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EIDC 707 A STREET.ANCHORAGE.AlASKA.lIIl5Ot;llI07l27t423
ASSESSMENT or THE EFFECTS OF
WITH-PROJECT INSTREAH TEMPERATURES
ON SUSITNA RIVER tCE PROCESSES IN
THE DEVIL CANYON TO TALKEETNA REACH.
DRAFT REPORT
Sus
'f,;l8
ASSESSMENT OF THE EFFECTS OF
WITH-PROJECT INSTREAM TEMPERATURES
ON SUSITNA RIVER ICE PROCESSES IN
THE DEVIL CANYON TO TALKEETNA REACH.
DRAFT REPORT
ASSESSK[hi OF THE EFFECTS OF WlTII-PROJECT UISTREAH
TEMPERATURES ON SUSITNA RIVER ICE PROCESSES [N THE DEVIL CANYO~
TO rALKEETNA REACH
DRAFT REPORT
Pnparec!by:
Arctic EnvirOnlllental Information and Data Center
University of Alaska
101 A Street
Anchorage,Alaska 99S01
Sublll1tted to:
Karza-Ebasco Susitna Joint Venture
111 H Stnet
Anchorage,Alaska 99501
For:
The AI.aka PQWer Authority
]24 W.5th Aveo~e.~econd Floor
Anchorage,Alaska 99501
Novembe r.J 984
This report was prepared by
Joseph C.laBelle.geomorphologist
TABLE Of CO~"TENTS
Page No.
LIST Of FIGURES......................................................1
LIST OF APPENDICES...................................................11
INTRODUCTION.........................................................I
PURPOSE.•••••••••••••••••••••••••••••••••••••••••••••••••••••.••I
SACKGROUND....•.•••••••••••• •••••••••••••••.••••••••••••••••••••4
SCOPE....................•••••••••••••••••••••••••••••••••••••••7
NATURAL RIVER ICE PROCESSES..........................................II
fREEZEUP.. . • . • • • • • • • • • • • • • • • • • • • . • . • • • • . • • • • . . • • . . . • . . . . • • . • • • • .I J
fRAZIL ICE GENERATION......................................II
COOK INLET TO TALKEETNA (LO~ER RIVER)•.•••.•...•...•....•••12
TALKEETNA TO GOLD CREEK (HIDDLE RIVER).....................16
GOLD CREEK TO DEVIL CANYON (HIDDLE RIVER)•.•••••••••••••••.21
DEVlL CANYON AND ABOVE (UPPER RIVER).......................22
ICE COVER AT PEAK Of DEVELOPMENT................................23
BREAKUP.........................................................24
EffECTS Of WITH-PROJECT INSTREAK TEMPERATURES ON SUSITNA RIVER
ICE PROCESSES........................................................28
WITH-PROJECT SIKULATlOSS.fREEZEUP..............................28
WITH-PROJECT SIKUUTIONS.BREAKUP 4)
FURTHER STUDIES......................................................44
REFERENCES...........................................................45
APPENDICP<:...........................................................46
LIST Of fiCURES
figure No.
I.Hap of Susitna Basin .•.........•......•............•......•.•..••
2.Average winter monthly air temperatures at Talkeetna .......••••.•
3.With-project instream ice simulations .••.••.•.....••••••••.•.•...
4.Observed natursl ice processes,Susitna River from
Cook Inlet to Talkeetna (Lower River)..•.•..•....................
5.Historic records of ice thickness measurements on the
Susitna River at Talkeetna .......•.•............•...•..••.......•
6.Observed natural ice processes,SuSitns River Crom
Talkeetnn to Devil Canyon (Middle River)...•••.••••••.••••.......
7.Important slough and side channel areas in the middle
Susitna River .......•••••••••......••.•••••••••..................
Page No.
