HomeMy WebLinkAboutAPA510PRELIMINARY ASSESSMENT OF ACCESS BY SPAWNING SALMON
TO SIDE SLOUGH HABITAT ABOVE TALKEETNA
BY
E.WOODY TRIHEY,P.E.
P.O.BOX 10-1774
ANCHORAGE,ALASKA 99511
PREP ARED FOR
ACRES AMERICAN INCORPORATED
BUFFALO,NEW YORK
NOVEMBER 1982
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Preliminary Assessment of Access by Spawning Salmon
to Side Slough Habitat above Talkeetna
by
E.Woody Trihey.P.E.
P.O.Box 10-1774
Anchorage,Alaska 99511
Prepared for
Acres American Incorporated
Buffalo,New York
November 1982
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ACKNOWLEDGEMENTS
The field data used in this report were collected by the Alaska Department of
Fish and Game (ADF&G)Su Hydro Aquatic Habitat and Instream Flow Group during
the 1982 summer field season.Special thanks are extended to the ADF&G
Aquatic Habitat and Instream Flow group staff for their assistance in extrac-
ting these data from a much larger data base and expediting their reduction
for use in this report.
Mr.William J.Wilson and Dr.Charles G.Prewitt (Arctic Environmental Infor-
mation and Data Center,University of Alaska)developed the species periodi-
city chart and provided technical review of the paper.Dr.Larry Rundquist
(Woodward-Clyde Consultants)provided assistance with the paper's organization
and technical review of the backwater profiles.Jean Baldrige (Woodward-
Clyde Consultants)and Mr.Charles D.Evans also provided technical review of
this paper.
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INTRODUCTION
The proposed Susitna hydroelectric project will alter the existing streamflow,
sediment and thermal regimes of the river.The project would reduce stream-
flows at Gold Creek during summer and increase them during winter.Suspended
sediment,turbidity and water temperatures are expected to follow similar
patterns (Acres American Incorporated 1982).Several anadromous and resident
species of fish utilize a variety of riverine and associated tributary habi-
tats to varying degrees throughout various seasons (ADF&G 1981a,1981b,
1981c).The anticipated changes in the streamflow,thermal,and sediment
regimes are expected to affect the quantity and/or quality of fish habitat in
the Susitna River throughout the year (Woodward-Clyde Consultants 1982).
Although some mainstem spawning has been documented,the most intensively used
spawning areas within the Talkeetna to Devil Canyon reach are located in
tributary streams and side sloughs (ADF&G 1981a).Of these,side-slough
habitats are most likely to be adversely effected by reduced streamflows
during the inmigration and spawning period.Natural flows at the Gold Creek
stream gage commonly range from 25,000 to 16,000 cfs during late August and
early September.A controlled flow of no less than 12,000 cfs from mid-August
to mid-September is proposed by the Alaska Power Authority.
Because of the magnitude of the proposed streamflow reductions during the
inmigration and spawning period,the availability,as well as the quality,of.
existing side-slough spawning habitat is of concern.The purpose of this
paper is to present a preliminary analysis of the influence that mainstem
discharge has on access to spawning areas in the side sloughs above Talkeetna.
The paper has been prepared at the request of the Alaska Power Authority and
in cooperation with the Alaska Department of Fish and Game,Su Hydro Aquatic
Studies Group.
Much of the discussion and the conclusions presented in the latter portion of
this report are based on direct observation by the author and other
experienced observers.Corroborative field data to support many of the
statements made in this report are,at present,both limited and provisional.
Continuing analysis of these and other 1982 data by the Su Hydro Aquatic
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Studies Group will provide a more reliable indication of the range of mainstem
discharges that are necessary for providing access by adult salmon to the side
sloughs.The ADF&G report is scheduled for June 1983.Until the remainder of
the 1982 data are analyzed by ADF&G,the statements presented in this paper
regarding the streamflows necessary for chum salmon to gain access to the side
sloughs must be viewed as the provisional opinion of the author.
~~~FouI;general categories offish habitat that exist along ~theSusitna River
between Talkeetna and Devil Canyon are identified,and an introductory
description of the physical processes that interact to provide side-slough
habitat is presented.Much of the discussion pertaining to slough processes
consists of hypotheses and is unsupported at this time.by data or analyses.
However,it is believed that further analysis of the data collected during the
1982 field season and data that could be collected during a well focused field
program in 1983 will substantiate these hypotheses and provide a basis for
quantifying associated relationships.To assist with recognizing the specific
focus of this paper,the sequence in which the various topics are addressed is
diagrammed in Figure 1.
SUSITNA RIVER FISHERY RESOURCES
The Susitna River basin supports populations of five Pacific salmon species
(chinook,sockeye,coho,chum,and pink),one additional anadromous salmonid
(Bering cisco).an anadromous osmerid (eulachon),and several resident species
(Arctic grayling,rainbow trout,burbot,Dolly Varden,round whitefish,
humpback whitefish,longnose sucker,threespine stickleback,Arctic lamprey,
and sculpin).Rainbow trout,grayling,Dolly Varden and burbot are the
principal resident contributors to the Susitna River sport fishery (Mills
1982).The rainbow,grayling and Dolly Varden fishery is primarily located in
clear water tributaries,whereas burbot are generally found in the mainstem
Susitna River.
Sockeye and chum salmon originating in the Susitna basin are the most impor-
tant contributors to the total upper Cook Inlet commercial salmon harvest.
Coho and pink salmon are of lesser commercial value.Commercial harvest of
chinook has been very limited,because regulations prevent commercial fishing
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Fisher)'Resource
Spati~l and Seasonal Distribution
Evaluation Species
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GenerAl Habitat Categories Talkeetna to Devil Canvon
1.Hainstem
2:Side-channel
3.Side-slough
4.Tributaries
Ph h Habitat
Figure 1.
