HomeMy WebLinkAboutAPA1800app
TK
1425
.S8
F471
no.1800
app.
Before the Federal Energy Regulatory Commission, Application
for License for Major Project, Susitna Hydroelectric Project.
Exhibit E. Appendix E.2.A, Relationship between Main
Channel Flow and Slough Physical Habitat Variables
This report is listed at the end of the table of contents for Chapter 2. (The lists of
tables, figures, and photographs as listed on that table of contents page were
apparently not included in the publications.)
This report constitutes appendix E.2.A of:
Before the Federal Energy Regulatory Commission, Application for
License for Major Project, Susitna Hydroelectric Project. Volume 5A : Exhibit E,
Chapters 1 & 2.
This report has its own attachment called:
Before the Federal Energy Regulatory Commission, Application for
License for Major Project, Susitna Hydroelectric Project. Reference report
attachment to Appendix E.2.A. Incremental Flow Analysis of Mainstem Susitna
River Effects on Selected Side Sloughs, Exhibit E.
H~y Z ~-E lo.?s,co S Uj;;+N 0 0;n l-Ve h ve.....
I G~3
.Appl ;c"l;c,.)&DY l iUi!l'l S<:'••..
APPENDIX E.2.A
RELATIONSHIP BETWEEN MAIN CHANNEL FLOW
AND SLOUGH PHYSICAL HABITAT VARIABLES
Table of Contents
List of Tables
List of Figures
A.l IntrOduction
A.2 Se lection of Sloughs
A.3 Definition of Flow Regimes
A.4 Main Channel Flow and Physical Habitat
Variables of Sloughs
A.5 Summary of Methods of Analyses
A.6 Discussion of Results
A.7 References
-i-
i i
iii
1
1
2
3
5
10
14
\
List of Tables--
No.Title Page
A-I Thresho ld Discharge Estimates 3-1, 3-2
A-2 Ma ins tem Di scharge vs.Physical Habitat 4-1 4-2,4-3,
Variables,Slough 8A
A-3 Ma instem Discharge vs.Phys ical Habitat 4-4,4-5 4-6,
Var iables,Slough 9
A-4 Mainstem Discharge vs.Physical Hab itat 4-7,4-8,4-9
Variables,Slough 21
A-5 Mainstem Discharge vs.Physical Habitat 5-1 thrO!lgh
Variables,Rabideux Slough 5-16
-i i-
List of Figures--
No.Ti tle Pag e
A-I Slough Locat ion Map 2-1
A-2 Map of Slo ugh 8A 2-2
A-3 Map of Slough 9 2-3
A-4 Map of Slough 21 2-4
A-5 Map of Rabideu x Slough 2-5
-I I I -
A.1 Introduction
Side sloughs of the Susitna River consist of springfed overflow
channe 1s between the ma ins tem Susi tna and its side channe 1s and the
edge of the floodplain.The side sloughs are generally separated from
the ma ins tem by we ll-vegeta ted grave 1 bars..Exposed all uv ia1 berms at
the heads of the sloughs normally separate the sloughs from mainstem or
side channel flows.The controlling berms at the upstream end of the
side sloughs are approximately at the water surface elevations of the
mainstem for mean monthly flows observed during June,July,and August.
At intermediate and low-flow periods in the mainstem,the side sloughs
convey clear water from small tributaries and/or upwelling groundwater
which is essential to the existence of this habitat type.At
intermediate mainstem flows,the water surface elevation of the Susitna
River causes a backwater to extend well up into the sloughs from their
lower end.Even though substantial backwater often exists,the sloughs
function hydraulically very much like small stream systems and there is
a net discharge from the sloughs.At high flows the water surface
elevation of the mainstem river is sufficient to overtop the upper end
of the slough.
Over thi rty sloughs have been i dent i fi ed in the reach of the Susi tna
River between Devil Canyon and Talkeetna.These slough habitats have
been identified by the Alaska Department of Fish and Game (ADF&G)as
the ma in producers of chum sa 1mon in th is reach of the ri ver.This
reach will be impacted most by the regulated flows from the proposed
Susitna Hydroelectric Project.Numerous additional sloughs have been
identified between Talkeetna and Cook Inlet.
Incremental flow analyses have been prepared for three sloughs in the
reach from Talkeetna to Devi1 Canyon and for one slough in the reach
from Cook Inlet to Talkeetna.The analyses performed for these four
sloughs consist strictly of hydrologic and hydraulic relationships be-
tween the sloughs and the mainstem of the Susitna.The analyses des-
cribe the effects of mainstem flow on slough discharge,water surface
elevation,flow depth and velocity,wetted surface area wetted per i-
meter and water table elevations.These re1atio.nships provide the
hydraulic boundary conditions throughout a range of flows in the
Susitna River within which fishery habitats can be defined.
A.2 Selection of Sloughs
The ADF&G and R & M Consultants,Inc.(R&M)began collecting hydraulic
and hydrologic data in the Susitna River sloughs to describe the re1a-
t ionships between ma i nstem flow and slough physica1 character is tics.
Although hydraulic data is currently being collected as part of the
ongoing studies,data collected primarily in 1981 and 1982 werp uti-
1i zed for th is ana1ys is.For the incrementa 1 ana1ys is,three sloughs
upstream of Talkeetna and one slough downstream of Talkeetna have been
selected.These sloughs were selected on the bases of location
(representative reach of river),salmon productivity (the three sloughs
upstream from Talkeetna provide spawning habitat for 60 to 80 percent
1
of the adult salmon spawning in side sloughs),susceptibility to
ma instem flow (changes in mainstem flow under present condit ions affect
the physical characteristics of the slough),and data availability
(deta i led studies have been conducted in these sloughs).The
representative selected sloughs are:
Above Talkeetna:
o Slough 8A (approximate River Mile 126)
o Slough 9 (approximate River Mile 129)
o Slough 21 (approximate River Mile 142)
Below Talkeetna:
o Rabideux Slough (approximate River Mile 84)
Rabideux Slough is located in the upper portion of the Talkeetna to
Cook Inlet reach of the Susitna River and is,therefore,more likely to
be affected by altered flows from the proposed project than are sloughs
located further downstream.
The locations of the sloughs selected for these analyses are shown on
Figure A-I.Maps of each of the sloughs are presented in Figures A-2,
A-3, A-4,and A-5,respectively.
A.3 Definition of Flow Regimes
As the flow in the Susitna mainstem changes,several characteristic
flow regimes are evident in each slough.These regimes'are defined as
fo 11 ows:
o Regime I - This flow regime is characterized by a slough flow
which is essentially independent of flow in the mainstem
(i.e.,there is no backwater effect into the mouth of the
slough from the mainstem). In this flow regime, the slough
acts as a minor tributary to the mainstem.
o Regime II - This regime is characterized by mainstem back-
water extending into the mouth of the slough because the
mainstem water level acts as a hydraulic control.However,
the discharge from the slough is largely independent of the
mainstem discharge since the upstream berms at the heads of
the sloughs are not overtopped.
o Regime III -At sufficiently high flows in the mainstem,the
upstream berms of the sloughs are overtopped.Under these
conditions,the slough hydrologic and hydraulic characterist-
ics are nearly entirely dependent on the mainstem flows.
~
I
A factor which complicates the distinction of these regimes
several cases the sloughs may have two or more channels and
upstream berms which overtop at different mainstem flows.
2
is that in
associated
Therefore,
CANYON
10
I
MIl.ES
-LEGEND -
A USGS
Gaging Station
SLOUGH 2 1
SLOUGH 20
SLOUGH 19
o,
SLOUGH
WH ISKERS CREEK AND SLOUGH
----LANE CREEK AND SLOUGH 8
SLOUGH 6A
GOOSE CREEK-2~AND SIDE CHANNEL
GOO$.C'o
Suns";".C,.
SUNSH I NE CREEK AND S IDE CHANNEL
u ..._-WHITEFISH SLOUGH
/'
RABIDEUX
CREEK AND
SLOUGH
Figure A·'Slough Locati n Map
o
)U
'1 C/"Ot;s -fect;In19WAlre./.f,r..1
velD c;7 tf,'r/t;JJ~s
w~...'?ne~Sl4rt'''/
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Sl41f cr'-de
(jrolll1dwdt."r We 1/
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STAff aA GE
R ...IUaE RECORDER
SUR fACE TH ERMOa RAPH
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t
subsets of Reg i me II occur
topped Jy ma instem f low,
e levat ion is not overtopped.
Reg i mes II -A,I I -B,etc.
when one or more upstream berms are over-
but the ber m wit h the hi ghest t halweg
These i ntermediate r egimes are def ined as
Main stem di scharges wh ic h d ist i ngu ish the hydr auli c r egimes in th e
s lo ug h are r eferred t o as thresho 1d d is charges.For eac h of t he f ou r
s lo ug hs ana lyzed,thresho ld discharge est imates are presen ted i n Table
A-I a lo ng with the ranges of ma instem flows wh ich encompass th e f low
reg imes descr ibed above.Determ inat ion of these thresho ld va lues were
based on computations f r om available data ,fie ld observat ions,and
aer ia l photographs.
Descr ipt ions of these distinct f low reg imes are necessary to describe
how ma instem flow and s lough physical habitat variables are interre-
lated.The relationsh ips within each reg ime can then be used to
est imate the physica l habitat variables within and beyond the range of
observed values through interpolation and extrapolation for each
r egime.The methods and information used to def ine the relatio nships
between mainstem flow and physical habitat characteristics in the
sloughs are presented i n the Attachment to this Appendix.
A.4 Main Channel Flow and Physical Habitat Variables Qf Sloughs
The following slough physical habitat variables were analyzed with
respect to ·mainstem discharges :
o s lough d ischarge
o water surface elevat ions at the mo uth,near mid-slough,and
near the upstre am berms
o water dept hs at t he mouth,near mi d-s l ou gh,and near a ll
upst re am berms
o average velocities
mid-s lou¥~,and
s loughs .-
at cross-sect ions at
near the upst ream
the mout h,
berms of
near
the
o tota l wetted surface area
o wetted perimeters at cross-sections at the mout h,near
mid -slough and near the upstream berms of t he sloughs
o water table e levations in the vic inity of the sloughs.
!/Observed lateral velocity distributions and velocity ranges are
prov ided in the Attachment for selected cross-sections (transects).