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10
13
15
17
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8.Side channels and sloughs regularly influenced by
ice-induced flooding during breakup 27
9.lCECAL SilllU!a.tions,loIatana alone,L996,inflow matching
releases,........................................................29
10.ICECAL silllUlations,Watana alone,1996.4 C releases.............30
11.ICECAL slaulations,Watana alone,2001,inflow matching
releases.........................................................31
12.Watana and Devil Canyon,2002,inflow matching releases.........32
13.Watana and Devil Canyon,2020,inflow matching releases..........33
14.Simulated ice front progression arid meltout rates................35
IS.ICECAl.simulation,occurrences ""here with-project maximum
river stages are higher than natural conditions..................37
16.ICECAL simulation!),slough overtopping ••••••••••••••...••••......38
17.ICECAL simulations.1Il8ximum river stages ...•...............•.•...39
18.ICECAL simulations,total ".thicknesses ••..••••.........•.••..•41
19.[CECAL simulations,solid ".thicknesses •••...••••..........•..."
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APPENDICES
A.Suaitna River natunl1 atreu,flow$,and \lith-project reservoir disctt..rges.
8.ICECAL sil:lUlations of natural ce fronc progreuion in the lfIiddle Susltna
River.1971-12,1916-77.1982-83,1983-86.
C.ICECAL ~ilClllations of ice front progression,~..tana alone,1996.inflow
catching releases.1971-12,1976-77.1981-82,1982-83.
D.ICECAL sia:ulations of ice front progression,"atana alone,1996,6 C
releases,1911-12.
E.ICECAL siClulations of ice front progression,Watana alone,2001,InflO\l
lIlItching T@leasu,1971-72,1982~8).
f.ICECAL simulations of ice front progreo¥ion.Watana and Devil Canyon,
2002,onflo\l utchlng r~leases,1911-12, 1916-77, 1981-82,1982-83.
G.lCECAL simulations of lee front progression,Watana and Devil Canyon,
2020,inflow I113tchlng releases.1911-12.1982-83.
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ASSESSMENT OF TilE EFFECTS OF WITH-PROJECT INSTREAM TEMPERATURES ON SUSITNA
RIVER ICE PROCESSES HI TIlE DEVIL CANYON TO TALKEETNA REACH
INTRODUCTION
PURPOSE,IiACKGROUND.AND SCOPE
PURPOSE
Chanses in the instrealll tel:lperatures in the Susitna River with th~
Susitna River Hydroelectric Project in place would caus~significant altera-
tion of the processes and ti1lling of instream ice formation and dec87.This
report sumna~izea instream ice processc~as they have been observed under
natural conGitions for each year ..ince 1980 (RIIM Consultants,Inc.,19S0··81;
1982; 1983;1984).These ar"coapared with Simulation!>ot natural and with-
project inatresm ice processes as prouuced by Harza-F.bas~·usitns Joint Ven-
ture,utilizing the ICECAL computer model (Harza-Ebasco Susitna JOl.lIt Venture
1984a).The objective of running the computer model Simulations was to deter-
mine the effects of the propobed Watana and Devil Canyon dams on river ice
processes and the corresponding water surface elevations (staging)during the
winter season in the Suaitna River downstrea~of the dams.The Simulations
arc limited to the middle reac~of the Susitna River (frOlll the Susitna-
Chulitna confluence to Devi I Canyon),where th':l greatest changes due to the
project are expected to occur.
The ICECAL computer model generated all of the simulated river ice condi-
tions shown In this report.The model simulatell a daily sUCllll3ry of hydraulic.
t~mperature.and lee conditions throughout the m~ddlc reach of the Susitna
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River.The hydraulic and ice operations performed by ICECAL intlude the fol-
loving:
a.Hydraulic profiles are cocputed daily for the study rcach.
b.Temperatures for ice-covered portions of the river are co%puted.
c.Frazi1 ice generlltion is cOlOlputed for turbulent.open reaches ",here
vater temperature ha~dropped to 0 C,and frazi1 ice flov rntes are
tabulated as the ite is carried downstream.
d.Shore ice (border ice)growth proceeding from shore is computed.
e.As frazi1 ice cQalesces into loosely-consolidated slush floes,hy-
draulic conditions at the ice cover nrc analyzed to detercine vhe-
ther the floes ~ill accumulate at the upstream edge,or leading
edge.of the ice cover.If not,the ite may be svept under the ice
tover,or aubdutted.and deposited on the underside of the ice cover
dO\fflstream.