1.Nainste11l I,>ischarcc I
2.Local Runoff
3.Croundvater Inflov
4.Riverine Icc Processes
Schematic Diagram of Information F1CM
Influence on Sidc-Slou~h ACCCfiS
(Focus of 1'.1per)
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for chinook salmon until most of the run has entered natal streams.However.
chinook salmon are a very important sport fish in the lower Susitna drainage.
and are harvested in a local subsistence fishery at Tyonek.Therefore Susitna
River chinook stocks might be considered to hold a relative overall rank in
the Susitna basin at least equal to pink and coho salmon.
The five species of Pacific salmon that inhabit the Susitna basin utilize a
variety of habitats to·different degrees during various seasons (Figure 2).
Activity is implied by the relative abundance of a ,particular species/life
stage within the respective time periods.Degree of activity (intense or
moderate)was determined by the University of Alaska f s Arctic Environmental
Information and Data Center (AEIDC)from information presented.by Woodward-
Clyde Consultants (WCC)in Chapter 3 of the draft Exhibit E for the FERC
license application report (Acres 1982).
Identification of critical habitat components during each season of the year
is a necessary step in assessing impacts and developing a viable mitigation
plan.Various species .and life stages have different critical requirements
and respond differently to habitat alterations.A change in habitat
conditions that benefits one species or life stage may adversely.affect
another;and mitigation plans favoring one species may discriminate against
another.Therefore.selection of one or two species (evaluation species)in.
preference to the many life stages or species that utilize a particular
habitat type during any given season is an effective approach for prioritizing
seasonal habitat requirements and focusing mitigation efforts.
An evaluation species can be selected after initial baseline studies and
impact assessments have identified the dominant species of interest and those
habitats that are most vulnerable to potential impacts.For the purposes of
this report.species within the Susitna River with high commercial.sport,
subsistence,or aesthetic value were given priority.Those species within
this category whose habitat is thought to be most jeopardized by anticipated
proj ect effects were rated higher than those species whose habitat was not
considered as vulnerable (Table 1).Since no rare or endangered species
inhabit the Susitna River,it was not necessary to respond to this
consideration in the selection and prioritization of the evaulation species.
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Figure 2.Provisional Periodicity
Devil Canyon Segment of
1982).
Chart for Salmon
the Susitna River
in the Talkeetna to
(Adapted from AEIDC.
KrbJn.~ar Anr Hav June Jul Aun Sep Oc:l Hoy Oec:
Chino""I I I I I I I I I I I
-Adult '.8810ge ..••
-51'0",,109
-·-fn-ab.llon![."T'lenc"••••I!l •••
-·-Roarlng
-S.otl109 •••••
~
-fdull """'l",.__..
-Spo'"llnq ••••
-Ine:tb ollon![.Ulleoc........,
•Oulldg ration .._..
~
-Adult '.881198 ,...,
-Spa....lnq ....
-Ine:tballon/[••r'leo<:e ......I ••
-Rearing ••....
•1Ju1.lgr.llon ••..t
Coho
•Adull P..ell~e ........
-5(>.....1"'1 I·••
-Inc:d••llon!£..ergeo<:e ..........••
-Re.ring
-s...ollinq ••...
Sockeye
-"'<1 ..1t rau",)e ..........
-SI'.oolnq .....
-Inc:.l••llon/l"er'lc:nce w••••,....
...Ree-rt..-.q ...----...
...Ool,.i.qralioo"•••~•••t
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, J ........U ....c:k.j'e appe.r lo be ob.enl rrOlO thl.r.ach.
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Table 1.Evaluation Species and Life Stages for Side Slough Habitats in the
Talkeetna to Devil Canyon Reach.
Chum Salmon
•Returning adults;
•Spawning adults;
•Incubating embryos and pre-emergent fry;
•Emergent fry;
•Outmigrant juveniles.
Sockeye Salmon
•Returning adults;
•Spawning adults;
Incubating embryos and pre-emergent fry;
Emergent fry;
Outmigrant juveniles.
Chinook Salmon
•Rearing juveniles.
Coho Salmon
•Rearing juveniles.
Pink Salmon
Returning adults;
•Spawning adults;
•Incubating embryos and pre-emergent fry;
•Emergent fry;
•Outmigrant juveniles.
Resident Species
•Limited data base precludes
identification of relevant
life stage.
Because of differences in habitat location and seasonal habitat requirements,
not all salmon species are expected to be equally affected by the proposed
project.The greatest changes in flow-dependent habitat characteristics are
expected to occur between Talkeetna and Devil Canyon.Of the five species of
salmon that inhabit the Talkeetna to Devil Canyon reach,chum and sockeye
salmon appear to be the most vulnerable.This is due to their dependence on
the slough habitats along the margins of the floodplain for spawning,incu-
bation and early rearing (ADF&G 1981a,1981b,1981c.1982).Of these two
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species,chum salmon appear to be dominant (ADF&G 1981b).Chinook and coho
salmon,while having a greater commercial and sport value than chum salmon,
may not be as adversely affected by the project.These species are
principally tributary spawners;fry and juveniles rear in clearwater areas
such as the mouths of sloughs and tributaries (ADF&G 1981a,1981b,1981c,
1982).Postproject conditions in the mainstem (reduced velocity and
turbidity)may provide replacement habitat to offset any potential loss to
these traditional rearing areas that might occur._While _some pink_salmon
spawn in slough habitats in the reach between Talkeetna and Devil Canyon,the
majority of these fish utilize tributary habitats (ADF&G 1981a).Although
some adult residents appear to use the side-slough habitats between Devil
Canyon and Talkeetna,limited information regarding utilization of side-slough
habitat by other life history phases of resident species precludes a
meaningful prioritization at this time.The authors'prioritization of
evaluation species for side-slough habitat along the Susitna River between
Devil Canyon and Talkeetna is provided in Table 1.
