Loading...
The URL can be used to link to this page
Your browser does not support the video tag.
Home
My WebLink
About
SUS454
I I I I I I I ·I I I I I I ,I I I I I SUSITNA HYDROELECTRIC PROJECT F EDERAL ENE R GY REGUlATORY C:OMWIS810N CIDOJECT No . 7 i ,_. I , PREPAii!C BY ~------ ~&M CONSULTANTS, INC. ......_ ....._--.-.... -·- UNDE!I C:ONTIIACl TO G{J£00(6£"' §00&@©@ SUSITN.\ JOirlT VENTURE ASSESSMENT OF ACCESS BY SPAWNING SALMON INTO TRIBUTARIES OF THE lOWER _SUSITNA RIVER DRAFT REPORT MARCH 1885 DOCUMENT No. .____.....;.....;.:. _ __,_ __ -.,.-___ ALASKA POWER AUlHORITV ____ ---..:..----....:.....__ ____ ___.J I R2212 1 I I I I I I I I I I I I I I I I I I SUSITNA HYDROEL ECTRIC PROJECT ASSESSMENT OF ACCESS BY SPAWNING SALMON INTO TRIBUTARIES OF THE LOWER SUSITNA RIVER Report By : \Villi am S . Ashton R&M Consultants , Inc. and E . Woody Trihey E . Woody Trihey and Associates Under Contract To: Harza-Ebasco Susitna Joint Venture Prepared For : Ala>k• Power Autho,.ity DRAFT REPORT MARCH 1985 I I I I I I I I I I I I I I I I I I I R2212 TABLE OF CONTENTS list of Tables List of Figur·es list of Pho tos Acknowledgments 1.0 INTRODUCTION 2.0 OVERVIEW OF EX ISTING SYSTEM 2.1 Basin Ove r·v ie w 2 . 2 F ishe ries 2.3 Natural Flow Regime 2 .3 . 1 Mainstem Susit na Ri v er 2 .3 .2 lower Sus itna River· Tributaries 2.4 Potential Effec t s of an Altered lower River Flow Regime 2 .4 .1 General 2 .4 .2 Holding Areas 2 .4.3 Tributary Ac cess . 2 .4 .4 Tributary Mouth Stability 3.0 STUDY PLAN DESIGN AND METHODS 4.0 RESULTS AND CONCLUSIONS 4.1 General 4.2 Holding Ar e as • 4 .3 Tributary Access 4.4 Tributary Mouth Stability 5.0 REFERENCES EXHIBIT A EVALUATION OF SELECTED LOWER SUSITNA RIVER TRIBUTARIES P<~ge 2 3 4 5 5 5 5 7 9 10 10 10 12 12 13 14 14 14 14 16 17 A-1 -1- R22/2 3 LIST O F TA BLES T<~ble Number Description 2.1 2.2 3.1 4.1 Relative Contribution of Flows at Chulitna · Susitna-Talkeetna Confluence Change in Size of Tributary Backwat er Areas due to 1'/ith-Pr·oject Flows Depth and Velocity Criteria fo r Succ essful Upstream Migration of Adult Salmon Summary of Potential Effects of With -Pro jec t Flows on Tributaries of the lower Susitna River Page 9 11 13 16 I I I I I I I I I I I I I I I I I I I R22/2 ~ Figure NumbPr 2 .1 2 .2 2.3 2 .4 4.1 A-1 A-2 A-3 A-4 A-5 A-6 A-7 A-8 A-9 A-10 A-11 A-12 A-13 A-14 A -15 A-16 LIST OF FIGURES Description Location Map of the Susitna River and Major Tributaries from Mouth to Devil Canyon Salmon Migration Timing at Sunshine and Discharge for Susitna River and Selected Tributaries , 1981 Salmon Migration Timing at Sunshine and Discharge for Susitna River and Selected Tributaries, 1982 Salmon Mig ration Timing at Sunshine and Discharge fo•· Susitna River and Selected Tributaries , 1983 Comparison of Average Weekly Discharge for 1983 and With-Project Average Weekly Discharge Location Map of Alexander Creek Alexander Creek Location Map of Kroto Slough and Rolly Creek Kroto Slough Rolly Creek Location Map o f the Deshka River Deshka River Location Map of Willow Creek and Little Willow Creek Willow Creek Location Map of Little Willow Creek Little Willow Creek Location Map of the Kashwitna River Kashwitna River Location Maps of Caswell C reek and Sheep Creek Caswell Creek Sheep Creek R2212 ~ LIST OF FIGURES (Continued) Page Page F igure Number Description 6 A -17 Location Map of Goose Creek A -28 7 A -18 Location Map of Goose Creek A-29 A -19 Goose Creek A A-30 8 A -20 Goose C reek B A-31 8 A -21 Goos e C reek C A -32 A -2:! Location Map of Montana Creek A-34 16 A -23 Mo ntana Creek A -35 A-3 A -24 Location Map of Rabideux Creek A-37 A-4 A -25 Rabideux Creek A-38 A -6 A-26 Location Map of Sunshine Creek and Bi rch Creek A-40 A-7 A-27 Sunshine Creek A A -41 A -9 A-28 Sunshine Creek B A-42 A-11 A-29 Location Map of Bi rch Creek and Trapper Creek A-44 A-12 A-30 Birch Creek A-45 A-14 A-31 Trapper Creek A-47 A-15 A-17 A-18 A-20 A-21 A-23 A-24 A-26 -2- I I I I I I I I I I I I I I I I I I I R2 21 2 G LIST OF PHOTOS Photo Number Description A-1 A-2 A -3 A-4 A-5 A -6 A-7 A-8 looking upstream at the mouth of Alexander Creek (RM 9 . I). In the foreground is Aleunder Slough flowing from right to left. Photo taken 9/11 /84, d ischarge at Sunshine 23 ,600 cfs, discharge at Susitna Station 51 ,400 cfs . looking downstream at Kroto Slough (RM 36.3) flow is from the bottom to top of photo. Gravel bar in center of photo overtopped at approximately 38,000 cfs . Photo taken 9/11 /84, discharge at Sunsh ine 23 ,600 cfs . looking u pstream at Rolly Creek (RM 39 .0). The Susitna River ma i nstem is in the foreground flow i ng f rom left to r ight. Photo taken 91111~. d ischarge at Sunshine 23 ,600 cfs . looking upstream at the mouth of the Deshka River (RM 40.6). The Susitna River mainstem flows from" right to left in the foreground . Photo taken 8/31184." discharge at Sunshine 38,000 cfs . looking upstream at Willow Creek confluence (Rm 49 .1). Willow Creek flows from lower right to the center of the photo. Photo taken 8/31184, tiischarge at Sunshine 38,000 cfs . looking upstream at the Kashwitna River (RM 61 .0). Susitna landing boat ramp is in the top center of photo . The Susitna River mainstem flows from left center to lower right . Photo taken 9/11/84, discharge at Sunshine 23,600 cfs. Caswell C reek (RM 64.0) flows from right to left. This photo shows the side channel below the creek mouth. Photo taken 9/11/84, discharge at Sunshine 23,600 cfs. Sheep Creek (RM 66.1) flows from ri g ht to left. Sheep Creek side channel flows from top to lower left . Photo taken 9/11184, discharge at Sunshine 23 ,600 cfs . Page A-2 A-5 A-8 A-10 A-13 A-19 A-22 A-25 -3- R2:!/2 7 LIST OF PHOTOTS (Continued) Photo Number Description A -9 A -10 A -11 A -12 A-13 look i ng upst ream at the confluence of Goose Creek and Goose C r eek s ide channel (RM 72 .0). Goose Creek flows from top right towards bottom center The side channel was barely overtopped at 23 ,600 cfs at Sunshine on 9/11/84. Montana C reek (RM 77.0) flows from lower r ight to left center. The Susitna river ma i nstem f lows from upper le ft to lower left. Photo taken 9/11184, d ischarge a t Sunshine 23 ,600 cfs. looki ng upstr eam at Rabideux Creek (RM 83.1). The S us itna R iv er ma instem flow from center r ight to bottom center. Photo taken 8 /31184, d ischarge at Sunshine 38,000 cfs . looki ng upstream with Birch Creek (RM 89 .2) flowing from center r ight to center. Photo taken 9/11/84 d ischar ge at S unshine 23 ,600 cfs. looking upstream at Trapper Creek Side Channel ADF&G IFIM Study Site. Trapper Creek (RM 91.5) flows from center left to bottom center. Photo t~i(en 8/3 1184, discharge at Sunshine 38,000 cfs . Page A -27 A -33 A -36 A-43 A -46 I I I I I I I I I I I I I I I I I I I R22 /2 8 ACKNOWLEDGEMENTS The orutlal ai rphoto assessment wu done by Cui Sehoeh . Field d~ta were collected by Steve Bredthauer, Chip Green ~nd Bill Ashton . Debbie Stephens assosted in datoo analysis and figure prepu~tion . Steve Bredthauer a nd Ca rl ~choch contributed many useful editor~l comments . Orlando Parao~n oond Mark Cordery drafted the figures ~nd Bub Estus typed the report. lnfo rmootion regarding the t iming of ~dult salmon migrat ions on the lower Susitn~ River oond the use of lower river tribut;,ries by spawni ng ulmon was obtooined from Alask~ Oepoortmen t of Fish and Game SuHydro reports . I I I I I I I I I I I I I I I I I I I R20 /16 9 1.0 INTRODUCTION The r •·oposed Susitna Hydroelectric Project will alter the natural flow •·egime of the Susitna River by increasing winter flows and decreasing summer flows. Previous studies have evaluated the effects of the proposed Susitna project on the morphologic stability and fish access conditions at to·ibutary mouths and side sloughs within the Talkeetna to Devil Canyon reach of the Susitna River (R&M, 1982; Trihey, 1983; and Sautner, Vining and Rundqu ist, 198-1). This report provides an assessment of the potential effects of the with -project flow regime downstream of the Chulitna-Susitna-Talkeetna confluence on three areas: 1) the change in backwater zones (low velocity fisher-y holding areas) at tributary mouths; 2) access by adult salmon into tributaries; and 3) morphologic stability of the tributary mouths. The assessment is . based on visual evaluation of aerial. photographs, observations f~om helicopter overflights at selected lower river discharges, available U.S . G. S. streamflow data, and on-site field measurements made durin g a period of low streamflows. Within this report, the term backwater zone and holding area are used interchangeably. Section 2 describes the natural flow regime, the. timing of upstream salmon migrations and a general discussion of the effects a typical with-project flow regime might have on tributary mouth stability, adult salmon access into tributaries and the availability of holding a reas . Section 3 describes the methods used in the analysis , and section 4 summarizes the results of the analysis. Exhibit A presents a location map and aerial photos of each tributary, a brief description of fisheries use of, and potential with-project effects at each study site. -5- R~P 16 10 2 .0 OVERVIEW OF EXISTING SYSTEM 2.1 Basin Overview The Susitna Ri v er drainage basin is located in the southcentral region of Alaska . It is bordered on the west and north by the Alaska Range, on the east by the Copper River lowlands and the Talkeetna mountains, and on the south by Cook Inlet (Figure 2.1). The basin lies within two climatic zones and covers an area of 19,600 square miles. The upper basin (the portion of this basin above Devil Canyon) is in the continental zone, with the lower basin in the transitional zone. Continental climate is c haracterized by large diurnal arod annual temperature variations, low precipitation, low humidity and mean annual temperatures i.1 the range of 15-25° F. Transitional c limate is characterized by diurnal and annual temperature variations moderated by maritime influences, higher precipitation than continental climatic zones and mean annual temperatures in the range of 25-35°F (Hartman and Johnson, 1978). The mountainous areas of both climatic zones typically have higher precipitation values than valley areas. 2. 2 Fisheries The Susitna River contributes significantly to the Cook Inlet commercial salmo n harvest and sport fishing opportunities for residents of the Matanuska-Susitna Borough and Anchorage (Barrett et al, 1984). Important commercial and sport fisheries include five species of Pacific salmon: chinook, chum, sockeye, pink and coho. The primary salmon spawning areas within the lower Susitna Basin appear to be the clearwater tributaries such as \Villow Creek and the Deshka River (Barrett et al , 1984). !!Jc!:watcr areao in lower river side channels, sloughs, and the adjoining tributaries H emselves, are thought to provide important rearing areas for juvenile salmon and holding areas for adults. Timing of the adult salmon migration varies by species and from year to year. The rate of upstream migration by adult salmon appears to be retarded by mainstem ---------·---------- PIIEPAII[O 8V : ~ A&.M CONSULTANTS, INC. ··-----..... _ .. -·--·· -···- COOK INLET II~ITNA ltiYIIt AND MAJOit TltiBUTAitiES FltOM MOUTH TO DIYIL CAN YON O(YIL C:.tjlrljYOH ~ ,IOUIIII 1 .1 PREPARED FOR : [}{]&00~& Q [;@&:J·t~@ SU . I I A JO INT V I NT U itt I I I I I I I I I I I I I I I I I I I R~0/16 II flows above BO.tXIO cis (Barre tt e t a l. 1984 and 1985). Timing of the upst ream mrs ratro r fo r· fi ve specre s of Pacif ic salmon are presented in Figur·t·s ~-~ thr·ou g h 2 .4 based on 1981 -83 unit effor·t fishwheel catches for Suns hine statio n ( R ·1 SO). Typically chinook reach Sunshine station in ear·ly June , followe d by sockeye, p ink. chum and coho salmon . Low velocity bac~water areas near tributary mouths ar·e often used as holding areas b y ad ult salmo n d u r ing upstream migration. Pink and chum salmon have been o bs e rved spawning in the interface reach of some of the low e r river t r·ibutar·i e s (Bar·rett et al , 1985). Tr-i butaries in the lower Susitna Ri e r are predominantly used for spawning by p ink, coho and chum s a lm o n . wrth some tr-ib utaries having runs of chinook and sockeye (Appendix 7, Barr-ett e t al, 1985 ). The greatest numbers of fish in the t r ibutaries du r·ins 1984 occurr·ed fr·om late July through August (Appendix 7, Barrett et al, 198 5). 2 .3 Natural Flow Regime 2 .3 . 1 Mainstem Susitna River The Talkeetna to Devil Cany on reach of the Susitna is primarily a single channel and split channel ri ver . At its confluence with the Chul itna Ri ver the channel pattern changes from a split channel to a braided channel. This change in channel morphology is primarily due to th e increased input of sediment from the Chulitna River, additional flow from the Chul itna and Talkeetna Rivers, and a flatter channel gradient. The Sus itna River c.ontributes 43 percent of the annual flow at the Chul itna -Susitna -Talkeetna confluence, with the Chulitna and T alkeetna contl"ibuting 39 percent and 18 percent, respectively. Du rin g the !)uuuu~:;:•·, lhe Su si lncs Rivt!!,.·s dVerage contribution ranges from a high of 51 percent i n May to a low of 39 percent in July (T ab le ~.1). -7- JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC / \ )~., .......... ,,~,--, .. c .. t. ,., ut~fl "'"' ,., ,,,,,, CATCH PER UNIT EFFORT AT SUNSHINE FISHWHEE~, AMBO So•rce ' BARRETT , 1984 I f-,::lj -..........-~f• .. ~~--~ -· 1--fl$3~=1--11 SOCKEYE E=t=J ICHUM ES I PINK I E:$3 I COHO I I I I I I I I I I I I I I I I I I / ,.,_,__..,_ , ........ u ... . CATCH PER UNIT EFFORT AT SUNSHINE FISHWHEEL, RM 80 Source : BARRE TT, 1984 DISCHARGE _;32 ~~·.~'------~~~--R&M CONSULTANT S, INC. EtJ CHINOOK ~ SOCKEYE Ej2J fCHUM EO I PINK El3 !COHO •lll(f'A.[O fOIII : fi(Ji!lrnJ~Lil a§@&@©@ SUSI I ~:A. JO INf VEUTUR E -8- ....... ~-· ..... ' c •••• I/ I I ' I / \ I'V,c-... ... •'%~ ... c..~· •• , f ...... c..t• ,.,u .... CATCH PER UNIT EFFORT AT SUNSHINE FISHWHEEL, Rill 80 Source : BARRETT, 1984 DATA FROM Jlllt(f'.tllllfO et: ::t\k:~~·l RC.M CONSULTANTS, INC. JUN JUL SEP OCT NOV DE IEl=J I CHINOOK ~H I !SOCKEYE I I !CHUM EI=J I PINK I I I I fCOHO DATE I I I I I I I I I I I I I I I I I I I R20/16 12 The mean dao1y flows fo r the Susol na Ri \(•o· at the S u nsh ine gage, approllimately 20 moles downstream l o·om the lhr<'e ro vers conflue nce, are also presented in Figures 2 .2 tho·ough 2 .4 . along wolh the migration t imong informat ion fo r 1981 , 1982 and 1983 . T he onitial r ise in ma i nstem d is c h a rge on the spring results from snowmelt i n the lower basin during late Apro l o r early May . As t he ~now m el t r unoff decreases. streamflow in t h e clearwater tributaries declines (refer to Desh ka River and Wollow Creek in Figures 2 .2 through 2 .4). \'/hile the streamflow contro but ion from glacier melt to the maonstem Susi t na and i ts glacially fed trobutaries oncreases . A good example of a clearwater tributary flow decreasing whole the mains tem fl ow remains h igh occurred during June and July 1983 (Figure 2 .-1). The i nfluence of glaciers o n the mai nstem flow regome is more pronounced below the Chulitna·Susi tna · Talkeetna confl uence than i n the middle river. Glaciers cover 5 percent of the b~sin area above the Gold Creek stre.amgage increasing to 10 percent of the basin area at the Sunshine streamgage. The increase is due to the Chulitna and Talkeetna Rivers having 27 and 7 percent. respectively , of their basin area as glaciers. The percentage o f the lower r iver flow con t ributed by the Chuli tna inc reases during July and August due to i ts larger percen tage of glacierized basin area and lower basin rai nstorms (Table 2 .1). The in fluence of the Chulitna and Talkeetna Rivers decreases the relative importance of the middle Susitna River for maintaining summer baseflow in the lower river. By mid-September cold air temperatures at high elevations cause a decrease in the streamflow contribution from glacier melt and increases the importance of fall rain stoo·ms in maintain ing loweo· .-i ver streamflows . 2 .3 .2 lower SusitnA River Tributaries Tributaries to the Susitna River bt'low Talkeetna generally fall withi n two classifications : Susit'la Basin lowland streams and streams -9- D .., ..... 2 c .... .. J ~:;~;;, ~ ~ ,._ : •' 1 .. -"' "' -.. ... c .. "' I I I I I I I I I I I I I I I I •• I I R20/16 13 origina t ing in t h e Tal~eetna t.loun t ains . Dunng b,,,,, '"de s ummer storms. t he amount o f J"u noff per un1t area gener·ally •nc,~cdses as the basin s ize decre ases . S ma ller tribu t aries generally have a mo r e rapod and p roo1ou nced response to rainstoo·ms t han larger trobutao·ies or the ma i ns tern S usitna River . The Susitna lowla nds a re cove r e d with b irch and whole spruce fores t s on the better drained sit e s . with black spruce trees and sphagnum bogs on the poorly drained s i t e s . The area IS relatively f lat, woth low h i lls to the sout h and mountains to the \\est ranging on e lev ation up to 8 ,000 feet. l owla nd streams have rela t ively flat channel gradi- ents and n umerou s meanders . Snowmel t in late Aprol to early t.lay causes h igh s p ring streamflo\\S. Trobu t ary f low ty;:ucally declines during the s umme r while r e spond ing to rainfall \\hoch at times causes short term peak flo ws . lakes and bogs reta r d runoff from sui!VTier s torms c ausing lower peak fl o ws of longer dura t ion . Hence lower r iver •ributaries with lakes and bogs are generally buffered f rom flash y s piked flow even ts. S treamflow in lowland t o·ibutaroes ~re n ot influe nced by glacial melt . The Deshk a River near \"illow (USGS Station No . 