L
g.
Computations are made of the slush and solid ice component thick-
nesses of tht"river ice cover.
Meltout of the ice cover is simulated by computing the ~elting of
the ice cover and retreat of the ice front whom warm water,above 0
C,reaches the ice c~ver.
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Input data ntlU::ed by ICECAI..ir.:::ludes the follololin[l;
a.River cross-sectional geometry and bed roughness lor the study
reach.
b.Weather conditions (daily air teaperature and wind velocity)for the
study reach.
c,Water inflow hydrograph at upstr~ao boundary of study reach.
d.Daily fra~11 ice discharges at upstream boundary at study reach.
e.Water temperature profiles betwe~n the upstream bound~r/and the
location of the 0 C isothera.
Calibration of lCECAL was carried out using the observations of natural
ice processes during 1982-83 and 1983-64 by R&M Consultants,Inc.(Harza-
Ebasco Susitna Joint Venture 1984b).[CECAl..l!Iodeling runs utilized AEIOC's
SYNTEHP model predictions of the location of the 0 C instreal!l isothero
(Alaska,Univ.,AElOC 1984)as input.T~e lnOdel then computed water telllpera-
tures in ice-affected reaches of the river and simulated natural and with-
project ice conditions under the same hydrologic and climatic conditions use,1
in the instream temperature simulations.
This report briefly discusses only the effects of instream temperatures,
under natural and with-project conditions,on in8tresm ice processes.A later
report,to be produced by AEIDC with comprehensive input and review by a team
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composed of several participants in thp Susitna aquati~s:udl~~group,viII
thoroughly describe all river ice processes and tonditions.and viII dddreS5
th~effe~ts of vlth-proje~t instream ice processes on aquati~habitats and
fishery resources.
Throughout this report.thi!textual c,.;planlltions of both n,ltural and
vith-project river ice processes and conditions wj'l be generalized.in o~der
to give the reader a good picture of the general processes that octur nov.or
vould occur with-project.from year to year.Oetail~of processes that have
occurred naturally in specific years.ur vere simulated to occur in specific
years with-project,car.be found in the accompanyIng figure~,
BACKCROUND
The Susitna River drains an area of 19,600 sq ai.th~si,.;th largest river
basin in Alaska.The Susitna flovs 320 lIIi frolll its orl~ln at Susitna Glacier
to the Cook Inlet eetuary.Its baSin is bordered by the Alaska Range on the
north,the Chulitna and Talkeetna Mountains on the WC:lt and south,and the
northern Talkeetna plateau and Gulkana uplands to the east.This area is
largely withIn the coastal trough of Southcentrnl Alaska,a belt of lowlands
extending the length of the Pacific mountain syst~1II and interrupted by the
Talkeetna.Clearwater,and Wrangell Mountains.
Major Susitna tributaries include the Talkeetna.Chulitna.and Yentna
Rivers (Figure l).The Yentna River enters the Susitna at river mile (~~)28
(2ij miles upstream from the mouth at Cook Inlet).The Chulitna River riser in
the glaciers on the south slope of ~ount McKinley and flows south,entering
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.'.;;"""r::'::::-~••••
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the SuSltDa R1v~r near Tltlkeetn.a (1M 99).The Talk-edM River rlses in the
Tslkeetna Hountains.flows vest.and joins the Susitna ncar Talkeetna (RM 97).
