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HomeMy WebLinkAboutSUS134j;b{tu;v SI.l5. I~ Preliminary Assessment of Access by Spawning Salmon to Side Slough Habitat above Talkeetna Draft Report by E.Woody Trihey,P.E. P.O.Box 10-1 77 4 Anchorage,Alaska 99511 Prepared for Acre~American Inc. Buffalo,New York November 1982 ACKI~I~LEULEMENTS The field clara used in this report •....ere collec:tpd by the AOF&C Su Ilydro Aquatic Habitat and Instream Flow Fish Habit.:lt Utilization Group during the 1982 summer field season.Special thanks are extended to the ADFt';C Aquatic Ilabitat and Instream Flow staff for thf'ir assistance with extracting these data from a much larger data base .:nd expediting their reduction for use in this report. Hr.William J.Wilson and Dr.Charles G.Prewitt (Arctic Environmental Information and Data Center)developed the species periodicity chart and provided technical review of the paper.Dr.Larry Rundquist (Woodw~rd-Clyde Consultants)provided assistance with the paper's organization and technical review of thp backwater profiles.Jean Baldrige (Woodward-Clyde)also provided technical review of thi5 paper. I I t • t I • ;NTROnUCTI U~ Till'proposed Susitna hy<.JroC'lectric project will alter the ~xisting streamflow, sediment and thermal regimes of the river.Each of these have a direct influ~nce on the qtlality and/or quantity of fish habitat available throughout the year.It is proposed that post project streamfloW's at Gold Creek be reduced during summer and increased during winter.Suspended sediment, turbidity and water temperatures are expected to follow similar patterns (Acres 1982). Although mainstem spawning areas have been documented within the Talkeetna to Devil Canyon reach,the most intensively used spawning areas are located in tributary streams and side sloughs (ADF&G 198Ia).Of these.side-slough habitats are in the greatest jeopardy of being adversely effected by reduced streamflows during the inmigration and spawning period.Natural flows at Gold Creek commonly range between l8.000 and 25,000 cfs during late August and early September.A controlled flow of no less than 12,000 cfs at Gold Creek 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 primary purpose of this paper is to present a preliminary analysis of the influence 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. The field data used in the analysis are both limited and provisional. Continuing analysis of these and other 1982 data by the Su Hydro Aquatic Studies Group will prOVide a more reliable indication of the range of mainstem discharges that are necessary for prOViding access 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 I • I stre;lmfJows necestiary for chum saimon to gain ~ccess to the side sloughs must he '1i~wed as the provisional opinion of the author. To assist with understanding the limitations ('If the specific focus of this paper [our general categories of fish habitat wllich exist along the Susitna River between Talkeetna and Devil Canyon,are identified and an introductory description is presented of the physical processes whi~h interact to provide side-slough habitat.The sequence in which these topics are addressed is diagrammed in Figure I.Much of the discussion presented in this paper is unsupported at this time,by data or analyses.However,it is believed that the data collected during the 1982 field season and that which could be collected during 1983 will substantiate these hypotheses and provide a basis for quantifying their associated relationships. 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.burhot.Dolly Varden,round whitefish. humpback whitefish,long nose sucker.threespine st ickleback.arct ic lamprey. and sculpin.Rainbow trout,grayling,Dolly Varden and burbot are the principal resident species contributors to the Susitna River sport fishery (Mills 1982).The rainbow.grayling and Dolly Varden fishery is primarily located in the clear water tributaries whereas burbot are generally found in the Susitna River. The five species of Pacific salmon which inhabit the Susitna basin utilize a variety of habitats to different degrees on a seasonal basis (Figure 2). Habitat utilization is implied by the relative abundance of a particular species/life stage in a certain habitat.Degree of utiliza~ion (high.medium. or low)was determined from the FERC License Application Exhibit E Draft Report (Acres 1982).Sockeye and chum salmon originating in the Susitna basin are the most important 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 li.ited.because regulations c 0 c 0u ~, 0 Q e 0c 0 0 ~ c.. •: "0 •L •C •• C C ,- .!!