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HomeMy WebLinkAboutAPA2971k4YDROELECTRIC PROJECT FEDERAL ENERBV REGULATORY COMM98S18W PROJECT Nos SP $4 PREPARED BY DRAFT REPORT UNDER CONTWAG'T TO BARZA"EBA8G0 DECEMBER I ~86 SUSDTNA JOINT VENTURE DOCUMENT Ns, 2Q7q SUSITNA HYDROELECTRIC PROJECT RESPONSE OF PBOTOSPNTHETICALLY ACTIVE MDaEATION AT WE EUPHBTIC SURFACE TO UTERED "IE"Um$D%W Am PLOW REGIMES OF mE MIDDLE SUSPTNA RIVER Report by Triheg and Asscciatss Gregory S. Reub Robert C, Wilkinssn Robert G, Elder Under Contract to Warza-Ebasco Susitna Joint Venture Prepared for Alaska Power Authority Draf :- Report December 20, 1985 NOTICE ANY QUESTXOHS OW 66MHEgBTS COPIICBRNIEHG TEXS RSPORT SBOmD BB DIREaED TO THE WLASM POWER AUWORHTY SUSHTBW PWOJBLT OFFHCB RESPONSE OF EUPWTI C SURFAE MEA TO CHANGES B N DISGWMGE MD TU~gDl~0.eobBeeCrOeee~eQ,eO~eOe~m~~e~ee~e~~7 arimsr 4 producPIvI-ty is impwl-ant to the prduc$ion oQ food orgarilsms for J~ver)!!~ salmonids. Primary produdlvlSy in sfreams and rivers is dependent on the ab i l tl-y of sun! ight to reach the streambed in suf f !c!znt amounts Po suppor'r photosynthesis. Algal production is rsls-i-ed Po the tntensl@ of I lgkt as we! l as depth of pnefratlon (Hynes 1979). Factors affecting I lght penetration -to streambed surfaces w l l l also affect primary prductlvl ty (Ll oyd 19851, Two Importanl- factors *hat i nf l uance $he amount of l fght reach lng the streambed are depth, as ~egu l ated by streamf l ow, and turb l d i ty. I t f ol l ows, therefore, that de*erm lnl ng the effects of streamf low and 'l-urbi dl ty on i igh% penetraOIon can bs used to estimate their ef Iects on pr lmary prducfton. The suphot! c zone is def lned as that port! on of the submerged stream~ed where l lght intensity is greater than one perant of the i lght intensity at the water surface, The lower B fmilt 08. ?his zone Is termed %he c~rnpensation depth The signlflcance of the compsnsal-ion depth is that I-t approxi mates the pol nt where energy f txation by al gal photosynl-hesi s Is equal to the organtsmsf own rezplratory requlrenaeslls (Moss 19801, Thus, compensatfon depth can be used as the lower boundary in The relatlonshlp between turbldl ty and depth of l lght penetration. The I lm l* of photosynthetical l y effsctlvs penePratian mlist be dsf tned fhrough f lsl d measurements of i lght ssttenuatlon. "BP this paper presenfs prel $minary resul%s from a slmula.klan model PhaeF w<;s developed $0 forecast Phe response of pRotssynthe?ical ! y asdrive $-ad i ation (PAR) at the euphoti c zone to ckainges I n ma I ns$am d I scharge and furbidit-y. Themodel was applledat- elghP s$udy sites locaPed in -?Re middle Susl%na River. Results from site-specific and $!me series analyses are used te, ref lne the suphotlc surface area reslponss mode! in.l-roduced in Apr l l 1985 (Reub et a!. 1985). One purpose of th Is *@chnlcal memo is Po demonstrate the utility of the model for evaluating the indl uence of al tared streamf lows and turbid[ ties on pr lmary pfmdrec%lon in the middle Sus itna River. Anomsher purpose i r. to prcw i de spa lnftlal forecasf of changes in the amount of llghP energy available for photosynthesis on a seasonal basis as a result of proJect constrar& ion and operation. The euphotlc surface area response model esPl mates the amount of BAR that reaches ?he euphotlc surface area a? a cert.aln tlme. This Is accompl lshed by determining the amount of PAR that reaches the submerged streambed at a certain depth within the compensatlon depth and mul t l pl y ing that amount of energy ti mes the surf ace area found at that depth. This gives $he total energy received at depqh, whtch ! s then summed for al l depths down to the compensation depth. This surncatlon represents the total amount of PAR ava l l ab l e for an srlll re sli te. Tha model can be expressed in mathemat-lcal terms by the fol low ing basic quaBfon: ~h~re Et = Gross Rafe of Energy Inp& fo Euphottc Surface Area a0 Time in sinstelns 1, = Areal h%e of Energy l nplrt to Surface Area at- DspSh z (sfnstelns/sq ft) A, = Surface Area at Depth z (fG1 Tile steps necessary to numerical l y dsf i ne the parameters In Phs above quation are shown in Figure 1. Solar insolaiisn, Purbldlty regimes and malnsPern d ischarge (boxes on l eft of f l ow dl agram) vary sn a seasonal basis and are conslderd the "dr lv lng war lablssw in th ls model. Sol sr Insola$lon, or the l lght available a1 the water surface, and tut-bldlty eleferm lne the amount of i ight that is exti ngu i shed as it passes through the wePsk COI umn. Mainstem discharge detsrm lnes the depth of wafer and $he amount of wet%ed surface area within a slge, The euphotic surface area response model uses stream cross sectlon and stage-d 1 seharge data (1 FGI hydrau l ic model sl to apportion the entl re wetted surface area of a study site into incremental depths as a function of discharge. Comgensatlon depth, influenced by turbidity, is used to def ine which depths are w i th i n the euphotlc zone. Thil s model than forecasts stream f low a~d turb id i trdepsndent responss curves lor the amount of PAR transrnltPed through the water column. The model does not forecast actual photosynthetic rates. 14 is assumed $ha$ pr lrnary lnsPream Flow Group, now known as lnstream Flow and AquaPlc Systants Group (Milhouse e.P al. 1984). PER DEPTH REGIMES DEPTH ZONE AREA8 AND BY EUPNOTIC I SURFACE AREA as3 - --- CELL CROSS 88 Figure 1 . A flow diagram of Phe basic components used in The eupkol-lc surface area respon node!. product [ OR an! y oscurs on the submerged sfreambsd bePtd@@n *the 8s edge and a poln-t botlnded by ths compensation dep'h. Because J-ia is model is InPended for river lne appl lca*toss, primary produc$ic~n is no* ~lssunngd Po occur bg ,a6 Ith % n The wa?er col umn as BP waul d were D ak~s OY 8~l-~i3r 18% be ! ng evaI uatad. The fsl l ow i ng methods sect l on prav 1 dss ana l y Bi ca I descriptions of Phe model components and prssen8s actual input data used Tn fhe modele - amsun* cf PAR svaiiabie io the surface of the wa-l-er depends on The letltude of the river basin, time of year, basin topography, and p~eva8I ing metewologrca! condiQlons. Only a fea stetd!