3
Tab le A-1
THRESHOLD DISCHARGE ESTIMATES
(cfs
Susitna River
Discharge at
Sunshine
Susitna River Discharge
at Gold Creek~~""';';"'--2-S 1ough Slough
9 21
(cfs)(cfs)
~lough
8A
(cfs)
Discharge at which
mainstem acts as a
hydrau lic control
of s lough water-
surface elevat ion
at mouth (Regime
II flow begins)
10 OOo!!,11 OOo§./,21,40oZ!<10 00021,
Discharge at which
intermediate berm
is overtopped
(Regime II-A flow
begins)
Discharge at which
hi ghest benn is
overtopped (Regime
III f low beg ins )
N/A -Not applicab le
26,00oY1l
30,0001'
32,00oi!
N/A 6/
20,50o§./
23,0001'
24,80o!!
26,00o.W
N/~
65,00010/
II flow exists during very low
Regime II assumed to occur for
and 15,000 cfs.
1/Field estimate.
2/Ba sed on field observations on June 29,1982.
3/"Slough Hydrology,Interim Report,"R&M,Dec.1982,p.2-l.
-j Based on aerial photo.
~/Based upon data in "Preliminary Assessment of Access
of Spawning Salmon to Side-Slough Habitat abo ve Talkeetna,"
E.W.Trihey,Nov.1982.
6/Slough 9 and Rabideux Slough do not have intermediate berms.
7/Based on staff gage data i n "Susitna Hydro Aquat ic Stud ies,
Phase II Base Data Report,Vo lume 4:Aquat ic Hab itat and
I nstre am Flow Studies 1982,Appendix A,Alsaka Department of Fish
and Game,1983," Table 4-A-3, p.4-A-67.
8/"Susitna Hydro Aquatic Studies,Phase II Basic Data Report,Vo lume
4: Aquatic Habitat and Instream Flow Studies,Part I,ADF&G,
1983," Table 41-3-2,p.43.
9/ Aerial photos indicate Regime
mainstem flows of 15,000 cfs.
discharges between 10,000 cfs
10/Based on aerial photos.
3-1
TAB LE A-I (Cont 'd)
REGI ME DISCH ARGE EST I MA TES
Susitna River
Sus itna Ri ver Discharge Discharge at
at Go ld Creek Suns h ine
Slough Slough Slough Rabideux
8A 9 21 SlOU 1h{cfs}(cfs)<cfs)<cfs
Reg ime I <10. 000 <11.000 <21.400 N/A
Regime II 10.000- 11.000-21.400-10.000-
26.000 20.500£1 24.800 65.000
Regime I I-A to 26.000-N/A 24.800-N/A
II-n
30.00ol!26.000
Reg ime II I >30. 000 >23. 000 >26.000 >6 5.000
lI "S loug h Hydr ol ogy,Inter im Report."R&M.December 1982.P.2-1
Based on ae rial photography th is flow i s estimated to be 32 .000
cfs.
f/"Pre l im i na r y Assessment of Access of Spawn ing Sa lmon to
S ide-S loug h Habitat above Ta lkeetna ."LW.Tr ihey ,Novembe r.1982.
Based on data in "Sl out h Hydrology , I nter im Report ".R&M Consu l-
tants.December .1982.p .2-1.this flow is 23.000 cfs.
3-2 -
For the reach from Talkeetna to Devil Canyon,the relationships between
mainstem flows and the slough physical habitat variables were analyzed
for average daily discharges of the Susitna River at Gold Creek (USGS
gage no.15292000)for ice-free conditions.Physical characteristics
of the sloughs are presented for mainstem flows ranging from 1000 cfs
to 31,000 cfs in increments of 2000 cfs and at 12,000 cfs.
Tables A-2, A-3,and A-4 present tabulated results of the effects of
the mainstem discharges on physical habitat variables for Sloughs 8A,
g, and 21,respectively.The methods of analysis and the information
used in preparing the tables are presented in the Attachment,Parts 1,
2, and 3.
For analyzing the effects of mainstem flow on Rabideux Slough,located
downstream from Talkeetna,it was necessary to expand the range of
flows considered.Contributions from the Chulitna and Talkeetna Rivers
constitute approximately 40 and 20 percent,respectively,of the
natural flows in the Susitna River at the Sunshine Gaging Station.
The Chulitna and Talkeetna flow contributions,therefore,reduce the
influence of Susitna River flows measured at Gold Creek on the physical
characteristics of Rabideux Slough.Mainstem flows at Gold Creek of
1000 to 31,000 cfs encompass only the low flow conditions downstream
from Talkeetna as measured at the Sunshine Gaging Station (USGS Gage
No.15292780).In order to account for the wider range and higher
average flows encountered at Rabideux Slough,three flow conditions at
the Sunshine Gage Station were defined based on the Chulitna and
Talkeetna River flows.The incremental flows of the Susitna River at
Gold Creek were ·added to the sum of flows from the Chulitna and
Talkeetna Rivers.In this way the majority of pre-and post-project
flow conditions and the effects on Rabideux Slough physical
characteristics could be analyzed.The three flow conditions used for
the analysis were:
Condition 1:Sum of the mean daily low flow for the Chulitna and
Talkeetna Rivers during September,typically the lowest
flow month during the ice-free season.The low flow
contribution from each river consists of the gO percent
exceedance flow.Flows at Gold Creek were added incre-
mentally to the sum of these flows to define the lower
third of the potential range of flows observed at
Rabideux Slough.
Condition 2: A medium flow range at Rabideux Slough was derived from
the fifty percent exceedance flows in the Chulitna and
Talkeetna Rivers using the mean monthly flow in August.
August flows were selected because of the salmon migra-
tion activity which occurs in August.Gold Creek flows
ranging from 1,000 to 31,000 cfs were i ncrement al ly added
to the sum of the mean August monthly flows from the
Chulitna and Talkeetna Rivers to provide a medium flow
ran3e at Rabideux Slough.
4
-
Sheet 1 of 3
Table A-2
MAINSTEM DISCHARGE VS.PHYSICAL HABITAT VAR IABL ES
SLOUGH 8A
Water Su rface Elevat ion Flow Depth
Sus i tna River
Slough Inter -Inter-
Discharge at Discharge Mid-mediate Upstream Mid -mediate Upstream
Gold Creek at Mo uth Mouth Slough Berm Berm Mouth S1f~~h Berm Be rm
(cfs )(cfs )(ft,msl)(ft,ms])(ft ,mslli (ft,msIT (ft)---rm-(ft )
1,000 3 559 .4 568.6 N/A N/A 1.1 0.2 0 0
3 ,000 3 559.4 568.6 N/A N/A 1.1 0.2 0 0
5,000 3 559.4 568.6 N/A N/A 1.1 0.2 0 0
7,000 3 559.4 568.6 N/A N/A 1.1 0.2 0 0
9,000 3
559.4 568.6 N/A N/A 1.1 0.2 0 0
11,000 8 561.4 568.8 N/A N/A 3.1 0.4 0 0
12,000 8
561.8 568.8 N/A N/A 3.5 0.4 0 0
13,000 8 562.1 568.8 N/A N/A 3.8 0.4 0 0
~15,000 8 562.5 568.8 N/A N/A 4.2 0.4 0 0
I 17,000 8 562.8 568.8 N/A N/A 4.5 0.4 0 0....
19,000 8 563.0 568 .8 N/A N/A 4.7 0.4 0 0
21,000 8 563 .2 568 .8 N/A N/A 4.9 0.4 0 0
23,000 8 563.3 568.8 N/A N/A 5.1 0.4
0 0
25,000 8 563.4 568 .8 N/A N/A 5. 2 0.4 0 0
27,000 8 563.5 568.8 573.2 N/A 5.3 0.4 0.1 0
29 ,000 11 563.5 568 .8 57 3.3 N/A 5.4 0.4 0.2 0
31,000 43 563 .6 569.8 573 .4 N/A 5.5 0 .4 0.3 0
N/A -Not Appl icable
Note :See Figure A-2 for locat ion 'of mouth,mid -slough,intermediate berm,and ups tream berm.
See Atta chment,Pa rt I,for narrat ive and wor ksheets explaining method of dete rmin ing s l ou gh ph ysical
habitat var iabl e s.
Sheet 2 of 3
Table A-2 (Cont'd)
MAINS TEM DISCHARGE VS.PHYSICAL HABITAT VARIABLES
SLOUGH 8A
Average Velocity Wetted Perimeter
Sus itna River Inter-Wetted Inter-
Discharge at Mid-mediate Upstream Surface Mid-mediate Upstream
Gold Creek Mouth ~I7Ugh Berm Berm Area Mouth Slf~~h Berm Berm
~(ft/sec)( sec)<ft/sec>(ft/sec r (ft2)(ftr (ft)(ft)
1,000 0.06 0.3 N/A N/A 305,000 62 54 0 0
3,000 0.06 0.3 N/A N/A 305,000 62 54 0 0
5,000 0.06 0.3 N/A N/A 305,000 62 54 0 0
7,000 0.06 0.3 N/A N/A 3U5,000 62 54 0 0
9,000 0.06 0.3 N/A N/A 305,000 62 54 0 0
11,000 0.03 0.4 N/A N/A 480,000 147 59 0 0
12,000 0.03 0.4 N/A N/A
500,000 152 59 0 0
~13,000 0 .02 0.4 N/A N/A 520,000 155 59 0 0I
N 15,000 0 .02 0.4 N/A N/A 570,000 160 59 0 0
17,000 0.02 0.4 N/A N/A 610,000 163 59 0 0
19,000 0.02 0.4 N/A N/A
650,000 165 59 0 0
21,000 0.01 0.4 N/A N/A
700,000 166 59 0 0
23,000 0.01 0.4 N/A N/A 740,000 167 59 0 0
25,000 0.01 0.4 N/A N/A 780,000 167 59 0 o .
27,000 0 .01 0.4 0.5 N/A 830,000 168 59 7 0
29,000 0.02 0.4 2.5 N/A 870,000 169 59 15 0
31,000 0.07 0.4 7.0 N/A 910,000 170 59 81 0
N/A -Not Applicable
Note:See Figure A-2 for locat ion of mouth,mid-slough,in termediate be rm,and upstream berm.
See Attachment ,Part 1, for narrative and worksheets expla ining method of determ ining slough physical
habitat variables.
