HomeMy WebLinkAboutAPA2430'EDERAL ENERGY ReGULATORY COMM.88.0N
PROJECT No.711.
SUSITNA
HYDROELECTRIC PROJECT
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EVALUATION
OF ALTERNATIVE
FLOW REQUIREMENTS
FINAL REPORT
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A JOINT VENTURE
NOVEMBER 1984
DOCUMENT No.2430
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SUSITNA HYDROELECTRIC PROJECT
Document No.2430
Susitna File No.4.3.4.1
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EVALUATION OF ALTERNATIVE FLOW REQUIREMENTS
Report by
Harza-Ebasco Susitna Joint Venture
Prepared for
Alaska Power Authority
Final Report
November 1984
ARLIS
Alaska Resources
Library &Information ServiCeS.
Anchorage,Alaska
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ROTICE
AllY QUESnOllS OR CClQlElITS CONCERNING
THIS REPORT SHOULD BE DIRECTED TO
THE ALASU POIER AUTHORITY
ARLIS
Alaska Resources
Library &Information Services
Jlnchorage,AJa~ka
Section/Title
SUSITNA HYDROELECTRIC PROJECT
EVALUATION OF ALTERNATIVE
FLOW REQUIREMENTS
TABLE OF CONTENTS
1.0 INTRODUCTION
1.1 LICENSE APPLICATION FLOW CASES
1.1.1 Range of Flows....,1.1.2 Selection of Case C
1.2 REFINED FLOW CASES
I.2.1 Power and Energy
~.,1.2.1.1 Project Operation
1.2.1.2 Power and Energy Flow Case
1.2.2 Environmental Cases
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2.0 DETAILED DISCUSSION OF REFINED FLOW CASES
2.1 ENVIRONMENTAL FLOW CASES
2.1.1 Case EI
2.1.2 Case En
2.1.3 Case EIII
2.1.4 Case EIV-2.1.5 Case ElVa
2.1.6 Case EIVb
2.1.7 Case EV-2.1.8 Case EVI
3.0 COMPARISON OF FLOW CASES
3.1 ECONOMIC COMPARISON.....3.2 ENVIRONMENTAL COMPARISON
3.3 SELECTION OF PREFERRED INSTREAM FLOW REQUIREMENTS
4.0 ENVIRONMENTAL FLOW REQUIREMENT CASE EVI
4.1 MANAGEMENT OBJECTIVE
4.2 FLOW CONSTRAINTS
4.3 PROJECT FLOWS
4.4 IMPACT ASSESSMENT
5.0 BIBLIOGRAPHY
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--LIST OF TABLES
Number Title Page
1 Weekly Mean Flows at Gold Creek for Flow Case C 7
-2 Water Weeks for Water Year N.8
3 Flow Constraints for Environmental Flow Requirement
Case El 13
4 Flow Constraints for Environmental Flow Requirement
Case EII 16-\
5 Flow Constraints for Environmental Flow Requirement
Case EIIl 21
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6 Flow Constraints for Environmental Flow Requirement
Case ElV 24
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7 Flow Constraints for Environmental Flow Requirement
Case ElVa 29
8 Flow Constraints for Environmental Flow Requirement
Case ElVb 33
9 Flow Constraints for Environmental Flow Requirement
Case EV 36
10 Economic Analysis of Flow Cases 44-
11 Flow Constraints for Environmental Flow Requirement
Case EVl 47
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LIST OF FIGURES
Number Title Page
1 Environmental Flow Requirements Case El 14
2 Environmental Flow Requirements Case Ell 17
3 Environmental Flow Requirements Case £III 22
4 Environmental Flow Requirements Case ElV 25
5 Environmental Flow Requirements Case ElVa 30
6 Environmental Flow Requirements Case ElVb 34
7 Environmental Flow Requirements Case EV 37
8 Environmental Flow Requirements Case EVl 48
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SUSITNA HYDROELECTRIC PROJECT
EVALUATION OF ALTERNATIVE FLOW REQUIREMENTS
1.0 INTRODUCTION
1.1 LICENSE APPLICATION FLOW CASES
1.1.1 Range of Flows
The flow cases analyzed in the License Application for the Susitna Project
ranged from the operational flow that would produce the maximum amount of
usable power and energy benefits from the project,referred to as Case A,to
the one which would result in minimum flow-related impacts on the downstream
fishery resources rela ti ve to natural condi tions,referred to as Case G.
Eight additional flow scenarios were analyzed between these two extremes.
The monthly flow requirements at Gold Creek for each of these cases are
presented in the License Application,Table B.54.
1.1.2 Selection of Case C
To determine the net economic value of the energy and power produced by the
Susitna Hydroelectric Project.the mathematical model known as OGP
(Optimized Generation Planning)was used to determine the present worth of
the long-term (1993-2051)production costs of supplying the Railbelt energy
needs by various alternative means of generation.The analysis was per-
formed for the best "without Susitna"(all thermal)option as well as for
the "with Susitna"option using the ten flow cases mentioned above.The
results of the "with Susitna"analysis are presented in Table B.57 of the
License Application.The resul ts of this analysis can be summarized as
follows:as summer flows are increased for environmental reasons the net
power and energy benefits decrease.This decrease in net benefits becomes
more pronounced as minimum summer flows are increased above those required
in Case C.
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Based upon the instream flow studies conducted up to the time of the license
submittal,it was concluded that for flows of the Case A magnitude,severe
impacts would occur to the existing fish populations,particularly in the
middle river,and these impacts could not be mitigated except by compensa-
tion through construction and operation of hatcheries.Case C requirements
minimized these impacts through control and timing of flow releases.The
August 1 to September 15 minimum flow of 12,000 cfs was the primary focus of
Case C and was intended to provide access into side slough spawning habitat.
With August flows in the 12,000 cfs range (Case C),salmon can access a
number of traditional spawning sloughs.To further insure that salmon could
obtain access to slough spawning areas at a flow of 12,000 cfs,a series of
habitat alterations were incorporated into the mitigation plan presented 1n
the License Application •
Cases A,AI,and A2 do not allow mitigation of the impac ts caused by the
changed flows through habitat alteration.Based on economic analysis and
the fishery analys is,it was judged that the loss in ne t energy and power
benefits for Case C was acceptable,while the loss associated with Case C1
was on the borderline between acceptable and unacceptable.The potential
decrease in mitigation costs associated with higher flows would not offset
the loss in net energy benefits.Thus,Case C was selected as the flow case
presented in the License Application.
1.2 Refined Flow Cases
1.2.1 Power and Energy
1.2.1.1 Project Operation
The Power Authority's goal is to operate the project to maximize power and
energy benefits within environmental and operational constraints.Environ-
mental constraints include maximum and minimum downstream flows (termed flow
requirements)and maximum rates of change of flow.Operational constraints
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include:a m1n1mum reservoir level,a maximum reservoir level which if
exceeded results in a prespecified operating procedure,maximum output of
the turbines,minimum turbine output,and system electrical energy demand.
Generally,the project would be operated to store high summer flows when
energy demands are low and then releasing these flows in winter when energy
demands are high.To maximize the power and energy benefits of the project,
the reservoir should be close to,or at,the normal maximum operating level
at the beginning of October of each year and close to,or at,the minimum
operating level at the end of April of each year.This permi ts greater
power and energy generation in the months from October to April when energy
is most valuable.During this period,energy would be generated in direct
proportion to the system electrical demand.This is accomplished in average
and high flow years by discharging water from the reservoir to match weekly
or monthly target reservoir water levels and 1n lower flow years by
producing a specified minimum energy in each weekly or monthly period.The
target water levels and minimum energy production are established based on
the historic streamflow record.The natural inflow to the reservoir and the
water taken out of storage to meet the target reservoir elevations are used
to produce energy during each specified time interval.In low flow years,
if the energy produced by meeting the target reservoir water levels is less
than the minimum energy production,addi tional water is wi thdrawn from
storage to provide the minimum prescribed energy.The minimum energy is
determined using a dry hydrological sequence with a specified frequency of
occurrence.The end of this dry period corresponds to the beginning of the
spring snow melt runoff period by which time the reservoir is drawn down to
its minimum elevation.
From May to September,the target reservoir elevation is increased from one
time step to the next to store the summer flows for release the following
winter.Water levels are established so that the energy produced remains a
fixed proportion of the system energy demand for each time step with the
objective that the reservoir is at or close to the normal maximum operating
level at the end of September.Further,it is desirable to avoid premature
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filling of the reservoir because this would result in release of water with
less energy producing benefits.Minimum flow requirements during summer may
be greater than the flow resulting from normal energy production.When this
occurs,energy production is increased up to the system energy demand until
the minimum flow requirements are met.Since only usable energy can be
produced,the remainder of any minimum flow requirement after the power
house flow is subtracted 1S made up by releases from the fixed cone valves.
As in winter operation,summer reservoir operation is required to produce a
minimum specified energy during each time interval.
1.2.1.2 Power and Energy Flow Case
An operational flow regime (P-l)was established to provide a basis for an
economic comparison of alternative flow regimes resulting from various
environmental constraints.Case P-1 maximizes power and energy benefits of
the project irrespective of environmental considerations.Project benefits
are optimized based on two objectives.In minimum flow years,the project
would operate to minimize the thermal capacity requirements in the railbelt
system.In all other years,the project would operate to take advantage of
the most efficient operation of thermal generating units.To achieve these
objectives,the project would operate to permit thermal energy generation at
a constant level throughout the year.In terms of reservoir operation,this
is accomplished by subtracting the annual energy available from the project
from the total annual energy demand.The remaining energy is assumed to be
distributed uniformly through the year and would be generated by thermal and
other hydro plants.For each time interval,the Susitna project would
provide the difference between the system energy demand and the constant
thermal energy production.This strategy is subject to the added
consideration that the October to April energy is limited by the usable
storage and natural reservoir inflow.This limitation could result in two
periods of constant thermal generation:an October to April period and a
May to September period.The October to April period would require a higher
level of constant thermal energy generation because of the reservoir storage
limitations.
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Case P-l flows average 9,700 cfs at Gold Creek during the October to April
period.Beginning in October,flows are gradually increased,reaching a
peak in December.From January through May,flows gradually decrease.