15294100) p rovide a n e xample of stre am flows for a lowland tributary, Figu res 2 .2 through 2 .4. Streams o rig i nati ng i n the T al keetn a Mo u n t ains have a lpine veg eta tion cove r ing the portion o f t he basin abov e approximately 2 ,000 f eet , w ith forests o f birch a nd whit e spruce on better d r ai n ed s it es. a nd black spruce trees and sphagnum bogs on the poorly d r ained sit e s . The streams have relativ e ly steep c hann e l g o·adi ent s in the mo untains a r.d transition to relativ ely flat c hannel gradie nts and me anders in the lowlands . Snowmelt in late April to e arly May c auses high s prin g streamflows . Tributary flows t y pic ally dec line duo·ong the summer while r e sponding to r·::l;,f .::!! ·.·:h :ch a t time: ::~u~c: :;hort t erm ;;.cak flows . 1\"illow Co·eek ne ar ll'illow (USGS S tation No. 15294005) p r ovid e an example of a T a lkeetna Mountain s t r eam, Figures 2 .2 through 2 .4 . -10- R20/1G 14 2 .4 Potential Effects of an Altered lower River Flow Regime 2 .4 . 1 General The effect of the altered flow regime o f t he middle Susotna Rove r caused by the project wi ll be dampen ed o n t he lower Susitna Rher by the major tributarie s -th e C huli tna River ( RM 98). t h e Tal~eetna River (RM 97) and the Yentna R iver (RM 28). \\loth-proJect flo ws on the lower river are e x pected t o be h i gher than natural fl ows during the winter and lower than natural flows durong the summer. \~it h -p roject fl o ws wilt i ncreas e the return perood fo r a goven ma gnitude flood . Fo r in stan c e . the natural flow l\\o-year r~t urn period flood for natur a l cond it ions a t S unshine woll hav e a return period of appro><i mately t e n (B r edthauer and Drage. 1982 ). sev eral possible with -project years d uring proJect operatoon T hi s analysis was based nn ~n c of flo w regimes and os present ed to illustrate the effect of the proposed p rojec t on t he frequency of channel forming floods occ urri ng in the lower Susitna River. Project i nduced reduc t ions of mid -summer ma onstem disch arge may potentially affe ct adult salmon acce ss in to lower Susotna Rover tributaries by: 1) decreasing the size of backwater a r eas avaolable to migrating salmon for res t i ng or h o lding areas n e ar tributary mou t hs; 2) decreasing the water depth in the t r ibut a r y mou t h cau sing i nsufficient depth for adult salmon to enter the tributary; a nd 3 ) a change in the morphologic stability of the tributao·y mouth o r adjoi'ling slough/side channel thereby inh ibitin g access i nto the tributaries during periods of low tributary f low . 2 4 .2 Holding Areas One principal affect of with-project f lo ws on t o·obutao·ies woll be a reduction in the s ize and depth o f low v elocit y ba c ~wateo· areas nea r the tributary mouths. Quantifi cat ion of thos e ffect IS complic a ted I I I I I I I I I I I I I I I I I I I Rl0/16 15 becaus e the upstream ex tent of thes e bad .. \\ater areas 'a roes as a functoon of mainstem stage. c hannel geoml't ry .md trobutary flow . The decrease in maonsteon and side channe l water s urhc l' elevatoo ns in the lower Susitna River caused by po·oj ect opera t ion woll vary depend - ing on the shape of the channel c r oss ·so:>c tio n . For a given c hange i n discharge the stage change wi ll be go·eateo· at a confined channel section such as at the Parks Highway Bo-idge (the locatoon of the USGS Sunshine stream gage) than at a wide, b o·aided c h annel sec t io n , such as the Delta Islands, where a small oncrease in stage g r eatly increases the channel cross-sectional area . 1 he change from natural flows o n the lower ro ver caused by project operation will generally result i n increased flo ws i n the late fall and winter, lower flows during the summer. and nearly equal flows in spring and early fall. During extremely d r y years, wi th -p roje ct flows may e><&eed natuo·al flows in late summer .and eao-ly fall . The general effects of the alteo·ed flow regime on the size of backwater areas are shown in Table 2 .2 for v arious tri butary flow condit io ns . Du r ing with-project summer flo w condotions when trib utary flows are h igher than a verage long t e rm .tributary flows, the size of backwater areas at tributary mouths will decrease ( +) (Table 2 .2). During with-project summer flow condit ions when trobutary flows are less than average long term tributary f lo ws . the s i ze o f b ackwater areas ~N~Y increase (tL have no change (-). or decrease (t ) (Table 2.2) depending upon the r e lative p e r centages of which wi th -project flows and tributary flows are lower . The nature and d egree o f c hange of the backwater area ~t each tributary is a functio n o f channel gradient , the runo ff characteristics o f the bason (such as percentage of b~sin ~s !o:--~~t ~ !6:kcs er b~ss# thereby c a u s ing ;lvv~ar t ime t o peak and lower peak flows) and wh e ther the tributaries join t he mai nstem d i rectly o r through a s ide channel. -11- TABLE 2.2 CHANGE IN SIZE OF TRIBUTARY BACKWATER AREAS DUE TO WITH-PROJECT FLOWS MAINITEM WITH-.. ROJECT FLOW HIGHER TRANSITION PERIOD LOWER LATE FALL MAY & SE"T FLOW SUMMER FLOW FLOW .. "'" > c ~ oa Q Q . .. Q c > " c 0 i ... ... .. > " c c c c 6 --... .. Q > :::> c !! c ... .. ~ " 0 0 c 6 ... c Q -.. .. Q • ,. c SIZE OF BACKWATER AREAS AT TRIBUTARY MONTHS, ,0 INCREASES, II A PPRO X IMATELY THE SAME, OR Q DECREASES, DEPENDING ON TRIBUTARY FLOWS AND MAINSTEM WITH -PROJECT FLOwS . I I I I I I I I I I I I I I I I I I I Rl0/16 16 2..1 3 Tribubry Access r robutaroes enter the lower Susitna River either in side channels or sloughs or directly i nto the mainstent. The affect of the altered flow regune on fosh access onto tributaries entering in side channels or sloughs d~ends on the with-project flow relative to the mainstem dischuge re«uired to overtop the head of the side channel or slough . Overtoppong dischuges rneuured at Sunshine nnge from less than 13 .900 cfs at Wollow Creek to 36.600 cfs at Kroto Slough . For the with-project flow regime being used in this analysis. on an average weekly basis 36.600 cfs will be exceeded 95 percent of the time from June 24 to August 11 (Harza-Ebasco. 1984). For t he tributaries which enter tile mainstem di r ectly the upstream extent of the backwater will decrease. u will the depth of flow. 2 .4 .4 Tribubry Mouth SUbility Morphologic stability of the tributary mouths in s ide channels and sloughs depends on the peak flow of either the mainstem or the tributary . Where deposition of sediment carried clown stream by the trobutao-ies presently occurs it would likely occur somewhat closer to the tributary mouth under with-project flow u a result of the upstream extent of backwater in the tribubry being o-edueed . Si nce the flows in the trib utaries will not be affected by project operation. tributary peak flows will cont inue to transport material from the tributary . -12- I I I I I I I I I I I I I I I I I I I 3 .0 STUDY PLAN DESIGN AND METHODS The vi •Je<t l\ e of this evaluat ion is to determi ne whether alteration of the 10\,er Susttna Rtver f low regime by t he proposed Susitna Hy droelectric ProJect ts lt l..ely to affect the availability of holding areas for adult salmon near trtbutary mouths, aeeess by adult salmon into tributary streams for spawntng or morphologic stability of the tributary mouths . The abil ity of ftsh to pass through a given strum ruch is pri~Mrily a function of the spee•es o f f•sh and life st.1ge being considered, environmenbl stresses the fish are uposed to dur ing migration. water depth and velocity in the passage reach , length of the passage reach and a vai lability of resting areas . Pauage crit eria most often con sidered are water depth . water veloe tty and passage reac~ length . Previous passage criter i a used for evaluating aeeess and passage conditions tn the mtddle Susitna River (RM 98.0 to RM 152.0) include a set of curves developed for adult chum ulman (Sautner , Vining and Rundquist, 1~). Passage abtlity was rated as a funetion of water depth and reach length . T he middle river curves were developed for slough spawners from field measurements , liter .. ture v alues and professional j udgement of ADFt.G, W~ward Clyde and E.W. Trihey t. Associ.1tes p erson nel. Water velocity was auumed to be less than 2.0 fps, a n d two generalized channel types were defined. Passage criteria for the lower Susitna River needed to include the five Pacific salmon , therefore the passage criteria used are those recommended by Thompson (1972) a nd applied by T r ihey (1983) fo r the middle S usitna River tributaries Indian River and Portage Creek (Table 3 .1). T he proeP.du r es used fo r evaluating tributary access in the lowe r Susitna Rive r i .. c.l u u": i .. iti .. l .. irphoto assessme n t of the "onditions at the t r ibutary mouth. field