Sheet 3 of 3
Table A-2 (Cont'd)
MAINSTEM DISChARGE VS.PHYSICAL HABITAT VARIABLES
SLOUGH 8A
Water Table Elevation
Susitna River
Discharge at
Gold Creek
(efs )
1,000
3,000
5,000
7,000
9,000
11,000
12,000
13.000
15,000
17.000
19.000
21.000
23.000
25.000
27.000
29,000
31.000
N/A -Not Applicable
Mid-
Slough
Well A
(ft.ms 1>
565.6
565.6
565.6
565.6
565.6
565.6
565.6
565.6
565.6
565.6
565.6
565.6
565.6
565.7
565.7
565.7
565.7
Mid-
Slough
Well B
(ft .ms 1>
568.0
568.0
568.1
568.2
568.3
568.3
568.4
568.4
568.5
568.5
568.6
568.6
568.7
568.7
568.8
568.8
568.9
Upstream
Well
(ft.mslT
574.7
574.7
574.8
574.8
574.8
574.9
574.9
574.9
574.9
575.0
575.0
575.0
575.0
575.0
575.1
575.1
575.2
Note:See Figure 2 for well locations.
See Attachment.Part 1. for narrative and worksheets
explaining method of determining water table elevations
4-3
Sheet 1 of 3
Table A-3
MAINSTEM DISCHARGE VS.PHYSICAL HABI TAT VARIAB LES
SLOUGH 9
Water Su rface Elevat ion Flow Depth
Sus itna River Slough
Discharge at Discharge Mid -Upstream Mid-Upstream
Go ld Creek at Mouth Mouth Slough End Mouth Slf~~h End
(cfs)(cfs)(ft,msll (ft,msf>(ft ,ms IT (ft )rrt)
1,000 3 589 .6 593.3 N/A 0 .1 0 .9 0
3,000 3 589 .6 593 .3 N/A 0.1 0.9 0
5,000 3 589.6 593 .3 N/A 0.1 0.9 0
7,000 3 589.6 593.3 N/A 0.1 0.9
0
9,000 3 589 .6 593.3 N/A 0 .1 0.9 0
11,000 3 589.6 593 .3 N/A 0.1 0.9 0
12,000 6 589.9 593.3
N/A 0.4 0.9 0
13,000 6 590.1 593 .3 N/A 0.6 0.9 0
.j:>15,000 6 590 .l:'593.3 N/A 1.0 0.9 0I
.j:>17,000 6 591.0 593 .3 N/A 1.5 0.9 0
19,000 6
591.4 593 .3 N/A 1.9 0.9 0
21,000 22 591.7 593.4
602.8 2.2 1.0 1.8
23,000 80 592 .1 593.9 603.4 2.6 1.5 2.7
25,000 152 592 .6 594.3 603.9 3.0 1.9 3.1
27 ,000 232 59 2.9 594 .5 604.2 3.4 2.1 3.4
29 ,000 320 593.3 594 .8 604 .5 3.8 2.4 3.7
31,000 405 593.7 595.2 604 .6 4.2 2.8 3.9
N/A -No t Appli cable
Note:See Figu re A-3 for location of mouth ,mid -slough ,and upstream berm .
See Atta chment,Part 2,fo r na r rat ive and wor ksheets expla ining "method of determini n9
slough phys ical habit at var iab les.
Sheet 2 of 3
Table A-3 (Cont'd)
MAINSTEM DISCHARGE VS.PHYSICAL HABITAT VARIABLES
SLOUGH 9
Average Velocity Wetted Perimeter
Susitna River Wetted
Discharge at Mid-Upstream Su rfa ce Mid-Upst r eam
Gold Creek Mouth ¥l,ugh End Area Mouth SIOU~h End
lcfs )(ft/sec)( t se c)(ft/seC>(ft2)(ft)(ft (ft )
1,000 0.8 0.1 N/A 130,000 27 89 0
3,000 0.8 0.1 N/A 130,000 27 89 0
5,000 0.8 0.1 N/A 130,000 27 89 0
7,000 0.8 0.1 N/A 130,000 27 89 0
9,000 0.8 0.1 N/A 130,000 27 89 0
11,000 0.8 0.1 N/A 130,000 27 89 0
12,000 0 .8 0.1 N/A 230,000 ..29 89 0
~13,000 0.5 0.1 N/A 300,000 33 B9 0
I 15,000 0.2 0.1 N/A 390,000 4B 89 0U1
17,000 0.1 0.1 N/A 470,000 7B B9 0
19,000 0.1 0.1 N/A 530 ,000 145 89 0
21,000 0.1 0.4 0.4 590,000 185 96 50
23,000 0.3 0.8 1.0 640,000 193 117 80
25,000 0.5 1.0 1.4
690,000 193 136 100
27,000 0.6 1.3 1.5 740,000 194 148 150
29,00 0 0.7 1.4 1.5 780 ,000 195 150 22 0
31,000 0.7 1.4 1.5 820,000 195 15 2 290
N/A -Not Appl icable
Note :See Figure A-3 for lo cation of mouth ,mid -slough,and upstream berm.
See Att achment,Pa rt 2, for nar rat ive and worksheets explaining method of dete rm ining
slough physical habitat variables .
Sheet 3 of 3 .
Table A-3 (Cont'd)
MAINSTEM DISCHARGE VS.PHYSICAL HABITAT VARIABLES
SLOUGH 9
Water Table Elevation
Susitna River Mid-
Discharge at Slough Upstream Upstream
Gold Creek Well Well A we 11 B
(cfs )(ft,ms 1)(ft .ms 1)(ft .ms l)
1,000 593.3 599.3 602.9
3,000 593.3 599.5 603.1
5,000 593.5 599.6 603.2
7,000 593.6 599.8 603.3
9,000 593.7 600.0 603.5
11,000 593.8 600 .2 603.5
12,000 593.9 600.3 603.6
13,000 594.0 600.4 603.7
15,000 594 .1 600.5 603.8
17,000 594.2 600.6 603.9
19,000 594.3 600.8 604.0
21,000 594.5 601.0 604.1
23,000 594.6 601.2 604.3
25 ,000 594.7 601.5 604.4
27,000 594.9 601.6 604.5
29,000 595.0 601.8 604.6
31,000 595.1 602.0 604.8
N/A -Not Applicable
Note:See Figure A-3 for well locations.
See Attachment,Part 2,for narrative and worksheets
explaining method of determining water table elevations .
4-6
-
Sheet 1 of 3
Table A-4
MAINSTEM DISCHARGE VS.PHYSICAL HABITAT VARIABLES
SLOUGH 21
Water Surface Elevation Flow Depth
Sus itna River Slough Inter-.Inter-
Discharge at Discharge Mid-mediate Highest Mid-mediate Upstream
Go ld Creek at Mouth Mouth Slough Berm Berm Mouth Slf~Th Berm Berm
(cfS)(efs )<1t,msfl (ft,ms]")(ft,mslT eft ,ms IT (ft)(ft)(ft )
1,000 5 744.7 744.9 N/A N/A 1.6 0.6 0 0
3,000 5 744.7 744 .9 N/A N/A 1.6 0.6 0 0
5,000 5 744.7 744.9 N/A N/A 1.6 0.6 0 .0
7,000 5 744.7 744 .9 N/A N/A 1.6 0.6 0 0
g,OOO 5 744.7 744.9 N/A N/A 1.6 0 .6 0 0
11,000 5 744 .7 744 .9 N/A N/A 1.6 0.6 0 0
12,000 5 744.7 744.9 N/A N/A 1.6 0.6 0 0
....l3,OOO 5 744.7 744.9 N/A N/A 1.6 0.6 0 0
I 15,000 5 744.7 744.9 N/A N/A 1.6 0.6 0 0......
17,000 5 744.7 744.9 N/A N/A 1.6 0.6 0 0
19,000 5 744.7 744.9 N/A N/A 1.6 0.6 0 0
21,000 5 744.7 744.9 N/A N/A 1.6 0.6 0 0
23,000 9 744.8
745.1 N/A N/A 1.6 0.7 0 0
25,000 9 745.0 745 .1 754.6 N/A 1.9 0.7 O.O!.!0
27,000 12 745.3 745.3 754.8 755.5 2.2 0.9 0.2 O.O!.!
29,000 19 745.6 745.8 755.1 755 .6 2.5 1.4 0 .5 0.1
31,000 34 746.0 746.3 755 .5 755 .6 2.9 2.0 0.9
O.1
N/A -Not Appli cable
Note:See Figu re A-4 for location of mouth ,mid -slough,intermediate berm,and up stre am be r m.
See Attachment ,Part 3,f or na r rative and worksheets expla ining method of determining slough phy sical
habitat variables.
lIFlow depth is l ess than 0.05 f t.
Sheet 2 of 3
Table A-4 (Cont'd)
MAINSTEM DISCHARGE VS.PHYSICAL HABITAT VARIABLES
SLOUGH 21
Average Veloc ity Wetted Perim eter
Sus itna River Inter-Wetted Inter -
Discharge at Mid-mediate Upstream Surface Mid-mediate Up stream
Go ld Creek Mouth n/ugh Berm Berm Area Mouth Slf~Th Berm Be rm
(cfs )(ft/sec)(sec)(ft/secr (ftlsee)(ft2)(ft)-(ft )(ft )
1,000 0.1 0.5 N/A N/A 46,000 50 25 0 0
3,000 0.1 0.5 N/A N/A 46 ,000 50 25 0 0
5,000 0.1 0.5 N/A N/A 46,000 50 25 0 0
7,000 0.1 0.5 N/A N/A
46,000 50 25 0 0
9,000 0.1 0.5 N/A N/A
46,000 50 25 0 0
11,000 0.1 0.5 N/A N/A 46 ,000 50 25 0 0
12,000 0 .1 0.5 N/A N/A
46,000 50 25 0 0
13,000 0.1 0.5 N/A N/A
46,000 50 25 0 0
~15,000 0.1 0.5 N/A N/A
46,000 50 25 0 0I
<Xl 17,000 0.1 0.5 N/A N/A
46,000 50 25 0 0
19,000 0.1 0.5 N/A N/A 46,000 50 25 0 0
21,000 0.1 0.5 N/A N/A
46 ,000 50 25 0 0
23,000 0.2 0.7 NIAll N/A 115,000 98 26 0 0
25,000 0.1 0.7 O .~N/A 155,000 101 26 3 ·0
27,000 0.1 0.7 1.4 -180,000 103 36 24 4
29,000 0.2 0.7 1.4 -200 ,000 10 5 45 44
12
31 ,000 0.2 0.8 1.0 -220,000 108 55 65 20
N/A -Not Applic able
Note :See Fi gure A-4 for location of mou th,mid -slough,i ntermedi at e berm,and up stream be rm.
See Atta chm ent,Part 3 , f or na r rat ive and wo rk sheets explain ing method of determin ing slo ugh phy sical
hab itat va r iables.
!/Veloc ity i s l ess th an 0.05 f t/sec.