Maximum December flows at Gold Creek could reach as high as 14,000 cfs but
more often would be approximately 12,000 cfs.During the winter,minimum
flows are rarely less than 7,000 cfs.Flows less than 7,000 cfs occur only
in unusually low flow years at the end of the winter period.
The average flow during summer operation (May-September)~s the same as in
winter.During this period,however,flow variability is much greater than
during winter operation.During high flow years,the monthly or weekly
average discharge at Gold Creek might approach 20,000 cfs in May,June or
July.In August and September when the reservoir is more likely to be full,
discharge at Gold Creek could exceed 20,000 cfs.In low flow years,the
flow at Gold Creek could be as low as 4,500 cfs for extended periods.
Summer flow would be less than 7,000 cfs about 30 percent of the time.
1.2.2 Environmental Cases
The environmental flow scenarios presented in the License Application
contained flow constraints to satisfy particular habitat needs during
specific time periods.These constraints focused on species,habi tat,and
timing criteria thought at that time to be important or cri tical.The
constraints were derived to satisfy limited resource management objectives.
For example,the environmental flow components of Case C were designed to
maintain suitable conditions for upstream migration of adult salmon during
the early summer and provide access to side sloughs by chum salmon for
spawning during August and September.This approach failed to consider any
flow constraints to protect chum incubation.
Results of several additional studies and analyses have become av.ailable
since submittal of the License Application.These new data have allowed the
Power Authority to develop more detailed and refined environmental flow
requirements to meet specific management objectives.The Power Authori ty
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has evaluated eight new environmental Cases.Each new Case is an expansion
or refinement of Case C in the Lic~nse Application.However,where Case C
(Table 1)was a combination of power demand flows over the entire year with
minimum environmental flow requirements only for cri tical times,the new
cases establish weekly minimum and maximum environmental flows for an entire
year.(See Table 2 for relationship of calendar weeks to water weeks.)The
minima and maxima are limits within which the project is constrained to
operate if stated management objectives are to be achieved.Actual flows
within these limits will depend on operational criteria aimed at maximizing
the power and energy benefits of the project.
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Table 1
SUSITNA HYDROELECTRIC PROJECT
WEEKLY MEAN FLOWS AT GOLD CREEK
FOR FLOW CASE C
Water Gold Creek Flow (cfs)Water Gold Creek Flow (cfs)
Week Minimum Maximum (1)Week Minimum Maximum
14 5,000 40 6,000
15 5,000 41 6,000
16 5,000 42 6,000
17 5,000 43 6,400(3)
18 5,000 44 11,100(4)
19 5,000 45 12,000
20 5,000 46 12,000
21 5,000 47 12,000
22 5,000 48 12,000
23 5,000 49 12,000
""'"24 5,000 50 11,900(5)
25 5,000 51 7,400(6)
26 5,000 52 6,000(7)
27 5,000 1 5,000
28 5,000 2 5,000
29 5,000 3 5,000
30 5,000 4 5,000
31 5,700(2)5 5,000
32 6,000 6 5,000
33 6,000 7 5,000,.....34 6,000 8 5,000
35 6,000 9 5,000
36 6,000 10 5,000-37 6,000 11 5,000,
38 6,000 12 5,000
39 6,000 13 5,000
......(1)Maximum flow constraints were not established for Case C
(2)2 days at 5,000 cfs then 5 days at 6,000 cfs
(3)5 days at 6,000,1 day at 7,000,1 day at 3,000 cfs-(4)1 day each at 9,000,10,000 and 11,000 and 4 days at 12,000 cfs
(5)6 days at 12,000 cfs,1 day at 11,000 cfs
(6)1 day each at 10,000,9,000,8,000 and 7,000 cfs and 3 days at 6,000
r-cfs
(7)8 days at 6,000 cfs
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Table 2
SUSITNA HYDROELECTRIC PROJECT
WATER WEEKS FOR WATER YEAR N.
WEEK WEEK
NUMBER FROM TO NUMBER FROM TO-
day month year day month year day month year day month year
1 1 Oct.n-l 7 Oct.n-l 27 1 Apr.n 7 Apr.n
2 8 Oct.n-l 11+Oct.n-l 28 8 Apr.n 11+Apr.n
3 15 Oct.n-l 21 Oct.n-l 29 15 Apr.n 21 Apr.n
1+22 Oct.n-l 28 OCt.n-l 30 22 Apr.n 28 Apr.n
5 29 Oct.n-l 1+Nov.n-l 31 29 Apr.n 5 May n
6 5 Nov.n-l 11 Nov.n-l 32 6 May n 12 May n
.-7 12 Nov.n-l 18 Nov.n-l 33 13 May n 19 May n
8 19 Nov.n-l 25 Nov.n-l 31+20 May n 26 May n
9 26 Nov.n-l 2 Dec.n-1 35 27 May n 2 June n
10 3 Dec.n-1 9 Dec.n-l 36 3 June n 9 June nr'"'11 10 Dec.n-l 16 Dec.n-l 37 10 June 16 JuneIn n
12 17 Dec.n-l 23 Dec.n-l 38 17 June n 23 June n.
13 21+Dec.n-l 30 Dec.n-1 39 24 June n 30 June n
14 31 Dec.n-l 6 Jan.n 1+0 1 July n 7 July n
15 7 Jan.n 13 Jan.n I+l 8 July n 14 July n
16 11+Jan.n 20 Jan.n 42 15 July n 21 July n....17 21 Jan.n 27 Jan.n 1+3 22 July n 28 July n
18 28 Jan.n 3 Feb.n 41+29 July n 1+Aug.n
19 4 Feb.n 10 Feb.n 1+5 5 Aug.n 11 Aug.n
20 11 Feb.n 17 Feb.n 1+6 12 Aug.n 18 Aug.n-21 18 Feb.21+Feb.1+7 19 Aug.25 Aug.n n n n
22 25 Feb.n 3 Mar.n 48 26 Aug.n 1 Sep.n
23 4 Mar.n 10 Mar.n 1+9 2 Sep.n 8 Sep.n
r-24 11 Mar.n 17 Mar.n 50 9 Sep.n 15 Sep.n
25 18 Mar.n 21+~r.n 51 16 Sep.n 22 Sep.n
26 25 Mar.n 31 Mar.n 52 23 Sep.n 30 Sep.n
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2.0 DETAILED DISCUSSION OF REFINED FLOW CASES
2.1 ENVIRONMENTAL FLOW CASES
Environmental flow cases EI through EVI t as discussed below tare
based on interpretation and analysis of all the data and informa-
tion available regarding Susitna River fisheries resources and
their habitats.Flow constraints contained in each case are based
on the physical characteristics of particular habitats and uses of
habitat by particular species and life stages under natural flow
conditions.The potential for new habitat with the same
characteristics but at different locations under project operation
flows was not considered.
Development of the flow cases emphasized maintenance of habitats
most responsive to mainstem flows.Rearing habitats in mainstem
backwater areas,side channels and side sloughs were given greatest
emphasis.Side sloughs are the most'important spawning habitat
affected by mainstem flows.Flow constraints for maintenance of
summer rearing habitat included two important considerations.
Minimum summer flow cons traints were es tab lished to preserve the
desired quantity of existing habitat and summer maximums were
established to prevent extensive dislocation of rearing juveniles
(i.e.,provide greater flow stability).Flow constraints for
juvenile over-wintering habitat were chosen to provide general flow
stability and to minimize mainstem over-topping of side slough
berms.
Mainstem flows affect both access to,and wetted area within,side
sloughs.Minimum flow constraints were chosen to provide a
specific minimum level of access and wetted area within chosen
critical sloughs.These flow constraints are limited to August and
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2.1.1
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September when chum and sockeye salmon enter the sloughs and spawn.
Several cases include spiking flows.These short duration releases
of relatively high volumes of water fulfill two purposes.Spiking
flows in June provide over-topping flows into side sloughs to clear
debris and sediments out of spawning areas and are not required
every year.Spiking flows during August and September are to
augment access conditions in side sloughs.
Minimim flow constraints are generally used to maintain a specified
level of habitat quantity.Maximum flow constraints are generally
used to provide flow stability (habitat quality)or minimize over-
topping of mainstem water into side sloughs.
The following sections present cases EI-EV.A more detailed des-
cription of EVI,the selected case,is presented in Section 4.0.
Case EI
Management Objective
Case EI 1.S a set of flow constraints necessary to maintain the
quality and quantity of existing habitats,and represents the "no-
impact"bound of the analysis.A corollary to this statement is
that Case EI achieves no net loss in productivity strictly through
flow control and proper timing of flow releases.Maintenance of
existing habitat and productivity does not require exact
duplication of natural flow patterns and,in fact,some
productivity benefits can accrue to downstream aquatic resources
through increased stability by flow regulation.
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o Flow Constraints
The EI flow constraints are shown in Table 3 and Figure 1.Summer
flow constraints were chosen principally to maintain existing
juvenile salmon rearing habitats.These flows also provide passage
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conditions for upstream migration of adults.A 45,000 cfs spike is
provided in June to purposely overtop sloughs and clean sediments
and debris out of spawning areas.This spiking flow is not
necessary in each year of operation.Flows of this magnitude may
be necessary once every three to four years to achieve this
purpose.Two flow spikes,23,000 and 18,000 cfs,are provided in
mid-August to allow unrestricted access by adult spawners into side
sloughs.Winter minimum and maximum flows were chosen to maintain
adequate over-wintering habitat and protect incubating eggs 1.n
side-slough habitats.
Project Flows
Case EI flows average 8,000 cfs at Gold Creek during the October to
April period.Powerhouse discharge is increased from October to
December and then decreased from December to April.December
discharge can be as high as 12,000 cfs,but averages 9,600 cfs.
The high minimum summer flow requirements result in low flows
during the months of October,March,and April in low flow years.
October flows are always greater than 4,000 cfs but 50 percent of
the time,they are less than 6,000 cfs.In March,minimum flows
approach 4,000 cfs.In April,flow is as low as 2,300 cfs during
dry years.