@s hi2ve measured solar radlatlon inputs in southcentral Alaska. Cof f in (1984) esl l ec8e3d $wo years of solar radlatlon daOa at various ixalions near the Slasltna River, isnd Branton et al. (1972) col l ected 11 years of sol ar radla*lon data at Palmar, Alaska. Thls analysis usas solar radlaflcrn deBa co:lected over a two-year perlod at 81g Lake, Alaska by Rowe (1985). The Big Lake data provide PAR values at the lake surface "rhroughou? the year (Tab! s 11. Tabla 1. EstlmaOed mean monthly ghotosynfhetlcally acPivs radlaPlon (PAR) In etnstelns per square foot. MJHm AVERAGE PAR^ AVERAGE PARI JNUMY FEBNMY MARCH APR l L MY JUNE Estimated for 1984 and 1985 at 819 Lake, Alaska Source: Tlmothy G. RWB (1985) The amo~int of PAR aval l able -to the surface 05 the water daperads on *he EaTBhudta of the river basin, time of year, basin topography, and prevailing mefeorolqlcal condltlonr Only a fe~ studies have measured solar- radlatlon lnpuPs in southosntrai Alaska. Coffin t1984) col l ec.t.ed *%fa years of sol ar radiation data at various l ocatlons near the Susl"rnro River, and Branton el- ale (13721 col lected 11 years of sol rrr ssdlaflcpn daPa aP Paliaer, Alaska. This analysis uses solar radiation daBa c~l Iselred over a tw-year period at Blg Lake, Alaska by Rowe (19851. The BIg hake data provide PAR values at the lake surface throughout $he year (Table 11, Table 1. EstlmaPed mean monthly photosynthetically active radlaS.lon (PAR) In efnstelns per square fwt. JWUMY FEBWMV MARCH APR l k MAY JUNE I Estimated for 1984 and 1985 a* Big Lake, Alaska Source: Timothy 6. Rowe (1985) 14Iddle Susltna River turhld%$y levels under natural condSPlons a"t Gold Creak range Prom 1 to 1,000 NIU (nephal omel-rlc turbldlBy ranlts) w lfh av@ra.ige summer turb l d l ties of approxi matei y 200 NIU and w l kh w l nter Surbidi?ier; of less than 5 HTU (Trlhey and Assaclal.ss el ai. 19851. kllth-project tlsrbldlPy levels are expected to be less variable during the year w l Th l ncreascts over natural l-urb i d l t l ns expected i n the w l nter and decreases expected during the summer months. Several proJect documents were rev lewsd to arr lvo at a natural turbid! ty reg i me that represenSs month l y val ues for the era? l re season (Acres American Inca 1982; Alaska Deparl-men* sf Fish and Game 1982, 1983a, 3 383b; Al aska Power Author lty 19851. Figure 2 i l lustrates the esti maP-ed natural turbidity values used in the tine series analysis. These values are des-lved by draw lng a smooth curve through data poi nts col l ected during -khs 1983 open water season at Goid Creel; Camp, Rlver M l le (RM) 136.8, and the Tslksefna Fishwheal. RM 103.0 (Estes e-l- el. 1984). Estlma*es of w lfh-proJect turbld l ty reg lmes were de$erm lnsd by Clarzb- Ebasco Susltna Joint Venture (Alaska Pover Authority 1985). Thelr analysis uses an NTUITSS (toPal suspended sediment) rat.lo of 2:1 $0 forecast turbid f ties for w i th-project cond i $ions (Tab I e 21, Several sfudles i dent.! fy the relationship between TSS and 9~rbidit.y~ Typical re! af lonsh ips developed In Al askan i entlc ( iakef env l ronments assocl atsd wi%h glaciated drainages include those at Eklcltna Lake (R d N Consul tan-[.% 19821, Grad l ey Lake (Otf Watsr Eng l neers I nc, 1981 1 and Tustumena Lake (Scoet.J. 1982). These st'ud lies sugges* NTU/TSS ra*los of lolk@@tno Fl~hwhesl (RM 103.0) Gold Creek Camp i RM 136.8 1 m-OQBerpf.i Egtimated Tkgrb!Qrti@~ Used in Model MONTHS Figure 2. AcTuaI turbidity values at Taikesfna Fishwheel (RM 103.0) and Gold Creek Camp (RM 36.8) wlf-h estimated turblditle~ used in this model, apprcwima%slgr 2:l or greater, This convsrs!on fac4or r-esu!trj in a mlnimai turbidity estimate (Alaska Power Aul-hority 19851, although I* rec~gnlzed $hat 3he actual ra9;o of NTU/YSS may vary consldsrabl y as @vi dencod by the range of val ues discussed in the above references. FOP. the purposes of Qur analysis on[ y two operational scenar los, SIage I and S$age I I I, were sval uated to l i l ustrate the range of w lPh-proQect csnd i t l ons that are expected to occur. Table 2. EsOlmsted manthly average turbiditles (NTU) for naPurial and w i th-proJecP scenar los. NATURAL! STAGE j2 STAGE 111~ NTUdTSS NTU6TS SS RAT00 2:l RATIO 2:1 dW&JMY FEBRUMY MARCH APR l L MY JUNE 3 UBY AmUST StrWTEM8ER OCTmER NOVOBER DEEWER Estimated from data col lected dur lng the open water season (Estes st a1, 19841, Es-t.lma$ed by converting TSS proJ@ctions %to NTU unl ts (Wl aska Power authority 1985). Since fhe rale of l ight exl-lnctlon and compensa$lon depPh must be caisulatsd o%Jsr $he range of turbldi ty l eve! s analyzed, a reliaBfonshlp between l ight exglncf Ion (k) and turbid! ty was generated using Sus1*f1a - spec 1 f lc data col l ected dur lng Ahgost and SspIember 1985. To*! verttcal l lght exalnctlon cosff lclent measurements Mere made using $he meThodology described by Van Nieuwanhyse (1983). Twenty measuremeruts of compeosaBlor8 depth were made near the coni l uence of the Sus! S-na, Chml itna and Tal keetna r ivers under turbid i *les rang lng from 5 4-0 179 Iflkl, high* eactlnction csaf'lclents were p!cttd against. turbid!% ard *he relattonshlp was described by l lnear regresslcn anal ysls (Figure 3). Figure3. Linear regressloo of Susitna-specific light. exPlnctlon coefflclenPs versus turbldlty, Tho ~-@Ia?BonsRlp between compensation dep$h and turbid fty fop %he Susltaaa River Is described by the equaPion Z, = 4,68/0.021(NTU)+0.25 QFBgure 41, This equal-ion was formulafe@ by !ncorpora-i.lng the regrassion quatl on present4 In Figure 3 inl-o the der 8vatioo1 descr i bed by Van Nlsuwenhuyse (19841, TURBIDITY [NTU'S) 480 500 888 Figure 4. Relation*ip between turbidity and compansatlon depth for the Susl$wa River, msnl.hly streamflows ware used in this analysis. Average weekly atalnstem flows far $o?h nafural and w IPh-projecP csnd i tions were d@v@Poped by the Harza Ebaseo SuslPne Joint VenPut-e based on 34 years of- record at Gol d Crssk (Al aska Power Author! ty 19851, These f l ow5 were averaged Po obtain the month! y val ues tn Tab1 a 3. On! y sPreamf lows fop Stage I and SPage I I I operation scenat-los were used to eval uate w b 3%- p: oJec9 c~nditions. Table 3, Estimated mean month! y flows (cf s) for natural and w ith- project scanar i! os. M8NW NATURAL ST&E ID STAGE 111' JMUMY FEBRUMY MMCH AmIL MAY 3 UNE 4 ULY AUGUST SEPEWER @ER NVdEmER DECEMBER Source: Al aska Power Author [ty ( 1985 I. 1 These values represent an estlma$ed early SPage I I I flow scenario. Sqfraam chansael ge0me.l-ry in:' l uences the respons of $he eupho8.l c surface area Po changes in discharge (water surface el evatlon) and turbldi ty. Si4-a-e geometry was determined using the IFi cross sect-lans surveyed for The mlddle Susrtna River model log studies. These cross sectlons were used to dsscr f be the i aOeral d 9 s%r 8 but l on of streambed el eve%lon% Cel I depth was determined using the water surface elevation (WSEL) correspotad l ng to a g i ven d l scharge and the sPreambad el evatisns al stag %Re surveyed cross section. The kiSEL% sued in this analysis were forecast us l ng hydrau l ic model s and assocla$ed ra9ing curve squations (Estes et a!. 