Sheet 3 of 3
Table A-4 (Cont'd)
MA INSTEM DISCHARGE VS.PHYSICAL HABITAT VARIABLES
SLOUGH 21
Water Table Elevation
Susitna River
Discharge at
Gold Creek
(cfs )
1,000
3,000
5,000
7,000
9,000
11,000
12,000
13,000
15,000
17,000
19,000
21,000
23,000
25,000
27,000
29,000
31,000
(ft,msl)(ft,msf)
y
(ft,ms n
1/No well data available for Slough 21;for a description of
expected water table conditions in Slough 21, see Attachment,
Part 3.
4-9
Condition 3: A high flow range at Rabideux Slough was derived from the
sum of the 10 percent exceedance flows from the Chulitna
and Talkeetna Rivers on a daily basi s during the month of
June,which is typically the high flow month of the year.
The range of flows at Gold Creek were added incrementally
to this sum to provide the high range of flows at
Rabideux Slough.
The resu 1ts of the ana lyses of the effects of ma ins tem flow on the
hydraulic characteristics of Rabideux Slough are presented in Table A-5
for the three flow conditions and result in a total range of flows at
Rabideux Slough from 10,000 cfs to 85,000 cfs.Discussion of the
methods used i n the analyses for Rabideux Slough are presented in
the Attachment,Part 4.
A.5 Summary of Methods of Analyses
This section contains a sunmary of the methods used to derive the
following parameters:
o slough discharge
o threshold discharges
o water surface elevation
o flow depth
o velocity
o wetted surface area
o wetted perimeter
o water table elevation.
Since the methods vary among the sloughs,a separate sunmary is given
for each.More detailed descriptions are found in the attachment for
Sloughs SA,9,and 21 and Rabideux Slough.
The slough physical parameters given in Tables A-2 through A-5 should
be considered estimates of the average values.Slough discharge is
influenced by mainstem water level effects on groundwater upwelling,
local runoff,and regional groundwater. For this reason field measure-
ments of the relations between slough discharges and Susitna River
mainstem discharges showed considerable variability in all Regimes but
especially in Regimes I and II.To simplify the analyses a constant
slough discharge was assumed for each slough for each of Regimes I and
II.
A.5.1 Slough SA
A map of Slough 8A is shown on Figure A-2.Methods of analyses are
given in the Attachment,Part 1.
Threshold Discharges
The threshold Susitna River discharge for overtopping the upstream berm
(30,000 cfs to 32,000 cfs)was estimated from aerial photography of the
5
-
Sheet 1 of 16
Table A-5
MAIN ST EMDISC HARGE VS.PH YS ICAL HABITAT VAR IAB LES
RAB IDE UX SLOUGH
Sus itna River c ondtt t III Cond it ion iY Cond it ion 31.1onltlon-
Discharge at Ma instem Slough Ma instem Sl ough Ma instem Slough
Gold Creek Discharge Discharge Discharge Discharge Discharge Discharge
(cfs)(cfs ) (cf s )(cfs)(cfs)(cfs)(cfs)
1,000 10,000 0 31,000 0 55,000 0
3,000 12,000 0 33 ,000 0 57,000 0
5,000 14,000 0 35,000 0 59,000 0
7,000 16,000 0 37,000 0 61,000 0
9,000 18,000 0 39,000 0 63,000 0
11,000 20,000 0 41,000 0 65,000 0
12,000 21,000 0 42,000 0 66,000 8
13,000 22,000 0 43 ,000 0 67,000 20
15,000 24,000 0 45,000 0 69,000 60
17,000 26,000 0 47,000 0 71,000 108
19,000 28,000 0 49,000 0 73,000 165
21,000 30,000 0 51,000 0 75,000 230
23,000 32,000 0 53,000 0 77 ,000 300
25,000 34,000 0 55,000 0 79,000 380
27 ,000 36,000 0 57,000 0 81,000 .468
29 ,000 38,000 0 59,000 0 83 ,000 560
31,000 40,000 0 61,000 0 85,000 660
1.1 See l ast page of th is tab le for explanat ion of cond it ions.
Note: See Figure A-5 for l ocat ion of mouth ,mid-s lough,and upstream berm.
See Attachment,Part 4,narra t ive and worksheets e xpla ining method of
determ ining s lough phys ica l habitat var iables.
5-1
Sheet 2 of 16
Table A-5 (con't)
MAIN STEMDISCHARGE VS .PHYSI CAL HAB ITAT VARIAB LES
RAB IDE UX SLOUGH
Cond i t i III Condition zY Cond it i on 311onttton -.
Water-Water-Water-
Sus itna River Surface Surface Surface
Discharge at Mainstem Elevation Mainstem Elevat ion Mainstem Elevat ion
Go ld Creek Discharge at Mouth Discharge at Mouth Discharge at Mouth
(cf's )(cfs ) (ft .ms 1)(cfs )(ft.msll (cfs l (ft .msll
1,000 10,000 255.3 31,000 257.B 55.000 260.5
3.000 12.000
255.5 33.000 258.2 57,000 260.7
5.000 14,000 255.8 35.000 258.4 59.000 260.9
7.000 16.000 256.0 37.000 258.7 61 ~000 261.0
9.000 18.000
256.3 39.000 258 .9 63.000 261.2
11.000 20.000 256.5 41.000 259.1 65.000 261.4
12.000 21.000
256.6 42 .000 259.2 66.000 261.5
13.000 22.000
256.8 43 .000 259.3 67.000 261.6
15.000 24.000
257.0 45,000 259.5 69.000 261.7
17.000 26 .000 257.3 47,000 259 .8 71 .000 261.9
19.000 28.000 257.5 49.000 260.0 73.000 262.1
21,000 30 .000 25 7.8 51.000 260.1 75.000 262.3
23 .000 32.000 258.0 53.000 260.3 77 .000 262 .5
25,000 34.000
258.3 55.000 260.5 79.000 262.7
27.000 36.000 258.5 57.000 260.7 81.000 262.8
29.000 38.000 258.8 59.000 260.9 83.000
263.0
31.000 40.000
259.0 61.000 26 1.0 85.000 263.2
!I See las t page of this table for explanat ion of condit ions.
Note: See Figure A-5 for location of mouth .mid-slough.and upstream berm.
See Attachment.Part 4.for narrat ive and wo rksheets explaining method of
determining slough phys ical hab itat variables.
5-2
-
Sheet 3 of 16
Table A-5 (con't)
MA I NSTEM DISCHARGE VS .PHYS ICAL HABITAT VARI ABL ES
RAB IDEUX SLOUGH
Conditi on 1.!/Cond it ion 2!!Con d it i on 3.!/
Wate r-Water-Wat er-
Surface Surface Surface
Sus itna River Elevation Elevation El evat i on
Di scharge at Ma instem at Mainstem at Mainstem at
Go ld Creek Discharge Mid -Slo ugh Disc harge Mid-Sl ou gh Discharge Mi d-Sl ou gh
(cf s )(cf s)(ft ,m sll (cfs )(ft ,msll (cf's )(ft ,m sl)
1,000 10,000
N/A2/31,000 260 .3 55,000 260.6
3,000 12,000 N/A 33,000 260.3 57,000 260.7
5,000 14,000 N/A 35 ,000 260.3 59 ,000 260.9
7,000 16,000 N/A 37 ,000 260.3 61 ,000 26 1.0
9,000 18,00 0 N/A 39,000 260.3 63,000 261.2
11,000 20,000 N/A 41,000 260 .3 65,000 261.4
12 ,000 21,000 N/A 42,000 260.3 66 ,000 261.5
13,000 22,000 N/A 43,000 260 .3 67,000 261.6
15,000 24,000 N/A 45,000 260.3 69 ,000 261.7
17,000 26,000 260.3 47,000 260.3 71,000 261.9
19,000 28,000 260.3 49,00 0 260.3 73,000 262 .1
21,000 30,000 260.3 51,000 260.3 75,000 262.3
23,000 32 ,000 260.3 53,000 260 .3 77 ,000 262.6
25,000 34,000 260.3 55,000 260.5 79,000 262.9
27 ,000 36,000 260.3 57,000 260.7 81,000 263.2
29 ,000 38,000 260 .3 59 ,000 260.9 83,000 263.4
31,000 40,000 260.3 61,000 261.0 85 ,000 263.7
.!/See last page of th is table for explanation of condit ions.
2/Transect 7 r eported as dry at d ischarge of 25,800 cfs (ADF&G 1 9 8 2~
Note:See Figure A-5 fo r location of mouth,mid-slough,and upstream ber m.
See Attachment,Part 4,for narrative and worksheets explain ing met hod of
determin ing slough physical habitat var iables.
5-3 I
Sheet 4 of 16
Table A-5 (can't)
MAINSTEM DISCHARGE VS.PHYSICAL HABITAT VARIABLES
RABIDEUX SLOUGH
Condition 1Y Condition 2Y Condition 3Y
Water-Water-Water-
Surface Surface Surface
Sus itna River Elevation Elevation El evation
Discharge at Mainstem at Upstream Mainstem at Upstream Mainstem at Upstream
Gold Creek Discharge Berm Discharge Berm Discharge Berm
(cf s )(cfs)(ft,msl)(cfs )(ft,msl)(cf's )(ft,msl)
1,000 10,000 N/A 31,000 N/A 55,000 N/A
3,000 12,000 N/A 33,000 N/A 57,000 N/A
5,000 14,000 N/A 35,000 N/A 59,000 N/A
7,000 16,000 N/A 37,000 N/A 61,000 N/A
9,000 18,000 N/A 39,OOO N/A 63,000 N/A
11,000 20,000 N/A 41,000 N/A 65,000 N/A
12,000 21,000 N/A 42,000 N/A 66,000 262.8
13,000 22,000 N/A 43,000 N/A 67,000 262.9
15,000 24,000 N/A 45,000 N/A 69,000 263.0
17,000 26,000 N/A 47,000 N/A 71,000 263.1
19,000 28,000 N/A 49,000 N/A 73,000 263.1
21,000 30,000 N/A 51,000 N/A 75,000 263.2
23,000 32,000 N/A 53,000 N/A 77,000 263.2
25,000 34,000 N/A 55,000 N/A 79,000 263.3
27,000 '36,000 N/A 57,000 N/A 81,000 263.4
29,000 38,000 N/A 59,000 N/A 83,000 263.5
31,000 40,000 N/A 61,000 N/A 85,000 263.8
N/A -Not Applicable.
1/See last page of this table for explanation of conditions.
Note:See Figure A-5 for location of mOllth,mid-slough,and upstream berm.