Because of the high minimum summer requirements of Case EI,flow
during May is purposely held low'-Average flow during May is 6,000
c fs.During years when snowmelt is delayed,minimum flow will be
close to the minimum flow constraint of 2,000 cfs.During the
months of June,July,August and September,project flows are the
same as the minimum flow requirements 80 percent of the time.
During the other 20 percent of the time,the project operation
flows are usually only slightly greater than the m1.n1.mum
requirements.Flows would closely follow the minimum constraints
during June through September,except during periods of high run
off.
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Impact assessment
The flow constraints in Case EI were chosen to maintain existing
spawning and rearing habitats.No loss of production 1S antici-
pated.Certain aspects of water quality will be changed by project
operation.The natural temperature and turbidity regimes will be
altered.Mainstem water temperatures will be generally cooler in
the summer and warmer in the winter.However.these changes are
well within the known tolerances of fishes utilizing mainstem
habitats (APA.1984a)and no significant change of production is
anticipated (see Power Authority comments on DElS Nos,AQR100.
AQR108,AQR1l9 and AQR123).Turbidity levels will be less in the
summer and greater in the winter than under natural conditions.
Turbidity levels in the winter will be less than natural summer
levels and are within the range of tolerance for existing Susitna
River stocks.The projected temperature and turbidity impacts are
generally the same for all the cases and will not be repeated for
each •
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Table 3
SUSITNA HYDROELECTRIC PROJECT
F""'FLOW CONSTRAINTS FOR ENVIRONMENTAL
FLOW REQUIREMENT CASE EI.
,....
Water Gold Creek Flow (cfs)Water Gold Creek Flow (cfs)
Week Minimum Maximum Week Minimum Maximum-,.....
14 2,000 14,000 40 14,000
15 2,000 14,000 41 14,000
16 2,000 14,000 42 14,000
17 2,000 14,000 43 14,000
18 2,000 14,000 44 14,000 40,000
19 2,000 14,000 45 14,000 40,000
~20 2,000 14,000 46 (2)40,000
21 2,000 14,000 47 (3)40,000
22 2,000 14,000 48 14,000 40,000
23 2,000 14,000 49 12,000 14,000
24 2,000 14,000 50 10,000 14,000
25 2,000 14,000 51 8,000 14,000
26 2,000 14,000 52 6,000 14,000
27 2,000 14,000 1 6,000 14,000
28 2,000 14,000 2 6,000 14,000
29 2,000 14,000 3 5,000 14,000
30 2,000 14,000 4 4,000 14,000
31 2,000 14,000 5 3,000 14,000
32 2,000 14,000 6 3,000 14,000
-.33 2,000 14,000 7 3,000 14,000
34 2,000 14,000 8 3,000 14,000
35 2,000 14,000 9 2,000 14,000
36 10,000 10 2,000 14,000
37 (1)11 2,000 14,000
38 14,000 12 2,000 14,000
39 14,000 13 2,000 14,000
(1)Base minimum flow of 10,000 cfs.45,000 cfs spike;3 days up,
3 days down.
(2)Base minimum flow of 14,000 cfs.23,000 cfs spike;1 day up,1 day
down.
-(3)Base minimum flow of 14,000 cfs.18,000 cfs spike;1 day up,1 day
down.
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1 --1-1--)--1 ---I 1
Figure 1
ENVIRONMENTAL FLOW REQUIREMENTS CASE E I
1 -1
OCT',NOV '.0JUL·•AUG ..8EPJUNMAYAPRJAN.FEB
10,000
60,000 1 I I I I ~lllllr~il,ll,fi 1 I I I 1NOTE
1.DISCHARGE FOR
I¥IITNA ItIYIItII~II 2'&i~litI1'\\~
40,000 :.::.,...::.:.:.:.:.:.:.::.:.:.:.:.:.:.:.:.:'::::.E~~E~~tfi .8~"•
';:il~rll~ll'~I((!il!f.
WEEKLV INTERVAL'
,....en
IL.
(.)......,30,000 I I I I I =:J [iAC.I:i:::::::::i:i::::::t::::::I:::::::iIi:m:::i:::::::::U:f:i.:::::::r::t:::::::.I I I I
W
"~
llI(:z:(.)20,000 I I I I I I I r;'''''''f ~·"·'···""";"f.·"··'i"..······('·..············..·t ..·····.fI)-·'.'.i."~,i•.wb.'_~u....k~"")(...",~~I I I I I I
is
o Mitigation
Case EI was designed to maintain existing habitat.Potential loss
of these habitats would be minimized through timing and control of
flow releases.Mitigation efforts to rectify,reduce or compensate
for impacts would not be necessary.An extensive monitoring
program would be conducted to measure the success of this plan in
achieving the desired goal of no net loss in productivity.
2 •1.2 Cas e E II
o Management objective
Case Ell 1S a set of flow constraints necessary to maintain 75%of
existing chum salmon side-slough spawning habitat.This is not
~~synonomous with maintenance of 75%of chum salmon production in the
Susitna River system.Estimated numbers of chum salmon spawners in
s ide sloughs of the middle river were less than 2%of the total
escapement past Sunshine Station during the past three seasons
(1981-83:ADF&G,1984a).
o Flow Constraints
Case Ell flow constraints are presented in Table 4 and Figure 2.
Early summer minimum flow constraints are intended to provide for
successful exit of juvenile chum from slough spawning areas and for
initial downstream passage and rearing.A 35,000 cfs spike 1S
provided in mid-June to overtop sloughs and clear spawning areas of
sediments and debris.Minimum July flows of 6,000 cfs will provide
for successful upstream passage of migrating adults.Maximum flow
cons traints are not necessary during this period to satisfy the
management objective.Minimum August flows of 12,000 cfs will
provide access to side sloughs by adult spawners.An 18,000 cfs
spike is provided in early September to augment access
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Table 4
SUSITNA HYDROELECTRIC PROJECT
FLOW CONSTRAINTS FOR ENVIRONMENTAL
FLOW REQUIREMENT CASE Ell •
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Water Gold Creek Flow (cfs)Water Gold Creek Flow (cfs)
Week Minimum Maximum Week Minimum Maximum
14 2,000 16,000 40 6,000
15 2,000 16,000 41 6,000
16 2,000 16,000 42 6,000
~"nI 17 2,000 16,000 43 6,000
18 2,000 16,000 44 11,000
19 2,000 16,000 45 12,000 30,000
20 2,000 16,000 46 12,000 30,000
21 2,000 16,000 47 12,000 30,000
22 2,000 16,000 48 12,000 30,000
23 2,000 16,000 49 (2)30,000
24 2,000 16,000 50 9,000 16,000
25 2,000 16,000 51 9,000 16,000
26 2,000 16,000 52 8,000 16,000
27 2,000 1 6,000 16,000
28 2,000 2 6,000 16,000
29 2,000 3 6,000 16,000
30 2,000 4 6,000 16,000
31 2,000 5 3,000 16,000
32 4,000 6 3,000 16,000
33 6,000 7 3,000 '16,000F-34 8,000 8 3,000 16,000
35 8,000 9 3,000 16,000
36 10,000 10 2,000 16,000
37 10,000 11 2,000 16,000
38 (1)12 2,000 16,000
39 6,000 13 2,000 16,000
(1)Base minimum flow of 6,000 cfs.35,000 cfs spike;3 days up,
3 days down.
(2)Base minimum flow of 12,000 cfs.18,000 cis spike;1 day up,1 day
down.-
410454
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16
J el -u J 1 1 1 ···~····l I )J 1 J 1 ]
Figure 2
ENVIRONMENTAL F'LOW REQUIREMENTS CASE E l[
DECNOVOCTSEPAUG
NOTE
1.DISCHARGE FOR SUSITNA
RIVER AT GOLD CREEK
2.PERCENT OF TIME NATURAL
FLOW IS EQUALLED OR
EXCEEDED.CURVES ARE
.BASED ON 34 YEARS OF
WEEKL Y AVERAGED FLOWS
WITH OCT.1-7 AS FIRST
I-----.+-I-WEEK OF 52 WEEKLY
INTERVALS
JULJUNMAYAPRFEBJAN
:?:..;::.;<.,::;:::>:'"';';':':','
10,000
10 000 • ,i •.:.,.,:.).~.:·.·.·.·.·.1·.-.·.·.·.··..~-:.:..:.:..'¥~.:.:.:.:-:·.·.·.·.·.·1.:.:.:.:·:·:·.·:·.·,·.·.·.·.·.·.:.·.:.:.:.:.;•
0',j I ,j ,,I ,1 I ,
40.000 I I I t~:~::::·:·:(i!ii:::::::::~:~:):::::l:::::::;:;t~:~:~:~:~{/~::::)((i:i:!:!f:!lr::!:t.ti',::::::i:'::::I:::::::::X:::::::::::::·:::~:t~:n~:~
w
"a:-e:z "~OOO ,I,---r-'-~~---1 ••u I 1':::::::::::::::::::::,:.:,:::::::::::::
(I)-C
.......en
ILU 30,000.....,
-
.-
-
-
-
o
o
410454
841030
to important.side slough sites.Minimum flow constraints during
the winter resemble natural flow conditions and are simply to
prevent unusual dewatering of spawning sites.Maximum winter flow
constraints of 16,000 cfs provide a moderate level of protection to
eggs incubating in side sloughs.
Project Flows
Project flows for Case Ell are similar to those of Case EV except
that the October to April flows would be higher for Case Ell to
reflect the fact that the July minimum flows for Case Ell are lower
than for Case EV.Flows from May to September would average 10,700
cfs and would be at the minimum flow about 55 percent of the time.
Impact assessment
Several of the Case Ell flow constraints are conservative.The
June spiking flow to clean side slough spawning habitat does not
have to occur every year.This spike could be provided once every
several years and still achieve its purpose.The summer spiking
flow may be in excess of that necessary to maintain access to 75%
of the existing side slough spawning habitat (see Power Authority
comment on DEIS No.AQR072).However,a 25%loss of chum salmon
side slough spawning habitat will be assumed for this analysis.
Sockeye salmon also spawn in the side sloughs most frequently used
by chum spawning.Spawning habitat loss for sockeye salmon is
expected to be similar to the losses for chum.The minimum summer
flows are adequate for upstream passage and tributary access to
migrant adults and since coho,chinook and pink salmon spawn almost
exclusively in tributaries,no loss of spawning habitat would occur
for these species.