••0 "•L ~• ~~••~;;,, ~C •VA ~_'lCI"'O_ "O~~":::C"'W1"-•-C Q "V _N ........-C•V 5 V "c-o ••••~~ ~~ ~,C c:0 ~ V -~x c 0 ::~ "o 0•~::L•-~ :3 • ~ 2 ~,·.!!~ ~•0 ,,,~~u ::':•~ ~~-..··-•0 ;;';;~u-•c 0,•u ••,c 0 ·~u·C ;;ii 0 <u ,-~~x•~·-~~• f: ,•u;;"'.•..",7~,.,U~"•~ = ---- SALMON,RIVER ~.~. .. ~~ ••.c:•.~• ...... CHART FOR THE SUSITNA TO DEVIL CANYON' ....,- ...c .._' PERIODICITY TALKEETNA PROVISIONAL ...........................................................••••••·c."!............-~~~1;';W~"';';;;';'~';';:~~~~::~=~~~=i=::~=J=:::~=~1~;~~~, [ I r >""eX .....""c...r-r I I r-I I I"""MIxIIiii rt'r:!My . I I 'UQY~~~'~~ffi~~:~L~~:=I:::::~Jt:::::~Jf'I_:l~f.:·,'·l ~.,.•.[O ".,...... .::_..~':'.':::".'~"",.'••'.I " I ,.'=;': __--I FIGURE 2_ ......tQllI..TIOl'ol ~.-~....cu...T'O'"1J....... ove..~C.'NO OI.tT ..IO...TION-------....""O.,,"ION &........N'NQ i lNCue""'ON l ...._,NO -t I ..OVC.-..TC"".'O OV"..-a...TIC'" .0 ...oo.""oQOoO .:u:::::I l~-;~~~;~-;-;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;·;;·;;·:;;;;;;~;.~.~.=======----------..~.~~~~-----."..~~~~~~~~~--==._==._~--~--~-~-=~1ItC"""""O I -..•'.IO¥C.lIII_IHTC""''''O -.----- I I OUT~......NI,.,I",I,,I,!,I",I,·~..,I"I"I,I I I '*DEVELOPED FROM PROVISIONAL DATA GATHERED BY ADF e.G THROUGH DECEMEER,,98, l E.NO 01""INCUO"'TION '-£"100 OE.TE."MINE.O ""OM WOOO..........O "'NO CL.YO£IISt"21 spc.cles "'CCOUNT9 ••••c.•••• LEGEND CHINOOl<.AlMON COMO .~"'-"ON CHUM e&,L.MON ~INI<8"'L.MON SOCl<CYC 8 ..L....ON ""G'"VT'L.'Z""'ON MeOIUM UT'L.'Z.&,T'ON LOW uT I L.I:""'ON prevent cummercial fishing fur ddnook unr i 1 moSl uf the run has entereu natal streams.However,chinook salmon arc a very imp"rtilllt sport fish in the lower Susitna drainage,and are harvested in a local subsistence fishery at Tyonek. Then~fore Susitna River chinook stocks might be con~.Ldered to hold a relative overall rank in the Susitna basin at least equal to pink and coho salmon. Selection of an evaluation !:ipecies 3:ld life stages to represent the life stages of species Yhich utilize a particular habitat type during each season of the year is an essential step in assessing impacts and developing mitigation plans.Various species and life stages have different critical life 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 which favor one species may discriminate against another.The selection of an evaluation species prOVides a mechanism to prioritize seasonal habitat requirements thereby reducing such potential conflicts.An evaluation species can be selected after the initial baseline studies and impact assessments have identified the dominant species and existing habitats most vulnerable to potential impacts throughout the year. For the purposes of this report,species within the Susitna River with high regional visibili ty and commercial,sport 1 subsistence,or aesthetic value were given priority by the author.Those species within this category whose habitat is thought most sensitive to project effects were rated higher than those species whose habitat was not considered as vulnerable (Table 1). The five species of Pacific salmon were identified as evaluation species for the Susitna River below Devil Canyon based on information presented to date in the aquatic studies baseline reports,preliminary impact assessments,and their commercial,sport and subsistence harvest contributions, Since the greatest changes in existing physio-chemical characteristics of fish habitats are expected to occur in the reach between Talkeetna and Devil Canyon,the fishery resource using that portion of the river was considered to be the most concern.Because of differences in habitat location and seasonal habitat requirements,not all salmon species are expected to be equally affected by the proposed project.Of the five species of salmon which inhabit the Talke~tna to Devil Canyon reach chum and sockeye salmon appear to be the I I must \'ulnerabl~.This is dUl'to their dependence on slough habit;lr-S for ::;pawning,incubation and {'arly rearing (/\OF&C 1981a,1981b.1981c.19~2).Of the two species,cllum salmon appear to be the dominant species (ADF&G 198Ib). Chinook and coho salmon,while having a greater commercial and sparr value th~n chum salmon,may not be as adversely impacted by the projt:cr.These species are principally trihutary spawners and reaT in clearwater <lreas such as the mouths of sloughs