See Attachment,Part 4,for narrative and worksheets explaining method of
determining slough physical habitat variables.
5-4
-
Sheet 5 of 16
Table A-5 (con't)
MAIN ST EM DISC HARGE VS.PHYSICAL HABITAT VARI ABLES
RAB IDEUX SLOUGH
Sus itna River Condition III Cd "zY Cond it i on sl'on t t t on
Di scharge at Ma instem F.1 ow Depth Ma instem Flow Depth Ma instem Fl ow Depth
Gold Creek Discharge at Mouth Discharge at Mouth Discharge at Mouth
(cfs )(cfs )(ft)(cfs)(ft)(cfs )(ft)
1,000 10,000 .0.4 31,.000 2.9 55,000 5.6
3,000 12,000 .0.6 33,000 3.3 57,000 5.8
5,000 14,000 0.9 35,000 3.5 59,000 6.0
7,000 16,000 1.1 37,000 3.8 61,000 6.1
9,000 18,000 1.4 39,000 4.0 63,000 6.3
11 ,000 20,000 1.6 41,000 4.2 65,000 6.5
12,000 21,000 1.7 42,000 4.3 66,000 6.6
13,000 22 ,000 1.g 43,000 ...4 67,000 6.7
15,000 24,000 2.1 45,000 4.6 69,000 6.8
17,000 26,000 2.4 47,000 4.9 71 ,000 7.0
19,000 28,000 2.6 49,000 5.1 73,000 7.2
21,000 30,000 2.9 51,000 5.2 75,000 7.4
23,000 32,000 3.1 53,000 5.4 77 ,000 7.6
25,000 34,000 3.4 55 ,000 5.6 79,000 7.8
27,000 36,000 3.6 57,000 5.8 81,000 7.9
29,000 38,000 3.9 59,000 6.0 83,000 8.0
31,000 40,000 4.1 61,000 6.1 85,000 8.3
1I See l ast page of th is tab le for explanat ion of cond itions.
Note: See Figure A-5 f or l ocati on of mouth ,mid-s lough ,and upstream berm.
See Attachment,Part 4,for narrat ive and worksheets expla ining method of
determining slough physical habitat variables .
5-5
Shee t 6 of 16
Table A-5 (con 't)
MA I NS TEM DI SCHARGE VS.PH YSI CAL HAB ITAT VAR IAB LES
RAB IDE UX SLOUG H
Cd"III Cd "zY Cond it i on -}..Ionltlon-on t t t on
Sus itna Riv er Flow Dept h Flow Dept h Flow Depth
Disc harge at Ma instem at Mainstem at Ma ins tem at
Go ld Creek Discharge Mid-s lough Discharge Mid-s l ough Discharge Mid-s lough
(cfs)(cfs)(ft)(cfs)(ft )(cfs)(ft )
1,000 10,000 oy 31 ,000 0.3 55 ,000 0. 5
3,000 12,000 0 33,000 0.3 57,000 0.7
5,000 14,000 0 35,000 0.3 59 ,000 0.9
7,000 16,000 0 37,000
0.3 61,000 1.0
9,000 18,000 0 39,000 0.3 63,000 1.2
11,000 20,000 0
41,000 0.3 65,000 1.4
12,000 21,000 0 42,00 0 0.3 66,000 1.5
13,000 22,000 0 43,000 0.3 67,000 1.6
15,000 24,000 0
45,000 0.3 69,000 1.7
17,000 26,000 0.3 47,000 0.3 71,000 1.9
19,000 28,000
0.3 49 ,000 0.3 73,000 2.1
21,000 30,000 0.3 51,000 0.3 75,000 2.3
23,000 32,000 0.3 53,000 0.3 77 ,000 2.6
25,000 34,000 0.3 55,000 0.5 79,000 2.9
27,000 36,000 0.3 57 ,000 0.7 81 ,000 3.2
29 ,000 38,000 0 .3 59,000 0.9 83 ,000 3.4
31,000 40,000 0.3 61,000 1.0 85,000 3. 7
!!See l ast page of t his tab le f or explanation of condit ions.
2/Transect 7 reported as dry f or di scharge of 25 ,800 cfs (ADF&G , 1982).
Note: See Figure A-5 fo r location of mouth,mid-slough,and upstream berm .
See Attachment,Part 4,for narrat ive and wo rksheets exp lain i ng method of
determ ini ng s lo ugh phys ica l ha bitat var iables.
5-6
-
Sheet 7 of 16
Table A-5 (con't)
MA INSTEM DISCHARGE VS.PHYSICAL HAB ITAT VARIABLE S
RABIDEUX SLOUGH
C d "11/Condit ion 2Y C d i t i -)!on ltlon -on t t t on
Flow Depth Flow Depth Fl ow Dep th
Sus itna Ri ver at at at
Di scharge at Ma instem Upstre am Ma instem Upstre am Mainstem Ups tream
Gold Cr eek Discha rge Benn Discharge Benn Di scharQe Be nn
(cfs )(cfs )(ft )(cf s )(ft)(cfs)(ft)
1,000 10,000 0 31,000 0 55,000 0
3,000 12,000 0 33,000 0 57,000 0
5,000 14,000 0 35,000 0 59 ,000 0
7,000 16,000 0 37,000 0 61,000 0
9,000 18,000 0 39,000 0
63,000 0
11,000 20,000 0 41,000 0 65 ,000 0
12,000 21,000 0 42,000 0 66,000 0.3
13 ,000 22,000 0 43,000 0 67 ,000 0.4
15,000 24,000 0 45 ,000 0 69,000 0.5
17,000 26,000 0 47,000 0
71,000 0.6
19,000 28,000 0 49,000 0
73,000 0.6
21 ,000 30,000 0 51,000 0 75,000 0.7
23,000 32,000 0 53,000 0
77 ,000 0.7
25,000 34,000 0 55,000 0 79,000 0.8
27,000 36,000 0 57,000 0 81,000 0.9
29,000 38,000 0 59,000 0
83,000 1.0
31,000 40,000 0 61,000 0
85,000 1.3
!!See l ast page of th is table for exp lanat ion of condi ti ons.
Note: See Figure A-5 for l ocati on of mou th, mid -s lough,and upstre am benn.
See Attachment ,Part 4,·f or narrat ive and works heets expla ining method of
determ ining s lough phys ical hab itat variables.
5-7
Sheet S of 16
Tabl~A-5 (con't)
MAINSTEM DISCHARGE VS.PHYSICAL HABITA T VARIABLES
RABIDEUX SLOUGH
Condit ion 111 Cond i t i on -):./C d""-}!on l tl on
Sus itna River Ave rage Average Average
Discharge at Mai nst em Ve loc ity Ma instem Velocity Ma instem Ve loci ty
Go ld Creek Discha rge at Mouth Discharge at Mouth Discha rge at Mouth
(cfs ) (cf s )(ft/sec)(efs)(ft /s ec)(efs)(ft/sec)
1,000 10 ,000 0 31,000 0 55,000 0
3,000 12,000 0 33,000 0 57,000 0
5,000 14,000 0 35,000 0 59,000 0
7,000 16,000 0 37,000 0 61,000 0
9,000 18,000 0 39,000 0 63,000 0
11,000 20,000 0 41,000 0 65,000 o 2/12 ,000 21,000 0 42,000 0 66,000 0·02/13,00 0 22 ,000 0 43,000 0 67,000 O.D=='
15,000 24 ,000 0 45,000 0 69,000 0 .1
17,000 26,000 0 47,000 0 71 ,000 0.2
19,000 28 ,000 0 49 ,OOO 0 73,000 0 .2
21,000 30,000 0 51,000 0 75,000 0.3
23 ,000 32,000 0 53 ,000 0 77 ,000 0 .4
25 ,000 34,000 0 55,000 0 79, 000 0.5
27,000 36,000 0 57,000 0 81,000 0.6
29,OOO 38,000 0 59,ooO 0 83,000 0.7
31,000 40,000 0 61,000 0 85,000 0.8
11 See l ast page of t h is tab le for explanation of cond it ions.
1V Vel oci ty i s l ess than 0.05 ft/sec.
Note: See Figure A-5 for locat ion of mo uth,mid-s lough,and ups tream ber m.
See Attachment,Part 4,for narrati ve and works heets expla ining me thod of
determ ining slough phys ical habitat var iables.
5-8
-
·.
D
She et 9 of 16 lUI
Table A-5 (can 't)
MAIN ST EMDISC HARGE VS.PHYS ICAL HABITAT VAR IA BLES
RAB IDEU X SLOUGH
Cond iti on I.!!Cond i t i on i.!!Cond iti on sY
Average Average Average
Sus itna Ri ver Ve loc i ty Ve loc ity Ve loc ity
Discharge at Ma instem at Mainstem at Mainstem at
Gold Creek Discharge Mid-Slough Discharge Mid-S lough Discharge Mid-Slough
(cfs )(cf's)(ft/sec)(cfs)(ft/sec)(cfs )(ft/sec)
1,000 10,000 0 31,000 0 55,000 0
3,000 12,000 0 33,000 0
57,000 0
5,000 14,000 0 35 ,000 0 59,000 0
7,000 16,000 0 37,000 0 61,000 0
9,000 18,000 0 39,000
0 63,000 0
11,000 20,000 0 41,000 0 65,000 0
12,000 21,000 0 42,000 0 66 ,000 0.3
13,000 22,000 0 43,000 0 67,000 0.5
15,000 24,000 0 45,000
0 69,000 0 .9
17,000 26,000 0 47,000 0 71,000 1.1
19,000 28 ,000 0 49,000
0 73,000 1.3
21,000 30,000 0 51,000 0 75,000 1.3
23 ,000 32,000 0 53,000 0
77 ,000 1.3
25,000 34,000 0 55,000
0 79,000 1.2
27,000 36,000 0 57,000 0 81,000 1.2
29,000 38,000 a 59,000 a 83,000 1.2
31,000 40,000 a 61,000 a 85,000 1.2
.!!See l ast page of th is table for explanat ion of cond itions.
Note:See Figure A-5 for location of mouth,mid-slough,and upstream berm.
See Attachment,Part 4,for narra tive and worksheets expla ining method of
determ ining s lo ugh phys ica l habi tat var iables.