Tributaries in north~rn portions of the SUlitna basin orisinate in the
glaciers of the eaStern Alsska Range.The east and west forks of the Susitr-a
and McClnren Rivers join the mainstem Susitna River above RM 260.Below the
glaciers the brAided channel traverses a high plateau 3nd continues south t~
the Cshetns River confluence near RM 233.There it takes a sharp turn lJest
and flows through a steeply cut canyon which contains the ~atana (~~184.4)
and Devil C&nyon (L~151.6)dam sites.In this predominantly singl~-channel
reach the gradient is quite steep.avenging approxlaately 10 ft/ni (Acres
~erican 1983).8elo~Cold Creek (RM 137)the river alternates between single
..nd multiple channels until the confluence ...ith the Chulitn;:,;and Talkeetna
Rivers (RH 97),bel~1J which the Susitna broadens lnto widely braided ch~nnel$
for 97 miles to Cook Inlet.
the proposed proj~ct consists of two dams to be constructed over a perled
of about 15 yeara.The Watana dam \lould be completed 1n 1994 at a site 3 ci
upstream from Tsusena Creek (RH 184.4).This dcvelop~nt lJould include an
underground powerhouse dnd 885 ft high earrhfill dam,\lhich \lould impound a
reservoi~&8 mi IODg \lith e surface area of 38,000 acres and a usable storage
capacity of 3.7 million acre feet (maf).The dam would house multipoJe level
intakes and cone valves.Instlllled generating capacity would be 1020 llIega-
watts (Hw),...ith Iln estimated average annual energy output of 3460 gigawatt
hours (JIoIh).
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Th~~oncrete arch De~il Canyon da=would be co~pletcd by 2~2 at a site
]2 m1 downstreaa of the Watana dam site.It would be 645 ft high and ~~uld
impound a 26 ail~-long reaervoie with 7.800 surface ~crel snd a StOrage capac-
ity of .36 O8f (Acres American 1983).Installed generating capaciey would be
about 600 MY.with an average annual eoersy output of ]450 ~·h.30th reser-
voirs would be drawn down during the high energy delll3no winur r:onths ,nd
filled during the summer aonths when e~ergy require~entB arc lowest.
Construction and subsequent c"...racion of the Susitna dacal are expe.:c~d ro
alter the norllli\l themal regtll'le of the river.Hatnstel:1 wllter temperatures
dO\olTlstrealll frOl!l the project would be cool ...r In the SUl!lt:l...r and warc.lr in the
winter than under natural conditions.A change In the river ice regtQe do\olTl-
Itrca~froCl the project is expected due to altered te~peratures and increased
\/inter flO\ols.
SCOPE
This report describes the expected changes in instreao Ice processes that
would result fr01ll Susitn.Hydroelectric Project operations.Natural ice pro-
cesaes s~ri~ed in this report include observations =ade during the winters
of 1~80-81,1981-82.1982-53,and 1983-84.Computer I;lcula:icns of natural
and with-project icO!processes were run for lhe winters of 1971-72.1976-77,
1981-82,and 1982-83,The winters of 197.-72 and 1981-82 are relatively
cold.whereas the winter of 1982-83 is average in temperature.the winter of
1976-77 1s warmer than average.Clioatlc data for these years is su~rized in
Figure~.Natural streaoflows for these year~at Gold Creek are shown i~
Appendill A.
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Figure 2,Av@rage vinter aonthly ai'telllperatures at Talkeetna,
selected years.(Data SUlllI:la r 1ted tra.Natlcnal ~e~ther
Service)•
1971-12 1976-11 1980-81 1981-82 198Z-~)198)-54
November -II.9 -2.2 -3.5 -6.8 -a.5 -5.2
Oec:eaber -I).to -7.I -20.1 -II.i -7.1 -10.1
January -17.8 -2.6 -1.8 -17.I -!O,8 -11.0
February -12.8 -2.)-6.1 -10.0 -1.5 -'L6
HaTch -12.3 -8.8 -0.4 -4.9 -3.5 0.'
April -6.I -0.7 -0.1 0.0 I.,1.7
A••-12.4 -4.0 -5.3 -8.4 -5.9 -5.1
(cold)(\Jarlll)(warn)(cold)(avS·)(avS.)