The summer minimum flow constraints established for Case Ell would
not maintain 100%of the existing juvenile chinook rearing habitat.
18
-
-
-
--
o
410454
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The 6,000 cfs minimum flows during water weeks 39 through 43 would
result in the significant loss of existing chinook rearing habitat.
A 75%loss of existing chinook rearing habitat 1n the middle river
is thought to be a worst case estimate and will be assumed for this
evaluation.
Chum salmon juveniles also utilize mainstem affected habitats for
rearing.Sampling in the middle river indicates a majority
(approximately 60%)of the chum have left this reach prior to water
week 39 so the loss of rearing habitat would not be as great for
chum as for chinook.A worst case estimate for loss of rearing
habitat for the chum juveniles remaining in the middle river is
assumed,therefore,to be 40%.
Mitigation
Case Ell minimizes some impacts through control and timing of
flow releases.Potential impacts to slough spawning chum and
sockeye salmon are minimized by special flow releases timed to
clean spawning substrate and provide access to spawning areas.
Impacts to rearing habitats are minimized through minimum summer
flow constraints and increased stability through flow control.
The remaining impacts to slough spawning habitat would be rectified
by structural modification of slough mouths to provide suitable
access conditions at 12,000 cfs.Similar alterations would be made
within the sloughs to provide passage through critical reaches.
Loss of rearing habitat within the river would be rectified through
replacement habitat naturally provided at other locations on the
river at lower flows.The impact assessment only considered loss
of habitats utilized under natural flow conditions.The channel
structure of the middle Susitna River results in comparable habitat
being created at different locations when discharge changes.This
is supported by studies in the literature (Mosley,1982)and by
preliminary results of 1984 studies of the Susitna River.However,
these studies do not suggest total replacement at flows as low as
19
6,000 cfs.Remaining impacts to rearing habitat that could not be
rectified by flow control would be compensated by construction and
operation of a propagation facility.
2.1.3 Case EIII
o Management Objectives
Case ElII ~s designed to maximize chinook salmon production
(rearing)~n existing habitats.Chinook do not use mainstem
.....
-
o
o
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influenced habitats for spawning so maximization in this case does
not include consideration of limitations to spawning habitat.
Flow Constraints
Case ElII flow constraints are presented in Table 5 and Figure 3.
Minimum summer flow constraints of 14,000 cfs are intended to
maximize the quantity of mainstem influenced rearing habitat at
sites utilized under natural conditions.These flows would also
provide migrant adults with upstream passage and tributary access.
Maximum summer constraints are not necessary.However,it is
assumed the project would store the maximum possible quantity of
water during the summer resulting in greater flow stability.
Winter flow constraints provide adequate rearing habitat during the
ice covered season.
Project Flows
Case EIII flows during the October to April period average 7900 cfs
at Gold Creek.The Case EIII winter flows are slightly less than
the 8000 cfs average for Case EI because of the high minimum flow
requirements for Case ElII during the month of May.
From May to September the average flow for Case EIII is 12,400 cfs.
Project flow are at the minimum flow requirement during the period
75 percent of the time.
20
~
Table 5
r--SOSITNA HYDROELECTRIC PROJECT
FLOW CONSTRAINTS FOR ENVIRONMENTAL
FLOW REQUIREMENT CASE EIII.
1t<JlllllF
Water Gold Creek Flow (ds)Water Gold Creek Flow (cfs)
Week Minimum Maximum Week Minimum Maximum-~
14 5,000 14,000 40 14,000
15 5,000 14,000 41 14,000
,~16 5,000 14,000 42 14,000
17 5,000 14,000 43 14,000
18 5,000 14,000 44 14,000
19 5,000 14,000 45 14,000
20 5,000 14,000 46 14,000
21 5,000 14,000 47 14,000
22 5,000 14,000 48 14,000
23 5,000 14,000 49 12,000
24 5,000 14,000 50 10,000
25 5,000 14,000 51 8,000
26 5,000 14,000 52 6,000
27 5,000 14,000 1 6,000 14,000
28 5,000 14,000 2 6,000 14,000
29 5,000 14,000 3 6,000 14,000
~30 5,000 14,000 4 6,000 14,000
31 5,000 14,000 5 5,000 14,000
32 5,000 14,000 6 5,000 14,000-33 6,000 14,000 7 5,000 14,000
34 7,000 14,000 8 5,000 14,000
35 8,000 14,000 9 5,000 14,000
36 10,000 10 5,000 14,000
,iIiiDl!III 37 10,000 11 5,000 14,000
38 14,000 12 5,000 14,000
39 14,000 13 5,000 14,000
.....
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21
4 W
1 j I 1 I 1 )1 i f 1 J 1
Figure 3
ENVIRONMENTAL FLOW REQUIREMENTS CASE Em
1
I
!
i
u
"Hl
50,000 .......-----r-----,.---""t"---"""'T"""-----,...-----~---__._--_.....,r'""""""--..".......,r__--------_
NOTE
1.DISCHARGE FOR
SUSITNA RIVER AT
GOLD CREEK
2.PERCENT OF TIME
NATURAL FLOW 18
eQUALLED OR
40,000 I I I I I -EXCEEDED.CURVES
ARE BASED ON 34
YEARS OF WEEKLY
AVERAGED FLOWS
WITH OCT.1-1 AS
FIRST WEEK OF 52
WE~KLY INTERVALS
1 !,Iu;~I I I I Jl~30,000
"-',
;w ,CJa:
~20,000 I ..I~MAX I I
-Q
~............
O·I ,Ii'1 ~1 1 l l ,
JAN FEB MAR APR MAY JUN JUl AUG SEP OCT NOV DEC
-
o Impact Assessment
No loss of chinook and chum rearing habitat is expected with Case
EIII £I·ows.The flow constraints and increased stabi lity under
project operation should improve rearing habitat quality and
quantity compared to natural conditions.
Case EIII £lows would affect access conditions into side sloughs
for chum and sockeye spawning.The 14,000 cfs flows during August
would provide some improvement over the 12,000 cfs £lows in Case
Ell.However,some additional loss is anticipated due to elimina-
tion of spiking flows.Slough 11 would be the most affected of the
major side slough spawning sites.Approximately 66%of the slough
spawning sockeye and 17%of the slough spawning chum utilize slough
11 (1981-83 average).Restricted access conditions would not
completely eliminate utilization of sloughs for spawning and,as
noted for Case Ell,the £low criteria used in this analysis is
conservative (see Power Authori ty IS comment on DEIS No.AQR072).
Haiever,for the purpose of this evaluation,a loss of 25%of
existing slough spawning habitat for chum and 70%slough spawning
habitat for sockeye will be assumed.
"""
-
o
410454
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Mitigation
Potential impacts to rearing habi tats,tributary access and
upstream passage of adults will be avoided or minimized through
timing and control of flow releases.Impacts to side-slough access
will be minimized by flow release.
The remaining impacts to side-slough access for spawning will be
rectified by structural modification at critical access reaches to
provide successful access.
23
"'-
Table 6
SUSITNA HYDROELECTRIC PROJECT
FLOW CONSTRAINTS FOR ENVIRONMENTAL
FLOW REQUIREMENT CASE EIV.
Water Gold Creek Flow (cfs)Water Gold Creek Flow (cfs)
Week Minimum Maximum Week Minimum Maximum
14 2,000 16,000 40 9,000 35,000
15 2,000 16,000 41 9,000 35,000
16 2,000 16,000 42 9,000 35,000-17 2,000 16,000 43 9,000 35,000
18 2,000 16,000 44 9,000 35,000
19 2,000 16,000 45 9,000 35,000
20 2,000 16,000 46 9,000 35,000
21 2,000 16,000 47 9,000 35,000
22 2,000 16,000 48 9,000 35,000
"""23 2,000 16,000 49 8,000 35,000
24 2,000 16,000 50 7,000 35,000
25 2,000 16,000 51 6,000 35,000
26 2,000 16,000 52 6,000 35,000
.-'1 27 2,000 16,000 1 6,000 18,000
28 2,000 16,000 2 6,000 17,000
29 2,000 16,000 3 5,000 16,000
I"'""30 2,000 16,000 4 4,000 16,000
31 2,000 16,000 5 3,000 16,000
32 4,000 16,000 6 3,000 16,000
33 6,000 16,000 7 3,000 16,000
34 6,000 16,000 8 3,000 16,000
35 6,000 16,000 9 3,000 16,000
36 9,000 35,000 10 2,000 16,000-37 9,000 35,000 11 2,000 16,000
38 9,000 35,000 12 2,000 16,000
39 9,000 35,000 13 2,000 16,000
-
....
410454
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24
-
J 1 1 1 1 1 ~·····ll I J )1 I ]1 1
Figure 4
ENVIRONMENT AL FLOW REQUIREMENTS CASE E]][
DEC
•
NOVOCTSEPAUGJULJUNMAYAPRMARFEBJAN
lil4JI
O'~•I ,•~••i •I I
40,0001 I i I I i II I I I
",GOO I iii iii i f NOTE I ,I •
1.DISCHARGE FOR SUSITNA
AIVEA AT GOLD CREEK
I I I I I I ~I I 12.PERCENT OF TIME NATURAL
FLOW IS EQUALLED OR
EXCEEDED.CURVES ARE
BASED ON 34 YEARS OF
WEEKLY AVERAGED FLOWS
WITH OCT.1-1 AS FIRST
WEEK OF 52 WEEKLY
INTERVALS
iJ'
r'"
~'.
~10,000
t:1~
~
Z
Htt3"-'r.::~o!;It;!
o
.~j
........en
IL I j r·;-;-,·"'ttj'j'j'j'i'j'j'j'tj"'jf'·"f'tj'·'j'";-'·;-'·'·'j'j'i'I'i'il'j'i'i'>j(''''ri'i'i'i'i'(ifi:i:i:i:i:i:i:i:i:i:i:i:j:i:i:i:i:i:}il I I IU.,000 I I I I ..!.~.!..!-.................•...•.......,.