checking o f the airphoto assessment during low fl ow conditions, a nd taking spot measurements at locations where pasuge ma y be a pro b lem . -13- R20.'1G 18 TABLE 3 .1 DEPTH AND VELOCITY CRITERIA FOR SUCCESSFUL UPSTRE.AM MIGRATI ON OF ADULT SALMON (FROM THOMPSON , 1972) Fish Species Chi nook ulman Coho ulman Chum ulman Pi nk ulman Soet..eye ulman Minionu• Depth (ft) 0 .8 0 .6 0 .6 0 .6 0 .6 Maxlmunt Velocity (fps) 8 8 8 7 7 The lowest wtt h ·projeet average weekly f lows estimated for the period June 3 to September 15 is 21 .500 efs at Sunshine (Harza-Ebasco, 1984). The September 16, 1983 aerial photography. with a flow at Sunshine o f 2 1, 100 efs, was selected for the init ial airphoto assessment and as the photo base for this report. These photos show reasonable worst ease passage conditions s i nce the mainstem flowrate is lower t han the expected with -project flows and the tributary flows are ;olso low . The photos were examtned for und bars, riffle ;oren a nd continuous water at tributary mo uths and i n side channels leading from t h e mainstem to the tributary mouths. Trtbut;ories with poten tial access problems were id .. n tif ied for follow-up aerial reconnaissance and on-site field measuremen ts . Depending on the tributary, field c h ecking consisted o f helicopter overfligh:s (Deshka Ri ver). boating up the side c hannel t o the tri butary mouth (S uns hine Creek). walking a long t h e side c hannel to the tributuy mouth (Trapper Creek ), and taki ng depth -velocity measurements at potentially critical passage reaches (Goose C reek). I I I I I I I I I I I I I I I I 'I 'I I R~O lu 19 ·l.O RESULTS AND CONCLUSIONS Th is a ssessmen t of access conditions at fifteen lower Susitna River tributaries fo und five locations that may presently restrict the movement of adult salmo n (Table 4. 1). Specific site evaluations are presented in Exhrbit A with oblique and vertical air photos showing the tributary confluence with the mainstem and an air photo mosaic showing the area surrou n ding the tributary mouth . The head of Kroto Slough becomes dewatered at mainstem flow of approximately 38,000 cfs, but there is still access i nto the lower part of the slough from the Yentna River. Potential access problems exist at Roll y Creek due to a debris jam near the mouth, at Caswell and Trapper Creeks because of shallow d e pths in an unstable side channel leading from the tributary mouth to the mainstem and in some r eaches o f Montana Creek where the water velocities may be excessive. The affect of the proposed project on the flow regime of the lower Susitna Ri v er will be dampe ned by the influence of. the major tributaries: the Chuiitna, Tc0 lkeetna, Oeshka, and Yentna Rivers . Effects of the altered lower river· flows on access conditions at tributary mouths will be further masked b y the dynamic variations of a braided river and the natural response of the tributaries to summer rain storms. Figure 4.1 compares a verage weekly natural flows for a representative year, 1983, with flows during project operation . This example is one of several possible with-project flow regimes and is presented to illustrate the potential changes in lower river flow regime. Based on the tributary evaluations provided in Exhibit A, it can be concluded that access by adult salmon into tributnies of the lower Susitna Ri v er s hould not be inhibited by with-project flows in the 25,000 to 30,000 cfs range. The size of backwater are01s will be affected (n shown in Table 2 . 2 ). however the degree of change is difficult to quantify due to the natural variability of tributary flows. Tribut01ry mouths should become -14- R20/1G 20 more stable with with -p r·oject flo ws al tho ugh the natural v ariation in a braided river· wrl l make q uantificat io n o f this change drfficult . 4 .2 Holding Arus Project affects on the ext ent of backwater a rea s va ry depending on the season, precipitation, the channel gradient and location of the tributary mo uth (in a side channel or the mainstem). The channel cross-section will dete r·mine the amount the rna instem stage dr·ops for a specified decrease in flow . For e xample, the lowest media n average flow at Sunshine during the f o u r we ek period June 3 to June 30 drops fro m 59 ,400 cfs under natural conditions to 34,900 cfs under weekly with -pro ject conditions (1996 load) (Ha rza-Eba sco, 1984). This c hange in streamflow causes a decrease in stage of 1.9 feet at the US GS Sunshine gage, whereas at \'l'illow Creek (RM 49.1) and Caswell Cr·eek (RM 64.0) the decrea se in channel stage for the same decrease in f low are 0 . 7 and 1. 1 feet, r especti vely . Using the stage c hange at Sunshine to determine the change in channel stage at other locatio ns o n the river may b e mi sleading . Where possible, stage-discharge curves developed at o r near the tributary mouths should be used to determine the potential effect 01 with-pr·oject flows o n stage. At 21 ,100 cfs the upstr eam e x tent of backwater is slight or nonex istent at each study site except the Oeshka River. In the flow range of 35,000 t~ 60,000 cfs in June and July the change in backwater extent may be severe at Sheep Creek due to the relatively flat tributary channel gradient(Table 5 .1). For most o f the other t r ibutaries there will be 01 moderate cha nge in backwater e x tent. 4 .3 Tributary Access At confluences of trib u ta ries with the main stem or side c h annels typically ther·e is a low water channel. Tributaries identified during the initial air photo assessment having potential acc ess problems had water depths ranging fr·om 0.4 to 3.0 feet at 17,800 cfs (Table 4.1). Exhibi t A describes where the water depths were measured . Three creeks hiive I I I I I I I I I I I I I I I I I I I •• l S~ Of I'OTE.TIAI. EFfECTS 011 WITH•I'IIOJ[CT rL~ 011 TRI8UlARILS 01 THE LOWER SUSITM RIVER tr.r.utu~ s.o .... St.-a ry or Adu 1 c. S. 1 eon Uuge or St,..•• lnt.errace Reach. 19&"( 1) ,., ..... COndit i ons liNter Trilputl ry Nouth I I r l.£t bu""' "···· C!!!....._nt'MJI lHH.u ~ YllJr Qtatd! CCtl Ate;,., ur Cr 9.1 ~t'OLO Sl ]6.] flo I ly Cr 19 .0 Oe~hk.a R •o.(. Will ow Cr -9 .1 L W I lOW Cr 50 .~ kaShw1tN R 61 .0 Cas 11 Cr 6'1 .(1 Sheep Cr 6.1 CiooH Cr 17.(1 Monu na Cr 77.u IUb i el uu.c Cr l l .l Sun5h•ne C r 8 ~.1 8• n:n cr 119 .2 Traoper Cr 91.5 Derin l nLtons : " " l( lt .... .... CltSPCo SPChCo CllSPCH Co PCit Ck S POl Co SPOICo CkSPCit Co CkPOICo Ci< S PCit Co Ck S POl Co Cl<S PCit Co Ck S POl Co Su.--yM Su~ POl , PCit p p PCit POl POl 1 lhll l nterr.ee reac n h r . nt. th nJ •• te r~ .ut.h up the trfbuury . Source 8a r'reu .• tL ••. 19&~-Ck • ch i nook., s z sockeye. P • p ink, en • chUII, and Co • coho . 2 .. roblea-there is an eJu sting cu·oble• v 'th r lsh access . dry ..... 2.11 1.~ 0.11 3 .0 0 .11 l.l .. ~ 0 .6 ror Dt sch:l f"9• at Sun&!!ine rcfsl 311.000 •3.300 n.1100 n.1100 17,1100 17,1100 l7,1100 22,600 20.700 Posstbltt Prnb te• -lne r e 1s t.ne pot.ent ial ror access probl"s aepend i ng on low tri buury flova. CSubri s J aas or cnanne 1 cn.nges. Ho Prob lea ... No problea v i th •ccess cu rrent.ly exists . Severe Cll•nge -The: extent or b•ckyater area could tte sevwrly reduced by v i th .. project flows Cl uf"ing June •ncs July. Moelent,• Change .. The ex tent or b.ackw•ter •re• could be aoderately reduced by by vh.h-project flows dur i ng J""'' and July. Sl i ght Ch.llnge ... The •xtent or backvliter .,.., COUld be Sl i ghtly reduced by Vi ttl-project f l ovt dur•ng JuM •net July. ,. Coocs .. No chJinge '" tri but•ry Muth Mrphology s.i nce 1951 rei r .. so.. change i n tr f buury -.outh Mf"'phology since 1951 Poor -Cha ngo i n t.r i buury ltOuth IM)rpnology rroe 1951 to present . -15- resher ies Acce ss Into Tr f ttyt.trie~:!Jf !a'QQ cr:ow l.!:!IR.!I!! ~ !!2!!ln " lt X X lt X lt lt lt lt trrect,s or W• th-Pro &ect. fl ows On Morpho logic Stab i l l ty gr Ic•SUU.Ict !!iYI.b l!la mun.t. ~ J.!l-~!liiiSSI lt COOd COOCI N/A COOd COOCI lt COOd COOCI lt Fa f r Fa i r lt COOd COOCI lt COOd COOCI lt Fa f r ,.,,. lt ,. i ,. ra l r/COOCI )I COOd COOCI l( fa I r ra l r/COO<I lt Poe .. Poo•/Fa l • lt fa i r COOCI lt COOd COOCI lt fa i r Fa i •/COOCI lt Fa I r faIr I I I I I I I I I I I I I I I I I I I R2 U/1G 2 1 water dep t hs less than t he recommended depth (Table 4 . 