'i984, and W l l l lard et a!. 19851, A rslatlonshfp between WSEb and discharge was esf-abl lshed for each transect, The snaxlmum resolution of $ha depth calculations is a function of ?he cel l sfza Point measurements of depth more accurate! y approxi mate the average depth of the cel l s as cel l s lze i s reduced. Depths sssocl ated u ith one-foot cel I n ldths were necessary for good rasol utlon at h lgR turbldlties (small incrsmelnts of depth). This cell resoluOlon was ach leved by l [near interpol atlon between surveyed streambed el evations on the C~OSS SBC~~O~S, The reach length represented by a particular cross section was d@*errrr f ned from lnspectlon of aer i al phoPography, long ll-ud l no! streambed prof l l es and f lei d notes. In those l nstances where right and l ef? streambank distances between sdJacent cross sect ions d l f fered, reach lengl-Rs for indlvldual cells were determlnad by I lnr~ar tnterpoleti~n using -the right and l efB bank d !stances, Gel l surfaca area is the area 39; ?"he r=w;.I-angle defl~led by ~nuitipl led $y mean reach lengi%h, *Q*B~ l Ight energy aval lable fo the euphatlc surface area is calculsnPed in fhrae s$sps. First, the compnsallon depth is defined as a func9ion of turbldlty. For each cell possesslag a dep*h equal toor less "raan Phe compnsati~n deplh, the cel l area is calculafsd. The sum of *hesa areas defines the euphoPic surface area. The model uses the decay functlsn describing l lght attenuation r lth depth to deta -m ine the amou~t of i lgh? energy reach lng the streambed n l th in each ce l l. The Potal l Eght energy reaching the euphotlc surface is calculated by skrmmln$ the l ight energies at the streambed surface for a1 l the cel is* These calculations are repeated for each combination of flow and aurbldlty being evaluated. Stream channel gemetry fnf l uancas the response of euphoPlc surf ace area to changes fn discharge and turbidity. It is therefwe f mpwtant *ha8 cross sectional data used in the model represent typical middle SuslPna Rlver habitat types that are expected to be af fecl.ed by all-ered dlscherge and turbidity levels, Six aaJor hablta? 3ypss have been IdenPIPled 117 Pha middie Slasltna Ri~lar (hDir&G 19aaI. 9.8 i buf ary, i.r lbuPaq mouth, and up L and s l ~.~gh ha$ F8ats are normal l y clear and not exgscfed to become turbid as a resui % of ?II@ cons8ruct l on and opesatl on of $he proposed Sus i tnna hydroel ectr lc pjwojesds However, l-hs natural turbldl%y regimes 19lthln malns%sm, side channel, end side slough habitats are expected to be al *eyedPd. A three- s8ep process was used ts select sigh* model sites that represen* mainstem, side channel, and side slough habitats. In1fIaI l y, proJect hydra1 og lsts and b lol og lsts were consul ted. Aar i al photography was rev %eb$ed -1-0 prov Ide a quick assessment of the response of we$*& surf ace area Po mainstem discharge at various slJ.ss and to identi fy vhe-l-her these slPes rn ight transform from Turbid to clearwater areas as mains*em discharge decl ines. Wydraul lc and morphologlc attrl butes ldentlf led by Waserude e-t al. (1985) to classify sites into representative groups were used as ind lators of @representativeness"? Tabie 4 describes the hydrologic and morphologlc charactsristfcs of the 10 retpresentativa groups developed by Aaseruds et a!. (1985). Also shown So the r lghi- of the def int tlsns are the model sites chosera for $his analysis. Representative groups w lth slm i l ar channel geometry and mwgholqlc attributes are represent4 by the same model or combination of models ( lee., groups i l l and V I I I, V and \I I, IX and XI. However, model res~I ts have not been extrapol ated to the rn iddla Suslt.na River in proport !on to the surface areas of the various representat lve groups. Upland sloughs (Group I) are not eqetcted to be affecl-ed by the proJect and Thus are act lncluded in the analysis. Tabas 4, Primary hydrologic, hydraulic and msrphoiogic characTsds%lcs of aepisswfat-lve groups 1&w$if!ec% for $he m!ddBs JusE%na R&vere Predomilnantly upland sloughs. The spaciflc areas comprlslng PhIs ProJect group are highly stable due to the persistence of non-breached Affec* condl-$lsns gl,e., possess high brea~hlgag flows), Speclflc area hy drau I I cs are chaisctgr !zed by pooled c B ear ~a-$@e w I %R vsl oc; B $1 es frequently near 0.0 fgs and dep%hs greaOer than 13 .fT, Pools aps csmasnly wnected by short reffie% where v@l~HOBes are less an 1.0 Bps and depths are I sss than 03 ft, Thls group lncl udes spec1 f lc areas commonly referred to as slde 1Z6*OR 58 ougha The59 s l tes are character lzed by reiat HveB y h lgh breach f ng i lows 019,500 cfs), cf ear a~dater caused by upwel l Sng graaundwa-%@r, and large channel Isng"rtew ld%dth raQ10s 4>15:4 1. Intermediate breaching flows and relat!~ely broad channel sections 1280@1). typify Ph8 S~BC~~IC areas within OhIs r@presentaQ%ve group, These sites are sBde channels which trawsfwm Owts side sloughs a$ Mainstem discharges renglng from 8,200 to 16,000 cfs. Lower breaching f l sus and sma! lsr length to v ldth ratios d %stl ngu lsh these s b tes Pram tho% 1 n Group I 4. klpwsl I lng groundwater Is presnt. Spec I f ic areas i n this group are s l de channel s that are breached sl 112.6L low discharges and possess intermediate mean reach velocltles (2.0 to 131~7L 5.0 fps) at a melns.9.m discharge of approx!mine.$sly 10,8900 cfs, Thls group includes nalnstam and side channel shoal areas which 136.3R transform to clear water side sloughs as mainsfem flows recede. (Frm tli) Traanrformatlsns general l y occur a0 moderate to h Bgh breach lag dB schargas, Thls group is slm l lar to the preceding one in *hat the habl tat 136a3R character of the specific areas is dom InaQed by chawne! morph~tiogy. These slbes are gr PrnarO l y sverf low channel s thaB paral !el +he sdJacew8 mafnstem. usual lgr separa.$ed by a sparsely vegetaQed grave! bare hipwe! l !ng groundwater may or may not be presenf, Habitat transfsrma't8sns w !thin %his group are variable bth in Qpe and timing of mcurrence. These speciffc areas are typical By sOde channels whfch breach at 119*2R variable ye% falriy %ow mainstem Qlscharges and exhi$!