly (lower) chum
spawning habitat duration
curve for upland sloughs.
FIGURE 56
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC.
229
HARZA~E BASCO
SUStfNA JOINT VENTURE
...
u ~·i
t-1
f: '
t.J
1!
.J
10
•
...... --. .. •••o••••••~••••
................. .......
···~. ···--. ··---..... •••• ,o •
....
--------------·:························· o•
oL------,2------,.~--~.~.-----=a----~.------
' '
.uouu s.,..,.
' ' "----'= D ~~----~~~--
aL-------------------~2----~.
12 ,. 2 • sorT
AUGUST
~ .
~ .
~ .. 111
~ a
~ a !...-----.......::::::::;..__ ____ :::::: II
u ...
·! ... u c ..
r .. L------
12 ,. 2 •
Mean weekly discharge (upper), AUGUST SEPT
chum spawning WUA for upland
slough (middle) and percent
change in WUA (lower) exceeded
fO, SO, and 10 percent of the
time for natural and Stage I
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
flows~ FIGURE 57 HARZA·E BASCO ENTRIX, INC. SUSITNA JOINT VENTURE
230
I
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I
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I
I
I
I
I
I
I
I
I
I
I
r··.
j
I
00 Operation
•
Habitat availability in upland sloughs under natural and
Stage II flows is compared in seasonal habitat duration
curves and weekly time series plots {Figure 56 and 58).
During the early part of the spawning season, available
spawning habitat could be decreased by up to 70 percent.
However, available spawning· habitat is expected to be
similar to natural conditions during the rest of the
spawni.ng period.
The contribution of upland sloughs to the habitat
availability provided by all groups for natuari and
Stage II operation is shown in Figure 36. The range of
percent contribution during Stage I I is expected to be
similar to natural conditions, except early in the
spawning season when the contribution is expected to be
slightly less than naturale
$tage III
• • Fi 11 i ng
Filling of Watana during Stage III would occur over
several years and consequently discussion of habitat
availability relating to this process are more
appropriately addressed under operation.
. • Operation
Habitat availability in upland sloughs under natural,
early Stage III operation, and late Stage III operation
is compared in season a 1 habitat dura't ion curves and
weekly time series plots (Figures 56, 59 and 60).
During early Stage III operation there is a 50 percent
chance or greater that available spawning habitat in
231
4 i
f j
~
....
~·
tO
.. ..
•
.. .. .. ..
...
......... c ••
·········· o•
..................... a•
oL-----,-2----~,.~. ~--~2.~--~2----~.~----
0 .,
AUOUST Sm-T
----.--
" ' ' ' ' ' ..........
.....
, .
......_ ___ !ill -----------l~----------~----~2~--~s 12 ,. 2 e SEPT AUC\1$1'
-,
• ~-! c
IU a 0
~ 0
u -a
Q1 1D,~2 ----1-.----='2e~---:2----:~
Mean weekly discharge (upper),
chum spawning WUA for up 1 and
AUCUS'J' SEPT
II
Ml1M.
s 1 ough {middle) and percent
change in WUA (lower) exceeded
90, 50, and 10 percent of the
time for natural and Stage II
AlASKA POWER AUTHORITY
flows. FIGURE 58
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC.
232
HARZA·E BASCO
SUSITNA JOINT VENTURE
I
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·~.· 'U
f l ll '
bJ
u '
'
; .
...
10
•
········~-~--..... ··-
..
"'• ..... .....
...... :tOJII
•••••••·••· o•-................. ,
. o• ................. ···-~·-···· ·····-····-::r~·,···••o;oo,· ... o •
oL------,2----~,~.----~2~.----~~~----~.---~--
<( II
i 11
~ .
~a
..... ..... .....
' .....
'
,.
' '
AUCUST
AUouaT SIIPT
' ,.
2C
, .
~----
2 •
'SO'T'
~ 0 ~----===: ·"=::::::;:::::=--j!
u-a
2 ...
0 a::_..,
w --·
Q. -til··,!-----~ .,..[ ' 111
AUGUST
28 2 a
SEPT
ALASKA POWER AUTHORITY
Mean weekly discharge {upper),
chum spawning WUA for upland
slough (middle) and percent
change in WUA (lower) exceeded
~0, 50, and 10 percent of the
time for natural and early
SUSITNA ;~YDROELECTRIC PROJECT
~----~··------~------r-----·~a.--------------~
Stage III flows. FIGURE 59 EN'TRIX, INC.
233
HARZA·E BASCO
SUSITNA JOiNT VENTURE
fi
: J -~
10
•
-·
.. .. .. 10JII
··Cil···'lll······· ······Q·-·-10 •
~-----..~to.
----------------~~~ •••••o~•••••••••••••••••••···••••••;••••••••••·--~
oL-----------~,.~--~2~.----~2~----~.-----~ 1 2 AU OUST SIEJII'T
' ;; j.
~ ..
tl :II
~ I +-------------------10 t
0 -· ~ ~ ...
0
-=--..,
..------~~
A.--~· =====------------su
-·-----~---:;:t::-----t2-----;.
12 1G 2.e se:PT
Mean weekly discharge {upper},
chum spawn1 ng WUA for up 1 Jnd
AU OUST
s 1 ough (middle) and percent
change in WUA (lower) exceeded
90, 50, and 10 percent uf the
AlASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
t 1me for natura 1 and 1 ate
Stage III flows. FIGURE 60 HARZA·E BASCO ENTRIX, INC.
SUSJTNA JOIN-T VENTURE
234
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upland sloughs would be reduced by up to SO percent.
However, in September of ear 1 y Stage I I I, ava i 1 ab 1 e
habitat would be similar to natural conditions. During
late Stage III operation substantial reductions in
available habitat would occ.ur throughout the spawning
season in most years.
The contribution of upland sloughs to the habitat
ava i 1 abi 1 i ty provided by a 11 groups for natura 1 , ear l;y
Stage I I I operation, and 1 ate Stage I I I opeY~at ion is
shown in Figures 41 and 42. During early Stage III
operation a slight decrease in percent contribution is
expected in August, whereas in September percent
eontri but ion wfll approach ·natura 1 conditions,. During
1 ate Stage I I I operation, the range of percent
contribution will be more narrow than under natural
conditions and percent contribution will usually be less
than natural.
(v) All G·r·oups
-Primary Evaluation_Species
Chum Salmon Spawning Adults
The amount of available chum salmon spawning habitat in all
groups increases with increasing mainstem discharge over the
range of 5000 to 35,000 cfs (Figure 61). All groups snow
increases in available habitat between 5000 and 20,000 cfs.
However, side slough is the only group that shows an
increase in available habitat in response tomainstem
discharges greater than 20,000 cfs.
~35
..
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,_..,. ......,
'-'-
0""
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0 +-------11---·"-• --..•~·----+---__ __._. ---+----• ---+t---·-t
0 5 10 15 20 25 30 35 40
FLOW (thousand cfs)
Chum salm<~~n spawning habitat
response crurve for a 11 habitat
types in the middle Sus1tna River~
I
FIGURE 61
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC. HARZA·E BASCO
SUSITNA IOINT VENTURE
·!
"
~-----~-----------~
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Stage I
Filling
The available spawning habitat in all groups for dr~y,
average, and wet years during Stage I filling is
presented in Table 14. If a dry year occurs during the
filling period, spawning habitat will be reduced by
approximately 75 percent in August nad 45 percent in
September. If an average year occurs during the filling
period, spawning habitat will be decreased by about 70
percent in August, by almost 65 percent in September. A
decrease in available spawning habitat in August of 60
percent and in September of 70 percent is expected if a
wet year occurs during filling .
•• Operation
•
. .
Habitat availability in all groups under natural and
Stage I flows is compared in seasona 1 habitat duration
·curves and weekly habitat time series plots (Figures 62
and 63}. During Stage I operation, there is a 40
percent chance that available spawning habitat in all
groups would decrease from 0 to almost 70 percent during
August and from 0 to 20 percent during September.
However, there is an equal chance that available habitat
in all groups would slightly increase in August and be
up to 40 percent higher in September.
Stage Il
Filling
Filling flows for Stage II would be of short duration,
consequently habitat availability during this period is
more appropriately discussed under operation.
237
{ )
I
I
Table 14. Estimated change in chum spawning habitat (WUA} in all habitats due I
to filling of the Watana -Stage I Reservoir.
Month
Dry Year
August
September
Average Year
August
September
Wet Year
August
September
Discharge (cfsl
Natural Filling
17,392
10,422
22,228
13,221
25,236
15,124
8,000
5,800
12,415
6,800
15,505
6,800
238
Chum Spawning WUA (sg ft) _
Natural Filling %Change
213,372
68,893
345,063
121,116
418,154
154,036
52,412
39,353
106,056
43,057
168,206
43,057
-75.44
-42.88
-69 .. 26
-64.45
-59.77
-72.05
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--SfME2
-SiAII:l
-MitrME3
o ~-.--~.--~--.~----m~~--,~.----~,.
Percent Cif T i H Equaled or Exceeded
-*lUW.
- -STI.IiE t
--STAGE 2
-STMiEl
-MI S'TAiiE l
0 +----t-...:.---~---..._.~--~-~----:!1_ ca c P.1 --
Percent of Ti ae Equaled or Ex~~
-MTIM.
--S1ME1
--STIG: 2
-st'MIEl
-IMI STIG: 3
0 ~---------o(---:!f!I\~'--~-=---~,IIJ 31 42 ..; -
Percent. of T i ae Equa 1 ed or Exceeded
Flow duration curve {upper)
and seasonal (middle) and
maximum weekly (1 ower) chum
spawning habitat duratian
curve for all habitat types. ALASKA POWER AUTHORITY
SUS!TNA HYDROELECTRIC PROJECT
HAR2A·E BASCO
I 1
FIGURE 62 ENTRIX, INC.
SUSITNA JOINT V~NTURE
239
l. '
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j; .. _;J
,--~-~--. ·]'~:IJU~~~=w..,;;~,~~.!'~·-~t~:.\ ·.~
-· '"-~·-"--.• '.~t-.
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............... ,., .......
------.............. Q .... .:::::::~-
• •• Cit ................ o•
~1-----~----~,.~--~a;.----~a~----~.------,a AUOUST S~
........ .... '-.......... ______ IJI
,L------,~e------2~e------~2----~a
12 _..UGUST SEJIIT
• <II( i •
10 I ~ ..
w a ~ 0 t--========--------==·-= : i u-a ...
~-41
~--t-------w L ...
-t1 .L------~----~~----12------sg 12 HJ 215 S""..,... AUGUST .,,.., Mean weekly discharge (upper},
chum spawning WUA for all
habitat types (middle) and
STMiE t
percent change in WUA (lower)
exceeded VO, 50, and 10
percent of the ~i~ for
natural and Stage I tlows ..
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
FIGURE 63
HARZA·E BASCO ENTRIX, INC. SUSITNA JOINT VENTURE
240
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o• Operation
•
Habitat ava i 1 abi 1 i ty in a 11 groups under natura 1 and
Stage II flows is compared in seasonal habitat duration
curves and weekly time series plots (Figures 62 and 64).
During mid-August there is a chance that available
spawning habitat may be reduced by up to 50 percent.
However, during the remainrier of the spawning seasom
available habitat is expected to be similar to or
slightly greater than natural.
Stage III
• • Fi 11 i ng
Filling of Watana during Stage II! would occur· over
several years and consequently discussion of habitat
availability relating to this process i~; more
appropriately addressed under operation~
•• Operation
Habitat availability in all groups under natural, early
Stage III operation, and 1 ate Stage III operation is
compared in seasonal habitat duration curves and weekly
time series plots (Figures 62, 65, and 66). During
early Stage III, available spawning habitat could be
substantially reduced in August (up to 80 percent) and
slightly reduced in September. A gain in available
habitat of up to 30 percent could occur during 1 ate
August.
Under late Stage III operating conditions available
spawning wil1 be substantially reduced. A loss of 20 to
80 percent is expected throughout the spawning season 40
2~1
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.-------------~--------------~~~· --------------------------~
...
:s•
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10
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.... .... ....
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SEPT
~ 0 ~-------~-~~
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~:I _,J_, ____________ __,.
12 1e 20 2 M 1 ~UGUST ean week y discharge (upper), SEPT
M1tiW.
STAC£ a
chum spawning WUA for all
habitat types (middle) and
percent change in WUA (lower)
exceeded 90, 50, and 10
.----.... --..-.... ~.··---------------~
percent of the time for
natural and Stage II flows.
FIGURE 64
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC.
242
HARZA·F. BASCO
SUSITNA JOINT VENTURE
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••••e.. -----._
··-·········-···········.aOJI
,,.•••o•••••••c••••••••••••••••••••••• a.
............ .aOJII
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XATlM.
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MJGUST SEPT
1 0 +----;;;.___...._.
u "211 ...
Q--«1 u • c ...g)' w
4., -tO.!--------
-1-----------b-----~--~ 12 tO 28 2 I
Mean weekly discharge (upperj, AuGu~
chum spawning WUA for a 11
habitat types (middle) and
percent change in WUA (lower)
exceeded 9'0, 50, and 10
percent of the time for
natural and early Stage III
flows. . FIGURE 65
SEPT
ALASkA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
E~ITRIX, INC.
243
HARZA·E BASCO
SUSITNA JOINT VENTURE
ff
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- -... - - - - - -.\": -~-- - - -a ,. 28
AUGUST
~ 0 !---------------101
u -a ~-·----!D t ...
~ ..