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With-prOject ice processes simulations summarized in this report include
several operations scenarios,shovn 1n Figure 3.These include the follO\o'ing
principal scenarios,each sinulated under severnl different climatic condi-
tions.
(a)Watana dam,operating alone,In a manner that would most closely
match natural fall and winter stream temperatures in the Susitna
River (inflow ~~tchlng)Cor high and lo~power generation (1996;
2001)•
(b)Wntan;:l and Devil Can}"on d;lms.opt:rating together,in a manner rltat
would most closely ~1tch natural f&11 and winter srreaD re~per3tures
In the Susirna River {inflow matching)for high and low power gener-
ation (2002;2020).
These scenarios would utilize the coldest water available and would pro-
vide downstream temperatures allowing ::he greatest opportunity [or an ins treaD
icc cover to fOlm on the Susitna River.
Cc)l.i'atana dam,operating alene,in a manner that ...ould allow a cons~ant
releaae of "C ~oater for low power generation (l996).This scenario
would provide downstream temperatures allowing the least opportunity
for the formation of lnstream ice on the Susitna River.This sce-
nario was provided prlnclpally as a sensitivity test.
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Figure 3.\lith-project instream ice simulations
(Hana-F.basco Susitna Joint Venture.(98411)
All scenarios use Case C flow requirelllE'nlS
Project Watana only operating Watana and Devil
status Canyon op~rl1t1ng
Release Inflow Inflow WArn Inf low Inflow
temperature matching matching 4C matching matching
Energy
demand 1996 2001 1996 2002 2020 •
1971-72 (cold)X X X X X
1976-77 (WSrlIl)X X
1981-82 (cold)X ,
1982-83 (average)X X X X
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All cOlllputer DOdel SUlUlationS discussed in this report addnu ('Illy the
Case C flow nquire_nts (Acns AlDeriCll.n.Inc.1983).l!another flO\l resi:e
is considered,new ICECAL runa would have to address that regi=e.
NATURAL RIVER ICE PROCESSES
~incer ice conditions and processes on the Susltna Riv~r have been ob-
&erved for several years by R&!'l Consultants,Inc.The follO\ling is a synthesis
of general ice process~s on the Susitna River as they have ~een obsen'ed under
nlltural conditions from 1980 throuSh 1984 (R&~Consultants,In .•1980-81,
1982.1983.1984).
FRtEZEUP
FRAZIL ICE GENERATION
Host river ice covers are for~ed as a result of the fo~'tlon and concen-
tration of frazil ice.1oi1ul.n river "U1cer beCOlllell slightly supercooled (to C),
frazll crysuh begin to fo=,usually by nucleation.Fine susper.cled ..edl-
ments in the water during freezeup season oay be the nucleAting agent in the
Su~itna River.Frazil crystals InItially fora principally as small di&coid
crystals only a fev ail1llleten In diameter.These gro,",rapidly to larger size
and begin 1.0 accUlll\llate as frazil slush cassel.often contributed to by snow-
fall into the river which fORU floating snow slush.The combined slush usu-
ally breaks up in turbulence Into In~J.\'idual slush floes that continue drift-
Ing downriver until stopp~d by jamel"~at river constrictions (Ashton 1978;
Michel 1971;Ostercamp 1978).
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frazil ice generally fir.t appears tn the river between Denali and Vee
Canyon by mid-SepteabeT.This ice drifts downriver.often acc~ulatlni Into
lao.ely-bonded slush floes.until il celts avay or exits Into Cook Inlet.
During freezeup,generally about 80 percent of the ice pa ••ing Talkeetna Into
the lower river Is produced in the upper Susitna River,",hile the recaln!ng ~O
perc~nt 1.produced in the Talkeetna and Chulitna Rivera.Below the Yentna
confluerll::e,usually -ore than 50 percent of the tee 11 generally produced by
the Yentna River.
COOK INLET TO TALKEETNA (LOWER RIVER)
Observed ice processes (or t~ts reach are summarized tn Figure '.