GENERAL HABITAT CATEGORIES
Fish habitat in the Talkeetna to Devil Canyon reach of the Susitna can be
divided into four general categories:mainstem,side-channel,side-slough,
and tributary habitats.Each general habitat category contains a spectrum of
physical attributes rather than a specific set of uniform characteristics.
Mainstem habitat consists of those portions of the Susitna River that normally
convey streamflow throughout the year.Both single and multiple channel
reaches are included in this habitat category.Groundwater.and tributary
inflow appear to be inconsequential contributors to the overall characteris-
tics of mainstem habitat.Mainstem habitat is typically characterized by
high-velocity streamflows and well armored streambeds.Substrates generally
consist of boulder and cobble size materials with interstitial spaces filled
with a grout-like mixture of small gravels and glacial sands.Suspended
sediment concentrations and turbidity are high during summer due to the
influence of glacial melt-water.Streamflows recede in early fall,and the
mainstem clears appreciably in October before an ice cover forms on the river
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in late November or December.Seasonal surface water temperatures in the
mainstem river appear to be primarily influenced by ambient air temperature
and solar radiation.Mainstem surface water temperatures are believed to be a
principal determinant of mainstem intragravel water temperatures.
Side-channel habitat consists of those portions of the Susitna River that
normally convey streamflow during the open water season but become appreciably
dewateredduring periods of low flow.Side-channel habitat may exist either
in well defined overflow channels,or in poorly defined water courses flowing
through partially submerged gravel bars and islands along the margins of the
mainstem river.Side-channel streambed elevations are typically lower than
the mean monthly water surface elevations during June,July and August.Thus
side channels normally convey streamflow throughout the summer.Side-channel
habitats are characterized by shallower depths,lower velocities and smaller
streambed materials than mainstem habitats.In general,the sediment and
thermal regimes of the side channel habitats reflect mainstem conditions.A
winter ice cover,similar to that which forms on the mainstem,generally
exists in the side channels.The presence or absence of clear water inflows
is not considered a critical component in the designation of side-channel
habitat.Tributary and groundwater inflow may prevent some side-channel
habitats from becoming completely dewatered when mainstem flows recede.
Throughout the winters of 1974-75 and 1981-82 groundwater inflow and upwelling
retained open leads in some side-channel areas (Barrett 1975a,1975b,1975c
and Trihey 1982).
Side-slough habitats are found in spring-fed overflow channels along the edge
of the floodplain,separated from the mainstem by well-vegetated bars.An
exposed alluvial berm often separates the head of the slough from mainstem or
side-channel flows.The controlling streambed/streambank elevations at the
upstream end of the side sloughs are slightly less than the water surface
elevations of the mean monthly flows for June,July,and August.At inter-
mediate and low-flow periods,the side sloughs convey clear water from small
tributaries and/or upwelling groundwater (ADF&G 1981c,1982).These clear
water inflows are essential contributors to the existence of this habitat
type.The water surface elevation of the river generally causes a backwater
to extend well up into the slough from its lower end (ADF&G 1981c,1982).
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Even though a substantial backwater exists,the sloughs function hydraulically
very much like small stream systems.Several hundred feet of the slough
channel often conveys water independent of mainstem backwater effects.
Except when the water surface elevation (discharge)in the mainstem river is
sufficient to overtop the upper end of the slough,surface water temperatures
in the side sloughs appear to respond independently of mainstem temperatures
(ADF&G 1981c,1982).-.Surface water temperatures in the side sloughs during
summer months are principally a function of air temperature,solar radiation,
and the temperature of the local runoff.During winter months surface water
temperatures are strongly influenced by upwelling groundwater.The large
deposits of alluvium through which the upwelling water flows appear to act as
a buffer or thermal reservoir,attenuating summer temperatures and providing
very stable winter temperatures.Although some exceptions have been noted,
intragravel water temperatures in upwelling areas are generally between 2 and
4°C throughout the year.
Tributary habitat consists of the full complement of hydraulic and morphologic
conditions that occur in the tributaries.Their seasonal streamflow,
sediment,and thermal regimes reflect the integration of the hydrology,
geology and climate of the tributary drainage.The physical attributes of
tributary habitat are not dependent on mainstem conditions except at the
tributary mouth,where the discharge influences access into the tributary and
the clear water tributary habitat extends as a plume into the turbid waters of
the mainstem (ADF&G 1981c,1982).
PHYSICAL ASPECTS OF SIDE-SLOUGH HABITAT
The physical characteristics of side-slough habitat appear to be dependent
upon the interaction of four principal factors:discharge of the mainstem
Susitna River,surface runoff patterns from the adjacent catchment area,local
groundwater inflow.and riverine ice processes.These factors interact to
varying degrees during different seasons of the year to provide a unique type
of fish habitat along the margins of the Susitna River (Figure 3).
Side-slough habitat is utilized predominately by chum and sockeye salmon,
although chinook,coho and pink salmon also inhabit the side sloughs at some
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I Figure 3.Artists sketch of a side-slough and adjacent Susitna River (courtesy
of AEIDC).
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time during their fresh water life.Resident species are also found in these
areas.
Mainstem Discharge
The amount of streamflow in the mainstem Susitna River principally influences
side-slough habitat conditions in two ways:1)intermediate level streamflows
cause a backwater effect at the mouth of the slough,which creates a speciaL .
type of slough habitat and facilitates access by fish into the slough (ADF&G
1981c,1982);and 2)high flows overtop the upstream end of the slough and
provide the dominant flushing action,removing debris and sediments from the
slough.
Streambed elevations at the downstream entrance to the side sloughs are
generally lower than the stage (water surface elevation)in the adj oining
mainstem channel.Thus the stage of the mainstem causes a hydraulic plug,
which impedes the flow of clear water from the mouth of the slough and forms a
clear backwater zone that may extend several hundred feet upstream into the
slough.