CJ
ffi -w ----. sn
a. ... ~-=--------------1~JL-·-----2~8;----~2t __ ,;.9
'2 ;g SEr-T ~UGUST Mean weekly di~charge (upper),
chum spawni~g WUA for all
ALASKA POWER AUTHORiTY
habitat types (middle) and
percent change in WUA {lower)
exceeded 90, 50, and 10
percent of the time for
natura 1 and 1 ate Stage I I I
SUSITNA HYDROELECTRIC PROJECT 1-----------r·:¢·
flows. FIGURE 66 ENTRIX, INC.
244
-----.. HARZA-E BASCO
SUSiiNA JOINT VENTURE
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{c) Rearing
percent of the timeo Available habitat will be similar
to natural conditions only 10 percent of the time.
The principal effort in assessing impacts to the rearing life stage
of fish species in the middle Susitna River has focused on chinook
salmon juveniles, the designated primary evaluation species/1 ife
stage. In order to describe the dynamic and site-specific response
of juvenile chinook re~~ing habitat to flaw-related changes in this
reach of the Susitna River, a set of distinct subenvironments was
defined {ft.aserude 1985). This set of subenvironments consisted of
nine groups considered to be representative of the range of habitats
present in the middle Susitna River. The habitat for each group as
a function of mainstem flow was then modeled {Steward et al. 1985).
Response of rearing habitat to project conditions within each of the
representative groups and for all groups combined are discussed in
Sections 5.1.2(c)(i) below.
The low abundance of rearing life stages of the secondary evaluation
species in the middle Susitna River has precluded establishing
definitive seasonal utilization patterns
functions necessary for a quantitative
and habitat response
impact analysis. The
response of the rearing life stage of secondary evaluating species
are discussed in a qualitative fashion for each of the traditional
habitat types {mainstem, side channel, side slough and upland
slough) in Section 5.1.2{c)ii.
{1) Representative Groups
-Representative Group I
This group includes upland sloughs, which are highly stable
areas connected to the main channel at their downstream end,
except in times of high flow events, when they may be
245
overtopped by turbid mainstem watersG The habitat response
curve and percent contribution of this group to total middle
Susitna habitat are shown in Figure 67a.
Stage I
•
•
Weekly simulations of Gold Creek flows during the first
summer of filling were not undertaken, however estimates
of month 1 y flows during June and September indicate
1 evel s to be at or near E-VI minimum 1 evel s. Flow
levels during July and August would depend on the
hydrologic conditions of that year. Under dry
conditions flow releases in July and August would be at
the E-VI dry year minimum of 8,000 cfs. In an average
year July and August flows would be about 12,700 and
12,400 cfs and in a wet year about 20,500 and
15,500 cfs.
The rearing habitat available during Stage I filling
would be reduced substantially since flows frequently
would be near E-VI minimums, much below the flows that
provide the maximum habitat levels for this group.
Habitat associated with monthly flow estimates for June
through September would be reduced 14 to 22 percent in a
dry year, 3 to 18 percent in an average year, and 7 to
23 percent in a wet year (Table 15).
Operation
Habitat ava i1 ability under natura 1 and Stage I flows is
compared in a weekly habitat time series and a seasonal
habitat duration curve {Figure 67b and 68). The rearing
habitat provided by Stage I operational flows would be
246
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-..,.....
< :::J
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0 .........
f-
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GO CD 60 ......
HABITAT 0::::
t--z:
X CONTRIB 0
40
..._, .... '-"-u 40
t-z w
(_)
0::
20 20 w a_
0 0:t----45r=-:.:::"·-::-:::··::-::,:.:1~::-::··=-:=·-~1F~-::--:::··:=-::::··+20:::··:-:::-·::-~-2F5::.:.:··=-:::··=-=+3~=-:::··:-:::··:3a-5--..l40 O
Juvenile chinook rearing
habitat response ~urve and
per~ent contribution to total
rear1 ng hab1 tat of Group 1
areas 1n the middle Susttna
Rtver.
--~--------" -~~ " -"~·" ~"---
FLOW (thousand cfs)
fiiUit£ S7A
ALASKA POWER AUTHO.RITV
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC. HARZA·E BASCO
SUSITNA tOlNT VENTURE
' I' L ·r
1
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IT· :'#,
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Table 15. Estimated change in chinook rearing habitat in Group 1 due to
filling under dry, average and wet conditions.
Discharge { cf~;} Rearing Habitat {sg ft WUA)
Month Natural Fil 'I ing Natural Filling Change
Dry Year
June 21,763 7,800 72,419 58,605 -19.08
July 19,126 8,000 75,179 59,016 -21.50
August 17,392 8,000 75,075 59,016 -21.39
September 10,422 5,800 62j424 53,439 -14.3·9
Average Year
"lune 27,815 8,800 69,495 60,403 -13 .. 08
-July 24,445 12,740 69,735 67,365 -3.40
August 22,228 12,415 71,846 66,153 -7.92
September 13,22.1 6,800 69,020 56,314 -18.41
Wet Year
,June 31,S80 10,752 74,925 63,531 -15.21
July 21, ;r53 20,547 69,345 74,160 6.94
August 25,236 15,505 66,822 73i238 9 .. 60
September 15,124 6,800 7~!, 727 56,314 -22.57
24:3
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Percent of Time Equaled or Exceeded
Piow dur~tion curve and
chinook rearing hab1t~t
duration curve for Group 1.
.---------..... _.~,, ... -----.-..iiiii;;:l=-----..... .
AlASKA POWER AUTHORfTY
SUSITNA HYDROElECTRIC PROJECT
. .. __ Fi_·,_~ UR£ &t_a L. L------------~----m.-----~--.. ~~--~'~-~-~~~~--------~--.. ----~--------~--_. i+.; ~ ·~
ENTRIX, iNC • HARZA·f :~ASCO
SUSITNA JOINT VENTURE
249
.....
.. ... ...
10
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11D
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WAY JUNE
Mean weekly discharge (upper),
chinook rearing WUA for Group
1 (middle) afld percent change
in WUA (lower)exceeded 90, 50,
~nd 10 percent .of the t 1 me for
natural and Stage I flows.
I I 1 l 1
STMiE 1
JULY .fiUCUST SEPT
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
FIGURE 68 ENTRIX, INC. HARZA-E BASCO
SUSlTNA JOINT VENTURE
250
·:::::::.::::::::~
fi ~·>
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-reduct'!d as much as 28 percent i 11 1 ate May and gradua 11 Y
increase throughout the season. By early August
approximately half the time there would be an 1ncrease
in habitat and half the time a decrease. The magnitude
of ~.:he decreases, however, would be greater than the
increases. By mid-September rearing habitat in upland
sloughs would be greater under natural conditions.
The habitat within sloughs in Group I would have about
the same stability in June and July during Stage I as
natur~l and have less stability than that provided und~r
natural conditions during July through September (Figure
69}.
The percent contribution of Group I to the total habitat
available would exhibit less variability than levels but
would remain about the same {figure 70).
Stage II
•
•
Filling
Filling flows under Stage II would be of short duration
and discussion of habitat availability are deferred to
Stage II operation.
Oper~tion
Habitat availability under natural and Stage !'' flows is
compared in a weekly habitat time series plot and
seasonal habitat duration curves {Figures 67 and 71).
Reductions in rearing habitat during Stage II operation
would be of greater magnitude and frequency than under
Stage I and natural flows for the rearing period through
mid-August. From mid-August to mid-September the
habitat available would be similar to that under natural
251
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r~ ·~ ..•
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1!50
!
i 100
!
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11.
0
27 3 1 o 17 2~ 1 a 1 s 22 2sa s 12 1 sa 2a :z sa 1 a
MAY JUNE JU~Y AUOUST SEPT
MAY
Percent change in flow {upper)
and chinook rearing habitat
{lower) from previous week in
Group 1 during Stage I
exceeded 10, 50 and 90 percent
of the time.
FIGURE 69
.JULY AUGUST
2 9 16
SEPT
--STAGE 1
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC.
252
HARZA·E BASCO
SUSITNA JOINT VENTURE
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STAiiE Z
MAY JUNE JUL'Y AUCiJST S£PIT
I :~---~~==---~--II §:
6-e
L ...
Mean weekly discharge (upper),
chinook rearing WUA for Group
1 (middle) and percent change
in WUA (lower)exeeeded 90, 50,
and 10 percent of the time for
natural and Stage II flows.
FIGURE 71
AUCUST
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC ..
254
HARZA·E BASCO
SUSITNA JOINT VENTURE
,. ,_
j ~-
'
conditions but decreased somewhat from Stage I
operational flowso
The highly stable nature of the habitat within the group
as measured by week to week changes in availability is
depicted in FigU,re 72.
The contribution of habitat· within this group to the
total middle Susitna River reari~g habitat is quite
sma 11 , a 1 i ttl e over 1 percent for both natura 1 and
project conditions (Figure 73). Co~sequently reductions
·in habitat amounting to 20-30 percent represent only a
fraction of the overall habitat.
Stage Ill
,
•
Fi11 ing
Filling flows during Stage Ill wou1d be similar to those
during operation and therefore juvenile
habitat-flow relationships are discussed
section.
Ooeration
chinook
in that
Habitat ava i 1 abi 1 i ty under natura 1 ant:~ early and 1 ate
Stage III flow.s is compared in weekly habitat time
series and seasonal habitat duration curves (Figures 67,
74 and 75). The rearing habitat provided by early Stage
III operational flows would be about 10-20 percent less
than natural in June, 0-20 percent less than natural in
July to mid-August, and by mid-September would be
similar to that provided by natural flows. In late
Stage III, reduction in habitat would be similar to
early Stage I I I through June; however, in contrast to
255
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-~o._~--~~~~~--~-·~~-+•--~~--~1--~~~~--+-~--~--~_.~
-«J M -
2? 3 10 17 2.. 1 • 15 22 2g s 12 ,g 28 2 g 18
MAY JUNE .rui..Y AUCUST SEPT
_.__ S"(Ab£ 2
-50 -. ·-f-I • I t I f t t I
~ 71 3 10 17 a~ 1 8 15r 22 29 5 12 19 28 2 9 1 s
.JI.JNE .JULY AUGUST SEPT
r -sr ··-AL.J..SKA POWER AUTHORITY
SUSITNA HYuROil~CTRIC PROJECT
••
Percent change 1 n fl ow ( \~pper)
and chinook rearins babitai;
(lower} from previous week in
Group 1 during· Stage II
•xceeded 10, SO and 90 percent
of the time,.
·-~--_.. _____ _.
f.IGURE; 12 ENTRIX, INC.
256
HARZA·EBASCO
SUSITNA JOINT VENTURE
·Wtt 'Ill'
·~r-..-...... ~) .. w.• '~~ _..,..-... ~ .... ~ .. --. .,_...__," __ '"""/}__, __ , ... .,....>.,~-.... --~,
(
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GROUP 1
5
~211 -~ a: 15
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MAY .1\JNf:
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z I
0
5
CD a:• ~
0 u §4
a: ~2
I
......
I
JULY
..... __________ _
--------,
~,--_____ \
\
\ \
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I I I I
UAY JtJNE JULY
YAY .IUNI: JULY
\
\
\
\
SO"T
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AUGUST s~ UA'f JUNE
GROUP 7 tO
~·
iil 0:5
§
u
I' 2
D
loi)OUST
Percent contrtbutton of
chtnook reartng habitat ta
Cnups 1-t tt total habitat
during Stage II ..
257
-~· ·-·-.... .., ..... -""'. --·~ ......
~ . -:. "
'r ,.__.., \ .~ .... , ,,.· ••• '":,.
JULY
JULY
.M.Y
. . '
GROUP 2 !II' GROUP 3
~..,
i
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[ I
I I -? _______ L ___ I
II
AUGUST SD'T ..... y
GROUP 5
!i: to
Ul
~5
0
AUGUST SEPT UAY
GROUP 8 25
!211
~
0: 15
~ u r II
..
0
ALIOUST WAY
FIGURE 73
,·
JUNf: .JULY AUGUST SEPT
GROUP 6
\
\
\
~
I I
I I
J I
/ I
I J -:: ---"
JUNE JULY AUGUST SEPT
GROUP 9
IIAlUW..
STM£2
JUNC JUL.Y AUQUST SEP'T
I
ALASKA POWER AUTHOR!"TY
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC. HARZA·E BASCO
SUSITNA JOINT VENTURE
... . .. : ... ,. . . ' ..
f' ' • ' • ~
. '"',•"'• ( ...
t4 •• t
i '
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i ,. . . . . : . . • 10 • ____ ._.,., ' .,..•.: ••••• c. ............... .
·······.~o• il
0· -
•
Mean weekly discharge (upper),
chi nook rearing WUJ~ for Group
1 {middle) and percent change
in WUA (lower)exceeded 90, 50,
and 10 percent of the time for
natural and early Stage III
flows.
FIGURE 74
·~
STAGE 3
.IULY
ALASKA POWER AUTHORITY
SUSITNA HYDROEltCTRIC PROJECT
ENTRIX, INC.
258
--HARZA·E BASCO
SUSITNA JOINT VEN'TURE
'.
-~~
..
••
•
.. .... ~ .... ·····~-.. .
• •••••••••••••••••::•••••o••••••••••••
-···········---~·~--------~~ . -·····
·~--~----------~--·--~~~~-----~--~~------~-~7.~
fCID -MATUW..
IIAXSTMiEl
f.
I a• i
& e.•
~ ~~~
I t t I t I I I f I I I I I I t t
• i •
i 41
~ 211
JULY
~ 0~ ~==-==:::::::::::::::=::::=.,
!· ~--L ...
Mean weekly discharge (upper),
chinook rearing WUA fdr Group
1 {middle) and percent chan~e
in WUA (lower)exceeded 90, SO,
and 10 percent of the time for·
natura 1 and 1 ate Stage I I I
flows.
FIGUR.E 75
AU CYST
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTJUC PROJECT
ENTRIX~ INC.