II
Il
II
5-9
_Sheet 10 of 16
Table A-5 (can't)
MAINSTEM DISCHARGE VS.PHYSICAL HABITAT VARIABLES
RAB IDEUX SLOUGH
Cond i t i 11/ C d""-}!Cond i t i sYonltlon-on ltlon on ltlon
Average Average Average
Velocity Velocity Velocity
Susitna River at at at
Discharge at Mainstem Upstream Mainstem Upstream Mainstem Upstream
Gold Creek Discharge Berm Discharge Berm Discharge Berm
(cfs )(cfs)(ft/sec)(cfs )(ft/sec)(cfs)(ft/sec)
1,000 10,000 N/A 31,000 N/A 55,000 N/A
3,000 12,000 N/A 33,000 N/A 57,000 N/A
5,000 14,000 N/A 35,000 N/A 59,000 N/A
7,000 16,000 N/A 37,000 N/A 61,000 N/A
9,000 18,000 N/A 39,000 N/A 63,000 N/A
11,000 20,000 N/A 41,000 N/A 65,000 N/A
12,000 21,000 N/A 42,000 N/A 66,000 1.3
13,000 22,000 N/A 43,000 N/A 67,000 1.4
15,000 24,000 N/A 45,000 N/A 69,000 1.6
17,000 26,000 N/A 47,000 N/A 71,000 1.7
19,000 28,000 N/A 49,000 N/A 73,000 1.7
21,000 30,000
N/A 51,000 N/A 75,000 1.8
23,000 32,000 N/A 53,000 N/A 77,000 1.9
25,000 34,000 N/A 55,000 N/A 79,000 1.g
27,000 36,000 N/A 57,000 N/A 81,000 1.8
29,000 38,000 N/A 59,000 N/A 83,000 1.6
31,000 40,000 N/A 61,000 N/A 85,000 1.4
N/A -Not Applicable
!!See last page of this table for explanation of conditions.
Note:See Figure A-5 for location of mouth,mid-s lough,and upstream berm.
See Attachment,Part 4,for narrative and worksheets explaining method of
determining slough physical habitat variables.
5-10
-
Sheet 11 of 16
Table A-5 (con 't)
MAIN ST EM DIS CHA RGE VS. PHYS ICA L HABITAT VARIA BL ES
RAB IDE UX SLO UGH
Cond t t i III Cond i t i zY Cond iti on ~on l tl on -on lt lon
Total Total Total
Su s it na River Wetted Wetted Wetted
Discharge at Ma instem Surface Mainstem Surface Ma instem Surface
Go ld Creek Discharge Area Discharge Area Discharge Area
(cfs )(cfs)(ft2)(c fs)(ft2 )(cfs )(ft 2)
1,000 10,000 120,000 31,000 160,000 55,000 210,000
3,000 12,000 130,000 33,000
170,000 57,000 220,000
5,000 14,000 130,000 35,000 170,000 59,000 230,000
7,000 16,000 140,000 37,000 180,000 61,000 240,000
9,000 18,000 140,000 39,000 180,000 63,000 250,000
11,000 29,000 140,000 41,000 180,000 65,000
260,000
12,000 21,000 140,000 42,000
190,000 66,000 270,000
13,000 22,000
150,000 43,000 190,000 67,000 280,000
15,000 24,000 150,000 45,000 190 ,000 69,000 300 ,000
17,000 26,000 150,000 47,000 200,00 0 71 ,000 320,000
19,000 28,000 160,000 49,000
200,000 73 ,000 340,000
21,000 30,000 160,000 51,00 0 200,000 75,000 360 ,000
23 ,000 32,000 170,000 53,000
210,000 77 ,000 380 ,000
25,000 34,000 170,00 0 55 ,000 210,000 79,000 400 ,000
27,000 36,000 180,000 57,000 220,000
81,000 420,000
29,000 38,000 180,000 59,000 230,000 83,000 450,000
31 ,000 40,000 180,000 61,000 240,000 85,000
470 ,000
I I See l ast page of this table for explanat ion of cond it i ons.
Note: See Figure A-5 for location of mouth, mid-s lough,and upstream·berm.
See Attachment,Part 4,for narrative and worksheets expla ining method of
determining slough phys ica l habitat variab les.
5-11
Sheet 12 of 16
Table A-5 (con' t )
MAIN ST EM DI SCH ARGE VS .PHY SI CAL HABITAT VARIA BLE S
RAB IDEUX SLOUGH
Cond i t i 11/Condition zY Cond it ion -)!on ltlon -
Sus itna River Wetted Wetted Wetted
Discharge at Mai nst em Perimeter Ma ins tem Perimeter Main stem Per imeter
Go ld Creek Discharge at Mouth Discharge at Mouth Discharqe at Mout h
(cfs)(cfs)(ft)(cfs)(ft)(cf's)(ft)
1,000 10,000 10 31,000 28 55,000 70
3,000 12,000 10 33,000 32 57,000 70
5,000 14,000 12 35,000 35 59,000 71
7 ,000 16,000 13 37,000 37 61,000 71
9,000 18,000 15 39,000 56 63,000 72
11 ,000 20,000 16 41,000 61 65,000 72
12,000 21 ,000 18 42,000 63 66,000 73
13,000 22,000 18 43 ,000 66 67 ,000 73
15,000 24 ,000 20 45,000 68 69,000 74
17,000 26,000 23 47,000 69 71,000 74
19,000 28,000 25 49,000 69 73 ,000 75
21,000 30,000 28 51,000 69 75,000 76
23,000 32,000 30 53,000 70 77 ,000 110
25,000 34,000 35 55,000 70 79,000 150
27,000 36,000 36 57 ,000 70 81,000 180
29,000 38,000 43 59,000 71 83,000 185
31,000 40,000 60 61,000 71 85,000 190
11 See last page of th is table for explanation of cond it ions.
Note: See Figure A-5 for location of mouth,mid-slough,and upstream berm .
See Attachment,Pa rt 4,for narrat ive and worksheets explain ing method of
determin i ng s lough phys ical habitat var iab les .
5-12
-
Sheet 13 of 16
Table A-5 (con't)
MAINSTEM DISCHARGE VS.PHYSICAL HABITAT VARIABLES
RAB IDEUX SLOUGH
Cond i t i 11/Condition -zY Condition 3Yonttton -
Wetted Wetted Wetted
Sus itna River Perimeter Perimeter Perimeter
Discharge at Mainstem at Mainstem at Mainstem at
Gold Creek Discharge Mid-Slough Discharge Mid-Slough Discharge Mid-Slough
1,000 10,000 ~.31,000 12 55,000 16
3,000 12,000 ~33,000 12 57,000 22
5,000 14,000 ~35,000 12 59,000 24
7,000 16,000 ~37,000 12 61,000 25
9,000 18,000 ~39,000 12 63,000 26
11,000 20,000 ~41,000 12 65,000 28
12,000 21,000 ~42,000 12 66,000 29
13,000 22,000 ~43,000 12 67,000 30
15,000 24,000 aY 45,000 12 69,000 30
17,000 26,000 ·12 47,000 12 71,000 31
19,000 28,000 12 49,000 12 73,000 32
21,000 30,000 12 51,000 12 75,000 33
23,000 32,000 12 53,000 12 77,000 35
25,000 34,000 12 55,000 16 79,000 210
27,000 36,000 12 57,000 22 81,000 300
29,000 38,000 12 59,000 24 83,000 310
31,000 40,000 12 61,000 25 85,000 310
!!See last page of this table for explanation of conditions.
2/Transect 7 reported as dry at discharge of 25,800 cfs (ADF&G,1982).
Note: See Figure A-5 for location of mouth,mid-slough,and upstream berm.
See Attachment,Part 4,for narrative and worksheets explaining method of
determining slough physical habitat variables.
5-13
Shee t 14 of 16
Table A-5 (can't)
MAIN STEM DI SCH ARGE VS.PH YS ICAL HAB ITAT VARIA BL ES
RAB IoE UX SLOUGH
Cd""11/C d i t i ~C d i t i ~on ltlon -on l tlon on i t t on
Wet ted Wetted Wetted
Per imeter Perimeter Per ime ter
Sus itn a Rive r at at at
Discharge at Mainstem Upstream Ma instem Upstream Mainstem Upstream
Go ld Creek oi s charqe Berm Discharge Berm Discharge Berm
(cfs )t.cfs)(ft)(cfs)(ft)(cfs )(ft )
1,000 10,000 0 31,000 0 55,000 0
3,000 12,000 0 33,000 0 57,000 0
5,000 14,000 0 35,000 0 59,000 0
7,000 16,000 0 37,000 0 61,000 0
9,000 18,000 0 39,000 0 63,000 0
11,000 20,000 0 41 ,000 0 65,000 0
12,000 21,000 0 42,000 0 66,000 40
13,000 22,000 0 43,000 0 67,000 75
15,000 24,000 0 45 ,000 0 69,000 150
17,000 26,000 0 47,000 0 71,000 230
19 ,000 28,000 0 49,000 0 73,000 305
21,000 30,000 0 51,000 0 75,000 380
23,000 32,000 0 53,000 0 77 ,000 455
25,000 34,000 0 55,000 0 79,000 530
27,000 36,000 0 57,000 0 81,000 610
29,000 38,000 0 59,000 0 83,000 685
31,000 40,000 0 61,000 0 85,000 760
!!See last page of this table for explanation of condit ions.
Note :See Fig ure A-5 for location of mouth, mid-s lough,and upstream berm.
See Attachment,Part 4,for nar rat ive and worksheets expla ining method of
determin ing slough physical habitat variables .
5-14
-
I
I
Sh eet 15 of 16 I
I
I
I
I
I
I
I
Table A-5 (con' t )
MAINSTEM DIS CHA RGE VS.PHYSICAL HABITAT VARI ABLES
RABIDEUX SLO UG H
Cd"11/Condi ti on 2Y Cond it i on -).!on ltl on -
Sus itna River Water Water Water
Di scharge at Mai nst em Tab le Mainst em Tab le Mai nst em Table
Go ld Cr e ek Discharge Ele vation Discharge Elevat ion Disc harge Elevat ion
(c f's )(cf's )(ft ,ms 1)(cfs)(ft ,ms 1)(cfs )(ft ,m sll
1,000 .10,000 31,000 55,000
3,000 12,000 33,000 57,000
5,000 14,00 0 35 ,000 59,OO O
7,000 16,000 37,000 61,000
9,000 18,000 39,000 63,000
11,000 20,000 41,000 65 ,000
12,000 21 ,000 42,000 66,000
13,000 22,000 2/43,000 Y 67 ,000 2/
15,000 24 ,000 45,000 69,000
17,000 26,000 47,000 71,000
19,000 28,000 49,OOO 73,000
21,000 30,000 51,000 75,000
23,000 32 ,000 53,000 77 ,00 0
25,000 34 ,000 55,000 79,000
27,000 36 ,000 57 ,000 81,000
29 ,000 38,000 59,000 83,000
31,000 40 ,000 61 ,000 85,000
!!See last page of th is table for explanat ion of cond itions.