1). Cuwell Creek was measur·cd a t 1i ,SOO cfs. below the 21 ,100 cfs considered the bue low flow ~rrd well below the 30,000 to 35,000 cfs range for low with -project fl ows mid -June through September. For with-project flows there shoud be s uffrc ient water depth for access . Below 20.000 to 23,000 cfs the head of Goose Creek side c hannel becomes dewatered and water depths in the s ide channel are dependent on tributary flows . The shallow water depths were measured during a non-overtopped condition . Water depths during overtopped periods s hould be suffic ient for access . Shallow depths in Trapper Creek were measured during a non-overtopped condit ion when the water depth was dependent on tributary flows . During overtopped periods the re should be sufficient water depth for access . S ite specrf ic quantification of with -project water depths available for adult ulmon access in to lower r iver tributaries is not considered necessary because the measured and estimated water depths at 21 ,100 cfs are suffic ient for passage . Th is flow rate is exceeded 100 percent of the time during the period June 3 to September 15 (Figure 4 .1). With-project flows may have an effect on the upstream extent of . backwater areas at the tributary mouths , however the decrease in size of these areu is not expected to cause access problems . 4 .4 Tributary Mouth Stability Due to the relatively low gradients of the tributary strums, it is not anticipa ted there will be down cutting of the channel bed at the confluence , wh ich could result in problems with perched tributaries . Currently only one tributary mouth is morphologically unstable . Since 1!151 the s ide chan nel upst ean ,;,( Montan• Creel.. h.s yr<>wn in size and become more stable. However, the creek mouth continues to shift its location from year to year . The general effect of with -project flows will be to reduce the frequency of the cha nel -forming flows, thereby slightly increasing the stability of the side chann'els . 16 '"' .._. C.•••• 1 /! / \ .,.c....... "'c.-- ~· ... '-""''~t ....... , CATCH PER UNIT EFFORT AT SUNSHINE F I SHWHEEL , RIIIO SourH : BAfiRE Ti, 198C l EE= !CHINOOK EP::: !SOCKEYE ! j I CHUM Ei:3 I PINK 1 83 tco_Ho DATE ••r:,.a•LD r()lt . r~~ru~&o§§&~~ I I I I I I I I I I I I I I I I I I I R20/1G ~-1 R20/16 25 6 .0 REFERENC ES Barre tt , ll.M .. F.M. T hompso n. and S.M. 11/ic k. 1984 . Adult Anadromous Fish In vestigatio ns , ~lay -Octo ber 1983. Susitna Hydro Aquatic Studies Repo r t Ser·res . No. 1. Alaska Department of Fish and Game. Anc horage, Alaska . 1985. Adult Anad r·o rnous Fish Investigations, May-October, 1984. Susitna Hydr·o Aq uat rc s tud ies Rep o rt Series . No . 1 . Alaska Depart- ment o f Fish and game . Anchorage, Alaska . Bredthaue r , S. and B . Drage. 1982. Ri ver mo rpho logy . R&M Consul- 'tants , Inc . Anchorage, Alaska. Harza-Ebasco. 1984 . Week ly fl ow duration curves and observed and filled weekly flows for· the Susitna Ri ve" Basin . Anc horage, Alaska. R&M Consultants, Inc. 1982 . Tributary Stability Analysis . Anchorage, Alaska. S autner. J . S., L. J . Vining. and L.A. Rundqu is t . 1984. An Ev aluation of Pass;oge Conditions fo r Adu lt Sa lmon in S lo ughs and Side Channels of the ~Iiddie Susitna River. Susitna Hydro Aquatic Studies Report Series No . 3 Chapter 6 . Alaska Department of Fish and Game. Anchorage, Alaslo.a . Thompson . K. 1972. Determining streamflows for fish life. In Proc:eed- ings, lnstream Fl ow Req uireme nt Workshop Pacific Northwest River Basin Commission . Van cou v er, Washington p. 3 1-50. Tri he y , E .W. 1983. Prelimi nary Assessment of Access by Spawning Salmon into Portage Creek and Indian River . Prepared for Alaska Power Autho r ity. Alaska Department of Commerce and Economic Development, Anchorage, Alaska. · u.s. Geological Data Rept . u.s . Geological Data Rept. u.s. Geological Data Rept. 17 Surv ey . AK -81 -1. Sur·vey. AK-82-1, Surve y . AK-83·1. 1982 . \Vate r· Resources Da t a for Ala ska, \Va ter Anc hor·age, Alaska. 1983 . \Va t e r Resou r·ces Data fo r· Alaska , 11/ater Anchorage, Ala ska. 1984. 11/ater Resour·ces Data for Ala ska , \Vater Ancho r age, Alaska. I I I I I I I I I I I I I I I I I I I R20/1G 26 EXHIBIT A EVAL UATION OF SELECTED LOWER SUSITNA RIVER TRIBUTARI ES The f ollowing ~re descrrptr.-ns o f lht> h )·<!rolosy and frsheries use of select · eel lower Susitna Rover trobutaroe s . The se <!escrrp tr ons are based on initi~l aerial photo evalu~to on o f access p r oblems. freld dat~ collected to confinn the ev~luat ion . and analysos o f the pot ential e ffect o f wrth ·project flows on backwater areas and morpho logrc stability o f the trobutary mouth. The fisheries use of the to·rbutar·y mouths fo r spd"ning or passage is from .. Appeoodi• 7 • Adult Salmo n Lowe r S usitna Ri ver Spawn ing Surveys ... by Levesque and Seagren (Barrett. et a l. 1985). Depths reported for tributaries ar·c passage depths \\her·e cr·oss·secllons wc r·e measured and ma•imum depth where only spot measur·ements were made. Passage depth is the average of the mean dept h and the maxrmum depth (Sautner. Vini ng and Rundquist. 198-1). Aerial photosraphs (at 1 .. = 501}') of each study site· are provided for a fl ow at Sunshine o f 21 .100 cfs except for Caswell and Sheep Creeks. w here the lowest flow at "!hich urial photography is available is at 59.100 cfs. The tributaries ~re given in upstrum order. Tr ibut~ry loc~tions ~re marked on the lower Susrtna River aerial mosaics (at 1-=2000"). A-1 I I I I I I I I I I •• ·I I I I I I I I R20/1G 27 A lexander Creek Alexander Cr·eek (Figure A -1 an d A -2) o ngin;,tes rn the Sus itna lowlands and flo ws s o utheast to the Susitna River. The flow r·cgime is simrl ar to the Deshka River (Figure 2 .2 . 2 .3 a nd 2 .-1), except t hat fl o w from Alexander Lake wrll result i n a hrghe r· basef low du ri ng dr y summ e rs and during the winter. The cree k is a p o pular fi s h ing s tr·eam . Ye ar-ar·ound residents live ju s t upstre am f r·orn th e conflu ence with the S usitna Rive r· (Photo A-1). Ther·e is boa t access a t 21 .100 cfs (at S un s h ine) f.-orn Coo k Inlet up the west channel. Pot e ntial f is h acces s is u p this side c h a nne l o r thro ugh the east channel then th ro u g h a s lough ( RM G) to the we st channel. The affect o f wit h -project fl o ws on the rnor·ph o logic s t abilit y o f the t ribu tary mouth and fis h eries ac c e s s i nto the t ributa r·y wrll be minima l d ue to the flow contributio n fr·om the Yentrr a River·. F is h e rie s use o f Alexander Creek was not r·eported rn Append rx 7 (ADFr.G, 1935 ). A-2 R2 0/16 23 PHOTO A-1 Looking upstream at the mouth oi A lexande r Cr·eek ( R~l 9. 1). In t h e foreground is Alexander Slough fl ow i ng fr·o rn r ig ht t o le ft. Photo taken 9/11 /84 discharge at Sunshine 23,600 cfs, drsc h ar·ge a t Su srlna S t a tio n 51,400 cfs . I I I I I I I I I I 'I I 1: '• • • -• TRIBUTARY ACCESS STUDY STUDY SITE LOCATION MAP FIGUREA-1 LO W E:R S U SITNA RIVEfi OAf( C' .~,l~A'"1' S(PT ~1. IHl SCAl.[ ·lOOO wn zJ or z • f-::===--=----O&fl Z-7· I <~ ~L-H.W.H.U:CD I I I I I I I I I I I I I I I I I I I DP[P:.RfCl 8Y ~ .... :;-.------- R&M ::ONSULTANTS, INC:. DATE OF PHOTOGRA PHY· SEPT. 1Stn. 18&3 SCALE: 1' = 600' DISCHARGE ot S UNSHINE: 21,100Ch FIGURE A-2 P E O FOR ALEXANDER CREEK r-.: ·.t t I I I I I I I I I I I I I I I I I I I H20, IG 2!1 Kroto Slough Kroto S lough flows from Kroto Side Channel t o the Yen t na Rover. llelow ~rns tem flows of 38,000 ch the head of Kroto Slough becomes dewatered I Fogure A ·3). F low on to the upstream end of the slough os en t o rely dependen t o n side channel flows . although small lowlond trobutanes ent~>r a lo ng the slough . The so de cha r.nel t ypically has water unto I a few wee l..s proor t o freezeup . There is a controlling berm at the head of th ~ slough (poin t A. Figure A·4). An ADF&G Resident ·Juvenole stur':• sole lpoont B. F rgu r c A ·4) studied the effect o f change in s t age o n sevPral habot at pa r·ame ters . Passage by the upstream berm is unc ertain at ratur·vl fl ows b<'low 38,000 c fs , whic h u sually occur during ca dy May and late August. Thll gravel bar at the mouth of the slough w i ll t e nd to b ecome more stable due to the lower magnitude o f the annual f lood puk under woth ·po·o,cct con do too ns (Photo A·2). The head of Kro to Slo u gh may be used by sockeye and coho salmon l.> a ccess Whitsol Creek, and by c hrnook and coho salmon to access Fosh Cree'<. 1<~11 l b J() PHOTO A·2 Lool..ong do\\nstrearn at Kroto S lough (RM 36.3 ). flow is from bottom to t o~ o f phot o . Gr·avel bar on center o f photo overto ps a t approKimate ly 38,000 c fs . Pho to taken 9/11 /84, drsc harge at Sunshrne 23 ,600 c fs . LOWER SUSITNA RIVER ALASKA POWER AUTHORITY SUSITNA HYDROEL£CTPIC PR().JECT TRIBUTARY ACCESS STUDY ~-----------1 STUDY SITE LOCATION M.&,P FIGURE A-3 L OWER SUSITNA RIVER OAT£ Of JIIHOTOGIIWI'KT Sl.l't tt,llll 5CAL( ••• 2000. SH(fT ,, 01 2:1 CM'I'( Z·J ·I • I I I I I I I I I I I I I I I I I I PREPARED BY - ~ DATE OF PHOTOGRAPHY; SEPT. 181•. 1 983 J5!<Pf\VJ! SCAL E: 1•= 500' ~ ~:':~~~!~':· D I SCHARGE at SUN SHIHE:2 1 .1 00cfa FIGURE A-4 P REPARED FOR : l}n.£00~,6\c ~@.