and tributaries (ADF&G 1981a.b,c.1982).Post- project conditions in the mainstem may provide replacement habitat to offset potentia]Joss of mainstem rearing areas.While some pink salmon spawn in slough habitatf"in the reach between Talkeetna and Devil Canyon.the majority of these fish utilize tributary habitats (ADF&G 1981a).A limited data base regarding the other life history phases of resident species precludes their prioritization with respect to side-slough habitat utilization. GENERAL HABITAT CATEGORIES For the purpose of this report fish habitat in the Talkeetna to Devil Canyon reach of the Susitt'ld can te divided into four general categories:mainstem, side channel.side-slough,and tributary habitats.Each general habitat cate- gory contains a spectrum of ~hysical attributes rather than a specific set of uniform characteristics. Mainstem habitat consists of those portions of the Susitna River which nor- mally convey streamflow throughout the year.Both single and multiple channel reaches are included in this habitat category.In general this habitat category is characterized by high-velocity streamflo~s and well armoured streambeds.Substrates generally consist of boulder and cobble size materials with interstitial spaces filled with a grout-like mixture of small gravels and glacial sand.Suspended sediment concentrations and turbidity are high from late Hay through early October due to the influence of glacial melt water. Streamflows recede,and the water appreciably clears in the early to mid fall before an ice cover forms on the river in late November or December. Groundwater and tributary inflow appear to be inconsequential contributors to the overall characteristics of this habitat category.Seasonal temperatures of the mainstem river respond primarily to air temperature and solar radiation. Ma1nstem surface water apvears to establish mainstem intragravel water temperatures. I Table L.Evaluation Species and Life Stages for Side Slough lIabitats 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 Salmen Returning adults; Spawning adults; Incubating embry,)s and pre-emergent fry; Emergent fry; Outmigrant juveniles. Resident Species Limited data base precludes identification of relevant life stage. Side channel habitat consists of those portions of the Susitna River vhich nonaally convey streamflow during the open water season but which become appreciably dewatered during periods of low flow.The controlling streambed elevations at the upstream entrance to the side channels are less than the water surface elevations of the mean monthly flows for June.July and August. Side-channel habitats are characterized by shallower depths.lower velocities ..-c.-.._.. 7 • • -----h"1'-'--,I II',I I ' and smaller streambed materials chall rnai~efD habitats.In general the streamflow,sediment,and thermal regimes of tilC side chaOtlCl habitats reflect nttenuated mainstcm conditions.Tributary and groundwater inflow may prevent some side-channel habitats from becoming completely dewatered when mainstem f lows recede.Howeve r.the presence 0 f these 1 Imi ted in flows cou Id conceivably not be considered a critical com?onent of side-channel habitat.A winter ice cover,similar to that which foms on the mainstem.generally exists in the side channels.Groundwater inflow and upwelling retained open leads in some side-channel areas throughout the winters of 1974-75 and 1981-82 (Barrett 19'5a,b,c and Trihey 1982). Side-slough habitats are found in spring-fed perched overfIo,",channels which only convey glacial meltwater from the mainstem during median sumcer and high flow periods.At intermediate and low-flow periods the side sloughs convey clear water from small tributaries and/or upwelling groundwater (ADF&G 1981c, 1982).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.Side sloughs generally exist along the edge of the flood plain,separated from the mainstem by well-vegetated bars.An exposed alluvial berm often separates the head of the slough from malnstem or side channel flows where as the water surface elevation of the river generally causes a backwater to ext~nd well up into the slough from its lower end (ADF&G 1981c,1982).It is important to note that, eVt,n though a substantial backwater exists,hydraulically the sloughs function very much like small stream systems.Several hundred feet of the slough channel often conveys water independe~t of mainstem backwater effects. Except when the discharge 1n the mainstem river is sufficient