During ~period of severe told and heavy fraztl ice production,tloating
slush ice ,;.~cu=ulates rapi~ly and bridges the river i1'the vitinity of R.'t 9.
generally between aid-~tober ~nd e.rly Sov~cber.vhen mini~=daily air
te~eratures are less chlln or equal to 0 C.This is ¥ufficiently cold to
caintain high ice concentrations dovn to RM 9.Flov discharge at Sunshine
during this period in 1992 ranged between 14.000 and 16.000 cfs.This bridg_
iorms •barrier against vhich slush ite drifting dovnrivtr attu~lates and
iorms an advancing leading edge ~ving upstreac.The advancing leading edge,
alao taIled the ice front.typically reaches the Yentna River confluence by
late October or early Novecber.In 1982,the lending edge advanced at about
11..5 miles per day for the first 57 miles.Temperatures in the lover river
are usually not cold enough for a long enough period of tiee to form a contin-
uous ice cover before the rapid advance of the Blush ice cover.
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Figure.".Observed Natural lc.e Processe.s
Susitns River frolll Cook Inlet to Talkeetna (l.o\Ier Rh'er)
(R&~Consultsnts,Inc.,1980-81,1982,1983,1964)
1980-81 1981 82 1982-83 1983-84
FREEZE UP
Avg.\linter cli-ate w.~Cold Avg.Av£,.
lee bridge for=s UnknOlJn r.....rll'Nov.DeL 22 Oct."lit RM 9-c1ate
RM 9-28.5
Avg.gradient,it/ai I.S
Ap,•freezing date Oct.31
AVB·ice.thickness,r,4.0
AVB·staging,r,<2 2.5
Shore ice width,"0
RM 28.5-42.5
Avg.grad1ent,ft/Illi 2.h
App.freezeup date Nov.,
Avg.ice thickness,"5.5
Avg.fltaging,"3.5
Shore ice loiidth,f,0
RJI42.5-51
Avg.gradient,ft/mi 2.9
App.freezing date I'ov.,
Avg.ice thickness,r,4.0
AVI.liuging,"2.8
Shore ice "idth,f,0
RM 51-18
Avg.gradient,!t/ai 5.'5.0
Ap,.freezeup date Early Sov.Nov."Avg.h:e thickness,r,'.8
AVI·stlilling,"H 5.I
Shore ice w1.dth,r,0-2
RH 18-98.5
AV8.8 rad ient.it/Illi 5.0 5.0
App.freezing date Lm t<ov.-Dec.8
mid-Dec.
AVI·ice thickness.r,'.3
AVI·staging,r,>4 4 .•
Shore ice \lidth."3-'
Sloughs breached u Alexander slough
freezeup Coose Cr~ek slough
Sunshine slough
Birch Creek slough
Breakup early Hoay Late Apr.Late Apr.Late Apr.
to early to ellrly to early
Hay ¥~y Hay
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Staling,the Increa!lf!in w~ter surface elevation of the river caused by
river lee imp.dina flev,15 usually'w during freezeup 1n rhl!lover riveT.
with staging generally about 2-4 feet as rar north as Sunshine.Staging in-
creases,generally to more than 4 feet,at Talkeetna.Several sloughs below
talkeetna are no~lly breached,but with alnlmal flev and little ice.Some
IU:.~u;:e flow 1s diverted into side channels.Tributaries in this reach g<:ner-
ally continue flowing for several weeks nft~r the Susitnn River ice cover hilS
fOl'llled.keeping larse art'as near thelr confluences free of ice.
As discharges decrease after freeztlup,the 1<:0:cover sags,I.'ith l!luch ot
it becOQlng 8round~d and confo~ln8 co the shape of the underlying channel.
Lo the vinter of 1982-83,mlnl~u=dlsch~rs~s =e.sured at Sunshine ~ere about
5,000 cis.Open leads persist in high velucity tOne5 throughout the winter.
Some aide channela and slougha probably remain ic~free due to relatively ~arc
(.bove 0 C)groundwater u~eliing.Flooded side ch.nnels build up shore ice,
a180 called border ice.la)'era that reduce the open WAter are:!in these loca-
tions.