£®©@ SUSITNA JOINT VENTURE KROTO SLOUGH I I I I I I I I I I I I I I I I I I I I Roily C r eek l h e heac!wate • s o f Ro ily C r eek a1·e in the Susitna lowlands in the Nancy La ke a r ea. T h e fl o w r e gime is s imilar to the Deshka River (Figure 2 .2, 2 .3 a nd 2.4). bu t wo uld have higher baseflow due to the influence of the lakes in the bas in . A log jam which formed in 1984 near the confluence w1th the mainstem may affect fish access to Roily Creek (Figure A-3, A-5 and Pho:o A -3 ). lv•th -projec t flows will •·educe the backwater zone, but s hou ld not a ffect t h e ac cess o r morphologic stability of the tributa•·y mouth . Chinoo ~ and coho s a lmo n spawn upstream. A-8 R20/IG 32 PHOTO A-3 Looking upstream at Rolly Creek ( RM 39. 0). The Susitna River main s t e m is in the foreg•·ound flowing from left to right. Photo taken 9/11/84, discharge at Sunshine 23,600 cfs. I I I I I I I I I I I I I I I I I I I P REPARED BY ~r.j ____________ __ R&M CONSULTANTS, INC. DATE O f PHOTOGRAPHY: SEPT. 18th, 1883 SCALE: t•: 5DD' DISCHARGE at SUN:lHINE: 2 t , t OOcto F I GURE A-5 P R EPARED FOR : ROLLY CREEK [}{)£00~£ a§@£@@@ SUS IT Nil JnJ NT VfNTUR( 1 I I I I I I I • I I R20/IG 33 Deshka Rive r The D<·s hka R i v~r· o r·igonates rn the Susitna lowlands and flows southeast to the Susitna River (Figure A-6). S ince October 1978, the USGS has maintained a cont in u ous r·eco r di n g disch ar·g e station 7. 9 miles upstream on the Des hka Rive r· f r om rts c o n fluence with the Susitna River (Figures 2 .2, 2.3 and 2.·1). Af te r the \e rrtna River, the Deshka River is the second large st tr·ib utary belo w Talkeetna. Backwater extended approximately 6,000 fee t upstream fro m the conflue nce while the mainstem discharge was 23 ,600 cfs. The r·e is suffrcient depth to allow fish access at 21,100 cfs , so wi th ·p r·oject fl ows s ho ul d not affect access . Island A (Figure A-7) has ac ti vely inc r·e ased in size since 1951, although r·ecently it has started eroding. With -p r oject fl ows will decr·ease the size of the backwater zone . The reduction in s ize, howeve r , depends on many factors, primarily rnains tem stage and magnitude of tl'ibutar·y fl ow . The tl'ibutary mouth may beco me mor·e stable because of slig htly lower peak mainstem flows. The erosion rate of Island A may decraase. Chinook, sockeye, pink and coho salmon spawn in the upstream habitats. A-10 R20/16 3-1 PHOTO A-4 Looking upstream at the mouth o f the Desh k a River (RM 40.6). The Susitna River main stem flows fr·om r ig ht to left i n the foreground . Photo taken 8/31 /84, discharge at Sunsh ine 38,000 cfs. I I I I I I I I I I SUSITNA HYDROELECTRIC PROJ.:CT TRIBUTARY ACCESS STUD Y - I LOWER SUSITNA RIVER STUDY SITE LOCAT I ON MAP ""' "'.""oro~••••" st•r '6 ·""' SCI.l[ ' • 2000 SH££T 11' LF 2a [),o\f[ 2-7-t. FIGURE A-6 I ~ H.UZA ·EiU:i!i lo.. ·~· ....... ... I I I I I I I I I I I I I I I I I I I SUSITNA S r~fl',J. 11 ·-.f ·.t ;:1: PREPAR E D BY FIGURE A-7 P D FOR ~ DATE OF PHOTOGRAPHY: S EP T. 1 6 th, IG83 R&M CONSUI..TANTS, INC. SCALE: l'•SO D' DESHKA RIVER _._ .. ----· -·--"9-. ·--......... DISCHARGE at SUNSHINE: 21, 100cfa I I I I I I I I I I I I I I I I I I I Rl0/16 35 Wollow Cre"k l"'llow Creek orogon~tes on the Tall....,tna \lount;11ns .nd IIO\H "est tho ough the Susotna lowl~nds t o the Susotnd R"e.· (fo!)urc A Sl Sonce June 19i8. the USGS has maonta oned a cont inuous rNo rcong doscharge stat oon on Willow Creek appro.,mately 15 moles upstream from ots conf1uence woth the Susotn~ River (Fogures 2 .2. ::! 3 .nd 2 .-l ). \\d ler depths a t 2 1.100 c h are suHicoent to allow passage f rom the maonstem onto \\'ollow Creel.. At a flow o f 17 ,800 c fs , the passage depth was ::! 8 f ~e t and 1.9 fee t a t cross -sections A and B. respecto vely (Fogure A·9l. fhese co·oss·sect ions are at o r near t h e s h a llowes t depth in the r·each. The mean v elocoty was 2 .4 per second fo o· a d ept h of 2.8 fee t at A. a nd 3 .0 fps fo r the maximum depth of 2 .2 feet at B. The substo·ate o·angc d from s and to sandy gravel at both A and B . \\loth -proJect fl ows may cause reducl'd b acl.wate r zo nl's, but should not aHect access or morpho logic stabohty of the trobutary mouth . P ink and chum salmon were observed sp;mnong on the trobut~ry just upstream of the mouth of \\follow Creek on 1984 (Buret! et al , 1985). Chonook, sockeye, chum ilnd coho salmon spawn i n the upstream habotats . A·13 R20/16 36 PHOTO A -5 Looking upst r eam at Willow Creek confluence ( RM 49. 1). \Vollow Creek flows from lower right to the cen ter of the photo . Photo tal.en 8/3 1/84 , discharge at Sunshi n e 38,000 ch . I I I I I TRIBUTARY ACCESS STUDY 1-------------l STUDY S I TE LOCATION MAP FIGURE A-8 LOWER SUSITNA RIVER OITt OP' PttaTOG~T :5£" t6 .tM3 SCAL£ e·· ZOCIO M(l 1• Of" Zl D&T( 1 •7 -1 • I I I I I I I I I I I I I I I I I PREPARED B Y ' I ~ R&M CONSULTANTS, IN C. I DATE Of PHOTOGRAPHY : SEPT. teth . 1883 SCALE' 1• = 500• DISCHARGE at SUNSHINE: 2 1.100 ela FIOUAE A-9 WILLOW CREEK PREPARED FOR : IXJ£00~£c§@£®@@ SUSITNA 'OINT VENTURE I I I I I I I I I I I . I I I I I I I I R20/1G 37 Little W1llow Cr'Hk Little Willow Creek origmates in the Talkeetna Mounta1ns and flows west through the Sus1tna lowlands to the Susitna River (Figure A-10 and A-11). The flow regime is sim1lar to Willow Creek (Figures 2 .2, 2.3 and 2 .4). Water depths for a mainstem !low of 21, 100 cfs are suff1c1ent to allow passage from the mainstem to Little Willow Creek . At a flow of 17 ,800 ch, the passage depth wu 1.5 feet at cross-section A (Figure A-11) and the mean velocity wu 2.0 feet per ucond at the muimum depth 1.6 feet. The substr~te wu a silty sand with some gravel covered with a layer of s ilt -clay. Ac.ceu to Little Willow Creek is through a 11de channel from the Susitna RIVer. At ~ flow of 17,800 cfs there were no apparent shallow riffles which would impede the pauage of fish into the s ide channel. The utent of backwater at 23 ,600, 38,000 and 52,000 ds are marl..ed 1n Figure A-11 . With -project flows may cause ~uced backwater zones, but should not affect access or morphologic stability of the tributary mouth . Pink salmon were observed near point A during 1984 (Barrett et al, 1985). Chi nook, sockeye, pink, chum and coho salmon spawn in the upstream habitats • A-16 I I I LOWER SUSITNA RIVER TRIBUTARY ACCESS STUDY STUDY SITE LOCATION MAP FIGURE A-1 0 ALASKA POWER AUTHO.~rTY SUSITNA HYDROELECTRIC PROJECT LOWER SUS!TNA RIVER 04Tf. fY PHOTOC'f.6.PriY S(PT f6,1M~ so.L.E l"•l()(X)• SHUT 1.) OF U DaTE 2-1· 1 4 I I I I I I I I I I I I I I I I I I I PREPARED BY :;--------DATE OF PHOTOGRAPHY: SEPT. 181h, 1883 ____;::!~ SCALE: t •: 600' ~':'.'. ~~:~.~,;~~.~-':· DISCHARGE at SUNS HINE: 2t,IOOcla FIGURE A-11 PARED FOR LITTLE WILLOW CREEK SlJSil N.\ VllN1 \It • .. 1 ..: I I I I I I I I I I I I I I I I I I I R}o , 16 38 Kashwitna River rhe K.tshwitna Rtvet· origtnates in t he Talkeetna Mountains and fl o ws west t hrough the Susitna low lands to the Susitna R iver (Ftgu t·e A-12). Glacter melt Ill the headwaters results in a higher baseflow du nng July and Augu st than other east bank tributaries w i thout glacie t·s. The r·iver t•esponds to summer r·a ins in a manner simila r· to Willow C t·eek . Fishenes access is ttu·ough a side channel It· om the main stem (Figure A-13). Th ts channel p t·ovides boat access from the boat landing in the Kashwitna Rive r to the main stem (Ph o to A -G). \\lith-pt·oject flows will dcct·ease the stze o f the backwater zone. The r eduction in size depends o n m.,ny facto t·s. pt·ima t·i ly mainstem stage and magnitude of tributary flow . The ba t· to the west of the boat ramp has been increasing in s ize since 1951. The r a t e o f 9•·ow th o f the bar may slow down wi th with -p t·oject fl o ws . Chtnook , pink, chum and c o ho spawn in upstream habitats. A-19 R2 tl, '6 3!) PHOT O A -6 Looking upstream at the Kashwitna River (RM 61 .0). S.usitna Landing boat ramp is o n the gravel bar in the top center to lower r ight. Phot o taken 9 /11 /84. d ischao·ge at Sunshine 23,600 cis. FIGURE A-12 ALASKA POWER AUTHORITY SUSITHA HYDROEUCTRIC PROJECT LOWER SUSITNA RIVER Dt.Tt 0T PHOTOGRAPHY $(, li, tM3 SC.I.L[ ,··lOCO' ~ 10 Of l:t GtT£ a.-f-1 4 I I I I I I I I I I I I I I I I I I I P RE PARED B Y ~ R&M CONSULTANTS, I NC. DA TE OF PHOTOGRAPHY: S EPT. 181ft, 11183 SCAL E : 1 ': 500' D ISC H ARGE II SUN SHINE: 2 1, 1 OOcfo FIGURE A-13 ~EO FO ~ KASHWITNA RIVER W&OO~& a §00&~@ ~ INA <)IN! Vf,..TURE I I I I I I I I I I I I I I I I I I i k~!l I~ .JU CasY.ell Creek The h,•ddwaters o f Caswell Creek are in the S usitna River low:ands in the Caswell lakl! area (Figure A-14). Caswell Creek has lower peak flows .. ltt'r raonfall events than does Des hka River or Willow Creek due o f t he onfluence o f lakes in the basin. Baseflow during the winter and during dry summers wo uld be r elat ively higher due to the influence of Caswell lake . l"ater dep ths for flow at Sunshine of 21,100 cfs would be sufficient on the c r eek and at the creek mouth to allow fish passage. Channel A ( Foguo·e A-1 S) is ·!ewatered at approximately 36,600 cfs thueby extending the tnbutary mouth approxi mately 800 feet to the southwest (Photo A -7). The low water mouth is a mobile bed o f silt and sand which changes with each high flo w event. During our s ite v isit (September 27, 1984 , 17 ,800 cfs) t h ere was a water depth of 0.2 to 0.4 feet for a length of 10 t o 20 f eet at the mouth . Water velocit ies were low . 