As mainstem discharge increases,the depth and size of the backwater zone at
the mouth of the slough continues to increase.At some point,the stage in
the mainstem river becomes high enough that turbid glacial flow from the
mainstem enters the slough at its upstream end.Once overtopped,flow within
the sloughs often increase rapidly from less than 10 cfs to more than 500 cfs
(ADF&G 1982,R&M Consultants,Inc.1982).These periodic high flows tend to
flush out detrital material and fine sediments,which commonly accumulate·in
low velocity areas near the mouth of the slough.Occasionally,high flows
transport sands and silts into the slough from the mainstem;however,the
overall effect of these periodic overtoppingsis generally thought to result
in a net transport of fines and organic material out of the slough.During
spring break up,large short-duration flows pass through the side sloughs.
Periodically,breakup flows are apparently of such magnitude that they remove
debris and beaver dams,redistribute streambed gravels and,at times,alter
the bottom profile or alignment of the slough.
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Local Runoff
During those portions of the year when mainstem streamflows are high enough to
cause a backwater effect at the mouth of the slough.but not high enough to
overtop the slough at its upstream end.the principal sources of streamflow
within the slough (slough flow)are from local surface runoff and groundwater
upwelling.Summer rainstorms appear to have a major influence on the amount
of clear water flow in side sloughs during_July and August.In general.local
surface runoff is thought to contribute a greater percentage to the clear
water flow in the slough during the ice-free period of the year than does
groundwater upwelling.However.a subset of side sloughs also exist that
depend predominantly on ground water throughout the year (ADF&G 1981c).
Unseasonably dry weather during August of 1982 resulted in the second lowest
mean monthly mainstem discharge in 33 years of record at Gold Creek.Average
daily streamflows fluctuated between 12.000 and 14.000 cfs for 14 days.The
mean monthly flow was 15.270 in comparison to the long term average monthly
flow of 22,200 cfs.During this time,groundwater inflow to small tributary
streams and upwelling within the side slough itself was the most significant
factor in maintaining sloughflow.It is hypothesized that.during a more
normal year,local runoff would have provided the greatest source of clear
water to the side sloughs.
Groundwater Inflow
Although groundwater upwelling normally contributes a lesser amount of water
to the total clearwater flow in the side sloughs than does surface runoff.the
upwelling is believed to be essential for attracting adult salmon into those
spawning areas that are not likely to freeze during winter.During winter
months.groundwater inflow and upwelling provide nearly all of the slough
flow.Even the water flowing into the slough from small tributary channels
most likely has entered that channel as groundwater.Groundwater inflow also
results in stable water surface elevations and a discontinuous ice cover.By
mid-winter the mainstem river is frozen over and nearly all tributary flow has
ceased.Yet substantial portions of the side sloughs remain ice free.Even
if winter air temperatures become cold enough to cause an ice cover to form
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over the side sloughs.substrates are not expected to freeze.Field work con-
ducted during the winters of 1974-75 and of 1981-82 indicate that surface and
intragravel water temperatures in upwelling areas commonly ranged between 2
and 4°C and had a significant influence on retarding the formation of an ice
cover and maintaining gravel substrates in an unfrozen condition throughout
the winter (Barrett 1975a.1975b.1975c and Trihey 1982).
Preliminary investigations indicate that the predominant slop.e of the -
groundwater table beneath the flood plain is down valley (Acres American
Incorporated 1982).The origin of the water that upwells in the side sloughs
is unknown at this time.It may be from a discontinuous local aquifer or it
may be from the mainstem river.
Upwelling water appears to flow from beneath the streambed into the slough in
a near vertical direction.Besides preventing substrates from freezing.
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upwelling is also thought to prevent deposits of silts and sands from suf-
focating developing embryos that are within the underlying streambed gravels.
The general oxygen content and direction of the upwelling flow is also
believed to keep the embryos oxygenated during the incubation period.Oxygen
being supplied from beneath the streambed should obviate the problems that are
normally associated with a deep silt mantle overlying spawning gravels.
Ice Processes
Ice processes in the mainstem river are important in maintaining the character
of the slough habitat.Besides reworking substrates and flushing debris and
beaver dams from the sloughs that could otherwise be potential barriers to
upstream migrants.ice processes are also considered important for maintaining
the groundwater upwelling in the side sloughs during winter months.
The increased stage associated with a winter ice cover on the Susitna makes it
possible for approximately the same hydraulic head to exist between the
mainstem and an adjacent sideslough during periods of low winter flow as that
which exists during normal summer flow (Figure 4).The river stage observed
during mid-winter 1981-82 associated with the ice cover formation on the
Susitna River appeared very similar to the water surface elevation associated
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Figure 4.COMPARISON OF CONCEPTUAL MID·SUMMER
&MID·WINTER HYDRAULIC GRADIENTS
BETWEEN THE MAINSTEM RIVER &ADJACENT
SIDE SLOUGH
b~:.•...~.Malnstem .~:~er ,~.\:Ide Slough
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Mid-Summer Hydraulic Gradient !