2/No wel l da ta avaible f or Rab ideux Slough ;fo r a description of expected water t able
condi ti on s,see Attachment A-4.
Note :See Figure A-5 for location of mouth,mid-slough,and ups tream berm .
See Attachment,Part 4 ,for narrat ive and worksheets expla ining method of
determini ng s lough phys ical habitat vari ables..
5-15
II
II
II
-
II
Sheet 16 of 16
Table A-5 (con't)
MAIN ST EMDISC HARGE VS.PHYS ICA L HAB IT AT VAR IAB LES
RAB IDE UX SLOUGH
MainstemDischarge =Osc +QC +QT
i n which,
QGC =
QC =
QT =
Condition 1:
Susitna River at Gold Creek (USGS Gage No.15292000)d ischarge
Chulitna River near Talkeetna (USGS Gage No .15292400)d ischarge
Talkeetna River near Talkeetna (USGS Gage No.15292700)d ischarge
QGC =1,000 to 31 ,000 cfs in 2000 cfs increments
QC =90%exceeded flow during the month of September
QT =90%exceeded flow during the month of September
Condition 2:
QGC =1,000 to 31,000 cfs in 2000 cfs increments
QC =average monthly flow i n August
QT =average monthly flow in August
Condit ion 3:
QGC =1,000 to 31,000 cfs in 2000 cfs i ncrements
QC =10%exceeded flow during the month of June
QT =10%exceeded flow dur ing the month of June
Note :See Figure A-5 for locat ion of mouth,mid-slough,and upstream berm.
See Attachment,Part 4,for narrat ive and worksheets exp laining method of
determining slough phys ical hab itat variables.
5-16 -
slough at a Susitna River discharge (measured at Gold Creek)of 31,100
cfs ,The thresho 1d discharge for overtopp i ng the i ntermed i ate berm
(29,000 cf s )was estimated by comparing computed and observed Susitna
River water surface elevations with the berm crest elevation.The
threshold discharge between Regimes I and II (10,000 cf s )was estimated
from field observations.
Slough Discharge
Slough discharges were estimated to be 3 cfs for Regime I and 8 cfs in
Reg ime II based on fi e 1d measurements (ADF&G t 1982).Slough discharge
for Regime IIA was estimated by computing d ischarge over the interme-
diate berm and adding this to Regime II discharge.
Water Surface Elevation
Water surface elevations at the slough mouth are based on a rating
curve developed from staff gage readings between 11,500 cfs and
26 ,500 cfs.Between 10,000 cfs and 11,500 cfs,and between 26,500 cfs
and 31,000 cfs,the rating curve was extrapolated.Hydraulic computa-
tions,assuming uniform flow,were made to estimate slough mouth water
surface elevations for discharges less than 10,000 cfs.
Mid-slough water surface elevations are based on in-field measurements
for mainstem discharges which exceed 10,000 cfs , For mainstem dis-
charges les s than 10,000 cfs,hydraulic computations were made.
Water surface elevations at the intermediate and upstream berms were
estimated using broad crested we ir computations.
Flow Dept h
Flow depths were computed by subtracting thalweg elevations from water
surface elevations,d et ermined as described above.
Velocity
Average slough flow velocities were computed by dividing the slough
discharges by flow cross-sectional areas.Lateral.distributions of
velocity were measured at cross sections about 1600 feet upstream of
the slough mouth and are shown in the Attachment.
Wetted Surface Area
For mainstem discharges greater than 10,000 cfs ,wetted surface areas
were estimated using aerial photographs for mainstem discharges greater
than 10,000 cfs.For mainstem discharges less than 10,000 cfs the
wetted surface area was estimated using computed slough water surface
profiles and surveyed cross sections.
6
-
Wetted Perimeter
Wetted perimeters at the slough mouth,mid-slough,and the intermediate
berm were measured from the surveyed cross sections and the water
surface elevations determined as described previously.
Water Table Elevations
Water table elevations were derived from data collected at observation
wells i n the slough.
A.5.2 Slough 2-
A map of Slough 9 is shown on Figure A-3. Methods of analyses are
given in the Attachment,Part 2.
Threshold Discharges
The thresho 1d Susi tna River ma ins tem discharges between Reg ime I and
Reg ime II (11,000 cf's l and between Reg ime II and Reg ime I II (20,500
cfsl are based on plots of measured mainstem and slough discharges.
Slough Discharge
The slough dis.charges are based on the same field measurements as for
Threshold Discharges.
Water Surface Elevation
Slough mouth water surface elevations are based on staff gage readings
for mainstem discharges greater than 11,000 cfs.For mainstem dis-
charges less than 11,000 cfs,the slough mouth water surface elevation
was assumed constant.This water surface elevation reflects an esti-
mate of flow depth at staff gage 129 .0 for a mainstem discharge of
10,000 cfs and a slough discharge of 3 cfs (Trihey,1982,Table 4,p,
21 i.
All mid-slough water surface elevations are based on a rating curve
derived from s taff gage readings.Upstream end water surface eleva-
tions are based on water surface profiles computed with the U.S.Army
Corps of Engineers computer program for water surface profiles,HEC-2.
Flow Depth
Flow depths were computsd by sub tract tnq the t halweg elevations from
water surface elevations determined as described above.
Velocity
Average slough flow velocites were determined by dividing slough dis-
charge by the flow cross sectional areas.Lateral and longitudinal
distributions of velocities obtained in the field are shown in the
Attachment.
7
wetted Surface Area
For mainstem discharges greater than 11,000 cfs,wetted surface areas
were estimated from aerial photography.For mainstem discharges less
than 11,000 cf s,the wetted surface area was estimated using computed
slough water surface profiles and surveyed cross sections.
Wetted Perimeter
Wetted perimeters were estimated to be equal to wetted surface widths
(top wi dths)for the slough mouth and the ups tream end of thi s slough.
Top wi dths were estimated from aeri a 1 photos and computed slough water
surface profiles and surveyed cross sections.Wetted perimeters were
computed from surveyed cross sections for mid-slough .
Water Table Elevations
Water fable elevations were derived from data collected at observation
wells in the slough.
A.5.3 Slough 21
A map of Slough 21 is shown on Figure A-4. Methods of analyses are
given in the Attachment,Part 3.
Threshold Discharges
The threshold Susitna River mainstem discharges between Regimes II-A
and I II (26,000 cf's ) and between Reg imes I and II (21,300 cf's )are
based on field measurements of slough and mainstem discharge.
Slough Discharges
Slough discharge estimates are based on the same field measurements
indicated in the preceding paragraph.
Water Surface Elevation
For mainstem discharges greater than 21,300 cfs,water surface eleva-
tions at the slough mouth are based on a rating curve derived from
staff gage readings .A constant water surface elevation at the slough
mouth was assumed for all mainstem discharges less than 21,300 cfs.
Mid-slough water surface elevations were estimated from staff gage
readings and average daily elevations from a stage recorder.Constant
water levels were assumed for Regimes I,II,and II-A.
Intermediate and upstream berm water levels were estimated from staff
gage readings.
8
-
Flow Depths
Slough flow depths were estimated by subtracting the thalweg elevation
from water surface elevations determined as described above.
Ve 1oc ity
Average .slough flow velocities were estimated by dividing slough
discharges by flow cross sectional areas.Average velocities for four
measured flows are shown in the Attachment.Lateral and longitudinal
distributions of velocities obtained in the field are shown in the
Attachment.
Wetted Surface Area
Slough wetted surface areas were estimated from aerial photography.
Wetted Perimeter
Slough wetted perimeters were assumed to be equal to wetted surface
width (top widths) based on aerial photography and field measurements.
Water Table Elevations
There is not sufficient information to estimate the water table level
at this slough since wells have not been installed.Geologic materials
are expected to be similar to sloughs SA and 9.
A.S.4 Rabideux Slough
A map of Rabideux Slough is shown on Figure A-S.Methods of analyses
for this slough are .presented in the Attachment,Part 4.
Threshold Discharges
There is very little flow in this slough until the upstream berm is
overtopped (Susitna River mainstem discharge 66,000 cfs).
Slough Discharges
Slough discharge estimates are based on four field observations.Two
observations of slough dischar~e when the upstream berm was not
overtopped (Regime II)indicated negligible flow in this slough .Two
observations of slough discharge when the upstream berm was overtopped
were used to estimate slough discharge in Regime III.
Water Surface Elevations
Water surface elevations at the slough mouth are based on staff gage
readings and a surveyed water surface level.Mid-slough water surface
1eve1s are based on surveyed water 1eve1s and measurements of top
9
wi dths from aeri a 1 photography projected on surveyed cross sect ions.
The transect at mid-slough has been observed to be dry at a mainstem
.discharge of 25,800 cfs.Mid-slough water levels are influenced by
water levels at -the mouth for mainstem discharges greater than _
53,000 cfs,Upstream berm water surface levels were estimated from
hydraulic computations assuming a triangular broad crested weir.
Flow Depths
Slough flow depths were determined by subtracting the slough thalweg
elevations from water surface elevations derived as described above.
Velocity
Average slough flow velocity was computed by dividing slough discharge
by the slough cross sectional area.Lateral and longitudinal distribu-
tions of velocities as measured in the field are shown in the Attach-
ment.
Wetted Surface Area
Wetted surface areas were estimated from aerial photography.
Wetted Perimeter
Wetted perimeters were estimated from field surveyed cross sections at
the slough mouth and mid-slough.Wetted perimeters were estimated to
be equal to wetted surface wi dths (top wi dths)measured from aeri a 1
photography at the upstream berm.
Water Table Elevations
There is not enough information to estimate water table levels at this
slough since wells have not been installed.However,groundwater
levels are expected to respond in a manner similar to sloughs upstream
of Talkeetna (Sloughs SA and 9).
A.6 Discussion of Results,
The following discussion refers to the results presented in Tables A-I
through A-5.
A.6.1 Slough SA
A summary of the results for Slough 8A is presented in Table A-2.
Regime II occurs over a mainstem flow range of 10,000 to 26,000 cfs,
and thus is the dominant regime characterizing Slough 8A in the range
of incremental flows analyzed.Intermediate and upstream berms are not
overtopped unt il mai nstem flows have reached 26,000 and 30,000-32,000
cfs,respectively (Table A-I).