259
HARZA~E BASCO
SUSITNA JOINT VEN'fURE -
•
early Stage III, rearing habitat in late Stage III would
remain at depressed levels through mid-September.
With-project stability of upland slough habitat in both
stages would increase early in the season during the
annual filling process. Later, during July and August,
the weekly percent. change in habitat would increase
under early and late Stage· III flows (Figures 76 and
77).
The percent contribution of upland sloughs to total
habitat available would be similar for both natural and
Stage I I I flows, about 1 to 1. 5 per1Cent, a 1 though the
variability would be somewhat less with project (Figures
78 and 79).
Representative Group 2
This groups consists of side sloughs with with moderately
high breaching flows (>20,000 ~fs) and enough upwelling \
groundwater to keep portions of the sites ice free during
the winter months. Duri n~J the su11111er rearing season, the
sites within the group are some of the more heavily utilized
ones by chinook juveniles, particularly in the breached
state. The habitat response and percent contribution of
this group to total middle Susitna River habitat is shown in
Figure SCL
Stage I
Fi 11 iillg
The rearing habitat available during Stage I filling
would be reduced substantially since flows frequently
woul'd be near E-VI minimums, much below the natural
260
aoo
1~0 ~
i 100
~
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~ ~ ~0
u
ffi
ffi a.
, •• . ' • • I I
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1 •• ' .. ~ ' \
' ' \
'---""'-'
3.7 3 10 17 2'4 1 8 1~ 22 2S 5 t2 1S 28 2 S 18
'~JAY JUNE JULY AUCJ-JST SEPT
i 3)
~ 20
-10 i ~ I o
f.'--·10 •
~ -~.i
< -3) t
i ·-«lit
-.50-+ I I I I
STAGE 3
--
I I t + I
20 27 3 10 17 2.C 1 8 15 22 29 s I I I lo ---+--!
12 19 26 2 s 1i
MAY .JUNE
Percent change in flow {upper)
and chi nook re,ari ng habitat
(lower) from previous week ·ln
Group 1 during early Stage III
exceeded 10, 50 and 90 percent
of the time.
FIGURE 76
.JUL.Y AUGUST SEPT
AlASKA POWER AUTHORITY
SUSJTNA HYDROELECTRIC PROJECT
ENT.RIX, INC.
261
HARZA-E BASCO
SUSlTNA JOINT VENTURE
..,
' .
••
I
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I
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I t • •
0"
-so~-+--~~--~~--~~--~~--~--~-~--~~--~~--~~
27 ~ 1 o 17 24 1 a 1 s 22 2sa s 12 1s 28 2 • 1 8
MAY JUNE JUL.Y AUCUST SEPT
MAX STAGE 3
-50 t I I I l f I I t I I I
20 ll 3 10 17 24 1 8 15 22 29 5 12 19. 2S 2 9 16
MAY .JUNE
PercQnt change in flow (upper)
and chi nook rearing habitat
(lower) from previous week in
Group 1 during late Stage III
exceeded 10. 50 and 90 percent
of the time.
FIGURE 77
.JUL.Y AUGUST SEPT
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC.
262
HARZAvE BASCO
SUSITNA JOINT VENTURE
..
----------~--------.._
IJ . .
'1.
5 GROUP 1 GROUP 2 !Ill GROUP 3
11 t
a• 531 ~CI ..,., -~l ~ i ~
Q!J a: ~!I 0::11 g ~ g
u (.J (.J r -[ ~31
~ tO \_-"
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I
-7----~---~------.J '
0 , .... 0 .-+-0
YAY .IUNI!: JULY AU OUST SI!JI"T tU.Y .IUNI!: JULY AUGUST SEP1' YAY .IUNI!: JULY AUGUST SII!:PT
GROUP 4 to GROUP 5 2!S GROUP 6
~ID 5' ~31
~.,. -~ .... ,..,, !:; , __ , ------...... -...... ~· CD -c ...__----~--, --.. a: .t5 § ... '\ tr.' ,.._ ....
\ a :z
0 I u \ u (.J f; r· \ ~ 4 ~ tD I i UJ I u ..... , l ffi a: I UJ
31 a.. 2 a.. 5 _;~~~~~---L-L ____
\ J . •
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(
0 ,._.
I .
t.IAY .IUNI!: JULY AUGUST s~ MAY JUI'tl: Jt!LY AUGUST SEPT UAY .JUNE JULY AUGUST SEPT
to GROUP 7 10 GROUP 8 Zl GROUP 9
' -I
I
:Z I ,-==r-----z:!ll I
0 0 l
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\ I
~' \ ii: 1!1 I
!z !z L
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__ _,
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2 I r·
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loiAY .IUN!: .JULY AU OUST Sti"T t.&4Y .JUNE JULY AU OUST KPT MA'f ..UNE .JULY AU truST SEPT
j
I
l
i ~
contrtbutton of ' Percent ALASKA POWER AUTHORITY l chinook rearing habitat tn
Groups 1-9 to total habttat SUSITNA HYDROELECTRIC PROJECT I
during early Stage III. I
ENTRIX, INC~ HARZA·EBASCO I FIGURE 78 SUSITNA JOINT VENTURE l ~ ~ 263 I
I
i
:::.:".\.~
I
!i ~ -~
Q:J
§
u
I' 1
D
10
GROUP 1
W.Y .JUNE .JULY AUGUST
GROUP 4 to
/ . ,----... /--.... __ ,,
/ ....
\
\
UAY .JUNE .JULY AUGUST S!PT
GROUP 7
10
.JUNE .JULY
MAY JUNE JULY
GROUP 2
AUCUST
GROUP 5
AUGUST SEPT
GROUP B ·
....
I' 1·\~ I \ I I
I \ I
:\ \
I \ \
,' ~\ I \
I . ____ ......... ..;
D ~.....-~>=-<-......:'----------~---=-• au.Y
Percent contribution of
chinook rearing habitat 1n
Groups 1-t to total h1bitat
during late Stage III.
264
JULY AU OUST
FIGURE 79
II GROUP 3
au.y .JUNE JULY AUCUST SEPT
25 GROUP 6
UAY JUNE JULY AUGUST SEPT
25 GROUP 9
JUNEf
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
HARZA·£8ASCO ENTRIX, INC. SUSITNA JOINT VENTURE
• • ,_.. ' •. ;.J ...
jA' ••
N
0\
U1
•
--·~---.. ·-.. . ·--·--·-----.. "---··--·----. F··= ·r-~~~ F -r ·-
....--
r---E -
<C
:::J
3: .... ----------___ _.... ___________ ... __
-------~
, .. .,/
HABITAT
__ .. _ X CONTRIB
~----------------------· --
100
80
60
20
:z
0 .......
0::: .,_
:Z'
0
(J
t-z w (J.
cr; w a..
0 +-----~------~----~~----~------+------;------~------+0
0 5 10
Juveni 1 e chinook rearing
habitat response curve and
percent contribution to total
rearing habitat of Group 2
areas 1n the middle Sus1tna
River.
15 20 25 30 35 40
FLOW (thousand cfs)
~------------~c----------------------~ A L A S K A ·P 0 W E R A U T H 0 R I T Y
SUSITNA HYOROELECIRIC PROJECT
~----------------~.~~--------------·
FIGURE 80 ENTRIX, INC~ SUStTNA JOINT VF,NTURf
HARZA·E BASCO
c, \ ,,
flows that provide the higher habitat levels for this
group.
Habitat associated with monthly flow estimates for June
through September would be reduced 19 to 61 percent in a
dry year, 31 to 71 percent in an average year, and 40 to
75 percent in a wet year (Table 16).
•. Ooeration
Habitat availability under natural and Stage I flows is
compared in a weekly habitat time series and a seasonal
h~bitat duration curve (Figure 81 and 82)o Stage I
flows would result in habitat reductions of approxi-
mately 20 to nearly 80 percent through early August.
During August and September about half the time there
would be a decrease in habitat and half the time an
increase over natural conditions.
The habitat within s 1 oughs in Group 2 would be more
stable in June and July during Stage I and have about
the same stability as that provided under natural
conditions during July through September (Figure 83)o
The percent contribution of Group 2 to the total habitat
available would decrease from natural levels of
approximately 10 to 23 percent to Stage I values of 6 to
9 percent from the end of May to mid July. The percent
i
I
I.
I
I
I
I
I
I
I
I
I
I
I
contribution of ~roup 2 waul d increase through the I
remainder of the season and by the end of August
approximate natural level (Figure 70)o ~~
266
I
I
~ ·~-"'~.!
r
ill ,.
', '
r
r
r
r
r
L ..
Table 16. Estimated change in chinook rearing habitat in Group 2 due to
filling under dry, average and wet conditions.
Month
Dry Year
June
July
August
September
Average Year
June
July
August
September
Wet Year
June
July
August
September
___ Discharge (cfs)
Natural Filling
21,763
19,126
17,392
10,422
27,815
24,445
22,228
13,221
31,580
27,753
25~236
15,124
7,800
8,000
8,000
5,800
8,800
12,740
12,415
6,800
10,752
20,547
15,505
6,800
Rearing Habitat (sg ft WUA)
Natura 1· Fi 11 i ng Change
678,304
528,973
469,579
301,335
1,306,241
978,032
717,305
366,080
1,209,072
1,305,358
1,087,103
419,100
267
261,826
264,810
264,810
244,373
279,140
350,286
341,036
251,124
306,904
605,570
428,237
251,124
-61.40
-49.94
-43.61
-18.90
-78.63
-64.18
-52.46
-31.40
-74.62
-53.61
-60.61
-40.08
p
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t ..
l
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• I••
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i ,.
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0~~------~=-----~~--~~=----------.... .,. .AA.'V' AUOUWT
1.1
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t.z
f
I \ ,I I ·• ~ a .• 101
i
.3
a
WAY JUNE JULY
• i •
; .
to r ¥ •
j·~~-T----~--~~~---11 ..
§ ..
s ..
&. .. ~------
Mean weekly discharge {upper),
chinook rearing WUA fo~ Group
.2 (middle) and percent change
1n WUA (lower)exceeded 90, 50,
and 10 percent of the time for
natural and Stage I flows.
FIGURE 81
JULY
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
SUSITNA JOINT VENTURE
HARZA·E BASCO ENTRIX, INC.
268
I
I
I .
I
I
I
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I
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I
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i
t
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0
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0 ....-
)( ,
4-
CJ -
3:
0
...J u..
3
2
-----.....
1 --
_NATlJW..
__ STAG£1
_-STAGE 2
_STAii£ 3
_MAX STAGE 3
0 ~--+---~+---r---~~~~~~~.--~--~~~-4--~100'
Per~ent of Time Equaled or Exceeded
Group 2
-NATURAL
--STAGE 1
--STAGE 2
-STAGE 3
--MAX STAGE 3
20 .4Q 6tl ~ 100
Percent of Time Equaled or Exceeded
Flow duration curve and
chinook rearing habitat
duration curve for Group 2. ALASKA POWER. AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
FIGURE 82 ENTRIX, INC.
269
t-IARZA·E BASCO
SUSITNA JOiNT VENTURE
f1
1, i.
r ·'
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r~
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l:,
t
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200
1~0
-M .....
i ~ § -20 i I a
I~:
....
·~-, .. ....
' ..
' .. .. ..
' .. .. ....
,. .. ·~ -·
\
' ' ' '
10X
\1on
'iO %
I
STAGE 1
-1 ~-+--+--r---+----4-+---+--+--+-~~--+-·· .. I t • t---4
m 21 3 10 17 2~ 1 e 15 22 29 5 12 19 2S 2 9 1s
~UNE
P1ercent change in flow (upper)
a1nd chinook rearing habitat
(low£r) from previous w~ek in
Group 2 during Stage I
exceeded 10, 50 and 90 percent
o-f the time. FIGURE 83
AUGUST !'lEPT
~:----------------------~----------------~ ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
~~----------------~--------~-------~--~
ENTRIX, INC.
270
HARZA·E BASCO
SUSlTNA JOINT VENTURE
l
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•
• •
Stage II
Filling
Filling flows under Stage II would be of short duration
and discussion of habitat availability are deferred to
Stage II operation •
•• Operation
Habitat availability under natural and Stage II flows is
comparerl in a weekly habitat time series plot and
seasonal habitat dur'ation curves (Figure 84 and 82).
Stage II operational flqws would result in habitat
reductions while May and June ranging from 20 to 80
percent with over half the reduction being greater than
60 percent.. Beginning in July the magnitude of the
reductions would decrease until mid-August at which time
the rearing habitat under Stage II would be equal to or
greater than that available with natural f1ows. This
pattern would continue through mid-September.
The stability of Group 2 would increase with-project
during June; however by July week-to-week changes would
increase substantially, sometimes exceeding 100 percent.
Stabi1 ~ity at the end of August through mid-September
would be similar to natural conditions (Figure 85).
The percent contribution of Group 2 to the total
available habitat would decrease from a range of 6 to 22
natura 11 y to about 6 percent with-project during 1 ate
May and June. The contribution of Group 2 would
incY'fJase through mid-summer and by mid August and
thr~ugh mid-September would be similar to ·natural
conditions (Figure 73}.
271
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f ~· .
f' lj
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L.
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(.18
·~ • 1 ..
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; ,.
10
•
• • ' • • . .... .
••
4
: • eiP" .. ::•• • ••• • • • • •, • • . .· ......
. ..
••..,•••••••••o
. .· .
0~~------~~----~----~~----------.AA.'f' AUOUII'i' ~
t.s
1.Z
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3 :i .• ....
/
I
, ___ .,.--..... --. ST~ Z
,,.
J J
~----::::. ___ ..,.,
0
WAY
Mean weekly discharge (upper),
chinook rearing WUA for Group
2 (middle} and percent change
in WUA (lower}exceeded 90, 50,
and 10 percent of the time for
natural and Stage II flows.