li!filil Sa nd
[eq·Sf Cobbles a Boulders
'''1:Malnst~~.RIY~r~~,s.ide SIOUg~
;?~....0 0 (;:1.0........,.~.~&"..~..~::e:&.~:·..;o:'.;.-'ti:-.;/.·./·~:·..:·:~~:':·:O'.:..::..~8.·:I.J:!·~:;;·~····:Ci~~.9.~.·9~q~::;,'··:·.~~':'....~~::..Ci./1;Qo:·.··~;/?;::.:~·:}??~::S?:::~~·~~;.;·\.:o;.~~.·fg:·:Q.:@Pot'o:.o."u.~.oo:f.l~o~c:.~o·Po·.:lO.::..-<.i.·A;'•
........,'0..'..;:''./l'''-'''•..-Y.••~••••••.r'-)•.••v·O···.·C::l··~'oC:;i'·o···..·'..·'e·".O·QV•.".·Y ..;,g~;?i~gg6"2!~·:C?J&::~~~a:~~~f¢F~..;:·Qi~:.~:.~b::~·'C2·oV~~·:;bp.!?c9:,~o··"·~oJi·:~·~P·;·~};1i)"~~~O..·:p.t:J..~O··O!~·O}:~4o:~I>:~fJOi·B:~~;~~o~9:2~Ji.:~~~2QtJ?~~~qd~~;;;:~b~~•.v (z:.1..:>....'c;)''.'·.···0 ·o··v.·/"""1,'.p '(./:'..~'".~!-,.;po ·.Vv,......•.··'0·'V·:o··~~'~..,,'"...0·:0:'.···:·..,,·..:.:":",",,'.0/·:(/:'0':'0'·..•·.O:-xP :':"':i:1;.~:"0:"";"<:j;O ....·"....a.:.q..q:,'....:.,...r--,::.r,\)..O'..~:-~;-;;.-:-;;;..",...,C'io:V.o:.'U ..·..o.~~:.·~.·.·.o.O.oo:$..::.".::..°;;':".0°.......·".........:><1"".·('-\'.(1.,,·....·.,,,~n ....·....0 C)·o·.·o ..·....o .•·.'-·C>..:·•-..,..••••<)0:".1'.'..,:.....'~
Mid-Winter Hydraulic GraClient !
---,~
)
·~t~·.
I
r
"ii.'
.,
.\
~
l
.,...-..,.,.
with summer discharges of 18,000 to 19,000 cfs.The ice formation covered the
mainstem and most side channels.When the ice cover was penetrated,the water
level generally rose in the auger hole to within a few inches of the ice
surface.Thus the midwinter hydraulic grade line of the mainstem is suspected
of closely paralleling the surface of the mainstem ice cover.
The alluvial depos~ts that form gravel bars and islands between the mainstem
river and side sloughs are highly permeable-making it possible for water
from the river to flow downgradient through the alluvium and into the sloughs.
Thus the increased stage associated with an ice cover on the river may provide
an important driving mechanism for maintaining the upwelling in the side
sloughs throughout the winter.
SIDE-SLOUGH ACCESS
The remainder of this paper addresses only one element of the preceding
discussion:the effect of mainstem discharge on chum salmon access into the
side sloughs during the spawning season.Slough 9 has been selected as'the
fo·cal point for this analysis.In general,access for upstream migrants into.
Slough 9 is somewhat more difficult than an average access condition
encountered by adult spawners in the Talkeetna to Devil Canyon reach.
Upstream access into Slough 9 is far better than access to Slough 16B or 19;
but much more difficult than access into Whiskers Slough or Slough 8A.It is.
a reasonable index of entrance conditions into Sloughs 20 and 21.
The streambed and water surface profiles that define entrance conditions for
Slough 9 on August 24,1982 are presented in Figure 5.The mainstem disch.arge
at Gold Creek was 12,500 cfs and flow in Slough 9 was 3 cfs.The profiles
originate in the Susitna River approximately 1000 feet downstream from the
mouth of the slough (R&M cross section 128.4Wl)and continue up the slough
terminating with the streambed elevation at the upstream entrance to the
slough.The profile is 7250 feet in length,and reflects a difference in
elevation of approximately 15 feet between the downstream (mouth)and the
upstream (head)ends of the slough.The uppermost 2900 feet of Slough 9 has
an average streambed gradient of 18.6 ft/mi;whereas t~e average gradient of
the lower 2900 feet of the slough is 5.6 ft/mi.In comparison,the average
15
'-·,·~.i .::!;~-1,__--,
i
')
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6DoOO:l5tOO50.00
1\1ll,.,:l'.l1 SILTtlSAND
1;,;Q'j.l ,GRAVEL a RUBBLE
~COSBLE a BOULOER
45tOO
-----::::;:--::::t-'~""",,'~l(}<J "~~:".<;).Q':"';;;'C>O.poc.oJ;So '.sULOUGH
I'",••"'>~'.'C>.~•....,.o 0'.<:;j'l!:••d<5.i(J.t:J..d.J .:..<f;,o~~'!5"'.•~.olSi~o(j;;§,~tf',"'.',· .~..."'''bn&.''f?iJ~Q?"2~!>'1i~%",·:lb"','O""'~,''''P<.''t'~<i:p.,(l~',;4~:'i=2~o:,.,Q~'O,'~,ts,,."$.,S>,.,'~9o.~I:><:i:s·<>"•..".~~,;>?'"."",,,,d,.,.."~\jl "0:'.'.''.,;'W "'ol"-~h{)'D,:~"';i5C)t.~;::C!"':;\1t>ov ..~.q.q~~:n.~&~,·...'·e:c:o,~<::t··~_toe r;:,c ••t)
••,f;j';~"'~~'()'Q",,~,<;!',I:f~\'\:t"""d o~-e,"Ug.p'.oo.'.:-&5'~Q6 ~Q,r:-'.~:6.<;.~i~..:~,<;\~.r"C,):<10~'O";<>c:S:I:>'~''9-."~;.:0:,,'".'i!;;>,:~,~"P6',<;)";;.C\~~.",.~o,;.""",c.P'i\l'1:lK''''''·<--:"",1.~~i'tS'~":'''''Y~l·'b<::ld:>.c?:P;'''{\·~'l<'·'S)?~!i'H!.::.;(\,,"q,",."Q,•
40.003Ot0025,0020tOO
SLOUGH 9
ICHOO10.005>000>00
IlEACIl GRADIENT •~,6 Il,m\
~~'I_"~Il...!!lb.B,-
;I'
o
-5.00
~:ooo :(j@,i~%lt~::;!{i'~:E%~w~l_t'{lr.,-
605
610
I-600ww
"-
~
z
Q ~9~I-~
W
..Jw
~90
STREAMBED STATION IN FEET PRELIMINARY DATA
Subject to Revision
~Qle J!/Z2/B?