~
III
"a:
lII(
:I:U .0.000 Ito I I
_'I
Q I I I ti/n:x::;:x;nmm@{@i@!Jil!ijC1T'f"'w"".'.., ·.J..!.t~I (fi·i·i·j '1........',','.~.'..,..!.~.!.!:!:,I I
2.1.4 Case EIV
o Management Objectives
Case EIV u designed to maintain 75%of the middle river side
channel rearing habitat presently utilized by juvenile chinook
salmon.
-
o Flow Constraints
The minimum summer flow constraint of 9,000 cfs (Table 6,Figure 4)
is intended to maintain approximately 75%of the existing middle
river side channel rearing habitat utilized by juvenile chinook
salmon under natural flow condi tions.The maXl.mum summer flow
constraint of 35,000 cfs is intended to produce moderate flow
stability and prevent severe dislocation of rearing juveniles from
preferred sites.
Winter constraints are designed to maintain flow stability within
reasonable boundaries.The 2,000 cfs minimum is within the range
of winter flows encountered under natural conditions,while the
16,000 cfs maximum would provide for flow stability and reduce the
appearance and disappearance of transient rearing sites which
occurs under natural conditions.
-
.....
o Project Flows
Case EIV minimum summer flow requirements would result l.n an
average flow of 9500 cfs at Gold Creek during the October to April
period.This is only slightly lower than the winter average flow
for Case P-l (9700 cfs).During higher flow years,when the
reserVOl.r is filled prior to October,winter flows would be the
same as for Case P-l.In lower flow years.flow at Gold Creek
would be about 1000 cfs less than for Case P-l.Minimum flows in
these years would be about 6000 cfs in October and March and about
4300 cfs in April.
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26
-
o
o
410454
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May flows for Case E-IV would average 8400 cfs.These flows are
lower than for Case P-l in order to store as much water as possible
prior to the 9000 cfs minimum requirement which takes effect in
June.June,July,and August flows are at the 9000 cfs minimum
requirement approximately 55 percent of the time.Average flow for
these months is 10800 cfs.In September,project flows would be
the same as the minimum flow requirement 35 percent of the time.
Impact Assessment
Case EIV would reduce the availability of existing chinook salmon
side channel rearing habitat by approximately 25%in the middle
river.Rearing habitat now used by chum salmon juveniles would be
reduced in side-sloughs.The major use of side slough habi tat by
juvenile chum salmon occurs during May and June and habitat
reduction would result from loss of over-topping flows during this
period.Loss of habi tat could be as great as 50%at the si tes
utilized under natural flow conditions (ADF&G,1984b:Fig.9 and
10).No rearing habitat loss is expected in the lower river due to
the dominant effects of the Chulitna and Talkeetna rivers.
Flow constraints during August and September would significantly
restrict spawning access to sloughs by adult chum and sockeye
salmon.Sane successful access would still occur but with signifi-
cant difficulty.A worst case assumption of 100%loss of access is
assumed for this evaluation.
Mitigation
Impacts on chinook and chum salmon rearing habitats would be
minimized through timing and control of flow releases.A minimum
summer flow constraint of 9,000 cf s would maintain a majori ty of
the rearing habitat utilized under natural flow conditions.
Increased flow stability under project operation would have an
augmenting effect on over-all quality of the rearing habitats,
27
....
....
....
especially for side channel si tes uti lized by chinook juveni les.
Re:naining loss of existing rearing habitat would be rectified by
providing replacement habitat through control of flow releases.
Flow reductions during the summer would reduce the quantity of and
access to individual rearing si tes uti lized under natural flow
conditions.However,the same flow reduction would result in new
sites with the appropriate physical conditions for chinook and chum
salmon rearing.This result is not unusual for rivers like the
Susitna with moderately complex channel configurations.The
availability of rearing habitat for chum and chinook salmon is
actually expected to increase over natural conditions with opera-
tion under Case EIV (See Section 4.0 for further discussion).
Loss of access to side sloughs would be rectified by structural
modification of critical access reaches •
2.1.5 Case ElVa
o Management Objective
Case ElVa establishes flow constraints which would maintain 75%of
the middle river side-channel rearing habitat presently utilized by
chinook salmon juveniles and provide some access to the most
productive side slough spawning sites for adult chum and sockeye
salmon.
",..o
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Flow Constraints
Case ElVa flow constraints are presented in Table 7 and Figure 5.
These constraints are identical to those discussed for Case EIV
above (Section 2.1.4)except for the inclusion of spiking flows in
water weeks 38 and 48 thru 50.The purpose of the spiking flows is
the same as discussed for Cases EI and Ell (Sections 2.1.1 and
2.1.2).The 30,000 cfs spike in week 38 is to over-top slough
berms to flush out accumulated sediments and debris.This flow
28
~
Table 7
SUSITNA HYDROELECTRIC PROJECT
FLOW CONSTRAINTS FOR ENVIRONMENTAL
FLOW REQUIREMENT CASE ElVa.
Water Gold Creek Flow (ds)Water Gold Creek Flow (ds)
Week Minimum Maximum Week Minimum Maximum
14 2,000 16,000 40 9,000 35,000
15 2,000 16,000 41 9,000 35,000
16 2,000 16,000 42 9,000 35,000
17 2,000 16,000 43 9,000 35,000
18 2,000 16,000 44 9,000 35,000
19 2,000 16,000 45 9,000 35,000
20 2,000 16,000 46 9,000 35,000
21 2,000 16,000 47 9,000 35,000
22 2,000 16,000 48 (2)35,000-23 2,000 16,000 49 (3)35,000
i 24 2,000 16,000 50 (3)35,000
25 2,000 16,000 51 7,000 35,000
26 2,000 16,000 52 6,000 35,000
27 2,000 16,000 1 6,000 18,000
28 2,000 16,000 2 6,000 17,000
29 2,000 16,000 3 5,000 16,000
30 2,000 16,000 4 4,000 16,000
31 2,000 16,000 5 3,000 16,000
32 4,000 16,000 6 3,000 16,000
33 6,000 16,000 7 3,000 16,000
34 6,000 16,000 8 3,000 16,000
35 6,000 16,000 9 3,000 16,000
36 9,000 35,000 10 2,000 16,000.-37 9,000 35,000 11 2,000 16,000
38 (1)35,000 12 2,000 16,000
39 9,000 35,000 13 2,000 16,000
~~
(1)Base minimum flow of 9,000 cfs.30,000 cfs spike;1 day up,1 day hold,
1 day down •
..-(2)Base minimum flow of 9,000 cfs.18,000 cfs spike;1 day up,1 day hold,
1 day down.
(3)Base minimum flow of 8,000 ds 18,000 ds.spike;1 day up,1 day hold,
1 day down.
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29
'I )1 1 1 -,J J j 1 -,1 1 1 )
Figure ,5
ENVIRONMENTAL FLOW REQUIREMENTS CASE Dl:a
10,000 I f i ,Iii Iii iii
•......................;:::::::::::::;:;:;:;:;::::::::::::,,:':::::j
111$11
NOTE
1.DISCHARGE FOR
I I I I I I r..,I I I I SUSITNA RIVER AT
GOLD CREEK
2.PERCENT OF TIME
NATURAL FLOW IS
EQUALLED OR
EXCEEDED.CURVES
ARE BASED ON 34
YEARS OF WEEKLY
AVERAGED FLOWS
WITH OCT.1-7 AS
FIRST WEEK OF 52
WEEKLY INTERVALS
40,000 I I I I I I 1 I I I I I
o'I I I I I I I I I I I I
10,000
w
CJ
II:-eX 10,000 I I I I I I I I
U
(I)-c
..--.
UJ
II.(J 10,000....,
JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
o
would not be necessary each year of operation but would be provided
at least once every three years.The spiking flows during weeks 48
thru 50 are to provide access to the most productive side slough
spawning sites.
Project Flows
Case ElVa flows would be similar to those of case EIV except that
during winter operation,flows would be reduced fran Case EIV
during lower flow years to account for the reduced storage because
of the required summer spiking flows.
Flow during June,July and August would be the same as the minimum
requirements more than 55 percent of the time.Releases fran the
fixed cone valves would be required to augment the powerhouse
discharge during those periods when spiking is required.
o Impact Assessment
Impacts on rearing habitats would be the same as discussed for Case
EIV except for some momentary disturbance and dislocation caused by
the spiking flows.The spiking flows would not cause a measurable
effect since their magnitudes are well within the range of natural
flood events and the rate of change in discharge would be limited.
Impacts on access to side slough spawning sites would be similar to
Case Ell.Case ElVa provides more spiking flows for access than
Ell,but the base flow would be 3-4,000 cfs less.Therefore,the
expected net loss would be similar to Case Ell,i.e.,a 25%loss of
slough spawning habitat for chum and sockeye salmon.
o Mitigation
Mitigation measures for loss of rearing habitat would be the same
as discussed for Case EIV.
....
410454
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31
Measures to rectify loss of access to slough spawning sites would
be similar to those discussed for Case Ell (Section 2.1.2).Sane
additional alteration would be necessary for Case ElVa due to the
lower base flows.
2.1.6 .Case ElVb
o Management Objective
Case ElVb flow constraints are designed to maintain 75%of the side
channel rearing habitat utilized by chinook salmon juveniles under
natural flow conditions and provide for some limited spawning
access to the most productive side sloughs by chum salmon adults.
o Flow Constraints
Flow constraints for Case ElVb (Table 8,Figure 6)are identical to
those discussed for Cases ElV (Section 2.1.4)and ElVa (Section
2.1.5)except for the magnitude of spiking flows.Spiking flows
for Case ElVb are of the same duration as those in ElVa,but peak
at lower discharges (cfs)•
....
....
""'"I
I
o
410454
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Project Flows
Case ElVb has flow requirements similar to Case ElVa except that
during periods when spiking flows are provided,the magni tude of
the spikes are reduced for Case ElVb.Therefore the average winter
flows with Case ElVb would be greater than for Case ElVa and less
than for Case ElV.However,because of the similari ties between
Cases ElV and ElVa,winter flows with Case ElVb operation would be
the same as Case ElV and ElVa most of the time.
Summer flows would be almost the same as those of Case ElVa most of
the time and only slightly different at other times.