$ a characterls%ic rlffls/pssl sequence. Pools are frsquenPly Barge backwater areas near The mouth sf The sltes, The spsci f I& areas In this group Osnd to dewater a? re! aPf we$ y high 12(30BR ma instem a( lscharges. Ths dl rect !ow of 8 1 ow at the head sf these 1 11 B channels tends to deviate sharply (>a8 degrees) from The adjacent maBnstepn. Model lng s l %es from Groups 1 8 and B B I possess lng ra~spr@~enta%I YG post-breach 9 ng hydrau b %C charxter istlcs are used to model the% specific areas. This group conslsts of malnstem and slde channels. Including 147.1L l X Indistinct ( I.@, shoal 1 areas. character !zed by low breaching 101.5L discharges. Speclf lc areas l-end to slther reteln thelr habltat type characfer- w tran~fwm frm fndlst8ncT 4-0 d8sTYnct channel sD Large mainstem shoals and the narg!ns of malns).sm channels which show 147.1 L signs ef upwe/ 1 Ing are included %n PRls repres8n%ative group. 101 3% IFrm 1x1 Source: Aase~ude et el, 1985 An B d I ustraCl ve sxamy ii e of supho?i c surf ace area response to var l at ions Fn$urbldlfy and flow is presented as Figuro5. Two types of channel yesmetry are used to demonstrate how the auphotic surface area responds $0 changes in water surface elevation (depth) and Po turbidity ac~wlpensatlon dep+h). The top two i l l ustratIons are, of a 'typical str@a@jb@d cross sscT%ron (transect 31 a$ Sl de Channel dA aP -two stream C lows%, Water surf ace elevation fw $he same sacearn f Bows are shown fw a 4yptcal cross secglon a? Fat Canoe i s l and (Transect 5) In the bo88om Two i8 lustration% Each ll lustratlon is divided in ha! F and the right end i eft portions of the i l l ustratlon are assigned d l fterent *urb t d i ty val uss. Compensation depths corresponding to these turbidity val ues are Indicated, and the w idth of the euphotlc surface area (shown by cross Ra*cRlng) Is approximated by the wldth of the overlying wafer surfacs. Side Channel 6A, representing broad shal low side channels, has a maximum dsp*h 05 about 3.2 feet at 10,000 cfs and 5.6 feet at 25,000 cfs. In contrast, sil tes such as Fat Canoe l s l and w l th a wel l- lncl sed, steep- s! ded channel have less var l atlon in sireambed el evatlons. Compnsa-tlon depths 4w the turbidity lcveis used in this i l lustration are 35 feet. for 50 NYU end 1.0 fodt for 200 NTU. Bn comparatively broad and shal low channels such as the Side Channel 6A site, relatively smal l changes in Turbidity or flow can have a dramaPlc effect on Phe size of $he euphotfc surface area. When the flow drops from 25,000 cfs to 10,000 cfs at 50 NTU, the w ldth of *he euph~*!c surface area I~C~~BSBS $8 percent in tR is sxampl a Slm I larl y, a* stream I 200 NTU I I 1 I WSEC a$ 25,000 cfs &a 4x1 aw 543 DISTANCE FROM LEFT BAN HEAO PIN ffTl M t cfs - i - rU2 L - 822.5 P 819 P- cr 817.5 > WSEL at df6 25,808 c f's tLI PL1 eid.5 EUPMBTIIC SURFACE AREA 3 Cr 8121 C COMPENSATION BE PTH @if .5 9% 8 H QO 90 1PO I% 11890 210 240 479 a l cfs 4:7 .^IS- . r -7 C M &O 93 I?? is;? !i: ii:' 24C ;I,^ 303 Figure 5. NypothetlcaI II Iustlpaffon of Phs affects ad: turbidity, discharge, and channel gsomeargr on suphoflc surface area re5pn"Se 'i! ol?s near l0,QQO cf s e change in .$urb!dify from 200 to 50 BdTU rssu!:-s a 75 percent increase in the euphotic s4~rf ace area, Bh is sensl8lvif.y =to iurbldlty and s$ream flow is due -to relatively broad, shal low areas (riffles, shoals and channel bol-*ms) bslng found if* Phis sl*ae, By reducing sPrecim flow from 25,006 $0 10,000 cfs aP 50 NTU at the Fa? Cawon island site, approximately a 10 per.-can* change in fhe w ldth of the euphoti c surf ace area is observed. Al stream f l ows near 10,000 cf s, a change in $urb ld iPy from 200 to 50 NTU locreases 8ha w l dth auphotlc surface area by 328 percent. This sensitivity to turbidity but insansltlvlty to streamflow Is attrlbutabie to the steep gradient shwel lnes and E nc tsed nature of the cross sect lonal geomefl-y. B@G~US@ sf the influence of channel geometry on eupho$ic SUT~~C@ area, 'tkre m~del was appl ied at eight locations on The m %ddle Saasl*na Riv@re bippl %@a*ton of ?Re model at each aiPe is discussed separa?Fsl y. Firs*, 1 *@ charrsct-sr lstl cs *ha$ lnf l slence *ha euphotic surf ace area response or@ descrl bed. Nex*, a f am l l y of l l ght energy response curves % s presented for slx turbid il.y val ues from 10 to 800 NTU and a range of mainsaleso discharges betwean 5,000 and 35,000 cf s. A PAR val ue of 50 elnstelns per square foot was used to defermine the fam ll y of sesi3onss curves fw each slta Final l y, annual response curves are presented for PRe slte uslng seasonal sol ar insol atlon, tprbldl ties and sl-reamf lows few both natural and Pwo w ith-proJect scenar lose The seasonal vaf ues for 9aclj var lab1 e used in the tl me ser les anel ysl s are presented in *Re mePhods sect ton, Tho tlms serles analysis curves for natural conditions include only the open water season (May through October). W l th-proJect curves are presented for the enPlre year; however, they do no$ incorporate any effects of ice and snow cover. For $his reason, the d iscussion of ant id pated proJect ef fsrts on ava l l abl e l lght energy a* the supha9lc surface is general l y li lm i fed to ihe open water season. Several factors suggest *ha* I lght i ntensi t.y beneath an ice and snow @aver is no? biologically slgnlflcant at this latitude. Two Impwtan* f actars are the seasonal redud l on in PAR dur i ng the w inter months and .the ref l @c.$lve ef feet of the snow and i ce cover on l rscom 4 ng i I gR*@ RWW~ 649851 campared the hourly PAR at- Big bake, Alaska far $he so arn@r so% s*%c@ (Ju~e 31 1 and wIn-$.sr ssoJs%%ce (December 211, $49 surflm@r s~ls*lce, Bbs lake received 558 Einstelns pr square me9er during *he 20 hours of day ll 83ht, whereas the s 9 x hours of day l lgh% aQ *Re, w l l~fer solsPBce provided only 0.9 Einstelns pea square mete~a Rowe aPsca found a majw sf l f ference between ref l wt l on coef f lc l snts $e~'w esn su:nmer and w lo-tor. During summer about f Eve to *e'en percsn$ of the sol ak rad!dtBlon !