Figure 5.Slough 9 Streambed &Water Surface Profiles;August 24,1982,
r
·1..I
",.
~,.
gradient of the river between the head and the mouth of Slough 9 is 10.9 ft/mi
(R&M Consultants,Inc.1982).
Although high velocities have been identified as blocking the upstream
migration of spawning fish in some Alaskan rivers,field observations of
entrance conditions at several side sloughs in the Talkeetna to Devil Canyon
reach indicate that it is nearly impossible for velocity barriers to exist at
these locations.Thus the ease_with which adult _salmon can enter the side
sloughs from the mainstem Susitna is primarily a function of depth.
The depth at the slough mouth is a function of the water surface elevation of
the mainstem and the discharge from the slough.Data obtained during the 1981
and 1982 field seasons indicate that the flow from Slough 9 is quite small,
unless the mainstem has overtopped the alluvial berm at its upstream end
(Table 2).On the basis of these data,3 cfs was selected as being typical of
the mid-summer sloughflow in Slough 9.
A staff gage was installed near the mouth of Slough 9,and numerous gage
height readings were recorded through September.The staff gage was installed
in the deepest water available within the passage reach to ensure that it
would not dewater before the passage reach.As a result,gage height readings
are 0.3 feet greater than the controlling depth at the mouth of the slough.
Water surface elevations were determined for each staff gage reading and
compared to the average daily mainstem discharge at Gold Creek (Table 3).A
plot of these data indicates that the relationship between mainstem discharge
and the water surface elevation in the mouth of Slough 9 is well defined for
the range of streamflows from 11 to 33,000 cfs (Figure 6).
To evaluate the influence of mainstem'discharge on fish passage,backwater
profiles were determined for the 2200 foot reach near the mouth of Slough 9
for incremental levels of mainstem discharge and a constant .sloughflow of 3
cfs (Figure 7).Two potential problem areas exist for adult salmon entering
Slough 9,a 125 foot reach approximately 400 feet downstream from the mouth of
the slough (passage reach A),and a 280-foot reach from 620 to 900 feet
upstream of the mouth (passage reach B).The approximate length and average
depth within the two critical passage reaches were determined for each
backwater profile (Table 4).
17
Table 2.A comparison of Slough 9 streamflow measurements with the average
daily mainstem discharge at Gold Creek.
Table 3.Comparison of water surface elevations (WSEL)at the entrance to
Slough 9 and the average daily mainstem discharge at Gold Creek,1982.
~..
.1lJ.rn
I /"-.
!
r-
[
J'·1
~-[
s~\,
.:;
:,";
G:~..:-..
,,
t r-
f
A~..
Date
6/24/81
7/21/81
9/30/81
10/14/81
6/23/82
7/15/82
7/20/82
8/25/82
9/4/82
9/9/82
9/18/82
9/20/82
*ADF&G 1981c and 1982.
II R&M Consultants 1982.
Sloughflow
(ds)
2.9*
714.0*
1.5*
1.2*
182.011
108.011
28.511
3.4*
8.4*
3.011
232.0*
145.0*
PRELIMINARY DATA
Subject to Revision
LJafe of Zz./8 z.
I
Mainstem
(cfs)
16,600
40,800
8,000
7,290
No Record
25,600
22,900
13,400
14,400
13,400
26,800
24,000
Gold Creek Gold Creek
t-:i WSEL*Discharge WSEL Discharge
"Date (ft)(cfs)Date (ft)(cfs)E~.
8/24/82 590.03 12,500 9/05/82 590.16 13,600
8/25/82 590.19 13,400 9/06/82 589.91 12,200
8/26/82 590.24 13,600 9/07/82 589.84 11,700
8/27/82 590.04 12,900 9/16/82 594.09 32,500
8/28/82 589.98 12,400 9/17/82 593.71 32,000
8/29/82 589.91 12,200 9/18/82 592.86 26,800
9/02/82 590.82 16,000 9/19/82 592.37 24,100
9/03/82 590.51 14,600 9/20/82 592.36 24,000
9/04/82 590.42 14,400 9/29/82 589.98 12,400
'~.
l
*ADF&G gages 129.2 W1A and W1B.
18
PREUf....HNARy DATA
4035
PRELIMINARY DATA
Subject 10 Revision
Date /I hZ/8e
I I
25 30
Figure 6.WATER SURFACE ELEVATION AT
MOUTH OF SLOUGH 9 VS.MAIN·
STEM DISCHARGE AT GOLD CREEK
2015
594.0
,,
589.5 "-'-'-------1
10
593.0
~.---en
:I:
C>
::>
0
...Jen
LL
0 592.0
:I:
I-::>
0
:E
z
z
0
~:>
l1J
...J
l1J 591.0
wu
it
0::
:::>
CI)
0::
l1J
I-~
590.0
Ii.~<'.-
j r---
r
r-
r
'r
iI
;\~.
:f..-..
I
i'l
[
~,
~L
,
l
It:~\\t-·1
MAINSTEM DISCHARGE fj)GOLD CREEK (J03 cfs)
19
..----'.'~.."t_~~~~~I <
..,"r-~
)
!~;c<c ---,.:~~
)
WSEl=592J
SlouQh Ilow ::3 eh
WSEl:592.45
SlouQh flow:20 eta
PRELIMINARY DATA
Subject to Revision
I..>ate II/z..Z/82
Oirectionol flo'll-WSEL:592.15
Moinstem:22,500 cIs
,WSEl:594.1
Mainstem:32,500 cfs
4.0
3.0
ADF a G Galles J
#129.2 WIA a WI~
WSEl:591.25 &.&:.A":.........~_
20 cMainstem:18,ooOClS .~&'~;:~:':1'~':':"';-'------1-~----------r-----------------------------..../.~>(~.{};~::~~':"'::~::::f!~~:::;j;<
--1.0 LWSEL=590.85 :(::-;.;,:.:-•...6000 .'.MOlnstem;;:I,cIs .:.:·~::i
•.....,'o.