32
Table 8
SUSITNA HYDROELECTRIC PROJECT
FLOW CONSTRAINTS FOR ENVIRONMENTAL
FLOW REQUIREMENT CASE EIVb
Water Gold Creek Flow (cfs)Water Gold Creek Flow (cfs)
Week Minimum Maximum Week Minimum Maximum
14 2,000 16,000 40 9,000 35,000
15 2,000 16,000 41 9,000 35,000
16 2,000 16,000 42 9,000 35,000....17 2,000 16,000 43 9,000 35,000
18 2,000 16,000 44 9,000 35,000
19 2,000 16,000 45 9,000 35,000
20 2,000 16,000 46 9,000 35,000
21 2,000 16,000 47 9,000 35,000
22 2,000 16,000 48 (2)35,000
23 2,000 16,000 49 (2)35,000
24 2,000 16,000 50 (3)35,000
25 2,000 16,000 51 7,000 35,000
26 2,000 16,000 52 6,000 35,000-27 2,000 16,000 1 6,000 18,000
28 2,000 16,000 2 6,000 17,000
29 2,000 16.000 3 5,000 16,000
30 2,000 16,000 4 4.000 16,000
31 2.000 16.000 5 3,000 16,000
32 4,000 16,000 6 3.000 16,000
33 6,000 16.000 7 3,000 16,000
~34 6,000 16,000 8 3,000 16,000
35 6,000 16,000 9 3,000 16,000
36 9,000 35,000 10 2,000 16,000
37 9.000 35,000 11 2.000 16,000
38 (1)35,000 12 2.000 16,000
39 9,000 35,000 13 2,000 16,000
~
(1)Base minimum flow of 9,000 cfs.25,000 cfs spike;1 day up,1 day hold,
1 day down.
(2)Base minimum flow of 9,000 cfs.14.000 cfs spike;1 day up,1 day hold,
1 day down.
(3)Base minimum flow of 8,000 cfs 14,000 cfs.spike;1 day up,1 day hold.
1 day down.
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33
j I J .I 1 .J J i J J J 1 J j I I J .~
Figure 6
ENVIRONMENT AL FLOW REQUIREMENTS CASE TIl b
10.000iii •,i i iii ,i •
I ...
40.00.I I I I I I I I I I I I
"""'"o
La.o
lIl,.IIII'
W·o.
CJa;:
<C
%o0"--Q
11:111
NOTE
1.DISCHARGE FOR
SU81TNA RIVER AT
GOLD CREEK
2.PERCENT OF TiME
NATURAL FLOW IS
EQUALLED OR
EXCEEDED.CURVES
ARE BASED ON 34
YEARS OF WEEKLY
AVERAGED FLOWS
WITH OCT.1-7 AS
FIRST WEEK OF 52
WEEKLY INTERVALS
JAN FEB MAR APR MAY JUN JUL AUG 8EP OCT NOV DEC
....
-
-
I~'
....
....
o Impact Assessment
Impacts on rearing habitats would be similar to those discussed for
cases EIV and ElVa above.
Impacts on access to slough spawning sites would be greater with
this case than with Cases Ell or ElVa.Severe access problems
would occur at sloughs 8A and 11.Complete restriction at these
sloughs would eliminate approxima te ly 32%and 80%0 f the
utilization of side sloughs for spawning by chum and sockeye
salmon,respectively (ADF&G,1984a).Flows that range from the
9,000 cfs base flow to the 14,000 cfs spiking flows would result in
a loss of access to approximately 40%of the slough spawning areas
(weighted for utilization:see Power Authority Comment on DEIS,No.
AQR072).A worst case impact of a 50%loss of slough spawning
habitat for chum and a 100%loss of slough spawning habitat for
sockeye salmon is assumed for this evaluation.
a Mitigation
Mitigation measures for loss of rearing habitat would be the same
as discussed for Case EIV.
Loss of access to sloughs for spawning chum and sockeye salmon
would be rectified by structural modification of the slough mouths
and critical access reaches within the sloughs.
2.1.7 Case EV
o Management Objective
....
.....
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Casle EV flow constraints are designed to maintain
existing chum salmon slough spawning habitat and
existing chinook salmon side channel rearing habitat •
35
75%
75%
of
of
the
the
Table 9
.....SUSITNA HYDROELECTRIC PROJECT
FLOW CONSTRAINTS FOR ENVIRONMENTAL
FLOW REQUIREMENT CASE EV.
Water Gold Creek Flow (ds)Water Gold Creek Flow (ds)
Week Minimum Maximum Week Minimum Maximum---
-~.
14 2,000 16,000 40 9,000 35,000
15 2,000 16,000 41 9,000 35,000
16 2,000 16,000 42 9,000 35,000,....
17 2,000 16,000 43 9,000 35,000
18 2,000 16,000 44 11,000 35,000
19 2,000 16,000 45 12,000 30,000-20 2,000 16,000 46 12,000 30,000
21 2,000 16,000 47 12,000 30,000
22 2,000 16,000 48 12,000 30,000
23 2,000 16,000 49 (2)30,000
24 2,000 16,000 50 9,000 16,000
25 2,000 16,000 51 9,000 16,000
26 2,000 16,000 52 8,000 16,000
27 2,000 16,000 1 6,000 16,000
28 2,000 16,000 2 6,000 16,000
29 2,000 16,000 3 6,000 16,000
30 2,000 16,000 4 6,000 16,000
31 2,000 16,000 5 3,000 16,000
32 ,4,000 16,000 6 3,000 16,000-33 6,000 16,000 7 3,000 16,000
34 8,000 16,000 8 3,000 16,000
35 8,000 16,000 9 3,000 16,000
36 10,000 35,000 10 2,000 16,000
37 10,000 35,000 11 2,000 16,000
38 (1)35,000 12 2,000 16,000
39 9,000 35,000 13 2,000 16,000
(1)Base minimum flow of 9,000 cfs.35,000 cfs spike;3,days up,3 days
down.
(2)Base minimum flow of 12,000 cfs.18,000 cfs spike;1 day up,1 day
down.
-
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36
--1 J ]J 1 -.J J 1 ]1 J J ]J I 1 J
......-
.0,000 I I Itt I t I I I I I
.....en
LLo.....,
w
C'a:cx:oen-Q
Figure 7
ENVIRONMENTAL FLOW REQUIREMENTS CASE Y
1.,000 I I I I I I I I I I I I I
NOTE
1.DISCHARGE FOR
8USITNA AlVEI'AT _
GOLD CREEK
2.PERCENT OF TIME
NATURAL FLOW 18
EQUALLED OR
EXCEEDED.CURVES +
ARE BASED ON 34
YEARS OF WEEKLY
AVERAGED FLOWS
WITH OCT.1-1 A8 -
FIRST WEEK OF 52
WEEKLY INTERVALS
.'
10,000 I I I I I I I 1':::;:;"""\':"N.';'!'..,..
:"::':,:,,':',;:;,[,,F:,:,[,:::;:Y';::'r':'u I MIN ~~•
01::t :e--~T I I I I I I ===t:==i
JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
-
,....
.....
....
o
o
o
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Flow Constraints
Casle EV flow constraints were derived by combining Cases Ell and
EIV.The basic guideline used was to chose the maxima and minima
for each week from Cases Ell and EIV that were most restrictive on
project operation.Flows to maintain chinook rearing habitat were
chosen for most of the year (Table 9,Figure 7).Flows for chum
spawning habitat were most important during weeks 36-38 and 44-49.
Project Flows
Case EV would result in an average flow of 8,600 cfs at Gold Creek
during the October to April period.Power house discharge would
increase from October to December and then decrease from December
to April.December discharge would be as high as 12,000 cfs but
would average 10,100 cfs.Minimum flows would approach 5,000 cfs
during October and March in low flow years.In these low flow
years,April flows could be.as low as 3,200 cfs.
During the May to September period,the flow at Gold Creek would be
the same as the minimum flow requirements 55%of the time and,of
course,higher,the remainder of the time.The average flow during
this period would be 11,400 cfs.
Impact Assessment
Loss of spawning habitat wi th Case EV flow constraints would be
similar to losses under Case Ell.Therefore,a 25%reduction of
side slough spawning habitat for chum and sockeye salmon will be
used for this evaluation.
The expected impacts on existing rearing habitat would be similar
to those discussed for EIV and ElVa above.Case EV flows would
result in a 25%loss of existing chinook salmon side channel
rearing habitat.
38
-
"...
I
o Mitigation
Mitigation measures for impacts on slough spawning habitat are
discussed for Case Ell (Section 2.1.2).
Mitigation measures for loss of existing rearing habitat are
discussed for Case EIV (Section 2.1.4).
.....
--
2.1.8
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Case EVI
A detailed discussion of Case EVI 1.S presented in Section 4.0.
This case is separated in this report from the other environmental
cases because it is the Power Authority's selected flow case (see
Section 3.0)and a more detailed description is warranted.
Basically Case EVI 1.S a variant of EIV wi th a flexible summer
minimum flow constraint to achieve more economic project operation
during low flow years (one in ten year low flows).
Case EVI impact would be similar to Case EIV and proposed
mitigation measures would result in no net loss of productivity.
Naturally reproducing population would be maintained through steps
to minimize and rectify project induced losses.A general
improvement in the quantity and quality of rearing habitat 1.S
expected over natural conditions.See Section 4.0 for the detailed
discussion of ths case •
39
-
.....
3.0 COMPARISON OF FLai CASES
3.1 ECONOMIC COMPARISON
Economic analyses of selected flow cases,ranging from P-1 to EVI,were
perfonned to determine the present worth of the long term (1993-2051)
production costs of each alternative.The analyses were completed using the
OGP model and the monthly average and firm energies of each flow case
obtained frcm the reservoir operation program.Railbe1t system expansions
for the period 1993 through 2020 were analyzed with the Watana project
coming on line in 1993 and Devil Canyon in 2002.The long-term system costs
for 2021 through 2050 were estimated from the 2020 annual costs,with
adjustments for fuel escalation for the 30-year period.