FIGURE 84
JULY AUQUST · SEPT
JULY AUCUST
AlASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC.
272
HARZA·E BASCO
SUSITNA JOINT VENTURE
•
I
I
I
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r .
.......
r·
f It
L
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l
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1.
200
1~0
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~ ~ ~0
~
LW
(.) a:: w a.
0
' . ' I \ / .
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I \
··----
' ' \
----~ . .. .. .. .. ...... .. ....
• •• I l
c ' , ••••
I l I I
I I I I
I 1 I I
I \ 1 I
I I 1 I ' , ' ' ' ' • ',1 !
I I
I I
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t
I
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I, . .. . .. .. ' .. ' . ' ' . ' ' ..... ~ /0" .v
-so--~~~~~~~--~~--~~--~~--~~--~~~~~~~
27 3 1 o 1 7 24 1 a 1 s 22 2a s 12 1 a 28 2 8 18
MAY JUNE JULY AUGUST SEPT
1 \ NAlUW..
-M STJ\GE 2 -
i
~ 10 X ...
i ~ 0
I~:
-1 I I I I I I -1 . I I · t I . I f
20 Zl 3 10 17 2. 1 8 15 22 29 5 12 19 26 2 9 16
MAY .JUNE
Percent change in flow (upper)
and chinook rearing habitat
(lower) from previous week in
Group 2 during Stage II
exceeded 10, 50 and 90 percent
of the time.
FIGURE 85
..JUI..Y AUGUST SEPT
ALASKA POWER AUTHORITY
SUS IT N A H Y 0 R 0 ELECTRIC P R 0 J E CT
ENTRIX, INC. HARZA·EBASCO
SUSITNA JOINT VENTURE
273
0
• •
Stage III
Filling
Filling of high Watana would occur over a period of
several years and therefore rearing habitat availability
is more appropriately discussed under Stage II I
operation.
.• Operation
Habitat availability under natural and Stage III flows
is compared in weekly habitat time series plots and
seasonal habitat duration curves (Figures 86, 87 and
82). Stage III operational flows would result in
habitat reductions similar to Stage II, 20 to 80 percent
in 1 ate May and June with over ha 1 f the reduct i ems
greater than 60 percent. In July the magnitude of
reductions would decrease and continue this trend
through August. By September the habitat availability
would approximate natural conditions. In the iate Stage
III, the annual filling process would continue in July
extending the period of habitat reductions through that
month. In August through September, habitat would
increase by remain below that available for natural,
Stage II and early Stage III conditions.
The stability of Group II would increase during late May
and June of early Stage III (Figure 88). In late Stage
III this increased stability would extend through July
and August as flows are maintained at or above E-VI
minimum constraints {Figure 89).
The contribution of Group 2 to the total available
habitat would ~ecrease from a range of 6 to 22 percent
maturity to about 6 percent in early Stage III during
274
..
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c~·
fa
• In
I~· i ,. . . . . . . . ' . ' ' ' . . ,. ................ ~.--.. ..-.;-·.i •• -••• -•• -•••••••••••••
• ...... 0 • •
0
1.5
t.~
f
a .•
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0
3
5 •• ......
D
•
~ .
:1
; .
Ill 31 0
"""' . .,..,.
STAG~: 3 _ ...
lll'l
JUNE JULY AU OUST
~ • ~----4-----,..---.---,.~~~-j i
u -· 2-c u
~ ...
L ... r--.:;._ _ ___:::::;:_ ____ __,
~~~~-+-+-+~~~----~~.-------~~ .IUNE
Mean weekly discharge (upper),
chinook rearing WUA far Group
2 (middle) and percent change
in WUA (lower)exceeded 90, 50,
and 10 percent of the time for
natural and early Stage II1
flows.
FIGURE 86
.IULY AUGUST
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC.
275
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1 n WUA ( 1 ower) exceeded 90, 50 t
and 10 percent of the time for
natura 1 and 1 ate Stage I I I
flows.
FIGURE 87
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and chinook rearing habitat
(lower) from previous week in
Group 2 durihg early Stage III
exceeded 10, 50 and 90 percent
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FIGURE 88
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Percent change in flow (upper)
and chi nook rearing habitat
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exceeded 10, 50 and 90 percent
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MAX STAGE 3
10%
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SUSITNA HYDROELECTRIC PROJECT
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278
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late May and -Ju0e. Increases in July would bring the
Stage III contribution to natural levels around August
(Figure 78). In late Stage III the 6 percent
contribution level would extend through July with some
increase in August and early September but natural
levels would not be reached (Figure 79).
-Representative Grouo 3
This group consists of side channels which breach at
intermediate mainstem discharges (8,000 to 16,000 cfs) and
transform into side slough at lower discharge. In contrast
to Group 2 side channels, sites within this group are larger
and convey greater volumes of water when breached.. In
addition, sites comprising this group represent some of the
~
most heavily utilized rearing areas in the middle Susitna
River under breached conditions. The habitat response and
percent contribution to overall habitat availability of this
group is portrayed for the range of natural and with-project
flows in Figure 90.
__ , Stage I
Filling
The rearing habitat during Stage I fi 11 i ng would be
reduced substantially since flows frequently would be
near E-VI minimums, much below the flows that provide
the higher habitat availability for this group. Habitat
associated with monthly filling flow estimates for June
through September would be reduced by 87-88 percent in a
dry year, 10-92 percent in an average year, and 22 to 93
percent in a wet year (Table 17}.
279
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Juveni 1 e ch1 nook rearing
habitat response curve and
percent contribution to total
rearing habitat of Group 3
a.reas in the m1 ddl e Sus 1 tn;
River.
FLOW (thousand cfs)
FIGURE g·o
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
ENT.RIX, INC. HARZA·E BASCO
SUSITNA JOINT VENTURE
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~ Table 17. Estimated chang~ in chinook rearing habitat in Group 3 due to
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filling under dry, average and wet conditions.
Discharge _{ cfs) Rearing Habitat (sg ft WUA)
Month Natural Filling Natural Filling Change
Dry Year
June 21,763 7,800 1,178,308 137,604 -88.32
July 19,126 8,000 1,293,441 150,046 -88.40
August 17,392 8,000 1,284,701 150,046 -88.32
September 10,422 5,800 553,277 73,345 -86.74
Average Year
June 27,815 8,800 843,033 229,381 -72.79
July 24,445 12,740 993,691 1,101,905 10.89
August 22,228 12,415 1,153,420 1,035,368 -10.23
September 13,221 6,800 1,166,589 96,193 -91.75
Wet Year
June 31,580 10,752 816,422 635,484 -22.16
July 27,753 20,547 844,924 1,250,440 47.99
August 25,236 15,505 951,618 1~365,033 43.44
September 15,124 6,800 1,347,903 96,193 -92.86
281
• Ooeraticm
Habitat availability under natural and Stage I flows is
compared in a waekly habitat time series plot and
seasonal habitat duration curve (Figure 91 and 92)o
Stage I flows would result in increases in habitat about
half the time and decreases in habitat about half the
time throughout the summer rearing period. From the end
of August tnrough mid-September, the magnitude of
habitat increases W{>U1d greatly exceed the habitat
decreases.
The stability of habitat in Group 3 sites would be less
in May and early June thatv naturally and about the same
for the remainder of the season (Figure 93)e
The contribut1on of Group 3 to the habitat availability
provided by all groups would be sl·ightly less than
natura 1 ~ in 1 ate Mat and about the same as natura 1 for
the rest of the season (Figure 70)e
Staqe II
•
•
Filling
Filling flows under Stage II would be of short duration,
consequently habitat availability during this period is
more appropriately discussed under· operation~
Ogeration
Habitat availability under natural and Stage II flows is
compared in a weekly habitat time series plot and
seasonal habitat duration curves (Figures 94 and 92).
Stage II operational flows would result in habitat
reductions from 0 to 80 percent with refraction of 70
282
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Mean weekly discharge (upper),
chinook rearing WUA for Group
3 (middle) and percent change
in WUA (lower) exceeded 90, 50,
and 10 percent of the time for
natural and Stage I flows.
FIGURE 91
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HARZA·E BASCO ENTRIX, INC. SUSITNA JOINT VENTURE
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Percent of Time Equaled or Exceeded
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Percent of Time Equaled or Exceeded
Flow duration curve and
chinook rearing habitat
duration curve for Group 3. ALASKA POWER AUTHORITY
SUSIT'NA HYDROELECTRIC PROJECT
FIGURE 92 ENTRIX, INC.
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Percent change in flow (upper)
and chinook rearing habitat
{lower) from previous week in
Group 3 during Stage I
exceeded 10, 50 and 90 percent
of the time.
8
FIGURE 93
a 15 22 251 5 12 11 28 2 ' HI
JULY AUCUST SEF'T
NAlUW..
STAGE 1
50%
9.1%
15 22 29 5 12 19 2S 2 9 16
.JULY AUGUST SEPT
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SUSITNA HYDROELECTRIC PROJECT
ENTRIX, iNC.
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Mean weekly discharge (Upper},
chinook rearing WUA for Group
3 (middle) and percent change
in WUA (lower)exceeded 90, 50,
and 10 percent of the time for
natural and Stage II flows.
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
HARZA·E BASCO ENTRIX, INC. FIGURE 94 SUSITNA JOINT VENTURE
286
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percent or greater about half the timea In July the
magnitude of the reduction would decrease and by mid-
August habitat availability would be about the same as
natural.
With-project habitat stability would decrease
substantially primarily as in week-to-week increases in
habitat during July and August that may exceed 300
percent (Figure 95).
The contribution of Gt'oup 3 to total middle Susitna
River habitat would decrease under Stage II from naturag
levels of 15 to 25 percent to 5 to 15 percent in May am,!
June. The percent contribution would increase during
July and would be similar to natural from mid-August to
mid-September (Figure 73).
Stage III
Filling
Filling of Watana during Stage III would occur over
several years and consequently dicussion of habitat
availability relating to this process are more
appropriately addressed under operation •
•. Operation
Habitat availability under natural and early and late
Stage III operation are compared in weekly habitat time
series plots and seasonal habitat duration curves
(Figure 96, 97 and 92). Early Stage III operational
flows would result in substantial reductions in habitat
through July at which point the frequencies of reduction
waul d decrease to about ha 1 f the time. In 1 ate Stage
III reductions of 40 percent or more would be prevalent
287
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MAY .JUNE
Percent change in flow {upper)
and chinook rearing habitat
(lower) from previous week in
Group 3 during Stage II
exceeded 10, 50 and 90 percent
of the time.
FIGURE 95
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STAGE 2
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15 22 29 5 12 19 26 2 9 1S
.JULY AUGUST SEPT
ALASKA POWER AUTHORITY
SUSITNA HYOROELECTRtC PROJECT
ENTRIX, INC.
8
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SUSITNA JOINT VENTURE
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Mean weekly discharge (upper),
chinook rearing WUA for Group
3 (middle} and percent change
in WUA (lower)exceeded 90, 50,
and 10 percent of the time for
natural and early Stage III
flows.
ALASKA POWER AUTHORITY
FIGURE 96
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ENTRIX, INC.
289
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SUSITNA JOINT VENTURE
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Mean weekly discharge (upper),
chinook rear-ing \1UA for Group
3 (middle} and percent change
in WUA {lGwer}exceeded 90, 50,
and 10 percent of the time for
natural and 1 ate Stage I~l
flows.
~--·---------------------------------------~
FIGURE 97
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
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290
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at least 50 percent of the time for the majority of the
rearing period.
Stability during early and late Stage III would be less
than natura 1 , expressed principally as 1 arge
week-to-\~eek increase in habitat during early June, July
and early August (Figure 98 and 99).
The contribution of Group 3 to middle Susitna River
rearing habitat decrease from natural levels of 15 to 25
percent to Stage III levels of 5 to 15 percent in early
summer to 5 to 25 percent in the second half {Figures 78
and 79).
-Group 4 -Side Channels
The group is comprised of side channels with low breaching
discharges, intermediate to high mean reach velocit·ies, and
substrates consisting primarily of cobbles and boulders.
This group pro vi des a substantia 1. amount of the rearing
habitat within the middle Susitna River as evidenced by the
high utilization of these sites by juvenile chinook salmon
during the summer months. The habitat response and percent
contributions of this group to middle Susitna River rearing
habitat ar·e depicted for a range of mainstem discharges
{Figure 100).
• Stage I
Filling
The rearing habitat during Stage I fi 11 i ng waul d be
increased substantially since flows frequently would be
near E-VI minimums, which are flow levels that provide
the gre:ater habitat avai 1 ability for this group than
higher natural flow. Habitat associated with monthly
291
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t.IAY JUNE JULY AUCUST SEPT
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20 27 3 10 17 2~, 1 8
MAY ..JUNE
Percent change in flow (upper)
and chinook: rearing habitat
(lower) from previou.s week in
Group 3 during early Stage III
exceeded 10, SO and 90 percent
of the time.
FIGURE 98
• . / l \,/ • \
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I t I I I t I I I -f
15 ?2 29 5 12 19 2S 2 9 16
.JUL. Y AUGUST SEPT
ALASKA POWER AUTHORt.TY
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INCc
292
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20 Zl 3 10 17 2. 1 8 15 22 29 5 12 19 26 2 9 16
MAY .JUNE .JUL.Y AI,J~~~T §~PT
Percent change in flow (upper)
and chi nook rearing habitat
(lower) from previous week in
Group 3 during late Stage III
exceeded 10, 50 and 90 percent
of the time.
FIGURE 99
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC.