_.~WSEl 82482:590.00 .;:.~'.::::-•.:'·..:f>...·F·;.".Moinstem =12,500 cIs •.•.~,;.~~.'\>":"{~'::r':""'~"'"Sloullh:3efs ".,::~.:
!"~3i){;::,:;}{{JP.";:::;.5 ·'·:\~~k~Wjt:«-t:;':~~:;~::~?i~~::;~~V,\\:+~ti!;::;(5",......R•••,,
(Mouth of SloUllh 9)
594
593
I-w 592w
I.L.
z 591
z 590Q
l-
N ~0 589w
....Jw
588
587
-5+00 0+00 5+00 10+00
THALWEG STATION IN FEET
-.'-
Figure 7.Backwater Profiles at the Entrance to Slough'9 for Selected Mainstem
Streamflows at Gold Creek_
f
Upstream passage into Slough 9 by adult chum salmon would not appear to be
restricted when mainstem discharges were 18,000 cfs or higher.Access becomes
increasingly more difficult as mainstem discharges decrease.An acute access
problem exists at streamflows of 12.000 cfs and less.
These statements are,in part,substantiated by field observations made by the
author the morning of August 24,1982 while conducting a foot survey to assess
spa\..ningconditions.in the lowe1"-5QOQfeetof .Slough9.The mainstem dis-
charge was 12,500 cfs and no appreciable backwater zone was present at the
entrance to the slough.Several chum salmon were observed grounded in shallow
"~Table 4.Entrance conditions at the mouth of Slough 9 for various mainstem
flows at Gold Creek and sloughflow of 3 cfs.
Mainstem Slough 9 Passage Reach A Passage Reach B
Discharge WSEL Average Reach Average Reach
(cfs)(ft)Depth (ft)Length (ft)Depth (ft)'Length (ft),,-...
(10.000 589.50 0.1 125 0.20 280
12.000 589.90 0.4 125 0.20 240
l,'14.000 590.35 0.85 125 0.20 200i
16,000 590.85 1.35 125 0.25 140
18,000 591.25 1.75 125 0.30 80
20,000 591.60 2.10 125 0.50 30
22,000 591.90 2.40 125 0.6 10
1 -water near the entrance to the slough (passage reach A).Depths were measured
at numerous points where the fish were grounded.A few isolated depths of 0.5
feet were measured,but the most representative depth restricting access at
the entrance to the slough was 0.2 feet.Approximately 500 feet upstream
several chum salmon were actively digging redds along both banks of the
slough.Further upstream between station 15+00 and 20+00 (refer Fig.5)chum
salmon were observed actively digging three redds in upwelling areas along the
west bank of Slough 9.(A total of twenty fish were counted).No rainfall had
occurred and mainstem streamflows had ranged between 12,200 and 13.300 cfs
during the five days preceding these observations (USGS 1982).This would
tend to indicate that the shallow depths at the downstream entrance to the
slough were not a complete blockage for upstream migrants.
21
f
,.
The mainstem discharge at Gold Creek fluctuated between 16,000 and 18,000 cfs
from August 30 to September 3,the result of rather typical fall rains.
Streamflow data are not available for Slough 9 during this period,although it
is known that the mainstem discharge of 18,000 cfs did not breach the head of
the slough.On September 5 the author conducted another ground survey of
spawning conditions in Slough 9.Many more chum salmon were observed in the
slough than were"observed August 24,and active redds were located as far up
the slough as station 37+00.From these observations it can be concluded that
a short term rise in mainstem stage in conjunction with an increase in
sloughflow can provide conditions that permit adult salmon to reach spawning
areas mid-way into the sloughs.
Pre-and Postproject Access
Typi<:al preproject entrance conditions at Slough 9 during the chum salmon
inmigration and spawning period were determined from a comparison of
streamflow duration curves (Figure 8)and the information summarized in Table
4.Preproj ect streamflows during August would seldom inhibit passage into
Slough 9 by adult spawners.Average daily streamflows equal to or greater
than 18,000 cfs have occurred 70%of the time during 33 years of record.
Adult passage could be hampered during September since streamflows equal to or
greater than 16,000 cfs have only occurred about 25%of the time,and mainstem
September flows of 12,000 cfs or greater only occurred 54%of the time.A
more refined evaluation of access to the side sloughs during the inmigration
and spawning period could be obtained from a flow duration curve specifically
developed for the mid-August to mid-September period.
The range of entrance conditions most likely to exist at Slough 9 under
postproject flows was determined from a comparison between the.proposed
average monthly streamflows during August for various project phases (Table
5),and the information summarized in Table 4.It is anticipated that adult
spawners will experience considerable difficulty in gaining access to
traditional spawning areas in the side sloughs under the proposed filling and
operational flows.However,these proposed streamflows may be sufficient to
provide some potential for rectifying impacts.Additional information and
22
r----,----~..:--.-'-----j----~-.--~--+----:~---_!----
--
10~
9
8
7
6
5
(J)
lL.40
z
3
w
C!I
a:
<t 2J:
0
(J)
0
l
..-
(J)
lL.