The results of the analyses are illustrated in Table 10.They indicate that
the energy benefits of the project are inversely proportional to the summer
flow volume required for fish.When mitigation costs are not incorporated,
Case P-l,~1ith no environmental requirements,had the lowest cumulative
present worth cost.For comparison with Case P-1,the maximum economic case
presented in the License Application (Case A)was also run using OGP.The
cumulative present worth of the costs was essentially the same as for Case
P-l.
Case EVI ranked third 1n lowest cost,some $8,000,000 greater than Case P-1.
Case EIV ranked next with a total present worth cost $15,000 ,000 greater
than P-1.Case C (proposed flow requirements presented in the License
Application),EV,and EI,had present worth costs increasingly greater than
Case P-1.
Case C and Case EV required the addition of one 200 MW coal-fired plant and
Case EI required the addition of two 200 MW coal units.The total installed
capacity is increased as minimum flow requirements in the months of May
through September are increased.This occurs because of the resulting de-
crease in available winter energy during low flow years,and the consequent
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40
,....
..-
-
~-
requirement for additional thermal capacity to meet peak demand.(Note that
the installed capacity from the Susitna Project remains the same for all
cases.)
The OGP program is primarily a long-term expansion plan program.Therefore
when small changes in flow requirements are assessed to determine cost
differences,the differences determined by OGP may not be exact.However,
it is believed that the relative economic ranking of the flow cases 1.S
correct and that the difference in costs among the flow cases actually 1.S
greater than shown in Table 10.
3.2 ENVIRONMENTAL COMPARISON
The environmental cases can be separated into three basic groups.Group 1
is designed to maintain rearing habitats and includes EIII,EIV,and EVI.
Group 2 is designed to maintain chum spawning in side sloughs and includes
only Case Ell.Case Ell is the most similar to Case C since protection of
side slough spawning habitat was the primary environmental consideration 1.n
both.Group 3 is made up of cases designed to maintain both rearing and
side slough spawning habitat.This group includes Cases EI,ElVa,EIVb and
EV.
The two most important potential impacts of project operation are effects on
mainstem influenced rearing habitats and spawning habitat in side sloughs.
The Environmental cases can be compared based on potential impac ts and
mitigation measures regarding these two categories.
The objective of mitigation planning for fisheries impacts of the proposed
project is to provide sufficient habitat to maintain naturally producing
populations wherever compatible with project objectives.Compensation
through construction and operation.of propagation facilities is a least
desirable action.Group 2 flow cases (Ell,C)would require compensation
for lost rearing habitat.Compensation within the Susitna Basin would
likely require a propagation facility designed to replace lost chinook
salmon production.
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41
--
The major mitigation action (other than flow control)for Group 1 (EIII,
EIV,EVI)and Group 3 (EI,ElVa,EIVb,EV)would involve rectifying for
impacts on side-slough spawning habitat.The extent of necessary structural
modification varies among the individual cases but the basic impacts and
mitigation methods are the same.Group 3 flow cases would generally require
less structural modification than for Group 1.
Mitigation actions described for all the environment'al cases would result in
no net loss of production due to project operation.However Group 2 flow
cases are least desirable since they require actions at greatest variance
from the mitigation objective.Group 3 cases are most desirable based only
on environmental consideration of potential impacts and the level of
required mitigation actions.
Representative cases were chosen from each group for evaluation and
comparisons based on power and economic objectives of the project.Cases
EIV and EVI were chosen to represent Group 1,Case C to represent Group 2
and EI and EV to represent Group 3.
3.3 SELECTION OF PREFERRED INSTREAM FLOW REQUIREMENTS
Cases P-l and A provide benchmarks to which the economics of the various
flow cases can be compared.These cases would require substantial
mi tigation,including the use of propagation facili ties.As mentioned
above,Power Authority policy is to avoid the use of propagation facilities
if habitat for naturally reproducing populations can be maintained.
Cases EI -and EV are cons idered to have unacceptable cost penal ties.The
addi tional fishery benefi ts from Case EI and EV flow requirements do not
warrant the loss of energy benefits.The same management objectives can be
obtained through effective mitigation techniques at much lower cost.Case C
has a management objective'to protect sloughs considered to be traditional
salmon spawning areas.However,Case C does not adequately consider other
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42
_.
-
management objectives which have been identified through ongoing studies.
For example,it does not include flow constraints for juvenile rearing
habitat.In addition,Case C,Case EV,and Case EI all require coal
generating units which may themselves produce adverse impacts.
Cases EVI and EIV are judged to be the superior flow cases cons idered.
Case EVI is selected as the preferred case because of superior energy
benefits.With a rigorous analyses of Cases EVI and EIV,it is expected
that the economic benefits of EVI over EIV would be greater than shown in
Table 10.
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43
TABLE 10
SUSITNA HYDROELECTRIC PROJECT
ECONOMIC ANALYSIS OF FLOW CASES
Case Cumulative present
Worth of Costs Difference Railbelt Generation
0993-2051)from P-l Capacity in 2020 (MW)
(1982 $in MILLIONSl/)(1982 $in MILLIONS)Coal I Total
I
~
P-l 5484 0 2350
A 5486 2 0 2350
EVI 5492 8 0 2451
~
EIV 5499 15 0 2451
-C 5590 106 200 2544
EV 5726 242 200 2633
....EI 6069 585 400 2756
II Costs do not include mitigation costs.
.....
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44
F'"
!
"""
4.0 ENVIRONMENTAL FLOW REQUIREMENT CASE EVI
4.1 MANAGEMENT OBJECTIVE
Case EVI flow constraints are designed to maintain 75%of the existing
chinook salmon side channel rearing habitat in all years except low
flow years (defined as years with expected summer discharge less than
or equal to the one in ten year low flow occurrence).Minimum summer
flows are reduced to a secondary but set level during low flow years to
achieve necessary but limited flexibility for project operation.
Establishment of environmental flow constraints based on the require-
ments of chinook salmon is a reasonable approach.Chinook salmon is
one of the species of major importance to commercial and non-commercial
fisheries in South-Central Alaska (Lie.Appl.,Ex.E,Chpt.3,p.E-3-l
through E-3-l5).Juvenile chinook utilize habitats within or closely
associated to the mains tem river for rearing during the entire year
(ADF&G 1984b).The high human use value and sensitivity to potential
project impac ts qualifies chinook salmon as an evaluation species.
Chum salmon spawning in side sloughs has been identified as the
combination of species and habitat that would be most significantly
affected by project operation (APA,1984b).However,loss of chum
spawning can be rectified by slough modification whereas loss of
chinook mainstem rearing habitat would have to be compensated by
construction and operation of artificial rearing facilities (e.g.a
traditional release-return hatchery).Compensation 1S the least
desirable option under the mitigation policies applied to the Susitna
Project (Lie.Appl.,Ex.E,Chpt.3,pp.E-3-3 through E-3-6).
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45
..-
4.2 FLOW CONSTRAINTS
Case EVI flow constraints are shown in Table 11 and Figure 8.The flow
constraints can be separated intQ three major divisions;winter flows,
summer flows and transitional flows •
Maximum flows are the most important winter constraints.Normal
project operation would produce the greatest discharges during the
winter months (November-March).The winter maximum is intended to
establish a boundary near the upper range of operational flows that
would result in flow stability and provide a reasonable level of
protection to over-wintering habitat.Side sloughs are especially
important in this context since chinook juveniles utilize this habitat
for over-wintering.The 16,000 cfs maximum flow would prevent over-
topping of all the major sloughs prior to freeze-up and stabilize
habitat availability during ice covered periods.
The winter minimum flow is established to prevent dewatering of rearing
habitats.The 2,000 cfs minimum is chosen based on natural flows and
represents a high mean natural winter flow.
Flow constraints during the winter to summer transition period (water
weeks 32-35)are intended to maintain flow stability and prevent rapid
drops i.n discharge due to decreas ing power demand in May.The minimum
flow constraints are most important during this period.
Summer (water weeks 36-48)flow contraints are designed to maintain
rearing habitats and provide greater flow stability.Chinook juveniles
are accumulating the major portion of their freshwater growth during
this period and they utilize side-channel sites that are directly
affected by mainstem discharge (ADF&G,1984b).A 9,000 cfs minimum
flow would maintain 75%of the existing habitat quanti ty at sites
presently utilized by chinook and increased flow stability would
improve habitat quality over natural conditions.
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46
"'""
Table 11
,-SUSITNA HYDROELECTRIC PROJECT
FLOW CONSTRAINTS FOR ENVIRONMENTAL
FLOW REQUIREMENT CASE EVI.-
Water Gold Creek Flow (cfs)Water Gold Creek Flow (cfs)
Week Minimum Maximum Week Minimum Maximum--
14 2,000 16,000 40 9,000*35,000
15 2,000 16,000 41 9,000*35,000
F'"16 2,000 16,000 42 9,000*35,000
17 2,000 16,000 43 9,000*35,000
18 2,000 16,000 44 9,000*35,000
19 2,000 16,000 45 9,000*35,000
20 2,000 16,000 46 9,000*35,000
21 2,000 16,000 47 9,000*35,000
22 2,000 16,000 48 9,000*35,000
.-23 2,000 16,000 49 8,000 35,000
24 2,000 16,000 50 7,000 35,000
25 2,000 16,000 51 6,000 35,000
26 2,000 16,000 52 6,000 35,000-27 2,000 16,000 1 6,000 18,000
28 2,000 16,000 2 6,000 17,000
29 2,000 16,000 3 5,000 16,000.....30 2,000 16,000 4 4,000 16,000
31 2,000 16,000 5 3,000 16,000
32 4,000 16,000 6 3,000 16,000
p~33 6,000 16,000 7 3,000 16,000
34 6,000 16,000 8 3,000 16,000
35 6,000 16,000 9 3,000 16,000
36 9,000*35,000 10 2,000 16,000
37 9,000*35,000 11 2,000 16,000
38 9,000*35,000 12 2,000 16,000
39 9,000*35,000 13 2,000 16,000
*Minimum s~mmer flows are 9,000 cfs except ~n dry years when the minimum
will be 8,000 cfs.A dry year is defined by the one-in-ten year low
flow.
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47
1 ]J I 1 1 J 1 ]1 .I i I ).