@as ref i ected, bul- I n the w l nter from 85 to 95 percenP was ref l esBed. These results agree wl$h studies on reflection by Roulet and Adams (1984) and Chow, ed. (196.41. Fa* Canoe represents typical malnstsm hablta*. This site and the following slfe (Whiskers West) are ass~ciated with Re~resenPatlve Groups IX and X (refer to Tab! e 4). The channel a-t. Fat Canoe i s approxi ma*@! y 820 feat wide throughout its length. The entire left bank is near vertical ; the r lght bank has a steep to moderate grad l en*. An exposd cobble shore! inair extends the ful 1 length of the right bank (approximate! y 2,070 feet). The breach irbg flow for th is site is I ess ?ban 5,000 cfs, Therefore, it wnveys turbid matnstesn water throughout the open wa?er season. The l lght ensrgy sval l able at the euphoPlc surface (PAR curves) show l l ttl e var lation To changes in flow (Fl gure 6A). This can be expl alned by the narrors n l dth of the euphotic zone along the shore! I nes and Ths csnstanf steep side slops of the lnclssd channel. The most stgnlflcaslll changes in l lght ensrgy (PAR) are assac l ated M ltR changes in Y CANOE ISLAND MAIMSTEM DISCHARGE (c f s JAN FEl #4R APR WAY JldN JbiL AUG SEP OCT tifW OEC MONTHS Figure 6. The, rsspnw af l lght energy sval l able to the supho$lc surf race area for (81 turbid lty curves and (B) fime series curves 8% Fa? Canoe I s % and -im~rbldlf=8es, which dfrectjy affec$. compensaPlon dep%h, Be8ween 5,00Q cf-5 awd 8,000 cf s, turbid i l-l es l ess d-ban 100 NThl resu 1 % I n descend l ~g curites, This is a$trlbutable to $he sl lgh* Infl uerace of i rrqu l ar B t! ss i n stream prof i : a F'B gur~ 68 i i ! ustrates *he tl me ser !as rlespons of' aval l abl o I Ight energy (PAR) at tha Frat Canoe i sl and s lta The AIQS* sl gn l f i cant d l Bdsrence be*~een natural ar,d w ith-prcjec9 "rends sccurs dur lng late summer and fa1 I (Ssptembar, October). Energy Inpu* to the system during this time 1% sign l f lcantl y higher under *he, natural scenar la This is a large deep side channel slmflar to That of Fat Canoe island that also represents mainstem habitat at flows above 10,600 cfs. Be! ow 8 9,666 cf s th ls s l ts represenOs s l de channel hab i tat bul rema l ns relatively deep. The left bank Is steep, and the right bank has a mdera*e slop. An exposed gravel bar exists at low flows. The study site is approximately 3,200 feel- long and 362 feet wide, with a surface area of 27 xres at 23,000 cf s and 21 xres al- 10,600 cfs. The Whiskers Wesf- side channel conveys approximately 30 peran* of tho total malnstam discharge and Oherefore remalns a relatively large channel even at low flows. The PAR response curves, l lke 'I-hose i i lustratad for Fa? Canoe is! and, are general l y ira+@nsiPlv@ Po varia-bions in streamf low (Figure 7A). The anomaly in *he PBR response curves b6ahsen 23,008 ilnd 30,000 cfs ref lscts $Re inundaPIon al a shoal MAINSTEM DISCHARGE 4414 F WAR QPA #BY &N Ah AU6 SEP OCT N6V DEC MONTHS Flgsars 7. The response of l lght energy avel l able to the suph~glc surface area for (8) TurbOdlfy curares and (B) tlme series curves a* Wh I skeas Wes$ S lQe Channel, cf 8$izfn 8&%@ upper portlsn of the model s%$e, As Phe (lepPh of '3 QVJ cors?O nues 3-0 increase over the sRoa1 l ighP irs-i.esrsl ty dscreas.ese The we* edBecP is re%Bec%ed in deand ing PAR curves above 30,OQO cfsa %Re l-8 me series response of PAW at the suphotla: surface P~lr Whiskers Wes* (Flgure78) Is slmllar to that for Fat Canoe island, A s%gn%Blcan8 dif ferance in avai I able I ighl energy exists bePween natural and boQh w t ?R-proJecP scenar lss dur l ng the f al l Prans l "rlon par %ode As both ne-i-ural and with-proJect turbldltles increase from May $0 July, al l Bhree curves show a sl gni f icant decrease in ave l lab l e l lgRI energy@ i % Is ear ldent that th is rtisponse is attr lbutab l e to i ncreasl ng turb ld l8q, rather than to increasing mainstem discharge because the PBX ressplase curves for al l turbid i ty level s at W h l skers West (F igurle 7A) show an iollsanslt!vlty to variations in malnstern dlscharga And i lke Fa* hnoe, Whlrjksas West shows slgnlf lcantly more i lghP energy available a* %Re errphod-lc surface in the fa1 l for natural turbldltles than for w l-l-h- project turbidity, even though fal l streamf isws are similar for al l *hr@e seenar f os, This site and the fol lowlng site (Fourth of July) are associated with Representative Group VI (refer 4-0 Table 41. Side Channe! 68 is approximately one mile long and 300 feet wide. At high flows, 1P $yplf les malnstsm habitst. Between 12,500 and 10,600 cfs, ~e channel narrows zonst derab l y and transforms into riff la/posl hsbifat found in many iarge, side channels at low flows The site breaches aP a mains-tern id kchai-ge 1 ess 5,100 cfs, and thus, cGnv@y s $urb 8 d ~ai@r *th$*~~igl'ic:4~'f the open waPer season, The lower ha1 f of the sl te 1s eharxtealasd by @&80siv8 mid-channel gravel bars and rlf fie areas The upper parP%ora of the ~Budy site is charac?s~Bmed by a are1 B defined single chiaQQ&i, both banks QP wh %cR gradual l y slope inward to form a broad, parzsbo! 1~ channel a A l arge gravel bar extends about 1,200 feet douslstretam from ?ha, upsPreaw berm along the left bank. Thls gravel bar bgcomes part! al l y exposed and $arms a r l df le area at mainstem discharges of 11,000 ccs, F f gape 8A shows Phat the l lght energy rselved by the srapho%ic surface, area is inf l ~enced by boPh d lscharge and turb l d i ty. The lnt~ractlon of channel geometry and flow has its greatest l nf l uence at flows around 8,000 cfs for Purbldll-tes less than 50 NTU, Al flows greater than about 9,000 cfs, the PAR curves for ai I turbidity level s descend due, to Oh@ lnfl uence that Bncceased depths have on the total PAR input Ps the suphotic zone. The mosB obvious trend dapic$ed by the time series PAR response curves (Figure 8BI Is the increased l lght energy ava l l able to the eupRoOlc surface during the P&i l transition period under natural conditions, which is suppressed by with-project turbldltles. During the summer months (June and July) the avai labls l lght energy is lower fw nafural anditions than for w ltbproject cond i tlons. Thls Is attrl butable to v lth-proJsct streamf lows bet ng less than natural streamf sows during Ph ls %!me period, and the lnf l uence of mainstem discharge and channel geometry on The energy input Po 4hs suphotlc surface. SIDE CHANNEL 6A A 0 40W 8QQQ la00 iM00 28000 24088 28000 32880 WOO 40000 MAINSTEM DISCHARGE (c f s) JAN EB HAW AH WAY ,BbDN 4UL &\ah; SEP QCT HOV BEG Figure 8. Ths reslpaslsa of 1 lght energy aval l able to the euphotlc surface area for (A) tcrrbldiPy curves and (8) time ser las curves al- SDde Channel 68, %his 1 akge side channel represents side chaniiei and mainstem shoa! iaabiPa6 at high f 1 ows that transf~rrns ts we! I-def Bned, singIe*hread si ds channel hab i ta* as sstreamf low decreases. Like S Bde Channel 68, Phis s6Pe is assocla$ed wlPh Representative Group IV (Table 41, A ~ool/rl ff l e sequence predom lnates througholat mast of the sit@ a* maderate fIows. In general, the right bank is gen-tly sloping as c~mgargd 80 the left bank which is moderafe to steep. A l arge, m~dodsra-0-e sloping point bar exs-ends from the inside of the bend on the, rlgh4 bank m Bdtlay Phrough the site. At matnst am flows above 10,000 cfs th