<.J
Z 3
4 J~O~'-I::~~-!:'~~[~:'I-C~~'I"'i';"~f'I:!-:;-I"!'-1-1~':-j:I~'i"'I'::I-I--I~I-li"'i-I"-I"-i"~"i":I''1--=-IO~YIFI·:i·:'i·;~I:=-i·=I~·:'l'I'ii'-'-I""'i:"-I';;"i'~I·,·'~:il:·~--"·i:;=I-·i'-·.-:':.----:::..:::-.;...~.."-:::.,j:".:::::.='---..:.:.._"':""t.__••_
:3 -...·-T_.:-r.j~'=.............::c::.f:-_••-"=~_"I.'..C
I r 'I'.,r-I I
o 10 20 30 40 50 60 70 8090 100
%OF TIME DISCHARGE EQUALLED OR EXCEEDED
-;--'1:::-"--:
+---<
--• , I
2
w
C)
a:
<t
::c
<.J
(/)
b
10
4 -nE:::~JZ:~I:J:TI~E~~~~~~~~~~=:---?s-J.=:~~~?=?"~-=-====.",rl..",.,-..,...",,~9 -t;;:t[g"-i'':~:::~';:;'-±:"':i'..;:;..~c;,'~"~:;:~':~'~f-~~-:~::~:~.~";:'~'~''~-='~~-~jf:-~'::'?''~-:~:-::i::~'E'~~~-~:~~;;-~::1"!i':'--~-:;S~'P':~::;:'f:'~':::-':s-..;.g_'~'..;:'.:;;;.:.;;:..~:_~r;-:t:.~,,~.~-;:-t;.-~.;c~:,:...·W·~,i,:.4·.:;:·~~:"'·~·,~~~·~;O.o~
8
7
-P"~'~..~...~,..~.~._~.=~~-~:-:~>!~-:~~::-~.~.~-~.ij~=-~::~:-~f~..·I~=I:·I::I:·I-!·I-:.;'i:-:~,·~r-~,~:':~~~:-:.:~:-~:,~".~'~..:~··'~~i>~oc·~,·~-~:=-~::i:~:-:-~.:~.::-~·=~s-:-":,,I;:~~":~-.::~~.~'~~-.~-_.:~-..-.~...-.......;._=~-------.~----_.--'~-_.:':~-'---~.".:.-"~-
6
5
~~~~~~.:~.g~.~.~·g·'~·~-'f;~-~-~·~·~~·S~E~=·-==t-=~P~T~·~E~M~lB[1~[!R~:·~·_.~.~·~Ir~:=i"~~·-~:~i-~-:,~·~-:~.,.~·F:~:~-:i.._:::=:::t=::
-'-.;..0:.,,<.!:j;:'~':L~:I:·":·~...:;···F..~,<:.,,'o:'.;':::-:i::,,::::;,,~:.t·;:~L'.=""'5'c:,."·,;".':o:L'i~'.:-:',':.:::
I!.
!
j-
Figure 8.August and September Average Daily Streamflow Duration Curves for
the Susitna River at Gold Creek.
L
23
analysis will provide a more refined understanding of the daily or weekly
fluctuations in mainstem stage and slough discharge that might be expected
under various postproject scenarios.This knowledge will be instrumental in
better quantifying impacts and evaluating alternative mitigation proposals.
Table 5.Comparison of average monthly pre-and proposed postproject
streamflows at Gold Creek.
Month
Preproject
Streamflow (cfs)b
Fillinga Watana Watana/Devilc
January
February
March
April
May
June
July
August
September
October
November
December
1500
1200
1100
1400
13200
27800
24400
22200
13300
5800
2600
1800
1000
1000
1000
1000
6000
6000
648012000~
9300
2000
1000
1000
9700
9000
8300
7700
10400
11400
920013400~
9800
8000
9200
16700
10600
10200
9300
8100
8700
9900
840012600~
10500
7800
9600
11300
='_i',..
a
b
c
d
Filling streamflows are target minimum values;actual streamflows during
filling will typically be greater.
Operation of Watana dam only.
Operation of Watana and Devil Canyon dams.
Includes a controlled flow of no less than 12,000 cfs from mid August to
mid September.
24
[
BIBLIOGRAPHY
Acres American Incorporated.1982.Chapter 2
Project FERC License Application Exhibit E.
Alaska.
in Susitna Hydroelectric
Draft Report.Anchorage.
Alaska Department of Fish and Game.
species/subject report.ADF&G
Anchorage.Alaska.
1981a.Adult anadromous phase 1 final
Su Hydro Aqua..tic ..Studies Program.
~l
,"
1981b.Juvenile
species/subject report.
Anchorage.Alaska.
anadromous fish study phase 1 final draft
ADF&G Su Hydro Aquatic Studies Program.
1981c.Phase 1 Final Draft Report.Aquatic Habitat and Instream
Flow Proj ect.Alaska Department of Fish and Game for Acres American
Incorporated.2 vols.if"""'
~[..
l
1982.Phase 1 Final Draft Report.Aquatic Studies Program.
Department of Fish and Game.Susitna Hydro Aquatic Studies.
Department of Fish and Game for Acres American Incorporated.
Alaska
Alaska
I
i'
I,
Barrett.B.M.1975a.December Investigations on the Upper Susitna River
Watershed Between Devil Canyon and Chulitna River.Alaska Department of
Fish and Game.Unpublished.8 pp.
1975b.January Investigations in the Upper Susitna River watershed
Between Devil Canyon and Chulitna River.Alaska Department of Fish and
Game.Unpublished.10 pp.
1975c.February Investigations in the Upper Susitna River watershed
Between Devil Canyon and Chulitna River.Alaska Department of Fish and
Game.Unpublished.10 pp.
25
Mills.M.J.1982.Alaska Statewide Sport
Federal Aid and Fish Restoration Report.
SW-I-A.
Fish Harvest Statistics ADF&G
Project F-9-14.Vol.22.No.
R&M Consultants.Inc.1982.
American Incorporated.
r Morrow.J.E.1980.The Freshwater Fishes of Alaska.
Publishing Company.Anchorage.Alaska.
Hydraulic and Ice Studies.
Anchorage.Alaska.
Alaska Northwest
~eport for Acres
Trihey.E.W.
Report.
1982.1982 Winter Temperature Study.February
Acres American Incorporated.Anchorage.Alaska.
24-28 Trip
I
I'.
University of Alaska.Arctic Environmental Information and Data Center.1982.
Phenology Chart for the Susitna River Salmon.Blueline.Prepared for
the Alaska Power Authority.
Woodward-Clyde Consultants.1982.See Acres American Incorporated.1982.
26