293
HARZA-E BASCO
SUSITNA JOINT VENTURE
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HABITAT
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,.......~ ~ f"""""""
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. 100
80 :z
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0 T-----+-----~----~----~----~----~----~----~0
0 5 10 15 20 25 30 35 40
Juven i 1 e chi nook rearing
habitat response curve and
percent contribution to total
rearing hab1 tat of Group 4
areas in the middle Susitna
River.
FLOW (thousand cfs)
FIGURE 100
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC. HARZA·E BASCO
SUSITNA IOINT VENTURE
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filling flow estimates for June through September would
be increased 28-128 percent in a dry year, 55-158
percent in an average year, and 10~107 percent in a wet
year (Table 18) •
•. Operation
Habitat availability under natural and Stage I flows is
compared in a w~ekly habitat time series plot and
seasonal habitat duration curve {Figure 101 and 102).
Stage I flows would result in substantial increases in
habitat throughout most of the summer rearing period.
From the end of August through mid-September, the
magnitude of habitat increases would decrease somewhat
and about half the time decreases would occur.
The stability of habitat in Group 4 sites would be
greater in May and June than natural and about the same
for the remainder of the season (Figure 103}.
The contribution of Group 4 to the habitat provided by
all gruups in the middle Susitna River would be at
levels much higher than natural for the rearing period
through mid-August. In late August and September
contribution levels would be similar to natural (Figure
70).
Stage II
• Filling
Filling flows under Stage II would be of short duration,
consequently habitat availability during this period is
more appropriately discussed under operation.
295
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Table 18. Estimated ch~nge in chinook rearing habitat in Group 4 due to
fi~ling under dry, average and· wet conditions
Month
Dry Year
June
July
August
September •
Average Year
June
July
August
September
Wet Year
June
July
August
September
Discharge (cfsl
Natural Filling
21,763 7,800
19,126 8,~00
17,392 8,000
10,422 5,800
27,815
24,445
22,228
13,221
31,580
27,753
25,236
15,124
,.
8,800
12,740
12,415
6,800
10,752
20,547
15,505
6,800
RearinQ Habitat (sg ft WUA)
Natural Filling Change
1,326,195
1,461,067
1,611,530
2,484,311
1,145,028
1,242,762
1,312,223
1,957,028
1,326,195
1,461,067
1,611,530
2,484,311
296
3,028,000
3,020,000
3,020,000
3,112,718
2,954,752
2,009,926
2,037,382
3,079,226
1,461,067
3,020,000
3,020,000
3,112,718
128o32
106o70
87o4Q
25.30
158o05
61.73
55.26
57o34
l0ol7
106o70
87o40
25.30
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.1
Mean ~eekly discharge (upper),
chinook rearing WUA for Group
4 (middle) and percent change
in WUA (lower)exceeded 90, 50,
and 10 percent of the time for
natural and Stage I flows.
FIGURE 101
o•
I • I I T a _., -
- -STAiiE I
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC.
297
H~.RZA·E BASCO
SUSITNA JOINT VENTURE
. '
l.
I.. .•
_H.\11JW. -3
0 --STAGE 1 0
0
·...,:::) --STAGE: 2 ....
X
2 _STAG£ 3 ,
q.. -MAX STAGE 3 (J -
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Percent or Time Equaled or Exceeded
Group 4
-3.
< => 3:
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C" --STAGE 1 G)
c: -----STAGE 2 0 ---STAGE 3 --E --MAX STAGE 3 -1.
1-< ...... -cc .7 < :r:
0
20 43 60 al 100
Percent or Time Equaled or Exceeded
Flow duration curve and
chinook rearing habitat
duration curve for Group 4.
FIGURE 102
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC. HARZA·EBASCO
SUSITNA JOINT VENTURE
298
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' \
10"
\10~
27 .l 10 17 2o4 1 a 15 22 2~ .:s 12 1sa 2e 2 • 1e
MAY JUNE JULY AUCUST SEPT
STAGE 1
20 'Zl 3 1 o 17 z• 1 a 1s 22 29 s 12 19 2S 2 9 1 s
MAY ..I UN!:
Percent change in flow {upper)
and chi nook rearing habitat
(lower) from pre·~ious week in
Group 4 during Stage I
exceeded 10, 50 and 90 percent
of the time.
FIGURE 103
..IUL.Y AUGUST SEPT
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC.
299
HARZA-E BASCO
SUSITNA JOiNT VENTURE
..
0 Operation
Habitat avai1ability under natural and Stage II flows is
compared in a weekly habitat time series plot and
seasonal habitat duration curves {Figures 104 and 100).
Stage II operational flows would result in habitat
increases from 0 to greater than 100 percent for much of
the rearing season. In late August and September
habitat availability would be about the same as natural.
With-project habitat stability would increase during May
and June, decrease in July and in August and September
would be about the same as natural {Figure IOS)o
The contribution of Group 4 to tot a 1 middle Sus i tna
River habitat would increase under Stage II from natural
levels of 20 to 30 percent to 55 to 70 percent in May
and June. The magnitude of the percent percent
contribution increase would decrease during July and
would be similar to natural from mid-August to
mid-September {Figure 73).
Stage III
..
•
Filling
Filling of Watana during Stage III would occur over
several years and consequently habitat availability is
more appropriately addressed under operation.
Operation
Habitat availability under natural and early and late
Stage III operation are compared in weekly habitat time
series plots and seasonal
(Figures 106, 107 and 100).
300
habitat duration curves
Early and late Stage III
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-tiJii--a.tA:+-:Y--+---+-.JU-N+-r;-+---+--+--.J+-U-LY--+--+-:A~U~OU-::ST~+:S=£P~T:-
Mean weekly discharge (upper),
chinook rearing WUA for Group
4 (middle) and percent change
in WUA (lower)exceeded 90, 50,
and 10 percent of the time for
natural and Stage II flowsc
ALASKA POWER AUTHORITY
FIGURE 104
SUSITNA HYDROELECiRIC PROJECT
ENTRIX, INC.
301
HARZA·E BASCO
SUSITNA JOINT VENTURE
l i .
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200
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MAY JUNE JULY AUGUST SEPT
1 NATI.RAL
-M -I so
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A__: ___ _ 10%
-1 · · ·-+ I I e t f I I I ! I I t J I I
20 27 3 10 17 2~ 1 8 15 22 29 5 12 19 2S 2 9 1 s
MAY .JUNE
Percent change in flow {upper)
and chinook rearing habitat
(lower) from previous week in
Group 4 during Stage II
exceeded 10, 50 and 90 percent
of the time.
FIGURE 105
JULY A~JGUST SEPT
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INt.":. HARZA-E BASCO
SUSITNA JOIN'r VENTURE .. --------~----0. ______________ ._ _______ 1 ________ ~---~----------~--------~-~
302
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.tUNE JULY AUGUST SEPT
STMIJ
~ a l----------~-~-----== i I
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Mean weekly discharge (upper),
chinook rearing WUA for Group
4 (middle) and percent change
in WUA (lower)exceeded 90, 50,
and 10 percent of the time for
natural and early Stage Iii
flows.
FIGURE 106
ALASKA POWER AUTHORITY
SUSlTNA HYDROELECTRIC PROJECT
ENTRIX, INC.
303
HARZA·E BASCO
SUSITNA JOINT VENTURE
•
10
s
0~-----------------~--· -----------~----------........ .IUHI: JU&.Y AUGU8T
3.!5
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~, ~·----~ 10 I
~ ~~ ~ 0 ~-------------~~--...;::=--11
1&.1
Q,
.JUNC: .JUt..Y AUGUST SEPT
Mean weekly discharge (upper),
chinook rearing WUA for Group
4 (middle) and percent change
in WUA (lower}exceeded 90, 50,
and 10 percent of the time fot 4
natura 1 and 1 ate Stage I I I
flows.
ALASKA POWER AUTHORITY
FIGURE 107
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC.
304
HARZA-E BASCO
SUSJTNA JOINT VENTURE
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operational flo.ws would r·esult in substantial increases
in hab'i tat through the majori t.y of the rearing season
often exceeding 100 percent over natural.
Stability during eariy and late Stage III would be
greater than natural, except for a few weeks during July
and early August in early Stage III when week-to-week
changes in habit1t would exceed natural (Figure 108 and
109).
The contribution of Group 4 t~1 m·~ ddl e Susi tna River
rearing habitat would increase from natural levels of 20
to 30 percent to Stage III levels of 40 to 70 percent
through mid-summer. The magnitude of the increase in
percent contribution would decrease in July during early
Stage I I I and in August during 1 ate Stage I I 1 and by
mid-September approach natural levels for both periods
of Stage III (Figures 78 and 79).
-Group 5 -Mainstem Shoals
This group inc 1 udes ma i nstem and side channe 1 areas which
transform into clearwater side sloughs at lower mainstem
discharges. Sites within this group are characterized by
fine sediment although ltrger substrates are possible if the
-shoal has stabilized and taken as gravel bar charact~ristics
(Aaseraude et al. 1986). The Group V habitat response curve
and percent contribution of the group to the tot a 1 middle
Susitna River rearing habitat are depicted in Figure 110.
As indicated in the figure, this group contributes on 1 y a
minor portion of the juvenile chinook habitat, even under
optimum flow conditions.
305
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27 3 1 o 17 24 1 e 1 s 22 2g s 12 1 g 2e 2 g 1 e
t.IAY JUNE JULY AUGUST SEPT
-M -
~ -60 t--l-eo
-1ooT I i I I I I
20 27 3 10 17 24 1
MAY .JlJNE
Percent change in flow (upper)
and chinook rearing habitat
{lower) from previous week in
Group 4 during early Stage III
exceeded 10, 50 and 90 percent
of the time.
I
8
FIGURE 108
STAGE 3
10 X
I I I I I I I I I~
15 22 29 5 12 19 26 2 9 16
..JULY AUGUST SEPT
I •
ALASKA POWER AUTHORITY
SUSlTNA HYDROELECTRIC PROJECT
ENTRIX, INC.
306
HARZA·E BASCO
SUSITNA JOINT VENTURE
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27 3 1 o 17 24 1 a 1 s 22 2sa s 1 2 1 sa 21 2 sa , a
UAY JUNE JULY At.:""UST SEPT
-" -
1
80
20 27 3
MAY .JUNE
Percent change in flow (upper)
and chi nook rearing habitat
(lower) from previous week in
Group 4 during late Stage III
exceeded 10, 50 and 90 percent
of the time.
FIGURE 109
.JULY
NATUW..
----MAX STAGE 3
AUGUST SEPT
ALAS.KA f!OWER .. 4.UTHOR11'Y
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC.
307
HARZA·E BASCO
SUSITNA JOINT VENTURE
•
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HABITAT :z
0 ....,_
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CD 60 .......
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-~----------~------__ .,..__ .. ....-.---..,--------··-----=-....._ ______ _ __ .-__ _
+-----~~~~------+-----~----~------+----~~-----+0
0 5 10 15 20 25 30 35 40
FLOW ( t·housa.nd cfs)
ALASKA POWER AUT·:~>DR I {Y
Juveni 1 e chi nook rear1 ng
habitat response curve and
percent contribution to total
rearing habitat of Group 5
areas 1 n the middle Sus 1 tna
River.
SUSITNA HYOROEL.fCTRIC PROJECT
FIGURE 110 ENTRIX, INC. HARZA·E BASCO
SUSITNA JOINT VENTlJft·i
""'_ ... ,..,.....,
l
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Stage I
•
Filling
The rearing habitat during Stage I filling would be
reduced substantially since flows frequently would be
near E-VI minimums, much. below the natural flows that
provide higher habitat availability for this group.
Habitat associated with monthly filling flow estimates
for June through September would be reduced by 39 to 67
percent in a dry year, 8 to 72 percent in an average
year, and 44 to 71 percent in a wet year (Table 19).
Operation
Habitat availability under natural and Stage I flows is
compared in a weekly habitat time series plot and
seasonal habitat duration curve (Figure 111 and 112).
Stage I flows would result in decreases in habitat from
0 to 60 percent more than half the time through July and
decreases in habitat up to 40 percent about half the
time for the remainder ·of the summer rearing period.
Habitat increases would also occur throughout the season
but with much lower frequencies than the decreases.
The stability of habitat in Group 5 sites would be
greater through July than naturally and about the same
for the remainder of the season (Figure 113).
The contribution of Group 3 to the habitat availability
provided by all groups combined would be somewhat less
than natural from 1 ate l\1ay through mid-July and about
the same as natural for the rest of the season (Figure
70}.
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Table 19. Estimated change in chinook rearing habitat in Group 5 due to
filling under dry, average and wet conditions.
Discharge (cfs) _ Rearing Habitat (sq ft WUA)
Month Natural Filling Natural Filling Change
Dry Year
June 21,763 7,800 190,477 64,128 -66.33
July 19,126 8,000 168,576 66,308 -60.67
August 17,392 8,000 166,653 101,999 -38.80
September 10,422 5,800 101~999 33,396 -67.26
Average Year
June 27,815 8,800 301,889 278,025 -7.90
July 24,445 12,740 278,025 171,206 -38.42
August 22,228 12,415 197,333 163,160 -17.32
September 13,221 5,800 177,797 49,232 -72.31
Wet Year
June 31,580 10,752 201,352 112,927 ··43. 92
July 27,753 20,547 302,585 164,178 -4.5. 74
August 25, 2~6 15,505 301,969 170,178 -43.64
September 15,124 6,800 172,569 49,232 -71.47
310
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Mean weekly discharge (upper),
chinook ~earing WUA for Group
5 (middle) and percent change
in WUA {lower)exceeded 90, 50,
and 10 percent of the time for
natural and Stage I flows.