to have overtopped the upper end of the slough,surface water temperatures in the side sloughs appear to be independent of those in the mainstem river (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 telDperature 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 appears to act as I • I a buffer or thermal reservoir;attenuating summer temperatures and providing very stable winter temperatures. Tributary habitat consists 01 the full complement of hydraulic and morphologic conditions which occur in the tributaries.Their seasonal s~reamflow, sediment,and thermal regimes reflect the integration of the hydrclogy. geology and climate of the tributary drainage.The physical attributes of tributary habitat do not appear to be dependent on mains tern conditions eXcEpt at the tributary mouth where rnainstem discharge influences access into the tributary and the tributary extends a clear water plume into the mainstem (ADF&G 1981c,1982). PHYSICAL ASPECTS OF SIDE-SLOUGH HABITAT The physical characterlst..l,.cs of side-slough habitat appear to be dependent upon the interaction of four principal factors:discharge of the mainste.., Susitna River,surface runoff patterns from the adjacent catchment area,local groundwater inflow and riverine ice processes.These factors are thought to interact to vary1 '1&degrees during different seasons of the year to provide a very unique type of fish habitat along the margins of the Susitna River (Figure J).Side-slough habitat is predominately utilized by chum and sockeye salmon,although chinook,coho and pink salmon also inhabit the side sloughs at some time during their fresh water life history.Resident species are also found in these areas. Hainstem Discharge Two ways in which the amount of streamflow in the mainstem Susitna River can influence habitat conditions 1n the side sloughs are:1)it causes a ba~kwater effect at the mouth of the slough which creates a special type of slough ha~itat and facilitates access into the slough (ADF&G 1981c,1982);and 2)it provides the dominant sediment transport mechanism in the slough. Streambed elevations at the lower entrance to the side sloughs are generally lower than the stage (water surface elevation)in the adjoining mainstem channel.Thus the stage of the mainstem causes a hydraulic plug which impedes q Figure 3.Artists sketch of a side slough and adjacent Susitl1a River (courtesy of AEIDC). ,".......i. '..{'.- ,.'-.~_.:. .'\........ l • r----~~"" /0 ~._(-j ':.'"/.' ...(••_.-! .... ------------1~I----- 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.Depending upon the magnitude of the mainstem discharge.flow within the slough may rC:lpidly increase from less than 10 cfs to more than 500 cfs (ADF&G 1982.R&N 19~2).These periodic high flows tend to flush out detrital material and fine sediments which have accumulated near the mouth of the slough.Occasionally high flows transport sands and silts into the slough trotJ the mainstem;however,the overall effect of these periodic overtoppings is generally thought to result in a net transport of fines out of the slough.During spring bl~ak up very large, short duration flows pass through the side sloughs.Periodically breakup flows are apparently of such magnitude that they can remove debris and beaver dams,redistribute streambed gravels and,at times,alter the thalweg profile or alignment of the slough. 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 the head end,the principal sources of streamflow within the slough (slough flow)are thought to be 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 may contribute a greater portion of the clear water flow to side-slough than does groundwater upwelling during the ice-free period of the year.However,a subset of side sloughs also exist which depend predominantly on ground water throughout the year (ADF&G 1981c,1982). Unseasonably dry weather during August of 1982 resulted in the second lowest mean monthly 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 II /il'/, monthly fiut"\,,;as 15,270 ill comparison to the IOllg term av~e monthly flow of 22.200 cfs.During this time,groulltlwatcr inflow to small tributary streams and upwelling within the side-slougb itself was the most significant factor in maintaining 510ughf10w.