Hinlaal shore ice develops In the mainste~because of insufficiently cold
air telllperaturea for long enough periods before the sluah ice covers this
reach.HOIo'ever.continuing cold air temperatures throughout the winter caUle
a buildup of a thickr.ess of clear ice beneath the .lIlush Ice cover.In this
report,"total"ice thickness refers ro the combined thickneljll of the sluah
Ice .nd clear ice byersj "solid"ice thickness refers only to the clear lee.
H1&toric.l total ice thicknese:es Cor various datet>at Talkeetna are shown in
Figure 5.
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I Fieur.:5.H1ator1c ri!:cord..of '00 thickness t1CallurelSentl
nn ,h.Susitr.a River At Talkeetna (!Iilello (1980)
'tlLXEFT.'oA
I ~'IU'e..mu ..de en s..lttn.a River
19U-1962 1962-196)1963-1'1#04
I !!!!!TIllcllnf!..Unc:hu)!!!.!.!Ihickne ..(tM.hesl !!:!!!Thtcll'......(l.rchu)_.
H 'c)Ice Ou.,Fiut tce ....•~tce_.
uo '.0 ....,.F'M:r.e -"...."..,
I ...."'.0 ....'"'.0 ...."•.n
00<.'"36.0 J.II.H n.o ....")2.0
JllII.n ".0 Feb.,n.s Jlln."26.0
Feb.""'.0 Feb."21,..0 Feb."3).0
I ..,.,.61.0 ...."I.).S ..,."".0..,.n 51.0 ..,."...,".411."".n..,.,"'.0 !'~)~.O ..,."30.0
I ..,."H.O MAy U Ice h«..,,'.0
MIIya Rlv..r open
I 196:.-1"65 1')65-1%6 1'&6-1<161
~ThIck......(tncllu)!!!!!Thlckneu t j"""u)~thickness t Inc:h.ea)...."Short {celt ....H Flnt Ice ...."HrI~let:
I ""."'.0 ....'"21)ffeue -"...."Freeu,.......,
00<."21.0 s.;.v.",.n ....J-24 OIanMI .,..
Jan.>0 ".0 ""."11.0 ....n ..,
I reb .•".0 ...."18.0 Jan,"18.0
Fflb."32.0 Jan."20.0 Feb."n.D..,."26.0 Jan ."18.0 ..,."18.0
Apr.)12.0 reb."uo.O ..,."25.0..,.,.UO.O ..,."".n ..,."21.5..,.>0 O1.nnel -..,."18.0 ..,."Icc bTu.Unl up..,.>0 n.D
M.ly 21 >0.M
tlW'P£JlS CREEK
l1e ••ur_nu qQ.on Suntn.a IIlvu
I 1961-1'68 1968-1969 1969-1"',)
Jan."n.o ""."lee Ja:-inl ...."'.0•,,,.,n.o ....,'.0 ...."'.0
Fel>.,.36.0 ...."2/0.0 Jan."12.0..,.>0 >0.0 Fel>.,>0.0 Jan.n 21.0
Apr.20 20.0 ,<0."n.~.!loar.,".n.~y /0 Open aru..~r."2/0.0 ,.,.r .II 32.0
!".Iy 11 Ice J'"l>roU...,."16.0 ..,."2'.0
Apr."lee br..altlnl up "',.H H.O
•..,.UO tcc brukln.up
Apr."Clannel "l'enlnA up
a~19'0-1971 !911-197:
tblellnea ..(tnche,)!!!!!Thleltfwu (lnche,).....,-11 Ice J ......<.U Hut Ice....."'.0 100".U rre<o.'Ze -"....."16.0 ...."..n
,~.'""'.0 ......,..
reb."30.0 J,n.,18.0
a,':'."36.0 JOIn."21.0,."32.0 Feb.,211.0
,<0.""'.0
•-15-
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TALKEETNA TO GOLD CREEK (HIDDLE RIVER)
Observed freezcup processes for this re~ch are 9u~rlzed in Figure 6.