ls bar and *he wide sha! low channel at the upstream end of the slte creal-s @xteaslve shoal areas. The downstream portion of the site is a large, msdera$el y deep backwater zone w l th i n a wel l-def ! ned single channel w lth sPeeper barnks. Since *the breach lng f low for th is s l te is about 5,000 cfs, the site general l y conveys turbld water throughout mosP of the open iga?er season, F lgure 9A prov ides a good t l l ustratlon of the repsonse of PAR to mainstem discharge and turbidity levels within shoal and rlffle areas typically assocla*ed wtth the mainstem and many large side channels. As strsamflows rlse above 5,000 or 6,000 cfs, water flows out of the ihar weg and beg! ns to l nundate adJacant gravel bars and rn i l d s! opl ng shore! l n@ areas. As a resu l t, the supho$lc surface area increases and available PAR at the s$reambed increases until depah of flow begins to exceed compnsaf ion depth The PW curves in Flgure 9A sho~ aan increase RTH OF JYLY SIDE CHANNEL 0 a00 8800 IaQQ f6Q80 aOQO 2400 28g806 3a00 W06 40800 MAINSTEM DISCHARGE NATURAL JAN Fa HAW APR MAY JUN JOk WUF S€P OCT N8V DEC MONTHS Figure 9, The responsg of l ight energy avail l able To the euphoTlc surf ace area for (A) Purbldlty curves and (8) Plms series curve+ a* Fourth of Jul y Side Channel awd 12,800 cfs, Above this discharge rangeb $he PM curves decrease for ale qurbidlBles grea-ter than 39 WU. R@vl@w of $he tfme series PAR plots (Figure 98) Indlcafes *ha? Bhe ne* @ff@~t of forecasted w l th-proJsct streamf l ows and turb l d lPes is an increase of avail abl EI l lght energy f ram June through rn id-August, but a decrease dur!ng fal l. This is attributable to the larger amount of %Roa l area corn ing i n$o the euphot i c zone as a resu l l. of B ow er summer s8reamflows than =cur naturallye Higher ?ban natural fall turbidltlas and sgproxlnnmte! y ?he same strsamf lows result in a net loss of euphotlc area f r~m m id-August through m id-Odober. 'bh is study site represents short, we! l-def lned straight sf da chan~eli s, and is associated with Rsprassntal-ive Group VII. It is similar On plan form tomany sites inthemiddleSusItnaRlver. Itschannel geometry consists of shallow riffles and gently sloping stream banks in the upstream portion sf the site, whlch gradual ly transforms lnPoa deep baekwa9er area at 9he dswnsPreem end, This site breaches a0 a mainstem f l sw of 10,000 cf s, The w l de r l f f la area at the head narrows considerably at flows below 16,000 cfs. At high flows the riffle dfsappsars and the sits bscomss a large run and backwater area P~!w 3-0 i$s head berm bgilng svegmqopped at melnst@m f lot4 QB l@I,OOO cf S, *!-I@ large backwa$er area has a s8gn $ f lcent ef fec-b on ava8 babd e B igh* energy, As wafer surf ace el evat ions increase between 5,000 and 7,004) 'fs, ox*ens%sn aP the water surface further upstream into the s18e Increases the slze of the supRoPfc surface area and the associated energy input Po the sl tel Tk is f s ref l ec%ed by $he ascend 8 ng PAW response for this flow range (Figure 10A). When The head berm is overWti-opp@d at 10,000 cfs, there is a substanti al increase in weP*ed surface area (suphotlc area). The maximum energy input to PRe site occurs slear 12,000 cls. Above th ls flow level, islcreasl ng dsgfh alad decreasing euphod.lc surface area causes a gradual decl lne in the armoun* 08 l ight energy raxh lag the streambed. Time series resgonse curves for Little Rock (Figure 10BI reflect trends sf m l% ar to those deser tf bed for Fat Canoe Is I and and W h liskess WssO, A ljlgnlflcant difference in available l lght energy (PAR) exists bePweew nafural and with-proJect scenarios durlng The fall. Since fall streamfl ows are s l rn f l ar and The site f s breached f w na%ural and w IPb project scenarios, the decrease in PAR val ues at the sfreambed are prlnclpally a function of higher with-proJect turbldltes. This site is similar to Little Rock except that its head berm is nof breached untl l 13,000 cfs, and mainslem discharge does not have a pronounced effect on the st te un t l l about 16,000 cf s. Pr lor 4-0 breaching, streamflow In the channel is maintained by groundwater Inflow. A backwa*er also exlsfs at the mouth of this slOe aP adera$@ 6 3508 7000 %O%O i486Q fEQO 2i0QO 2-0 mQDO 3i%Q 3W0Q MAINSTEM DISCHARGE $AN FEB MAR 4PA WAY 40H JUL AU6 SW BCT f4OV DEC MONTHS Figure 10. The response of l lght energy avai [able to $he euphoBlc surface area for (A) tclrbldl ty curves and (B) time serlss curves at hl*TB@ Rczk sffa isainsTem discharge The area upstream from $he backws-9.e~- Is dmlna'red ia~ a Qar~g, sha9 low rlifls that $ransforsns Into a moderately deep run as @isi&ns$-@rn discharge increases, BQ*~ the right anal l @I? streambanks pOs+%~s exposed shwel ines of moderate slop ~ae>cwpP when i wundated by high s%reamf Bows, The available I lgh-t energy at this sits responds dtffaranPly to the 8 nf! ~ence af mainstem d lschargs above 16,000 cf s depending upon *~lkbidlty (Figure 1181. When the site is control led by mainstem d ischargo above 16,000 cf s, -6hs ava l l abl e i lgh% energy decreases if til9-b i d f 8l es are greater $ban 50 NTU. Be! ow 50 NTU, the I nP l uence of anfral l %ng mainstem Il ow Increases PAR val ues. The apexes of the BAR curves for turbl d i ties l sss than 50 NTU are found around 28,000 cf s, xh l l e for higher turbid l ties, the maximum energy input occurs around 16,000 cfs. The Ol ms series response curves (Figure 11 8) lnd lcate w lth-project s$rsamf 9 ows and turb l d O PHes wou l d f nerease PAR at the streambed *hro-oughout summer. Dur tng the f all, a smal l decrease would exist. Th !s is atPri butable to the backwater and unbreachsd and ltlons exlstlng for bath soenar los and the rel aPivel y shal low depths in the sl te under these and 1 ttons. This slte is t~plcal of long slnuaus sloughs fha? are breached at Intcsrmedlate malnstsm discharges (16,000 ctsf, Slough 9 is assoclaOed w lth Rspressntatlve Grsup I I, Below 16,000 cfs Phe sl"r $transforms fr~@~ PPER SIDE CHANNEL Q 400 8QOQ 12000 85000 a600 24t(%08 2M80 2QM mBO 4888Q MAINSTEM DISCHARGE FIgure 11. Ths response af l lght energy sval lab!t3 to the euphotlc surface area for (A) ).urbldlty curmves and (L3) time serles carves at Cippsr Side, ehannei 11. a tij~-BBd s8de channel So a cslea~water slough maintained by ssaad: *~-%~M*~T!Bs and gr~undwater. The upper port ion sf fhe study s!