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 it is thought that groundwater upwelling normally contributes a lesser amount of water to the total clear water flow in the side s10ugl15 than does surface runoff.it is believed to be essential for attracting adult salmon into those spawning areas which arc not likely to freeze during winter. During winter months,groundwater inflow and upwelling most likely provide nea.rly all of the slough flow.Field work conducted during the winters of 1974-75 and of 1981-82 indicate that elevated surface and intragravel water temperatures exist in upwelling areas throughout the winter (Barrett 1975a,b, c and Trihey 1982).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 over the side sloughs substrates are not expected to freeze. Upwelling water appears to flow from beneath the streambed into the slough in a near vertical direction.Besides preventing substrates from freezing, upwelling is also thought to prevent deposits of silts and sands from suffocating developing embryos which are within the underlying streambed gravels.The general 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 avoid the problems which are normally associated with the deep silt mantIe spread over spawning areas. /L. lee I'roccsse$ • I l , t Ice processes in the mainstcm river arc imp0rtant ill maintailling the character of the slough habitat.Besides reworking substrates and flushing debris and Ileaver dams from the sloughs which :ould otherwi$c be potential barriers to upstream migrants,ice processes are also considered important for maintaining the groundwater upwelling in the s~de sloughs.The increased stage associated with a winter ice cover on the Susitna makes it pOSSible for approximately the same hydraulic head to exist betweer.mainstem and an adjacent side-slough during low winter flows as exists during ~'ormat summer flow (Figure 4). For example.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 with summer discharges of 18.000 to 19.000 cfs. Apparently,the higher stage caused by ice makes it possible for apprOXimately the same hydraulic head to exist between the mainstem and an adjacent side-slough during the winter as exists during late summer.The alluvial deposits which form gravel bars and islands between the mainstem river and side sloughs are highly permeable making it possible :or water from the river to flow downgradient through the alluvium and into the sloughs.Although the origin of the water which 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)it is likely that the stage of the mainstem river prOVides the principal driving mechanism for the upwelling in the side sloughs. 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 focal point for this analysis..In general,upstream access into Slough 9 appears to be more difficult than the average entrance condition encountered by adult spawners at those sloughs between Talkeetna and Devil Canyon in which spawning occurs..Upstream access into Slough 9 is apparently better than .' E•..c·0 :::lE I crcr< 'E .!!.... "~ ~•E E ::J C('.... :i access to SJough 1613 or 19;but far more difficult than access into \.Jhiskers Slougll ur Slough SA.It is therefore bclicv~d to he a reasonable illdex of entrance conditions into Sloughs 20 and L' The thalweg and water surface profiles which define entrallce conditions for Slough 9 on August 24,1982 are presented in Figure S.The mainstem discharge 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 dO\ol11stream froCi the mouth of the slough (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 area of Slough 9 !thalweg station 34+00 head)has an average streambed gradient of 18.6 ft/mi;whereas til.'verage gradient of the lower 2900 ft of the slough (thalweg station 56+00 -23+0G)is 5.6 ft/mi.The average gradient of the river through this reach is 10.9 ft/mi (R&M 1982). Although high velocities have been identified as blocking the upstream r::tigration of spawning fish in sante Alaskan rivers,entrance conditions and associat~d backwater effects in the lower portions of the side sloughs in the Talkeetna to Devil Canyon reach make it nearly impossible for velocity barriers to exist at these locations.Thus the ease at which adult salmon can enter the side sloughs from the mainstem Susitna appears to be primarily a function of depth. The depth of flow at the mouth of Slough 9 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 entered its head end (Table 2).On the basis of these data 3 cfs was selected as being typical of the mid-summer clearwater flow from Slough 9. A staff gage was installed at the entrance to height readings were recorded through September. i,l the deepest lola ter available in th~passage