0 .2 to 0 .6 fps . There could be difficulty in passage due to shallow depths . At 21 ,100 cfs there would be sufficient depths and velocities to ensure passage . With -project flows woll affect the extent of backwater up Caswell Creek . However, the area whoch would change would be 600 to 800 feet upstream from the tributary mouth . The stabolity of the tributary mouth would not be affected by woth-project flows . The shape of the s ide channel immediately downstream of the tributary mouth changes with each high flow and will continue to change shape under w it h-project con ditions . Pink and c hum salmon were observed spawning in the tributary just upstream of the mouth . Chinook , sockeye, p ink , chum and coho salmon spawn in upstream habitats . A-21 PHOTO A-7 Caswell Creek (RM 64 .0) flows from right to left . This photo shows the so de channe l b e low the creek mo u th . Photo taken 9/11 /84, discharge at Sunshine 23 ,600 cfs. TRIBUTARY ACCESS S T UD Y STUDY SITE LOCATION MAP FIGURE A 14 SUSITNA HYDROELECTRIC PROJECT lOWER SVSITNA RIVER Do\T£ Of' ll'HOTOGJtUtn' S£PT 16,1M3 KA£ ,-, zooo· HtT • Of' 21 OAT[ Z-7-14 I I I I I I I I I I I I I I I I I I I / PRE P t.REO BY R&M CONSULTANTS, INC. DATE OF PHOTOGRAPHY: AUG. 27th, 11183 SCALE: 1 •: 600' DISCHARGE at SUNSHINE: 511,100 cfa FIG U R E A-15 PRCP4RED FOR: CASWELL CREEK ~ ~.Jl'\,\ fl'J ~t Vf NJIJRf I I I I I I I I I I I I I I I I I I I lU ll 16 ~2 Sheep Creek S h ee~ o:o·ee~ Ol'l gona t es in the T alkeetna Mountains and flows west through the Susi t na Rover lowlands t o the Susitr• River. As Sheep Creek leav es the mo un t aons, a secondary channel fl o ws to Goose Creek. The p ercentage o f wa t e r going to Goose C ree k varies , depending on natural channel shift ing and man -ma de diversio n s at the confluence of the two creeks. The fl ow reg ime is simi lar to Willow Creek (Figures 2 .2 , 2 .3 and 2 .4). The sma ll ao·ea of glacier s in the headwaters will maintain a marginally higher baseflow du o·ing J ul y and August than that at Willow Creek. The M l'ial p ho to ( Fig u o·e A ·16) is :.9, 100 cfs, as the area was not covered i:> the 21 ,100 cfs p hoto g r aph y. At 21 ,100 cfs there is a con tinuous water cou r se in the side channel d ownstream from Sheep Creek (Photo A-8). Backwater in the tributary occurs at mainstem di scharges abo ve 23,01J0 cfs (Pho t o A-8 and Figure A-16). At 5 2 ,000 ds the backwater zone extends approximately 5,000 feet up Sheep Creek. The extent of backwater for three diffe r ent flows at Sunshine are marked in Figure A-16. The effect of with -project f lows will be limited to reduced backwater zones, and will not affect access o r morphologic stability of the tributary mouth . Pink salmo n were observed to spawn just u pstream of the tributary mouth. C hinook , s ockeye, chum and coho spawn i n upstream habitats. A-25 R2 0 '1G -:3 PHOTO A-8 Sheep C r eek (RM 66.1) f lows from right to left. Sheep Creek side channel flows from top to lower left . Photo taken 9/11 /84 , d ischarge a t Sunshine 23,600 ds . I I I I I I I I I I I I I I I I I I I DATE OF PHOTOGRAPHY: AUG . 27th. 1883 :-_.~....,._,_-------SCALE: 1*:600• R&M C O NSULTAN TS, INC. DI SCHARGE ol S U NSHINE : 58,100 cto FIGURE A -16 SHEEP CREEK I I I I I I I I I I I I I I I I I I I R20/1G 44 Coose Creek GoosP Creek orogo nates on the footh ills o f the Tall.eetna Moun t a ons and fl o ws we st through the Susolna ~iver lowlands to the Susotn a Rover I Fog u re A-17 and A-18). The channel starts as Sheep Creek leaves the mo unt aons The percentage o f water enteri ng Coose Creek from Sht'ep C r eek varot>s. de;>ending o n natural channel shifting and man made doversoo n . T he fl ow r egome os somolar to Wi llow C r eek (Figures 2 .2, 2.3 and 2.4 ). Coose Creel. spli ts onto four main chan nels, with two fl owong into the mainst em o f t he Susi t na Rover and two flowing into a side channel (Photo A -9). The sode channel overtops between 20.000 and 23 ,000 cfs, woth the a c tual overtoppo ng flow v arying from year to year due to channel changes ann debris accumulat:ng at the head o f the s ide channel. Wh e n the s ode channel is overto pped, t here is sufficient wate r depth and low \\ater velocoties to ensure fish passage into Goose CrPe k . \'later depths and v e locitoes were measured in the side channel downst ream o f the trobutary mouth when the berm was not overtopped. At c:ross-section A (F og u re A -18) the critical section h ad a water depth of 1 .0 feet , a velocoty o f 4 6 fps and a reach length of 20 feet. Section 8 (Figure A-19) had a c r ot oc al section water depth of 1.2 feet, a velocity of 4 .6 fps and a reac h length o f 20 feet . The d ischarge in the side channel was 39 c fs during t hese measurements . The shallowest wa ter depth , 0.4 feet, was at Sectio n C (Figure A-19). with a water velocity of 0 .9 fps and a reach leng th o f SO feet . During with-project flows, Sunshine flows will exceed 24 .000 cfs 95 percent of the time from June 3rd to September 8th . Pink salmon we re o bserved to spawn near the tributary mouth . Chonook, sockeye, pink, chum and coho salmon spawn in upstream h abitats . Since most of the adult inmigration occurs during the period when the sod e :h~nncl borm is overtopped (June J to :Jer.-te:n.ber 3), tl.e • e b 1,\l!c: t-ho .. L.e o f fi s h passage problems . The slight change in stage with \Yo th ·p o·oot'C t fl ows wi ll sloghtl y alter the backwater in t he channels flo wing into the ma i nstem, but should not severely affect potential ho ld ing areas . The tributary mouth has changed considerably since 1951 due to bedload R~ll lG -l:i lliO\ on g do wn Guose C o·eek and elevating the o ld mou th "ht're ot 0v ons ,, so de chdnnel a t poon t A ( Fo gu re A -21). From poon t A wate o· (lo ws both t o t he north and to t he southwest . T he eve nt which caused the change on t he mou th was pro bably a s torm in upper Sheep Creek basin who c;h caused a c;hannel c h a ng e . diverting most of the water down Coose Creek . PHOTO A-9 Looki n g upstream a t the confluence of Coose Creek and Goose Creek side channel (RM 72 .0). Goose Creek flows from top .-ight t o wards bott om center. The side channel was barely overtopped at 23 ,000 cfs, at Sunshin e o n 9 /11 /84 . I I SUSITNA HYDROELECTRIC PROJECT TRIBUTARY ACCESS STUDY I lOWER SUSITNA RIVER STUDY SITE LOCATION MAP oaT<"' ....,, ••• .,.,, 51:••••.,.., SCALt .•.zooo• St1(( I 0 .-1t OAT( 1 .. r . 14 FIGURE A-17 ! TRIBUTARY ACCESS STUDY STUDY SITE LOCATION MAP FIGURE A-18 I I I I I I I I I I I I I I I I I I I P R£P 4R£0 BY ~.7,---------------- R &M CONSULTANTS, INC. DATE OF PHOTOGRA PHY: SEPT. 1 61 h, 196 3 SCALE: 1' = 500' DISCHA RGE a1 SUNSHINE: 2 1 ,1 OO c ls F IG U RE A-19 PREPARED FQ R . GOOSE CREEK A I I I I I I I I I I I I I I I I I I I P RE P A R E D B Y ~;-:1 --------DATE OF PHOTO GRAP H Y : S E PT . 16 1h. 1983 ~~~---SCALE : 1·=soo • GOOSE CREEK 8 R &M CONSULTANTS, INC. D ISCH A RGE a t SUNSH I NE: 2 1 , 1 00 eta FIG UR E A-20 PRE P A RED FOR I I I I I I I I I I I I I I I I I I I PREPARED BY ~~~~.---------------- R&M CONSUL.TANTS, INC. ·-··· ··--·· ___ ... -.. ··-· D"TE OF PHOT OGR .. PHY: SEPT . 1 6 1h, 1883 SC .. LE: 1': 600' 0 1SC H .. RGE a1 SU N SHINE: 2 1,1 OOcla GOOSE CREEK c FIGURE A-2 1 PREPARED FOA ' . I I I I I I I I I I I I I I I I I I I R20/16 46 Montan~ Creek Montana Creek origi nate s in t he Talkee tn a 1\lvun ta ons • nd flo ws wes t t hrough the Susitna lowland s to the Susotna Ro e r ( Figur A-22). The flow regime is similar t o Will ow Creek ( ig ures 2 .2 . 2 .3 and 2 .