10
•
Slough discharges are generally low at mainstem flows l ess t han the
overtopp ing d isc harge and vary between 3 and 20 cfs.A correlat ion of
s lo ugh fl ows with mai nst em f lows at less tha n overtopp i ng d ischarges i s
not apparent a t t his l evel of ana lys is,perha ps because of l ocal runoff
and groundwater i nf l ow f rom up1and areas.Therefore,const ant s lough
f lows of 3 and 8 cfs were ass umed fo r Reg imes I and II,respect ively.
I n Reg i me I , water su rface elevat ions at the s lough mou th are con-
t ro lled by a berm downstream of t he mouth.Hence, for the 3 cfs d is-
charge the water surface e levat ion at the mout h remains constant.In
Reg ime II,water s urface elevat ions and depth at the slough mouth i n-
cr ease as Susitna River flows i ncrease because of a backwater ef fect.
The depths presented in Table A-2 r epresent max imum depths at cross-
sect ion WI (see Figure A-2). For Regime I,the depth at the controll-
i ng berm downstream of cross-section WI is estimated to be 0.1 ft.
For all regimes, the water surface elevations and depths at mid-slough
are dependent on slough discharge.At the upstream berms,depths are
zero until the berms are overtopped.
At mainstem flows less than 29,000 cfs,average velocities in the
slough are low because of the low slough discharges.
Wetted surface area is constant for all mainstem flows in Reg ime I.As
higher mainstem flows increase the backwater effect of Regime II,wett-
ed surface area increases.Wetted perimeter at the mouth also in-
creases as mainstem flows in Regime II increase.
Groundwater elevations at mid-slough ,Well A,do not appear to be
s ignif icantly correlated with ma instem discharge.At mid-slough,We ll
B,and the upstream wel l,there i s a direct re lationship with ma instem
d ischarge.This relat ionship i s dep icted on Sheet 3 of Tab le A-2.
Sl ough .2-
Summary i nform a ti on for Slough 9 is presented i n Table A-3.
For Reg ime I (mai nstem flow less than 11,000 cfs)and Regime I I (11,000
to 20,500 cfs),there is little var iat ion i n slough d ischarge •.Hence,
based on observed data,constant slough d ischarges of 3 cfs and 6 cfs
were assumed for Reg imes I and II,respectively.At d ischarges greater
than the upstream berm overtopp ing d ischarge (Regime I II), slough dis-
charge increases with mainstem discharge.Regime II I slough d ischarges
presen ted in Tab le A-3 represent values estimated from a plot of the
observed data.
In Regime I,water surface elevations at the mouth of Slough o9 are con-
trolled by a berm downstream of the mouth.For the assumed 3 cfs
slough discharge,the water surface elevation remains constant.At 3
cfs,the depth over the berm is computed to be 0.1 feet.In Regimes II
and III,the water surface elevations and depths at the mouth of the
slough increase with increas ing mainstem discharge.
11
The mid-slough water surface elevations and depths shown in Table A-3
are at a mid-slough pool.The water surface elevations and depths are
essent ially independen t of ma instem discharges for Reg ime I and II.
Howeve r,when the upstream berm i s overtopped,the i ncrease i n s 1o ug h
d ischarge r e sul ts in an i ncrease i n water surface elevat ion and dept h.
Once overtopped,the water surface elevations at the upstream berm
increase directly with mainstem Susitna water surface elevations.
The average velocities presented for the mouth of Slough 9 are the
veloc ities over the berm at the slough mouth. Since the cross sect ion-
a 1 area at the berm i s a mi n imum,veloc it ies are higher than for any
other cross section near the mouth.Mid-slough velocit ies are low
throughout Regimes I and II but increase when the upstream berm is
overtopped.
The wetted surface area remains constant throughout Regime I.However,
in Regime II,as the backwater from the mainstem i ncreases with
i ncreasing Susitna River discharge,the wetted surface area i ncreases.
The wetted perimeter at the mouth is cons tant through Reg ime I and
increases through Reg imes II and I II.Mi d-s lough and upstream berm
wetted perimeters do not change until overtopping 'occurs.
Water table elevations at Slough 9 presented in Table A-3 exh ibit
considerably more change with mainstem discharge than do those pre-
sented for Slough 8A (see Table A-2l.
Slough 21
Summary information for Slough 21 is contained in Table A-4.
Regime I flow at Slough 21 includes flows up to a mainstem discharge of
21,400 cf's ,Reg ime II flow occurs over a range of discharges from
21,400 cfs to 24,800 cfs.Reg ime I I -A,resu It i ng from overtoppi ng of
the intermediate berm,occurs during mainstem flows of 24,800 cfs to
26,000 cfs and Regime III occurs when the highest berm is overtopped at
26,000 cfs.
Slough discharges measured during Regime I flows were low,varying
between 2 and 12 cfs.Since there is no apparent corre 1at i on with
mainstem discharge,a constant slough flow of 5 cf s was assumed (see
Table A-4l.For Regime II,at mainstem flows between 23,000 and
25,000 cfs,a slough discharge of 9 cfs was assumed. For Regime III,a
relationship based on observed data was used to estimate slough dis-
charge.
As a result of the assumed constant slough flow for Regime I,the water
surface elevation and slough depth at the mouth are constant.The
depths presented refl ect a poo 1 depth upstream from the contro 11 i ng
berm and not the depths over the berm.As backwater effects and over-
topping of the upstream berms begin,the water surface elevations and
depths i ncrease.
12
•
At mid-slough,the water surface elevation (and depth)is constant
throughout Reg ime I.As slough d ischarge increases from 5 to 9 cf s,
(Regime I to Regime II),there is a slight increase in water surface
elevation (and depth).The increase at mid-slough is attributable to
the increase in discharge since the backwater effects do not extend
upstream to the mf d-s louqh location.
Average velocities throughout all flow regimes and for all locations
analyzed,remain low.As illustrated in Table A-4,velocities at the
slough mouth do not exceed 0.2 feet per second for the range of flows
considered.
In Table A-4,wetted surface area begins to increase due to backwater
(Regime II)at a mainstem flow of 21,400 cf's,At flows higher than
26,000 cfs,the increases in wetted surface area are the result of both
backwater and upstream berm overtopping.
Wetted perimeter at the mouth responds to mainstem flow in a manner
similar to wetted surface area.The wetted perimeter at the mid-slough
is essentially constant until the upstream berm is overtopped.
No groundwater elevation data is available for Slough 21.
Rabideux Slough
Summary information for Rabideux Slough is contained in Table A-5
(Sheets 1 through 16).
Rabideux Slough is affected by the backwater from the Susitna River
(Regime II)at mainstem flow conditions (at the slough)as low as
approximately 10,000 cfs.This regime persists until the upstream berm
is overtopped at a mainstem flow of approximately 65,000 cfs.
Measured slough discharges at flows less than the overtopping discharge
were either not measurable or were less than 1 cfs.Therefore,slough
discharge was assumed to be zero for Regime II.However, once over-
topped,Rabideux Slough discharge increases significantly.
Water surface elevation (Table A-5,Sheet 2) and depth (Table A-5,
Sheet 5)at the slough mouth in crease with mainstem discharge over the
range of flows considered.
The selected mid-slough location is dewatered at flows less than 26,000
cfs (Table A-5,Sheets 3 and 6).At higher flows,isolated ponded
water has been observed.Therefore,from flows of 26,000 cf's to
53,000 cfs a constant water surface elevation and a depth of 0.3 feet
were assumed.At flows greater than 53,000 cf s,water levels and
depths increase as the result of backwater from the mainstem.Once
overtopping of the upstream berm occurs,the water level at mid-slough
increases at a greater rate than during Regime II.The water surface
elevation (Table A-5,Sheet 4) and depth (Table A-5,Sheet 7)at the
13
upstream berm change only after the berm is overtopped.At the higher
overtopping discharges,the upstream berm becomes submerged because of
backwater.
Veloci ti es at t he mou th (T able A-5, Sheet 8 )are zero unt il overtopp i ng
occurs.However,because the cross sect ional area is relative ly large,
velocities at the slough mouth remain low even during an overtopped
condition.At mid-slough (Table A-5,Sheet g),velocities rema in l.o.w
during overtopping because of the backwater effect;Velocities at the
upstream berm (Table A-5,Sheet 10) during overtopping also remain l ow
because of backwater.
Total wetted surface area (Table A-5,Sheet 11)increases with increas-
ing mainstem discharge as a result of backwater up to the overtopp ing
discharge of 65,000 cfs,and as a result of both backwater and over -
topping once overtopping occurs.The wetted surface area includes the
areas of both the pond at the upstream end of the slough and the lower
slough even though they are not hydraulically connected at lower
flows.
The wetted perimeter at the slough mouth (Table A-5,Sheet 12)in-
creases because of the backwater effect.The wetted perimeter responds
to the shape of the cross section.increasing quickly at first and then
remaining relatively constant.At high flows,the wetted perimeter
exh ibits a l arge increase because of overtopping of the f lood plain.
The wetted perimeter at mid-slough (Table A-5.Sheet 13)is 12 feet or
less until backwater effects occur at a mainstem flow of 53,000 cf's,
At a discharge of 79,000 cfs.the water surface encroaches on the flood
plain resulting in a large increase in wetted perimeter.
The wetted per imeter at the upstream berm (Table A-5, Sheet 14 ) i s zero
unt il the upstream berm is overtopped.
A.7 References
Alaska Department of F.ish and Game."Susitna Hydro Aquatic Studies,
Phase I Final Draft Report",Volume 1. 1982.
A1aska Department of Fish and Game."Sus itna Hydro Aquat i c Stud ies,
Phase II Basic Data Report",Volume 4, 1983.
Chow.V.T ••Open Channel Hydraulics.McGraw-Hill,~ew York,1959.
R&M Consultants.Inc."Susitna Hydroelectric Project,Hydral ic Project,
and Ice Stud i es",for A1aska Power Authority.Anchorage,A1aska,
March 1982.
,"Susitna Hydroelectric Project,1982 Hydrographic Sur-
---v-e-y-s"""-.""""rfor Alaska Power Authority.Anchorage.Alaska,December
1982a.
14
•
__~-=~....'"Susitna Hydroelectric Project,Slough Hydrology Interim
Report".for A1ask a Power Authority,Anchorage,A1ask a,Decem-
ber 1982b.
Trihey,E.W.,"Preliminary Assessment of Acres by Spawning Salmon to
Side Slough Habitat above Talkeetna",for Alaska Power Authority,
Anchorage,Alaska,November 1982.
u.S.Army Corps of Engineers."HEC-2,
Manual".Hydrologic Engineering
January 1981.
15
Water Surface Profiles,Users
Center,Davis,Cal iforn ia,