I;' Slough 9,and numerous gage The staff gage was installed reach so that it would not Tahle 2.1\comparison of Slough 9 ~trcamflow measurements with the average daily mainstem discharge ;It GoLd Creek. Date Sloughflow Nainstem (cfs)(cfs) 6/24/81 2.9'16,600 7/21/81 714.0'40,800 9/30/81 1.5'8,000 10/14/81 1.2'7,290 6/23/82 182.00 No Record 7/15/82 108.01 25,600 7/20.'82 28.56 22,900 8/25/82 3.4'13,400 9/4/82 8.4"14,400 9/9/82 3.0#13,400 9/18/82 232.0'26,800 9/20/82 145.0'24,000 "ADF&G 1981c and 1982. U R&M Consultants 1982. I I I1..J..11 a.. Table 3.Comparison of water surface elevations (WSEL)at the entrance to Slough 9 and the average daily mainstem discharge at Gold Creek,1982. Gold Creek Gold Creek WSEL'Discharge WSEL Discharge Date (tt)(cfs)Date (tt)(cts) 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 "ADF&G gages 129.2 WIA and WIB. ,.. dcwater before the reach,As a result gasp height readings are 0.3 ft. , I greater thilll the control I ing depth i.lt th~mouth of the slough.Water surface elevations were determined fer eacll staff gage reading and compared to the average daily mainstem discha~·ge at Gold Creek ('fable 3).A plot of these data indicates the relationship between mainstem discharge and the water surface elevation in the mouth of Slough 9 is well defined for the range of stre~mflows from 11 to 33,000 cfs (Figur~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 C'o~~tant sloughflow of 3 cfs (Figure 7).Two potential problem areas exist for adult salmon entering Slough 9;a 125 foot reach approximately 400 fee~downstream from the mouth of the slough,and a 280 foot reach from 620 to 900 feet upstream of the mouth. The approximate length and average depth within the two critical passage reaches werc determined for each backwater profil~(Table 4). Upstream passage into Slough 9 by adult chum salmon would not appear to be restricted when mainstem discharges were 18 J OOO cfs or higher.Access becomes increasingly more difficult as mainstem discharge decrease.At streamflows of 12,000 cfs and less an acute access problem exists. Table 4.Entrance conditions at the mouth of Slough 9 for various mainstem flows at Gold Creek and slough flow 0 f 3 eEs. Mainstem Slough 9 Passage Reach A Passage Reach B Discharge WSEL Average Reach Average Reach (eEs)(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 14,000 590.35 0.85 125 0.20 200 16,000 590.85 l.35 125 0.25 140 18,000 591.25 l.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 'Kt::/.,!<Y DATA . ",;:~I(c'{i~ion .,ouh,"Ju·I,~r:..~~_ 594.0 35 r PRELIMINARY DATA Subject to Revisloa -".."1"/'" 25 302015 ,, 589.5 LL.'----' 10 593.0 ....,-:!:; en :I: Cl::> 0 ..J l/) •IL 0 592.0 :I: I-::> 0 :::E z z 0 I-:; W ..Jw 591.0 wu (t a:::> l/) a:w I-Figure 6.WATER SURFACE ELEVATION AT~MOUTH OF SLOUGH 9 VS.MAIN· STEM DISCHARGE AT GOLD CREEK 590.0 ..,,;,.,-: MAINSTEM DISCHARGE:,ii)GOLD CREEK (103 eft) 1<7 . C,:592J ::;I?lJQI1 flo1r :3 eft 'NSEl;592 45CSlouQI'I flo_:20 e" , '----ws..... WSEL=592.15 Moinstem =22,500 cis ~~----------r-----------------/>.~LWS.EL<590.85 ------------~~ Maln,tern:l 16POO cf. WSEI..:r 591.25t2.0 cMoinsttm:lIB,OOOCI.----- '.0 I ,WSEL'594.1 Moinslem:l 32,500 cf, 4.0 -------- AOF8G Go;"J. .'29.2 WIA a WI~ __•0'WSEL e 24 82 z 590.00 '.~o;.t·:.·...-,'"Mainstem :112,500 ef.....• .•};:;};::::~:i:'~.[J!;::';:"···~.5 ·>:·:}.·tii\SI;:;~:h~;:;~f:':::.::;..~..:-.::..::;::..::>i;:.:;:.;:;.\:.f:(:'. R 8M x-Sect *'ZB.4WI·'", . (Moulh of Slough 9) 594 593 t- III 592III... 3 591 -~590 ."t-~589III oJ III 588 587 -5+00 OtOO 5+00 10+00 THALWEG STATION IN FEET PRELIMINARY DATA S",bieci 10 Revi~icn Ugi.11121/t:z.... Figure 7.Backwater Profiles at the Entrance to Sl~ugh 9 for Selected Mainstem Streamflows at Gold Creek. I These stillcments are.in part,substantiated by field observations made the morning of August 24.19HZ.A foot survey was conducted tu assess spawning conditions in the lower 5000 ft of Slough 9 (refer Fig.5).The rnainstem di.scharge was 12.500 cis and no appreciable backw.:ncr zone was present in the mouth of the slough. Se,eral chum salmon were grounded in shallow water near the entranc~to the slo\!gh.Depths were measured at numerous points in the area where fish were groun~~d at the entrance to the slough.A few isolated depths of 0.5 it were measured.but the most representative depth at the entrance to the slough was 0.2 ft.