Figure 8
ENVIRONMENTAL FLOW REQUIREMENTS CASE JlI
11,000 • , , ,i •iii i ,
NOTE
1.DISCHARGE FOR
SU81TNA RIVER AT
GOLD CREEK
2.PERCENT OF TIME
NATURAL FLOW 18
EQUALLED OR
EXCEEDED.CURVES
ARE BASED ON 34
YEARS OF WEEKLY
AVERAGED FLOWS
WITH OCT.1-7 AS
FIRST WEEK OF 52
WEEKLY INTERVALS
INDICATES MIN FOR
LOW FLOW YEAR
O'I I I I , I ,I I ' , •
10.0"
40.000 I I I , I I I I I I I I
..-...
(II
La.
U 10.000"-'"
W
CJa:-c
::I:
U •••OM
U)-Q
JAN FEB MAR APR MAY JUN JUL AUG SEP oct NOV DEC
4.3 PROJECT FLOWS
Project operation flows for Cases EIV and EVI would be the same for all but
the lowest flow years.Only in one year in ten would there be a significant
difference.Because of this occurrence,October to April flows would
average only about 50 cfs more than for Case EIV.(Case EIV would result in
an average flow of 9500 cfs from October to April)
May to September flows would be the same as Case EIV,except during th'e one
in ten year low flow when the minimum flow would be 8000 cfs during June,
July,and August.Actual flow would be the same as the m~n~mum flow
requirements 55%of the time during June,July and August.
4.4 IMPACT ASSESSMENT
Case EVI is designed to reduce impacts of project operation as compared to
flow cases designed specifically for power generation.However,Case EVI
does not mitigate all impacts by flow release alone so further impact
assessment and mitigation planning is necessary.This section will address
significant potential impacts to each life stage of the five Pacific salmon
spec~es •
-
o
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Juvenile Rearing
Chinook salmon juveniles rear in both clear and turbid water
habitats.Substantial rearing occurs in tributaries and side
channels (ADF&G 1984b).Densities generally decrease in tributar-
ies and increase in side channel habitats through the summer.
Densities in side sloughs are relatively low during the summer but
increase markedly during September and October.Tributary habitat
would not be impacted by altered mainstem flows.Side channel
habitat would be most directly affected.Case EVI flows would
reduce the quantity of available rearing habitat at side channel
sites presently used by chinook by approximately 25%.
49
~,
,.,..
I
.....
Chum salmon rearing is essentially limited to tributaries and side
sloughs during the early summer (May-early June).Highest
densities during late June and July occur in upland sloughs and
side channels.Essentially all the juvenile chum have moved
downstream,out of the middle river,by the end of July.Case EVI
flows would not impact rearing habitat in tributaries and upland
sloughs.Chum salmon use of side channel sites is mostly for
short-term holding and rearing during downstream migration.
Case EVI flows would decrease the availabiliy of side channel
sites presently used by chum by approximately the same magnitude
estimated for chinook salmon.A 25%reduction will be assumed for
this assessment.There would also be a loss of chum rearing
habitat in side sloughs.Most of the loss would be due to a
reduction or elimination of over-topped conditions in side sloughs
during May and June under project operation.Loss of habitat
could be as great as 50%at the sites utilized under natural flow
conditions.
Sockeye juveniles rear predominantly in natal side sloughs during
the early summer and then move mostly to upland sloughs by July.
With project flows are not expected to affect upland slough
habitats.The responses of weighted useable area for sockeye and
chum are similar for side-slough rearing habitat.Therefore,loss
of sockeye rearing habitat would be approximately 50%•
....
Coho salmon
Impacts due
habitats.
rear mostly in tributaries and upland
to project operation are not expected
sloughs.
1n these
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Pink salmon juveniles move rapidly from their natal tributaries to
Cook Inlet.The mainstem and associated habitats are apparently
used only for migration corridors so project flows would not
impact pink salmon rearing.
50
o Downstream Migration
Downstream movement of salmon juveniles occurs throughout the
summer (ADF&G,1984b).Chum,pink and age 1+chinook salmon
migrate toward Cook Inlet during the early summer and are out
of the middle river reach by July.Sockeye,coho and age 0+
chinook move gradually downstream throughout the summer.Most of
this movement is associated with rearing and gradual relocation
into available rearing and over-wintering habitat.
~seeking alternative habitat sites,
preferred rearing areas.Project-frequency,duration and amplitude of
o Upstream migration
Some of this
Adult salmon migrate up the Susitna River toward spawning areas
throughout the summer.The 9,000 cfs summer minimum flows will
I""'"
I
o
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provide sufficient conditions for upstream passage of adults.
Spawning
Salmon that spawn in the middle river basin are only a small
proportion (less than 15%)of the total in the Susitna River
System (ADF&G,~984a).Most of the salmon that spawn in the
middle river basin use tributary habitats outside the influence of
51
.-
-
"'"'I
.-
-
l
i
o
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mainstem discharge.The spawning habitat most sensitive to
changes in mainstem discharge are the side sloughs used by chum
and sockeye salmon.Mainstem flows influence spawning success in
side sloughs through affects on access past critical reaches,
total useable areas within the slough and groundwater discharge.
Access into the major spawning sloughs (8A,9,9A,11 and 21)
would be restricted under Case EVI flows.An analysis using
values of side sloughs weighted by observed spawning use provides
an estimated loss of approximately 50%of side-slough spawning due
to access restriction at 9,000 cfs (see Power Authority Comment on
DEIS No.AQR072).However.considering the restricted access
together with reduced area and flow within the sloughs,a worst
case assumption of 100%loss of side-slough spawning habitat
without mitigation is assumed for this evaluation.
Mitigation
This section will present suggested actions to mitigate potential
losses due to project operation.Project operation in the absence
of environmental constraints is the appropriate starting point to
discuss mitigation so flow Case P-l will be used as a standard.
Project impacts would be minimized through timing and control of
flow releases by adopting the environmental flow requirements in
Case EVr.Case P-1 flows would fall below 9,000 cfs during June
through August in approximately 75%of the years of operation.
Mean monthly summer flows would be as low as 4,500 cfs in some
years.This would result in total loss of most of the mains tem
and side channel rearing habitat presently used by chinook and
chum salmon juveniles.Case EVI flows would m~n~m~ze this impact
by maintaining 75%of the existing side channel rearing habitat.
The residual 25%loss of side channel habitat and the loss of chum
and sockeye rearing habitat in side sloughs would be rectified by
habitat replacement at the more stable,lower flows (relative to
52
-
-
.....
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natural flows)under Case EVI.The original rationale for design
of Case EVI and the impact assessment discussed above are based on
impacts to habitat sites that are available and used under natural
flow conditions.The estimates of impact relied on data and
information collected at habitat sites presently utilized.The
analyses and estimates did not consider the addition of new
habitat sites with appropriate characteristics and qualities that
would become available at lower,more stable flows.
Chinook salmon prefer areas of moderate depth and velocity for
rearing in side channel areas.The quantity of habitat with
these characteristics depends largely on channel complexity.
There is relatively little of this rearing habitat available at
bank full flows.The habitat quantity increases as flows drop and
the flow channels become more complex.This increase will
continue until a maximum is reached and habi tat quanti ty would
then decrease as discharge decreases to a level sufficienty low to
restrict flow to a single thalweg channel.Comparision of channel
complexity at various flows gives some indication of how habitat
quantities will be impacted by project operation.Channel
complexity at 9-12,000 cfs.(approximate summer operational flows)
1S much greater than at 23,000 cfs (approximate mean summer
natural flows:See APA,1984c,plates 1-18 for pictoral
illustration).The quantity of side channel and mainstem rearing
hab'itat for both chinook and chum salmon is expected to increase
over natural conditions during project operation under Case EVI
flow requirements.Increased flow stabil i ty and decreased
turbidity is expected to improve habitat quality and augment
rearing potential in the middle river.
Case EVI minimum flow constraints during late August and early
September will minimize impacts of the project on chum and sockeye
spawning due to operation through control of flow releases
(compared to Case P-l).However,the residual impacts would be
53
....
....
!
.....
.....
F'"
I
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considerable and further mitigation would be necessary.Loss of
side slough habitat for chum and sockeye salmon spawning would be
rectified by structural modification of existing sloughs.Details
of these activities are given in APA,1984b,and will not be
repeated here.
The results of these mitigation measures are compatible with
mitigation policies and objectives presented in the License
Application (Ex.E,Chpt.3,p.E-3-147).Habitat quantity and
quality sufficient to maintain naturally reproducing populations
is provided.All significant impacts would be minimized or
rectified •
The results of these mitigation measures are compatible with
mitigation policies and objectives presented in the License
Application (Ex.E,Chapter 3,Page E-3-147).Habitat quantity
and quality sufficient to maintain naturally reproducing
populations 1S provided.All significant impacts would be
minimized or rectified •
54
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r,
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5.0 BIBLIOGRAPHY
Alaska Department of Fish and Game.1984a.Adult Anadromous Investigations.
Susitna Hydro Aquatic Studies Report No.1.
Alaska Department of Fish and Game.1984b.Resident and Juvenile Anadromous
Fish Investigations (May-October,1983).Susitna Hydro Aquatic Studies
Report No.2.
Alaska Power Authority.1984a.Assessment of the Effects of the Proposed
Susitna Hydroelectric Project on Instream Temperature and Fisheries
Resources,Watana to Talkeetna Reach.Prepared by AEIDC under contract
to Harza-Ebasco Susitna Joint Venture.
Alaska Power Authority.1984b.Interim Mitigation Plan for Chum Spawning
Habitat in Side Sloughs of the Middle Susitna River.Prepared by
Woodward Clyde Consultants under Contract to Harza-Ebasco Susitna Joint
Venture.
Alaska Power Authority.1984c.Response of Aquatic Habitat Surface Areas to
Mainstem Discharge in the Talkeetna to Devil Canyon Reach of the Susitna
River,Alaska.Prepared by:E.Woody Trihey and Associates under
contract to Harza-Ebasco Susitna Joint Venture.
Mosley,M.Paul.1982.Analysis of the Effect of Changing Discharge on
Channel Morphology and Instream Uses in a Braided River,Ohau River,New
Zealand.Water Resources Research.Vol.18,No.4.pp.800-812.
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