ALASKA POWER AUTHORITY
SUSITNA HYDROELECYRlC PROJECT
ENTRIX, INC. HARZA·E BASCO
FIGURE 111 SUSi'TNA JOINT VENTURE
311
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3 _ -STAGE 1
--SfAQ!, 2
2 _STAGE 3
__ MAX STAGE 3
1
0 l---+---~+---+---~+---+---~~--+-~~~--+-~100
Percent of T i me Equal ed or E; ~-~eeded
Group 5
.,
0 t I i
2D -4{) so Em
Percent of Time Equaled or Exceeded
-NATliW.
__ STAS£1
-·-STMiE 2
__ ST'*£ :1
_MAX STAG£ 3
Flow duration curve
and chinook rearing habitat
duration curve for Group 5. ALASKA PO\'VER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
HARZA·E BASCO
'
FIGURE 112 ENTRIX, INC. SUSilNA JOiNT VENTURE
31
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27 3
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,0 17 24 1
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a 1 s .22 2a s 12 1 a 2e 2 a 1 e
JULY AUGUST SEPT
STAGE 1
+ I t t I ·! I t ·· • ~ I ! t t I
20 ?:! 17 2~ 1 8 15 22 29 5 12 19 26 2 9 16
MAY ~UNE
Percent change in flo:w {upper)
and chinook rearing habitat
(lower) from previous week in
Group 5 during Stage I
~xceeded 10, 50 and 90 percent
of the time ..
FIGURE 113
~ULY AUGU .• -;{,'r SEPT
ALASKA POWER AUTHORITY
S U S I. T N A H Y D R 0 E l E C T R I C P R 0 J E C T
ENTRIX, iNC.
313
HARZA·c BASCO
SUSITNA JOINT VENTURE
.. •
Stage II
•
•
Fil 1 ing
Filling flows under Stage II would be of short duration,
consequently habitat availability during this period is
more appropriately discussed under operation.
Operation
Habitat availability under natural and Stage II flows is
compared in a weekly habitat time series plot and
seasonal habitat duration curves (Figures 114 and 112).
Stage II operational flows would result in habitat
reductions from 60 to 75 percent about half the time in
May, June, and July. By the end of July the magnitude
of these reductions would decrease and by end of August
habitat availability would be about the same as natural.
With-project habitat stability would increase substanti-
ally in May and June, decrease in July, and be
approximately the same or slightly greater in August and
September (Figure 115).
The contri but inn of Group 5 to tot a 1 mi dd'l e Sus i tn a
River habitat would decrease under Stage II from natural
levels of 2 to 5 percent to about 2 percent in May and
June. The percent contribution would increase during
July and would be similar to natural from mid~August to
mid-September (Figure 73).
314
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• . . • . . ... -····---········-··· .. . .... -: :·--~---..... -
.
: .· . • . -· . ·· -----···--·
0~~----------~--------~-~------~-a-u-~-----------
I
::t
~ so i
3 ..,
Ill 20 0
UAY JUNE JULY AUGUST
101 ---.-
STMiE 2
~ 0 +-4---+---4----r----~~~-~1
~ -20
~-4)
E
~--tO-t-----
~~----~---------
Mean weekly discharge (upper),.
chinook rearing WUA for Group
5 {middle) and percent change
in WUA (lowerlexceeded 90, 50,
and 10 percent of the time for
natural and Stage II flows.
FIGURE 114
AUGUST
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC.
315
HARZA-E BASCO
SUSITNA JOINT VENTURE
r.;
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27 3 10 17 2... 1 a 1:s 22 29 s 12 1 e 2e 2 a us
MAY JUNE JULY AUCUST SEPT
"' :\ I \ I '\ I \ ,
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' \ .. ~.
II \\ ,./ \
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-----·
: \ i \ : I \ ,. .. / 0 \ I ': .-.-1 % ' ' ~ ' ~ '-·-===~~~;-;·-~~~"~--~~--------~~-~----~~~=-50% 1"" ----~ ---=:~~ ~-==--:a ,~7.:0::;::::> <,......__ ~ ---.;:: ... -
MAY
.... / ... ____
~ ~-00%
.JUNE .JULY AUGUST
I
9
SEPT
I
16
STAGE 2
Percent change in flow {upper}
and chinook rearing habitat
(lower) from previous week in
Group 5 during Stage II
exceeded lOr 50 and 90 percent
of the time.
ALASKA POWER AUTHORITY
FIGURE 115
SUSITNJio HYDROELECTRIC PROJECT
ENTRIX, INC.
316
HARZA-E BASCO
SUSITNA JOINT VENTURE
I
I
I
I
!
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~
~ ''
J
.. , . 1
J
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1
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't u
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..
Stage III
0
•
Filling
Filling of Watana during Stage III would occur over
several years and C'onsequently habitat availability is
more appropriately addressed under operation.
Operation
Habitat ava i 1 abi 1 i ty under natura 1 and ear1y and 1 ate
Stage III operation are compared in weekly habitat time
series plots and seasonal habitat duration curves
{Figures 116, 117 and 112)~ Early Stage III operational
flows would result in substantial reductions (up to 70
percent) irr habitat through June. In July the
frequencies of reduction ~ould decrease and by August
would occur about half the time. In late Stage III
reductions of 40 percent or·more would be prevalent at
least 50 percent of the time through July. In August,
hab·itat availability would range from infrequent slight
increases to more frequent decreases up to 60 percent.
Stability during early and late Stage III would be
greater than natural for the majm"ity of the rearing
season, with the exception of some large increases (100
percent) in week-to-week habitat availability during
July and early August in early Stage III (Figures 118
and 119).
The contribution of Group 5 to middle Susitna River
rearir.=g habitat decrease from natural levels of 2 to 5
percent to Stage Ill levels of 2 to 3 percent in early
summer to 2 to 4 percent in the second half (Figures 78
and 79).
317
•
..
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. ................ .· . ::. . --.. ·.-.----... ~--·-·-· ..... --.. --... -. -· .C!-.. . ---··· 'Oll··~ ... ..eo•
0~--------~---------------------------..... .,.
0
JUNE JULY AUGUST SEPT
IU I ~-l ~
~ .
~a I
i :J
u -· ~ <4
~--
II
-tO
_, ~----~-------------------~----~ UAY JUNE JULY AUGUST
""
Mean weekly discharge {upper),
chinook rearing WUA f~r Group
5 (middl~) and percent change
in WUA (1i'1Wer) exceeded 90, 50,
aiid 10 p~rcent of the time for
natural a~~d early Stage III
flows ..
~-..,.---.aa..-.atP.\11. -----------.:~---1
FIGURE 116
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC. HARZ ~E BASCO
SUS!TNA JOINT VENTURE
._----------~·----------~~~~~~-~------~--~------~--~----~ 318
I
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-~ ~-... • ...... (' •• -0'1
0~*-~~~--------------~~-~----~N~~.·-,~--------~~-
~
i
~ 10%
~ m
I·~~--~---------+~~~~
u -a SJ:
i..,
u ' ~-.. ... Sl%
JULY AUGtJST
Mean weekly discharge (upper),
chinook rearing WUA for Group
5 (middle) and percent change
in WUA (lower)exceeded 90, SOF
and 10 percent of the time for
na'tural and late Stage III
flows.
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
HARZA·E BASCO ENTRIX, INCe FIGURE 117 SUSITNA JOINT VENTURE
•
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27 3 10 17 2-4 1 a 1~ 22 20 5 12 ua 28 2 Q 18
MAY JUNE JULY AU~UST SEP'f
NATl.JRAl
-M STAGE 3 -
--10 X
~~~~~~~~----~==~--~-~------~~ 00%
20 ~ Zl 3 10 17 2~ 1 8
MAY JUNE
Percant change in flow (upper}
and ch1nook rearing habitat
(lower) from previous week in
Group 5 during early Stage III
exceeded .10, SO and 90 percent
of the time.
FIGURE 118
--90 ~
I I
15 22 29 5 12 19 26 2 9 16
JULY AUGU$T SEPT
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
E,.--..tTRIX, INC.
320
HARZA-E BASCO
SUSITNA JOINT VENTURE
•
•• I
~
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J
~
~J
\ J
J
J
J
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150
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1 1:51 22 2~
..JULY
' ·~ I ~ . ' . ' . ' . '
I
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' ' ' '
• -----.... -.. . -, , .. ,so"'
---~-~...90"
12 ,. 25
AUCUST
2 • SEPT
, . 0"
NATURAL
---'!""'--· MAX STAGE 3
~ -!-_ ! I t I I I t I . f I f
20 27 3 10 17 2~ 1 8 15 22 29 5 12 19 26 2 9 16
MAY ..JUNE
Percent change in flow (upper)
and chi nook rearing habitat
(lower) from previous wee~ in
Group S during late Stage III
exceeded 10, 50 and 90 percent
of the time.
FIGURE 119
.JULY AUGUST SEPT
ALASKA POWER AUTHORI1iY
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC. HARZA·E BASCO
SUSITNA JOINT VENTURE
321
,.
-Representative Group VI
This group is comprised of overflow channels which parallel
the mainstema nd represent a transition area between schools
and side channels. The sites within this group breach at a
wide range of mainstem discharge. The habitat response
curve and percent contribytion of this group to the total
,
middle Susitna River rearing habitat are presented in Figure
120.
-Stage I
0
•
Filling
The rearing habitat during Stage I fi 11 i ng would be
reduced substantially since flows frequently would be
near E-VI minimums, much below the natural flows that
provide the higher habitat availability for this group.
Habitat associated with monthly filling flow estimates
for June through September would be reduced by 58-75
percent in a dry year, 46-75 percent in an a\~·arage year,
and 1 to 5 percent in a wet year (Table 20}.
Operation
Habitat avaiiability under natural and Stage I flows is
compared in a weekly habitat time series plot and
seasonal habitat duration curve (Figure 121 and 122).
Stage I flows would result in decreases in habitat
ranging up to 80 percent throughout the majority of the
summer rearing period. From mid-August through
mid-September, the magnitude of habitat decreases would
decrease and about half the time Stage I flows would
provide an increase in habitat.
322
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----.4
-~-~=------....---..,., _.,...--•-.r;::s::e==:=a• .,.,.,. .. -.. ~ ... --..... _.,
---f -r--:_ r-·-
HABITAT
------% CONTRIB
.
----~.....__,;;. ........... -
G4. .. ~--
100
80
60
20
z
0 ..,_
f-:::> m .......
a:::
t-::z:
0
(J
1-:z w
(.J
0::: w a..
__ ,
~------~----_-_-~ __ -_.i~~-------;------~------~~----~~------.~----~1 0 0
0 5 10 15 20 25 3D 35 40
FLOW (thousand cfs)
Juvenile chinook rearing
habitat response curve and
percent contribution to total
rearing habitat of Group 6
areas in the middle Sus~tna
River. FIGURE 120
.---~3---------------------------~-----t ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJ\ECT
HARZA·E BASCO ENTRIX, INC. SUSITNA JOINT VENTURE
I !
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'
Table 20& Estimated change in chinook rearing habitat in Group 6 due to
filling under dry, average and wet conditions.
Discharge {cfsl Rearing Habitat {sg ft WUA)
Month Natural Filling Natural Filling Change
Dry Yeqr
June 21,763 7,800 708,711 177,698 -74.93
July 19,126 8,000 653,226 186,971 -71 .. 38
August 17,392 8,000 615,371 186,971 -69 .. 62
September 10,422 5,800 256,040 108,309 -57.70
Average Year
June 27,815 8,800 850,918 211,848 -75.10
July 24,445 12,740 754,517 405,138 -46.30
August 22,228 12,415 726,215 387,206 .. 46.68
September 13,221 6,800 436~ l85 134,065 -69.19
Wet Year
June 31,580 10,752 947,797 272'1748' -71.22
July 27,753 20,547 849,505 €J1,626 -20 .. 94
August 25,236 15,505 761,384 541ill9 -28~93
September 15,124 6,800 532,313 134,065 -'14.81
324
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~---------~-------------~ ..... -........ ~ .. !'
...
10
•
.. ·· •' .. ..~
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• .
--··········
. ... . . .. ·-·
. . . . .. ..
0~------------------------------~-------"'"""' .AA.Y 4I.IOUII'I'
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0
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1:
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-1
'-,/
I ,. -/' ,. .... I .... ___ /
I
JUNE: JULY
..........
101
AUGUST SEPT
Mean weekly discharge {upper),
chinook rearing WUA for Group
6 (mfddls) and percent change
in WUA (lower)exceeded so, SO,
and l 0 ~ercent of the time for
natural and Stage I flows.
~. AtA.SKJ\ POWER AUTHORITY I SUSITNA HYDROElECTRIC PROJEC1'
Fi6URE 121 ENTRIX, INC. HARZA·E BASCO
SUSnNA JOINT VENTURE
1
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"~~----~--------------.a--------------------------------~--------·
-0
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0
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X .,
4-
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31:
0
-' LL..
3
2
1
_NATUW..
--STAGE 1
--STAGE 2
__ STAGE 3
_MAX STAGE 3
0 ~--~--~---~--~--~--~--~~~~--~~100
20 .co 60 ~
Percent of Time Equaled or ~xceeded
Group 6
-1
< :::J
3: ....., .a -NATUW.. 4-
CT --STAGE1 f)
c .& --STAGE 2 u --STAGE 3 -e -·"' -MAX STAGE 3 .... < .... -CD .2 < :r:
0
20 c 60 aJ 100
Percent of Time Equaled or Exceeded
Flow duration curve and
chinook rearing habitat
duration curve for Group 6.
FIGURE 122
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC. HARZA·E BASCO
SUSITNA JOINT VENTURE
._--~-----~--------------------------------.. ------------------· 326
J
J
J
J
J
J
1
J
1 .;
•
The stability of habitat in Group 6 sites would1 be
somewhat 1 ess than natura 1 for most of the reat•i ng
season, particularly mid-July to mid-August when weekly
changes in habitat can reach 70 percent {Figure 123).