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 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).Between August 19 and 24.streamflows ranged between 12.200 and 13.300 cfs.This would tend to indicate that the shallow depths at the downstream entrance to the slough were not a complete blockage for upstream migrants. Between August 30 and September 3 mainstem discharge at Gold Creek fluctuated between 16 and 18.000 cfs;the result of rather typical fall rains.Stream- flow data are not a-,ailable for Slough 9 during this period.although it is knOWT.that the mainstem of 18,000 cfs did not breach the head of the slough. On September 5 another ground survey was conducted 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 ~hort term rise in mainstem stage in conjunction with an increase in sloughflow can provide adequate conditions for adult spawners to reach spawning areas mid-way into the sloughs. The range of entrance conditions most likely to exist at Slough 9 during the chum salmon inmigration and spawning period was determined from a comparison between stre_flow duration curves (Figure 8)and the information sUllllllarized 1n Table 4.Under preproject streamflows passage into Slough 9 by adult spawnera would ..Ida.be a proble.during Auguat.Average daily streamflows ---.;....,...~~------- i=. .---1=_i ;~--'---_._-!--_.,--- ---r 0 --------: _"..·-'"".-,0".:,•."+-,,.,,<"'f "'"·;,c·' .~__..-:_..7_':-·-·~·-·-'F-?:.-:: AUGUST 7,',. ._---~...~ •'n._._ ....~;.:':'.~~-~:=--,..-=__-"r _,.'"".',r~O;.~.-.:.L :-'-'-::;-'i;-=~ -"-.,-..:-.,-:- ---'-~'j-' 'D·9 8 7 6 5 4 o T '0 20 0/0 OF 30 .TlME I I 40 50 60 70 eo OISCtiARGE EOUALLEO OR EXCEEDED 90 '00 -._1 -= ___.J" ----":,.-=---:::-' .•..,.;,'":"..':':':I '-:'_'.~,_.'---.•-:_:~~_;:,-;--,'...'".~,.''-:R::'-.'"...,',',~.<:-:..... -'.;1 .=--_ -'-:'_"-' -- -'.'--:",:,::..:,,',~-===._--..:--,-OF-=' SEPTEMBER iT~:':::>:=.-~---1?::·:·:-.:.-·::·:_.:E.:L:::':''''-"..".---= 2 o 4 "'... u z ... '"'"":z: u.. o 10' 9 8 7 6 5 Figure 8.August and September Average Daily Streamflow Duration Curv.'s for the Susitna River at Gold Creek. equal to or greater than 18,000 eEs have occurred 70%of time during ))years of record.Adult pa::isage could become limiting during September since streamflows in equal to or greater than 16.000 cfs have only occurred about 2S%of the time,and mainstem flows of 12.000 efs 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 under postproject flows was determined from a comparison between proposed average monthly streamfloW's during various project phases (Table S).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 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 Streamflow (cfs)bIPreprojectHllingaWatana Watana!Devil c January 1500 1000 9700 10600 Feb rua ry 1200 1000 9000 10200 March 1100 1000 8300 9300 April 1400 1000 7700 8100 May 13200 6000 10400 8700 June 27800 6000 11400 9900 July 24400 6480 9200 8400 August 22200 12000~13400~12600~ September 13300 9300 9800 10500 October 5800 2000 8000 7800 November 2600 1000 9200 9600 December 1800 1000 16700 11300 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 .id September. B (13L 1nCrJ\PHY Acret.:American Incorporated.1982. Project Ff-:KC License Applicat ion Alaska. Chapter 2 Exhibit L 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 Aquatic Studies Program. species/subject report. Anchorage,Alaska. 1981b.Juvenile anadromous fish study phase final draft ADF&G Su Hydro Aquatic Studies Program. 1981c.Phase Final Draft Report.Aquatic Habitat and Flow Proj ect.Alaska Department of Fish and Game for Acres Incorporated.2 Vol. 1982.Phase 1 Final Draft Repnrt.Aquatic Studies Program. Department of Fish and Game,Susitna Hydro Aquatic Studies. Department of Fish and Game for Acres American Incorporated. Instream American Alaska Alaska Barrett,B.M.1975a.December Investigations on the Watershed Between Devil Canyon and Chulitna River. Fish and Game.Unpublished.8 pp. Upper Susitna River Alaska Department of 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.Unpub lished.10 pp. '),--, Mill.,M.J.1982. Federa 1 Aid and SI/-I-A. Alaska Statewide Sport Fish Restoration Report. Fish Harvest Stat 1st ics ADF&G Project F-9-14,Vol.22.No. Morrow,J.E.1980.The Freshwater Fishes of Alaska. Publishing Company.Anchorage,Alaska. Alaska Northwest R &H Consultants,Incorporated.1982.Hydraulic and Ice Studies. for Acres American Incorporated,Anchorage,Alaska. Report Trihey,E.I/. Report. 1982.1982 Winter Temperature Study,February Acres American,Incorporated.Anchorage,Alaska. 24-28 Trip Woodward and Clyde.1982.See Acres American Inc.1982.