*@ an%ts$-s of pool habBtaP with a \rer*lcal right bank and a miad sloping 1 e4-t ba~k* The mlddlet pr$lan of ths site is principal iy riffle and run habl%at ~lth boBh bankshaving iarnlld slope. At high flows, "re re881 ew-i-1 re si Pa becomes a l ong run w l th a backwater area at i 4-s dow nc* The BAR response curves for Slough 9 reflect a sharp increase in Bhe available lighP energy above 16,000 cfs (Figure 128). This is a reshrl* of *he head berm bel ng overtopped and dramatic increase in wetted surface area Al"r~ough clearwater sxlsts at this site below a maln5tsm dlsshaage sf 16,000 cfs, the wetted surface area is $00 srnali J in comparison $0 the wet$ed surface area of the breached channel to in% B uence the responses of the PAR curves. The tlms ser lss PAR response curves for Slough 9 converge to form cane l ine for the fal l transl tlon per lod (September and October) (Figure 128). This occurs because both natural and wl$h-proJect fa! l s%reamf B ovs ass t nsuf f ic f en* to breach Phe s ai t-e and c D earw a*er f C OW sxtsts under bot-h scenar lose Bur ing summer, w i th-project f l ow s are al so lnsufflclsntto overtop this slte and slough flow remains clear. Hence, substanflall ly mere PAR is avaflable at this slte throughout the year for bath w i th-proJect scenar las than occurs natural l y. SLOUGH 9 MAINSTEM DISCHARGE JAM FEB MAR APR MAY JIK AU6 SEP OCT NDY OET MONT'HS 12. The response of l lght energy aval l abl e to Qhe su~hotis surface area for IA) turbidity curves and (B) 81me series curves at Slough 9. This s!b.e is tjplcai! of side sloughs PhaO are breached a* bfery high mainstem discharges (53,000 ~ls). This slfe is in P,eprese;n$a*%a/e Group T rhe site is approxlmafe-siy twarniles in ia7ng"s with an aver&$@ widqh of about 100 fee*. It is separated from the malnstem by Pwo Barge vegetated Jslands, Both the right and lefP banks are ral a9lvel y steep and slmilsp. fothose found in tributary streams. Below the breaching discharge of 33,000 cfs, approxlmaPel y 10 cf s of cl earwater flow is prov l dad By l ocal runoff and groundwater, The, PAR response funct!ons fw Slough 8A are sl m l l ar to those for Slough 9. Bel ow the breach l ng f l ow, the PAR response curves do not respond $0 malnstem discharge (F lgure 13A). Above 33,000 cf s the curves descend abrupBiy as a result of turbld malnstem water snterlng the sl*e. 'This Is apposite to that trend evident at Slough 9 (Figrlre 12AI. The Prend a* Slough BA is attrf butable l-o mainstem flow being contained w l-l-hln Plae steep banks of the channel al low lng an lnslgn l f lcant increase in we**ed surface area while the increase in depth decreases available l lsht energy at the streambed. The flme series response curves for Slough 88 are shown in Flguren 138 These resgonse curves ref l ect the l nf l uence of $he h l gh breach i ng P l ow (33,000) at tb is sl te in compar [son to the average monl-hl y malnsl-em dlschargss fa- naPural and w !f-h-proJect cond l t lons that do not exeesd 33,000 cfs. knee, sits-spec! f t6: Flow and turbid! tr val ues are fhe same MAINSTEM DISCHARGE lc Fs JAN R3 MAR c$M MAY M J& A W OCT NOV DEC MONTHS Figure 13. The response of l tght energy am! l abl e to the euwlo-fl c surface area for (81 turbidity curves and (8) Plms series curves at Slough 8A 'far i?! 1 %?pee swnarlos, end the sirngie time ser 8@% PAR cum@ rspres~r~*ts slaturel end w 11th-proJect c~nd iPBons. The shape of Bhe CU~VG ref lests sniy The seasonal change in solar redlation, raodel was devel oped *hat esti mafes the amounf sf pha-tosy n8hePl ra 1 1 acf !v@ radla%!on (PM) available to %ha suphotlc zone at se3ecl'sld sites En *tie m &dd il e Susl tna River. The model was desl gned -to accep* four lnl~uf verlables: (1 f mainstem dlschargs, (29 turbidity, (3) s~lipr i nso! atl on, and (4) chanfiel gemetry. Channel geme$ry var l es accord l ng $0 the site selected. The remaining three variables are seasonal ly depesadent, bu* natural var l atlon in malnstem discharges and turbldlPy w i B B be affected by projecO development The purpose of the model was Oo @st i mate the effects of al tsrsd rnalnstem dl scharge and Burbl d l ty reg lmes on PAR, The Atma8 r: .. dsvel opad in thr~~ general steps. The P irst step s l mpl y estimated the amounPs of euphotlc surface area aval lable at each site under dl f ferent ambinations of mainstem discharge and turbidi?y. Ph is pravlded Insight into how ava l lab re surface area responds to al tsratlons In %hese two variables. The second step lncl uded a constan* solar input and the a'ttenuatlon of this energy w lth depth under the same mainstem discharge and turbid l3-y rsgl mas anal yzad in step I. The resul ts of step 2 pr~vlded an analysis of photosynthef lcal ly usable l ighf energy from a constant solar input reach lng the surface areas calculated in step one and 9he ~GfecGs of mainstem discharge and turbidity on Phat energy, Flnal l y, step 3 carrel ated turhldfty w lth malnstem discharge as they covary in the middle Susttna Rlvsr naPural l y, and as they are expected 4-0 covary under w lTh-project cond l tlons, Monthl y combl nations of turbidity and malnsOsm discharge were then used in the mods! in a Time- ser iss incorporatl ng monthl y var lations ln solar insolaflon, The end r@sui"s suere es$lmePes for $he amount of PAR rsachirag the essphs-r'%c SU~%~C@ areas at each s i%@ ~UF % ng the Course sf a year far bo*h w th- proJect and neBurel and l tions. Three wnci uslsns can be draw w from Bhe re%@ 8 ts: First, ghotssynths$IcaIIy avaIIabIe light energy is unIv~lrsa16y sensli*llve fo changes in .b.urbldlt.y. ThaP is, at all sites, the PaPal amounP of light energy thaf reaches *he euphotlc zone, increases. as BurbldlPy decl lnes. Alfhocrgh %his should be in$ult%velly obvious, i* must be Oncl uded f n s discussion of concl usIlons because af I*% 8dreme %mportancs. Sssnd, mainstern discharge slgn l f icanlrl y lnf l uences l lght Onput to %he eerphotlc zone only a.6 selected sites, *hose w lth large shoal and rlf f lsl areas, such as Fourth of July and Side Channel 6A, and those *ha* are 1 Bkeiy to be lnf l usnced by the effects of breaching flows, such as Upper S l de Channel 1 1 and Sloughd 9. These sl tas exh l b l t opt l mal energy B nput ts the suphoTlc zone at spacif lc mainstam discharges. Third, the model l l l ustrates tha-i- whether the proJecT w ! l l have positive, neutral, or negat lve sf fects on %he amount of PAR reaching submerged surfaces depends upon the specif lc site affected, the 4-1 ms of the year, and the opsraflonal flow reg l mes szl ected. By app l y lng Those flow rsgl mes selected under the Case E-VI scenar lo Po the model, two further conclusions are suppw-tsd: Given Phe estimated with-groJec$ turbidl88es presented in the L. lc@~s@ Amendment, the proJect