The contribution of Group 6 to the habitat availability
pr·ovided by all groups would decrease from natural
levels of 10-15 percent to with-project levels of 5 to
12 percent through July. In August and September,
percent contribution would be similar {Figure 70).
Stage II
•
•
.Filling
Filling flows under Stage II would be of short duration,
consequently habitat availability during this period is
more appropriately discussed under operation.
Operation
Habitat availability under natural and Stage 11 flows is
compared in a weekly habitat time series plot and
seasonal habitat duration curves (Figures 124 and 122).
Stage II operational flows would result in habitat
reductions from 60 to 80 percent in May and June.. In
July the magnitude of the reduction would decrease and
by mid-August habitat availability would be about the
same or slightly greater than natural.
With-project habitat stability would decrease
substantially primarily due to week-to-week increases in
habitat during July and August. In 1 ate August and
September stability would be similar (Figure 125).
327
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...... .... ... ... ... ..
' ' .,
' .. .. .. .. ' .. .. ... '\' , ____ .
....
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, .. , .. , ..
, ', .-··--....
' ' ' '
10"
\10"
27 3 1 o 17 24 1 a 1 s 22 2~ s 12 111 2e 2 sa , e
MAY JUNE JULY AUGUST SEPT
NATLIW.
STAGE 1
20 27 3 10 17 2. 1 8 15 22 29 5 12 19 26 2 9 16
MAY .JUNE
Percent change in flow (upper)
and chinook rearing habitat
{lower) from previous week in
Group 6 during Stage I
exceeded 10, 50 and 90 percent
o.f the time.
FIGURE 123
.JULY AUGUST SEPT
.-----------------------------~-----~·------~ ALASKA POWER AUTHORITY
SUSITNA HYDROElECTRIC PROJECT
ENTRIX, INC. HARZ.-\-E BASCO
SUSITNA JOINT VENTURE .. ----------~------------~----------------.. ~----------------· 328
..
I
I
ll
J
J
J
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l•o
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I • I • -··· • ·::: ... a..:.:..:.:,.···----.-. ..... ·· .......
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_....: .............. ··
0~~-~-----------------~-~------~-ou~~----,----M#-,~
••
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0
3 ! .•
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0
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~ .
~ a
/
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'--./ I "' --.... _-_________ -:_-_ .... --/
"'
JUNE JULY AUCUST
STA;E 2
101
StP'T
I o +\-------,--.---,--~-~II
() ...
§ ..
c r--.t=~======~~----~ _, __ __._ _______________ _
.JUNE JULY AUGUST
Mean weekly discharge (tJJpper),
chinook rearing WUA fori Group
6 (middle) and percent change
in WUA (lower}exceeded 90, 50,
and 10 percent of the tiMe for
natural and Stage II flows ..
ALASKA POWER AUTHORITY
FIGURE 124
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC.
329
m:
HARZA·E BASCO
SUSITNA JOINT VENTURE
.. •
200
1:50
0
-so
-M -~
~ -i
I
I 0 ~ .,_ -I
-1
\ . ' , '
/ ' . ' I \
' ' ' • . ... , ' , ....... -'~ '····
c.oe .. ._~ ~
# .. ...... ..
27 3 10 17 24
MAY JUNE
• ,
.... -
1
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I ~
I ' ••o•-c
I I 1 I
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I I I i
1 \ I I
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a 15
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2~ 29
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12
I, ' .. ' ....
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18 28
JULY AUCUST
10X
_/o"
0"
2 8 18
SEPT
I I I I I I t
NATtiW.
STAGE 2
20 27 3 10 17 2~ 1 8 15 22 29 5 12 19 2S 2 9 16
MAY ..JUNE
Percent change in flow (upper)
and chi nook rearing habitat
(lower) from previous week in
Group 6 during Stage II
exceeded 10, 50 and 90 percent
of the time.
FIGURE 125
..JULY AUGUST SEPT
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC.
330
HARZA-E BASCO
SUSITNA JOINT VENTURE
~-
I
I
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•
•
••
The contribution of Group 6 to tot a 1 middle Sus i tna
River habitat would decrease under Stage II from natural
levels of 10 to 18 percent to about 5 percent in May and
June. The percent contribution would increase during
July and would be similar to natural from mid-August to
mid-September (Figure 73) •
.Stage III
Fi11 ing
Fi 11 i ng of Watana during Stage I I I waul d occur over
several years and consequently habitat availability are
more appropriately discussed under operation.
. • Operat.ion
Habitat availability under natural and early and late
Stage Ill operation are compared in weekly habitat time
s_eries plots and seasonal habitat duration curves
(Figures 126, 127 and 122). Early Stage III operational
flows would result in substantial reductions (60 to 80
percent) in habitat through June. The frequencies of
reduction would decrease in July and by August occur
about half the time. In late Stage III reductions of 50
percent or more would be prevalent through July. For
the remainder of the rearing period \"educt ions would
range from 0 to 70 percent.
Stability during early and late Stage III would be
similar ·to natural, except during mid-summer during
early Stage III when 1 arge increases in habitat would
occur (Figures 128 and 129).
The contribution of Group 6 to middle Sus i tna River,
rearing habitat decrease from natural levels of 10 to 18
331
.,_ .....
-..
44t ,. ·-• I ••
lao
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' ' ' . ' . 10 • • • .• c ------·-·----.--... ----.----........ ·-.::--..~ •
0
t
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f
a ·• z
0
3 3 ... ...,
""'"'
I
I
I
I
' I
MnM.
STNC 3
101
'----I I .------....-.:::..------,----
I
L&AY JUNE
WAY
Mean weekly discharge (upper),
chinook rearing WUA for Group
6 (middle) and percent change
in WUA (lower)exceeded 90, 50,
and 10 percent of the time for
natural and early Stage III
fl 0'.4S.
FIGURE 126
JULY AU OUST SEPT
II
-IULY SEPT
AlASKA POWER AUTHORITY
SUSITNA HYDROElECTRIC PROJECT
ENTRIX, INC.
332
HARZA·E BASCO
SUSITNA JOINT VENTURE
I
I
J
' 1
J
J
}
J
•
Pi .. · l:l
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L
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.. ... ... ,. ·-• ...
1-i ,.
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3 ! .4
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------~-==.=:=--..... ;;~ ===--, '
D +------~-+--___ __, I I I I I
UAY JUNE JULY AUGUST SEPT
•
j •.
I •. •s I :U-------------~~------,----------r: :~:: t~t:~==~~;;;;;;;;~~~~----~~-~ ..
Mean weekly discharge (upper),
chinook rearing WUA for Group
6 {middle) and percent change
in WUA {lowerl e~ceeded 90, 50,
and 10 percent of the time for
natural and 1 ate Stage III
flows.
ALASKA POWER AUTHORITY
FIGURE 127
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC.
333
HARZA-E BASCO
SUSITNA JOINT VENTURE
".\ ~~'..l!t":~;-=..:I'.~;>~•~.M-~"".{~I"f:>l.;<r£.)'F.i;i'•*;.~,..,,,,;.,~ . .,.,...,~ .. ,....,..,.;J;+ •• o,"';:~.-.~·~,_:_~.;....,..~·---;-,.._~.-._..._._~.·· -~...._~ _, ...;.,~--· -~-~.
200
1SO
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... ' 1!.
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••• ', :10-'-'_ ...... \ .. •• .••! A
27 3 1 0 17 2-4 1 8 1 :5 22 21 5 12 1 I 28 2 I 1 8
MAY JUNE JULY AUCUST SEPT
1\ I ' I I . \ I \ /\ ,. \ I \ I I I \
I \ i ' I , , '\ : . ., ' I I
' \ . \
I ...... "' i '\"
I
'
20 27 3 10 17 24 1 9 15 22 29 5 12 19 26 2 9 16
MAY .JUNE .JULY AUGUST SEPT
10%
NATURAL
STAGE 3
Percent change in flow (upper}
and chi nook rearing habitat
(lower} from previous week in
Group 6 during early Stage III
exceeded 10, 50 and 90 percent
of the time.
ALASKA POWER AUTHORITY
FIGURE 128
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC.
334
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MAY JUNE JULY AUCUST SEPT
NATURAL
-M MAX STAGE 3 -
f· . \
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I \
' ' I ,
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20 Z1 3 10 17 24 1 9 15 22 29 5 12 19 26 2 9 16
MAY .JUNE
Percent change in flow {upper>'
and ch 1 nook rearing habitat
(lower) from previous week in
Group 6 during late Stage III
exceeded 10, 50 and 90 pe~cent
of the time ..
FIGURE 129
.JULY AUGUST SEPT
ALASKA ROWER AUTHORITY
SUSITNA HYDROELECTRIC Pt.~OJECT
ENTRIX, INC.
335
HARZA-E BASCO
SUSITNA J()INT VENTURE
"
~;; . < . ..., . ..,..:.....;t~--··~...,... •+tttd!lft>tW ·-~~
percent to early Stage III levels of S percent in early .
summer (Figure 78 and 79).
-Representative Group VII
This group is comprised of side channels which breach at low
mainstem discharges. The areas within this group are
composed of a single riffle extendin~ from the head down to
a large backwater area at the mouth. The riffle generally
consists of rubble and boulder size substrates in contrast
to backwater areas in wh 1 ch sand and s i 1 ts tend to
predominate. The habitat response curves and percent
contribution of this gr·oup to total middle Susitna River
rearing habitat as a function of mainsterr1 flow are presented
in Figure 130.
Stage I
•
•
Filling
The rearing habitat during Stage I filling would
generally increase substantially since flows frequently
would be near E-VI minimums, near the range that.
provides the higher habitat availability for this group.
Habitat associ a ted with m1'lnth 1 Jf fi 11 i ng flow estimates
for June through August would increase 106-226 percent
in a dry year, 224-314 percent in an avera~1e year, and
35 to 367 percent in a wet year. In September there
would be a decrease of 2 J percent in a d\"'Y year, a
decrease of 1 percent in an average year, and a 31
percent increase in a wet year (Table 21).
Operation
Habitat availability under natural and Stage I flows is
compared in a weekly habitat time series plot and
336
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HABITAT z:
0 ......
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0::
1-:z:
0 u
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20 u.; a..
----....-----------.... . .. ............ .......__ ________ _
~----~~-----+------~------+-------------~-~------------4---------c-·---~----~o
0 5 10 15 25 30 35 40
FLOW (thousand cfs)
Juvenile chinook rearing
habitat response curve and
percent contribution to total
rearing habitat of Group 7
areas in the middle Sus1tna
River. FIGURE 130
----------~~~,-------------------------1 AlAS:CA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC. HARZA·E BASCO
SUSITNA JOINT VENTURE
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Table 21. Estimated change in chinook rearing habitat in Group 7 due to
·filling under dry, average and wet conditions.
Month
Dry Year
June
July
August
September
Average Year
June
July
August
September
~et Year
June
July
August
September
Oischaroe {cfs)
Natural Filling
21,763
19,126
17,392
10,422
27,815
24,445
22,228
13,221
31,580
27,753
25,236
15,124
7,800
8,000
8,000
5,800
8,800
12,740
12,415
6,800
10,752
20,547
15,505
6,800
338
Rea~inq Habitat (sg ft WUA}
Natural Filling Change
111,158
142,057
178,003
387,335
90,425
98,223
107,658
323,589
82,339
90,563
96,299
245,549
361,894
367,372
367,372
311,783
374,448
341,444
349,166
321,092
384,251
122,405
234,304
321,092
225.57
158.61
106.39
-19.,51
314.10
247.62
224.33
-0.77
366.67
35.16
143.31
30.76
r I,
L
l
L
L
seasonal habitat duration curve {Figure 131 and 132).
Stage I flows waul d result in substantia 1 increases in-
habitat throughout the summer rearing period. Increases
would range as high as several hundred percent,
particularly in early summer.
The stability of habitat in Group 7 sites would be
greater in May and June than naturally and about the
same for the remainder of the season {Figure 133).
The contribution of Group 7 to the habitat availability
provided by all groups would increase from natural
1 eve 1 s of 4 to 8 percent in May and June to 2 to 5
percent {Figure 70).
Stage II
•
..
Filling
Filling flows under Stage II would be of short duration,
consequently habitat availability during this period is
more appropriately discussed under operation.
Operation
Habitat availability under natural and Stage II flows is
compared in a weekly habitat time series plot and
seasonal habitat duration curve (Figures 134 and 132).
Stage II operational f'jows would result in substantial
increases in habitat availability for this group
throughout the rearing saason. Increases would be
greatest in May through July often exceeding 200
percent. Toward the end of August and in September
habitat availability would be about the same as natural.
339
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AU OUST
---..... __ ._. .... ---,. \
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JUNE. JULt' .MJGUST SEPT
•
STAGE 1
Mean weekly discharge {upper),
chinook rearing WUA for Group
7 (middle) and percent change
in WUA (lower}exceeded 90, 50,
and 10 percent of the time for
natural and Stage I flows.
ALASKA POWER AUTHORITY
FIGURE 131
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC. HARZA·E BASCO
$USITNA JOINT VENTURE
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__ STAGE 2
_STAGE 3
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0 +---~--~--·~~~--~--~--~--~---+---~
20 40 so eo 100
Percent of Time Equaled or Exceeded
Group 7
m
_N.\TlRAL
-_STAGE 1
__ STAGE 2
_STAGE 3
__ )&AX ST~ 3
0 ~--+---~--~---r---+--~---r--~--~--~
20 .40 GO 9l 100
Percent of T i me Equa. 1 ed or Exceeded
;
Flow duration curve and
chinook rearing habitat
duration curve for Group 7.