·1). Water depths du ri ng 21,100 cf s are sufficient t o a ll o w passage fr ·om t he mainstem to Montana Creek . Depending o n the fish specoes and lofc s t age, water velocit ies within the t robu t ary rna y padoally block fosh passage (Fogure A-23). During the past 30 yea rs t he sandbor s a\ the confluence of Montana Creek and the Suso \na ha e become more vegeta ted and morphologically stable . Howe er. the morphology o f the channel between measurem n t s it es A and B and the confluencP change each ear (Fogure A-23 and Photo A-10 ). At poon t A and B the wate r depth and veloco\y were 1 .8 feet and 3 .1 fps , and 1.1 feet and 2.8 fps , respecto ely . At point C the water depth and veloci t y were 1.3 feet and 7 .1 Ips , while at poi n t D t hey were 1 .1 feet and 3 .2 fp ". •lon t ana Creek h a s a r-e lative ly steep gradient, wi th essen t ia lly no backwater zone at mainstern flows of up to 38 ,000 cfs, and with 600 feet of back wate r a t 52 .000 cfs . The s ide channels enteri ng lvntana Creek from \he north are o ertopped between 38,000 cfs and 52 ,000 cfs . The effect of wilh -pr·oject flows woll be li mited to s lightly reduced backwater zones . and ' ill not affect access or morphologic stabili t y of the tributary mouth . Pink and chum salmon were obsLr ved spawning j ust upstream from the t robu ta ry mouth . Chinook and coho salmon spawn in upstream habrtats . A-33 R2 0/1G 4 7 PHOTO A -10 Montana Creek (RM 77 .0) flows from r i ht to left cen t r . The Susrtna River ma instem flows from upper left t o lowPr left. Ph o to tak n 9 /11 /84, discharge at Sunshine 23 ,600 cfs . LOWER SUSITNA RIVER ALASKA POWER AUTHORITY SUSfTN.t. HYDROELECTRIC PROJECT TRIBUTARY ACCESS STUDY I LOWER SUS!TNA RIVER STUDY SITE LOCATION MAP ""-. ~ , ............ '· s;.:._( :000.. ~("' Qf :• Col ... l 2'~7-4 FIGURE A-22 I I I I I I I I I I I I I I I I I I I PREPARED 8Y------------~~~~~~------------------------------------------------------------------~~~------------------_j ~-------DATE OF PHOTOGRAPHY : SEPT . 181h. 1983 FIGURE A -23 P PAR E D FOR R&M CONSULTANTS, INC. SCALE : ··=soo· MONTANA CREEK G::J&OO~&o§@&®©@ ·-·---·· • .---... _ ..... _. DISCHARGE at SUN SHINE: 21,100cta I I I I I I I I I I I I I I I I I I I R2 0/1G ·18 Rabideux C r eek RabidNIX Cr·e e k or·rgina t~s rn the Susrtna lowlands anc flows s o utheast to the Susi t na River (rigur·e A·2·ll. The flo w r·egime is simdar to the Oeshka River (Figures 2 .2. 2 .3 and 2 .4). At 21 ,100 cfs passage appears feasible . Ther·e is one n~a c h t hat may p ro v ide problems . The bar at t he mou th c h anges s hape yea r t o yea r·, c e pending on the h igh flows from Rabideux Creek ( Figur·e A -25 and Pho to A -11). The confluence with the Susitna River has b een mo r p h o lc.grcally stable since 1951. The effec t of with-pr·ojec t fl ows will b e limit e d t o r·educi ng t h e backwate r· zones a nd will not affect access o r· mo rpho lo gic sta bility o f the tr·ibutary mo uth . Chinook, s ockeye. p i nk. c hum and co ho salmon spawn i n upstr·eam h abitats . A-36 R20/16 49 PHOTO A-11 Looking upstream at Rabideux Creek (RM 83.1). The Susitna River ma instem flows from center right to bottom center. Photo taken 8/31 /84, discharge at Sunshine 38,000 cfs . I I I LOWER SUSITNA RIVER TRIBUTARY ACCESS STUDY STUDY SITE LOCATION MA FIGURE A-24 ~SKA POWER ALmiOBl1:Y susmu. HYDIIOfl.ECTIWC PROJECT LOWER SUSfTNA R1VER OAT( Off ~ SUT II.-) SCM..[ , ... 1000. SH[[f s 01 • ont 1-1 -u I I I I I I I I I I I I I I I I I I I PREPARE D BY ~ D ATE OF P HOTOGRAPHY· S EPT. 181h, 1983 ~ SCALE: t•: 500' ~...:.~ =~~:':!.~_'::'.:::.~~=-OISCHARGf-al SUNSHINE: 21,100eto FIGURE A-25 PR EO FOR : RABIDEUX CREEK I I I I I I I I I I I I I I I I I I I R20/1G 50 Sun s hine Cree k Sunsh rne Cr·eek o ngrna t es rn t h e Susitna River· lowlands and flows south- west to the Susit na Rrve r ( Fig ur·e A -26). The affect of the many lakes in the basin is t o f la tte n o ut the peak flows from rdinfall events and to ma ;ntain a r e latively h ig h e r· basefl ow, as compared to a basin without lakes . At a main>t c m fl ow o f 21 .100 c l the mouth of Sunshine Creek extends d o wn a side c hanne l (from point A to point B , Figure A-27 and A -28) t o Sunsh ine S lo ugh . Our·ing the site visit of September 19, 1984, 1 . 5 fee t was the critical max imum depth in the low water channel from the mai n stem S u sitna Ri ver t o the mo uth o f Sunshine Cree k . The affect of with -pr·o ject flows will Loe to r educe the magnitude of flood flows causing morpho logic changes in Sunshine S lo ugh . The slough would tend to be- come more stable . The ex t e nt of the backwater area may be reduced by with -po·oject flows, b ut this wou ld not affect access conditions . The tributary mouth has been relatively stable since 1951, and s hould not be affected by with -project flows . Pink and chum salmon were observed spawning just upstream of the tributary mouth during 1984 . Chinook, sockeye, pink, chum and coho spawn in the upstream habitats. A-39 SUSITNA HYDROELECTRIC PROJECT TRIBUTARY ACCESS STUDY I LOWER SUSITNA RIVER STUDY SITE LOCATION MA 1 ~.cw,.o;:r....., .... :,.~'. or u DAY( l-1· 1 4 FIGURE A-26 I I I I I I I I I I I I I I I I I I I P REPARE D BY ~ DATE OF PHOT OGRAPHY: SEPT. 181h, 1983 R&M CONSULTANTS , INC. SCAl E: 1'= S OD' ·-·----"' .... __ .. _-u .. -• DISCHARGE a l S UNS H INE :2 1 ,100 c:ta SUNSHINE CREEK A FIGURE A -2 7 PREPARED FOR : [}{]£00~& 0 §®&~©@ SUSITN•\ JOINT Vf N TU R E I I I I I I I I I I I I I I I I I P REPARE 0 BY ~&M CONSULTANTS, INC. ·-·---~· -·--·· __ ....... _ DATE OF PHOTOGRAPHY: S EPT. 18th, 1 G83 SCALE: 1': 500' DISCHARGE ot SUN SHINE; 2 1,1 OOch SUNSHINE CREEK 8 FIGURE A-28 PREPARED F OR ' ,.,,, /')1 ';1. !I;IUR! I I I I I I I I I I I I I I I I I I r H~U 16 :.1 Borch Crul.. Borch C red. o rogona tes in the Susitna River lowl~nds ~nd flows southwest t o the Sus otn a Rover (Figure A-26 and A -29). The affect of t he many l~kes on the b as on , especially Fish Lake, is to flatten out the peak flows from raonfall events and to maintain a relative high baseflow, u compared to a bas on woth o ut lakes . Birch Creek (Figure A-30) flows into Birch CrPc>k Slough, which flows into one of the mainstem channels (Photo A-12). Borch Cre-ek S lou3h has suffo cient water for fish access ~t 21 ,100 cfs . Th<> t!>t~nt o f the backwater area in Birch Cruk Slough may be reduced at '"th-proJect flows, but this would not affect access conditions . Betwl'!'n 195 1 and 197-1 an island between the mouth of Bi rch Creek Slough and the maons t cm Susotn~ has eroded aw~y . Since 1974 the tributary mouth has been relatively stable and should not be affected b y \\l lh -pro ject fl ows. Pi nk salmon were observed spawning near the mouth of Borch Creek and on Borch Creek Slough below the confluence in 1984 . C h i nook, sockeye, pink, chum and coho ulmon spawn in upstream h abitats . A-43 R20 16 ~>2 PHOTO A-12 Looking upstream wi th Birch Creek S lough (RM 89.2) flowing from center right t o center . Photo taken 9 /11 /84, discha rge at Sunshine 23,600 cfs . ~ ~ ~ • •' •' I I I I I TR IBUT ARY ACC ESS STUD Y STUDY SITE LOCATION MAP LOWER SUSITNA RIVER OAT( 01 ~O T ~GAAPH'f S(PT 16,1Hl SCAt.( 1 •• 2000• =~~T ~~'~:.u l l_--------------------------------------------------------------------------_l~F~IG~U~R~E~A~-2~9:_ ________ _L ________ L-------~ I I I I I I I I I I I I I I I .. .-·' . ;. ) . ', -.. R&M CONSULTANTS, INC. -· I I . ' ,. . ,(" >; ./ DATE OF PHOTOGRAPHY: SEPT. 181h, 1983 SCALE: 1' = 500' DISCHARGE at SUNSHINE: 2 1,1 OOcls BIRCH CREEK G{l£00~& 0 ~00&~©@ SUSITNA JOINT Vl NTUR£ • • • • • I I I I I I I I I I I R20/16 ~ Tr~p.,.r CrHk T r~pfX'r Creek orogonates on the Susitna lowlands and flows southl.'~s t to the Susot na Rover (Figure A·29). The flow regome os somol~r to that of the Oeshb Rover. but hu a s~ller magnitude of flow (Fogurl.'s 2 2. 2 3 and 2 4) At 21 .100 ds. Tr~pper Creek utends down a sode channel to the maonstM~ Susotna Rover. The channel is transoto ry . woth ots shape ~nd water depth varyong from yeu to year, dependong on the ~gnotude of the peak flow that yur. Pho to A-13 shows how the c hannel changed sh~pe from 1!183 to 1984 (Figure A -31). Duri ng t he field visot o f Septl.'mbcr 18. 1984. the channel s hape wn doHerent from that s h own In the ae roa l pho t o . Measured c r ito cal maxomum depths varied between 0 4 a nd 0 .6 feet. At 21 .100 ch f osh were able to access both Trapper Creek a nd the AOFt.G IFIM Trllpper C r eek study site (Figure A-31). S ince 1951 the ~i n channel of the Susotna Rover has shi fted from the west s ode to t he eut s ode o f the flood p laon , increasing the length of the sode channel 'rom the mouth of Trapper Creek to the Susitna River. The effect of woth ·proJecl flows wolf be to reduce the magnitude of the flood flows causong morphologoc ch~nges on the channel downslrum of Trapper Creek The ch~nnel would tend to become relat ively more suble and the vegeutoon may encroach o n the channel . The backwater ~ones wolf be reduced by woth ·project flows , but this should not affect ~ess condoloons. P ink ~nd chum salmon were observed spawning just upstream of the tr ibu t~ry mouth durong 1984. Chinook, sockeye, p ink, chum and coho ulmon sp~wn in upstream habitats . A -46 R20 l G !'>~ PHOTO A -13 Loo k ing upstream at Trapper Creek Side Channel AOF&G IFIM Study Site, T rapper Creek (RM 91 .5) flows from center left t o bottom cent e r . Photo take n 8 /3 1/84 , discharge a t Sunshine 38,000 cfs . • I PREPARED BY · ~ R&M CONSULTANTS, INC. DATE OF PHOTOGRAPHY: SEPT. 1 Slh, 11183 SCALE: 1': 500' DISCHARGE al SUNSHINE: 2 1 , 1 OOcfa FIGURE A-31 PREPARED FOR : TRAPPER CREEK SUS II>;_.\ JOI'>T VtrHuRE