I1 I have sign l f lcant nega*! ve @'ff@c*s on *he amount of PM aavs l l abB e to the e~photi~ ZORB only i 4'1 fell, and then, only at sslecfod sites, Those sites thaP rill b@ aiFfecPed are those that have low braachlng flaws, relatirely deep channel s, and are assoc t a$ed ~r l th mai~lsfem or sl de channel hablta?. Examples are Fat Canoe, Whlskers West, Side ehanslel 6A, k.l-f*le Rock, and FourPh af duly Side Chanael. The predlcPsd reduc*lons in PW at these siOes under r lth-project conditions srs a resu l* of the! r rsl at % vel y i ow braces. l ng % lows. Thus, rqard l ess ~f. ~Rethar Lhe projec? is constructed, these sites w l l l convey water al l year. But under w i th-project cond l Plans, negative impacts on PAR w ll l occur because of increased turbldltiss in the fall. C)$her slTes (e.g., Upper Side Channel Ill with intsrmedIa*e breaching flows nay also be affected, but not as greatly because of the lnf luence of turb!dlQ ilnf low and upwel l ing in nalntainlng clearwater input to these sites. (2) Bsnsf lcl al ef fscts from the proJect may occur dur ailg the summer months at a0 most al I sites for fwga reasons: (4 1 the reduction 04 turblditles expected dur lng 1-hese months, and (2) the effect of lower flews and water surface elevations exposing more of the bot$om to PAR. Again, however, these concl us! ons are supported only by the turbidity reg Imes wesented In the amendment. The mst prsnounced l ncreasas i n euphot! c energy Input under w lPh-proJect conditions will occur at $hose sites that demonstrate optimal amount.s of euphotic surface areas al flows that correspond to w Ith- project fi ows during ths sufnmsr. REFERENCES Aaserude, RG., J, TRiele, and D. Trudgen. 1985. Cab.egorlzaki~n and characterlzatlon of aqua? lc habl taP Pypes of the m lddl e Susltna RGver. E. bloody Tr l hey and Assoc l ates, Anchorage, AK* Tech@ l caB mmwa~dum~ 0 ~81, Acres Amsr lean Inc, 1982. Feaslbf l :ty report. Vsl ume 2, Env IronrslentaI repari', Sections 104. Final draft, Al ask& Power Author IBy. Susltna Hydrwlectrlc ProJect. 1 vole Alaska Dspl. of Fish and Game, Susltna Hydro Aquatic SPudles. 1982. Phase I final draft report. Aquatlc studies program, Repor? for Wcr~s Amer !can I nc. Al aska Power Author B Py. Sus i$na Hydroel sc*r lc ProJecP. 1 vo! * Alaska Dept sf Fish and Game, Susl tna Hydro Aquatic Studies, R983ae Phase I I basic data repor?. Yol. 4: huatic habltaa and ims$ream Plow studies, 1982, Anchorage, M. Part 1, p, 2. Alaska DqapP. of Fish and Game, Susltna Hydro Aquatic Studies. 198Jbe Phase I I basic data report. Vol. 4: Aquatic habl tat and l ns*ream flaw studles, 1982, appendices D-J. 1 vol. A! aska Pswsr Au%hor Ity. 1985. Before the Federal Energy Psgu l atory Cornlmlsslon. Appl lcatlon for l icense for major project. Susitna Hydroel ectr lc ProJect drat t l lcense appl lca*i on. Prepared by HarzbEbasco Susl$na Joint Ventura Sus ltna Hydroelectric ProJecB. 17 vols, Branton, C. I ., R.H. Shaw, and L.D. Al l en. 1972. Sol ar and net radiation at Palmer, Alaska 1960-71. University of Alaska lnsltltute of AgrlculOural Sciences Technical Bul letln, Number 3. 8 PP. Chew, V,T., ed. 1964. Pages 10-29 in Handbook of appl lad hydro! ~gy, an compend l um of waterresources technology. McGrarH i l l, NY. Coffin, J.F. 1984. Solar and longwave radlatlon data for Southcentral Aiaskn In: Alaskafs wa%er:: A crl$lcal resource $%,R Br@d9hauer, chaI rman). Proceed i ngs A! aska Section Amer lcan WaPer Resources Assclc laPlon. I nst l tu$e oof Water Rasoecrces. Un lvsrs l ty of Al ask* Far I tbanks. Report I W R- 1 06. Estes, C.C., and D.S. \I lncent-Lang, eds, 1984. Report No. 3. Aqua?lc Rab l tal- and lnstrsam f l ow i nvsst-l gat ions ( Way-October 19831. Chapl-er 4: Water qua! lty investigations. Susttna Hydro hua%lc Studies, Alaska Dept. of Fish and Game. Repor* far Alaska Power Authority, Anchorage, AK. Documlent 1933. 1 vol. Body Trlhey and Assxta$es and Woodward-Cl yde Consul tanks, 1983, bjorkfng draft. BnsBrearn flow relationships repsr8. Volume 1. Alaska Power Au$Rorl$y, Susl tna Hydroel ectr lc ProJecf Repor* %or HarzeEbesc~ SuslPna Jot nt Ven%ure, hchwaga. AK. HijIlard, N et a!. 1985. Hydraulic reIaflonsh!ps and madel cat l baatlsn procedures at 1984 study sl9es In the Tal keetna-*o- Dev B il Canyon segmeof of the? Stss lPna R lvar, Al aska L Woody 'Bb l hey end Asso& i a.tes. Report for Al aska Pe sr Author l %y, Anchor age, M. 1 vole Hynas, H,B,M. 1979. The ecology of running wat.err;, University of Boront~ Press. 555 pp. James, H.R., and E.A. Blrge, t 938. A l aboraPary sPudy of Pkhj absorpt%on of I lght- by lakg waters. Trans. ki ls. Acad, Se l. Arts ks$f, 31:l-154. 381-384. Lloyd, 13.S. 1985. Turbldl ty in freshwater habl tats in Al aska, HablBaP Dlv., Alaska DspP. of Fish and Game. Juneau, AK. 1011 pp. M % l haus, RT., D.L. Wey ner, and I. Wadd lee 1984. Users gu lde to the Physical HabltaP SlmulaPlon System. Instream FI ow Informatfsn Paper I 1. U.S. Fish Wild!. Ssrv. FWSIOBS - 81/G revised. 475 pp. tbss, 8. 1980. Ecoiogy of fresh waters. John W lley and Sons, NY. 332 PP. Otf Wafer Enginears I nc. 1981. Bradl ey Lake Water Quai lTy Repor*, Prepared for U.S. Army Corps of Engineers, Alaska District, Anchox-age, AK. September, 1981 . Rsub, G.R., E.W. Trlhey, and C. Wl lklnson, 1985. Prel iminafy analysis of the i nf l uence of altered middl e river discharge and turb ld l ty rgg l mes on the surf ace area of the euphot lc zone. E Woody Tr l hq and Associates, hnchwage, AK. Technical m andurn, 25 pp. RbH Consul Oants. 1982. Gl ac l al Lake Stud l es. Prepared for Acres her-.fcan Inc, Roulet, N.T. and W.P. Adams. 1984. I l lustration of the spal-l al varlabiilty of light entering a lake using an emplrlcal model. NydroblolqIa fO9:67-74. Rwe, T.G. 1985. Seasonal varlal-ion of photosynthePicaIly active radiation in Big Lake, southcentral Alaska In: Resolving AlaskaQs water resource conf l lets (L lnda Perry Dn lght, chairman), Proceed logs Alaska Sectlon Amer I can Water Resources Assscl at ion. institute of Water Resources. Unlversfty of Alaska-Fairbanks. Report I W R-108. 21 2 pp. Scot*, K 1982. Erosion and Sed I mantatton in the Kena I River, Alaska. USGS Professional Paper No. 1235. 35 pp. Ma0 !4tl%sueenRuyse, E 14383. The effects of placer mining on *ih@ pg. imary ptsduc.2. i v i ty of 1 nter lor A! aska s'a'reapns. M,Se Th@s E 5, UnFversBQ of AIaskeFalrba~ks~ 120 pp. bjfeuwenhuyse, EeL 1984, Prellt~lnary analysis of the reliatisnshlys betweest turbZdl ty and l lght penetration In 6he Susltna W lver, aska. & Wody Ir l hey and Assmiates, Bincharage, Me TachnIcaB mawandurn. 7 pp.