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
FIGURE 132 ENl'RIX, INC. HARZA-E BASCO
SUSITNA JOINT VENTURE
.. ------------------~--m.----.A------~~----~----~--------------------.. '1A1
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27 3 10 17 2-4 1 5 1~ 22 2i .5 12 1~ 2! 2 1J 18
MAY JUNE JULY AUGUST SEPT
1
-M -
.JUNE
Percent change in flow (upper)
and chinook rearing habitat
(lower} from previous week in
Group 7 during Stage I
exceeded 10, 50 and 90 pe~cent
of the time.
FIGURE 133
STAGE1
10%
.JULY AUGUST SEPT
ALASKA POWER AUTHORITY
.SUS!TNA HYDROELECTRIC PROJECT
ENTRIX, INC.
342
HARZA~E BASCO
SUSITNA JOINT VENTURE
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JULY
.~--101
SEPT
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-111D~+--t-_-+-_-+-____ --<-_______ --+-_
""y JULY AUGUST SEPT JUNE
51-"iE 2
Mean weekly discharge (upper),
chinook rearing WUA for Group
7 (middle) and percent change
in WUA (lower)exceeded 90, 50,
and 10 percent of the time for
natural and Stage II flows~
ALASKA POWER AUTHORITY
FIGURE 134
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC.
343
HARZA-E BASCO
SUSITNA JOINT VENTURE
..
With-project habitat stability would increase
substantially in May, June, and July. In August and
September, stabi 1 i ty waul d be about the same as natural
(Figure 135).
The contribution of Group 7 to tot a 1 middle Sus i tna
River habitat would increase under Stage II from natural
1 eve 1 s of 1 to 7 percent to· 7 to 8 percent in May and
June. The magnitude of the percent contribution
increase would decrease during July and would be similar
to natural from mid-August to mid-September (Figure 73).
Stage III
Filling
Filling of Watana during Stage III would occur over
several years and consequently habitat availability is
more appropriately discussed under operation.
Operation
Habitat availability under natural and early and late
Stage III operation are compared in weekly habitat time
series plots and seasonal habitat duration curves
(Figure 136, 137 and 132}. Early Stage III operational
flows would result in substantial increases in habitat
from May through August with September about the same as
natura 1 • In 1 ate Stage I I I these increases waul d be
similar but also extend into September.
Stabi 1 ity during early and 1 ate Stage I I I would be
greater than natural from May through mid-August
(Figures 138 and 139).
344
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27 3 1 o 17 24 1 a 1 s 2:1 2g 5 12 1 g 2e 2 g 1 a
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.JUNE JULY
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.WCUST SEPT
10 I
50%
00%
NATIIW..
STAt;E 2
20 ?J 3 10 17 24 1 8 15 22 29 5 12 19 26 2 9 16
MAY .JUNE
Percent change in flow (upper)
and chinook rearing habitat
(lower} from previous week in
Group 7 during Stage II
exceeded 10, 50 and 90 percent
of the time.
FIGURE 135
.JULY AUGUST SEPT
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC. HARZA-E BASCO
SUSITNA JOINT VENTURE .. ----------~------·------------~--------------------.. --~------------------..
•
•
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40
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-:::: = = :: =-- - -00:: - - - - - -___ , ___ 101 -r---""' \ ~
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JUNE JULY SEPT AUGUST
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Mean weekly discharge (upper),
chinook rearing WUA for Group
7 (middle} and percent change
in WUA {lower)exceeded 90, 50,
and 10 percent of the time for
natural and early Stage III
flows~
r---~----------------------~------..
J.
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
~--------~------r-----------------~ HARZA·E BASCO
l ~-
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' ~ FIGURE 136 SUSITNA JOINT VENTURE ' •--~------~------------_.~--~----~--~_.----------------~· 1
":f 'Will
ENTRIX, INCi
346
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_______________ ---~=--
1
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,.,--- - -:----..----- -------_,...------, ._,. "D
,--.-' / D
I
JUNE
Mean weekly discharge (upper},
chinook rearing WUA for Group
7 (middle) and percent change
in WUA (lower)exceeded 90, 50,
and 10 percent of the time for
natura 1 and 1 ate Stage I II
flows.
FIGURE 137 -
JULY AUCUST
'-
I
I
I
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC. HARZA·E BASCO
SUSITNA JOINT VENTURE
347
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~90" -so~~~~·~~·~~·~~·~~·--~·--~·--~·--~·--~·--~·~~·--~•--+•--~~~~~ 27 3 1 o 1 7 24 1 a 1 ~ 22 2v s 12 1 s 2s 2 v 1 a
YAY .JUNE JULY AUGUST SEPT
-H -
i
§
1
-20 i 0
~ -20
1-40
~ -60 l
STAGE 3
10%
i ~~j
I I Iii t iII I I I I I It I
Zl 3 1 0 17 24 1 8 15 22 29 5 12 19 26 2 9 16 20
~AY .JUNE
Percent change in flow (upper)
and chinook rearing habitat
{lower) from previous week in
Group 7 during early Stage III
exceeded 10, 50 and 90 percent
of the time.
FIGURE 138
.JULY. AUGUST SEPT
ALASKA POWER AUTHORITY
SUSITN~\ HYDROELECTR.lC PROJECT
ENTRIX, INC.
348
HARZA-E BASCO
SUSITNA JOINT VENTURE
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~,7 3 , o , 7 24 1 a 1 s 22 . 2e s 12 ,. 2e 2 • ta
MA'I• JUNE JULY AUCUST SEPT
20 27 3 10 17 24 1
MAY .JUNE
Percent change in flow (upper)
and chinook rearing habitat
(lower) from previous week in
Group 7 during late Stage III
exceeded 10, 50 and 90 percent
of the time.
FIGURE 139
NATt.IW.
MAX STAGE 3
10%
.JULY AUGUST SEPT
ALASKA POWER AUTHORITY
.SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC.
349
HARZA-E BASCO
SUSITNA JOINT VENTURE
,.
..
The contribution of Group 7 to middle Susitna River
rearing habitat increases from natural levels of 1 to 4
percent to early Stage III levels of 7 to 8 percent in
May and June. In July the percent contribution of early
Stage I I I flows waul d decrease and by August would be
similar to. natural levels {Figure 78). In late Stage
III the percent contribution would remain at high&~
levels than natural for the entire rearing .period
{Figure 79).
-Representative Group VIII
This group is comprised of areas which tend to dewater at
intermediate to high mainstem discharges although their
hydrologic, hydraulic, and morphologic properties are
similar to the side sloughs and side channels in Group II
and III. The habitat response curve and percent
contribution of this group to total middle Su~itna River
rearing habitat are depicted in Figure 140. As indicated in
the figure, WUA accumulates rapidly as sites become breached
and peak values are attained at approximately 27,000 cfs.
Due to the steep slope on the habitat response between
20, 000 and 27, 000 cfs, fluctuates in flow within the range
either naturally or with project would result in habitat
instability and wide variations in percent contribution to
total habitat avai1ability.
-Stage I
• filling
The rearing habitat during Stage I fi 11 i ng waul d be
reduced substantially since flows frequently would be
near E-VI minimums, much below natufal flows that
provide the higher habitat availability for this group.
Habitat associated with monthly filling flow estimates
350
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r--:r· '· . * r . '(' ~
100
80 z
0 ......
t-
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60 CD ......
0::
1-HABITAT
z:
0 u ----% CONTRIB
1-z
lJ.J
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0::::
LJJ a_ 20
·--------------------~ ..,--------, .. _, -------.,.,
+--~----~----~--~--~--------~+-----~~----~-------+------~------~0
0 5 10 15 20 25 30 35 40
FLOW (thousand cfs)
Juven fl e ch 1 nook rear1 ng
habitat response curve and
percent contribution to total
rear1 ng habitat of Group 8
areas in the m1 ddl e Sus 1 tna
River.
FIGURE 140
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC. HARZA·E BASCO
SUSITNA JOINT VENTURE
r,..
.• 1f •.
:;
.. ,
•
•
• •
for June through September would be non-existent in a
dry year, reduced percent in an average year, and 33 to
100 percent in a wet year {Table 22).
Ooeratio.n
Habitat availability under natural and Stage I flows is
compared in a weekly habitat time series plot and
seasonal habitat duration curve (Figures 141 and 142).
Stage I flows would result in substantial decreases in
habitat throughout much of the summer rearing period.
Beginning in mid-August, the magnitude of habitat
decreases would gradually decrease and by mid-September
habitat availability would be about the same or slightly
greater than natural.
The stability of habita·t in Group VIII during Stage I
wou~d decrease throughout most of the summer due
primarily to 1 arge week to week increases in habitat
which often exceed zoo percent. In September natural
and project changes in habitat would be about the same
(Figure 143).
The contribution of Group 8 to the habitat availability
provided by all groups would be substantially less than
natural in late Ma.y thtough mid-August during the
filling process as high flaws are stored in the
reservoir (F1gure 70).
Stage II
Filling
Filling flows under Stage II would be of short duration,
consequently habitat availability during this period is
more appropriately discussed under operation.
352
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1 ' i
r Table 22. Estimated change in chinook rearing habitat in Group 8 due to
filling under dry, average and wet conditions.
r·
~-
Month
Dry Year
June
July
August
September
Average Year
June
July
August
September
Wet Year
June
July
August
September
Discharge Ccfs)
Natural Filling
21,763
19,126
17,392
10,422
27,815
24,445
22,228
13,221
31,580
27,753
25,236
15,124
7.,800
s.,ooo
8,000
5,800
8,800
12,740
12,415
6,800
10,750
20,547
15,505
6,800
353
Rearing Habitat (sg ft WUA) _
Natural Filling Change
414,540
263,687
250,008
11,857
547,733
536,414
467,480
73,181
460,880
548,561
,543,840
135,768
0
0
0
0
0
64,601
55,901
0
16,552
369,992
164,776
0
-100.00
-100.00
-100.00
-100.00
-100.00
-87.96
-88.04
-100.00
-96.41
-32.55
-69.70
-100.00
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----+-----~--~~----.JUNE .JULY AUGUST SEPT
ST~,
111
II
Mean weekly discharge {upper),
chinook rearing WUA for Group
8 (middle) and nercent change
in WUA ( 1 ower) eAceeded 90, s.o,
and 10 percent of the time 'for
natural and Stage I flows.
ALASKA POWER AUTHORITY
i :.~ ~ I T N A H Y D R 0 E l E C T R I C P R 0 J E C T
FIGURF,. 141 ENTRIX, INC. HARZA·E BASCO
SUSITNA JOINT VENTURE
354
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Percent of Time Equaled or Exceeded
Group 8 -< :::)
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t-< t--CD 1 < :X:
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~ ~ ~ m 100
Percent of Time Equaled or Exceeded
Flow duration curve and
chino~k rearing habitat
duration curve for Group 8. ALASKA POWER AUTHORITY
FIGURE 142
SUSITNA HYDROELECTRIC PROJECT
ENTRIX, INC.
355
HARZA·E BASCO
SUSITNA JOINT VENTURE
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Percent change in flow (upper)
and chinook rearing habitat
{lower) from previous week in
Group 8 during Stage I
exceeded 10, 50 and 90 percent
8 15 22 29 5 12 19 26 2 9 16
.JULY AUGUST SEPT
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
HARZA·E BASCO of the time. FIGURE 143 ENTRIX, INC. SUSiiNA JOINT VENTURE
..
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•• Operation
Habitat availability under natural and Stage II flows is
compared in a weekly habitat time series plot and
seasonal habitat duration curve {Figures 144 and 142).
Stage II operational flows \'iOUld result in elimination
of Group VIII habitat reductions 50 percent of the time
through July and reductions ·to 90 percent or more in
June. At the end of July the magnitude of these
reductions would decrease and by mid-August habitat
availability would be about the same as natural.
With .. project habitat stability during Stage II would be
less than under natural conditions for most of the
summer rearing period. Week to week increases inhab1tat
of 200 percent or more would frequently occur. In
September natural and project weekly variations in the
amount of rearing habitat would be similar (Figure 145).
The contribution of Group 8 to total middle Susitna
River habitaL would decrease under Stage II from natural
levels of 3 to 9 percent to 0 to 1 percent in May and
June. The percent contribution would increase during
July and would be similar to natural from mid-August to
mid-September (Figure 73).
Stage III
• FiJ 1 tnq
Filling of Watana during Stage III would occur over
severa1 years and consequently habitat availability is
more appropriately discussed under operation.
357
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~y .JUNE ,JULY AUGUST SEPT
i o .t----,--r--·--,-~::::::---HI
(J-20
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-tml-.-M,.6;;:~~::::::;:::::::J::w:;U~NE-t----+--J""'ut:::...:f--+-"!:AU:-:':G:t.U=ST::+--+-;S::!:EP~T
Mean weekly discharge (upper),
chinook rearing WUA for Group
8 (middle) and percent change
in WUA {lower)exceeded 90, 50,
and 10 percent of the time for
natural and Stage II flows. AlASK.A. POWER AUTHORITY
SUSITN,&. HYDROELECTRIC PROJECT
FIGURE 144 ENTRIX, JN,C. HARZA·E BASCO
SUSITNA JOINT VENTURE
358
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MAY JUNE JULY AUC1JST SEPT
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~ -1~~-4~~~~~~~~~~--~~-r~--~~~~
20
MAY ~UNE ~ULY AUGUST SEPT
ALASKA POWER AUTHORITY
SUSITNA HYOROELECTR:c PROJECT
Percent change in flow (upper)
and chinook rearing habitat
(lower) from previous week in
Group 8 during Stage II
exceeded 10, 50 and 90 percent
of the time. ... --------······.:·~..-----------·
FIGURE 145 ENTRIX, INC. HARZA-E BASCO
SUSITNA JOINT VENTURE
..