Since there ....ere no observations of natural proteasea for the years 1911-72
and 1976-77.[""0 of the years tor whic:h all:Nutiona of with-project conditions
we~e run.lCECAL s~=vlationl of natural processes for these years were pro-
duced after calibrating the model aglinse yenrs of observation.SlClulated
natural freezeup effects on river stages and lee thicknessc~are su~rl:ed in
figures 17 to 19.
An ice bridge usually forms just upstren~of the confluen~e of the
SUllens nnd Chulitna Rivers sometime betveen early Noveabet and early December
In 1982.the flow discharge at Cold Creek during this period wSa about
4,900 eh.The ice bridge fot1lls ..new leading edge of ice front progression
r.lOving upstream hom the confluence to the vici.nity of Gold Cr..ek.In 1982,
the ice front progressed initially at a rate of 3.5 miles per day.U..p..nding
on cli=atic conditions,this bridge may fo~either ",h ..~ice cover progressio~
in the lower river reaches the confluence,or is "'ell short of it.In some
years with severe cold periods occurring during ice front progression,one or
more secondary bridges ..y forlll upstrcarll of the confluence bridge,forming
secondary leading ~dges.
Border ice uaually begins to fora in this reach by the acc~ulation of
fro~en slush layers along shore befor~che passsge of the ice front.This
narrows the main.tem open WAter ar••,through which the slush ice leading edge
progress.s.
-If>-
FiEu'te 6.Observed Natural Ice Processes -5ubltna River
frOlll Talkeetna [0 Oev'.l Canyon (Middle River)
(R&H Consultants,Inc ••1980-81,t982,1983.1984)
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FREEZEUP
Avg.winter cl~t~
Avg.indtent.ft/~l
Ice bridge fonu at
Susitna/Chulitna Confluence
lee leading edg"located
neu Cold Creek
1980-81
Nov.29
Dec.12:
1981-82
Cold
9.'
Nov.18
Dec:.31
1982-6)
Avg.
9.'
Nov.5
Dec:.1.7
1983-84
Avg.
9.'
Dec:.8
J.lt\.5
Lane Creek
HcKenzie Cr.
Curry
Slough.8
51.8.head
51.9,lOOuth
51.9,Sherman
S1.II,mouth
Cold Creek
PotClIge Creek
Jan.5
Jan.15
Dec:.21
De.:.9
~ov.22
Nov.29
Dec:.I
Dec:.f,
Jan.14
Dec:.23
Nov.9
Nov.20
Nov.20
Nov.18
Nov.15
'<ov.5
Nov.8
Early Jan.
add-Dec:•
~ld-Nov.
Dec.12
Dec.8
Dec.5
Dec.4
Dec.I
Dec.2
Dec.)
Approx.free~eup dates
Confluenc:e ~~98.6
R.~103.3
RM 104.3
RM 106.2
RM 108.0
RM 112.9
RM 113.7
II.H 115.9
JUt 116.7
RH !l8.8
RH 120.7
JUt 124.5
RM 126.5
JUt 127.0
JUt 128.3
RH 130.9
RM 135.3
RK 136.6
RM 148.9
343.07
343.57
0.65)
461.87
573.53
523.89
545.31
596.5'1
618.16
657.58
684.64
(6.7)
524.6
620.1
579.3
(6.9)
559.3
345.5
384.1
(5.3)
685.3
839.5
381.50
546.80
557.99
572.74
594.13
460.80
RM 98.6
RM 103.3
RM 106.2
RM 113.0
RH 113.7
RM 120.5
RM 123.3
RH 124.5
RH 126.1
RH 121.0
RM 128.3
RM 128.1
RM 130.I)
IU1 134.2
RH l36.5
RM 148.9
head
lIIOuth
51.8,
51.9,
51.9,Sher1Dan
Slough 8
Cold Creek
Ponage Creek
Lane Creek
Curry
Staging elevations during
freezeup.ft
Confluence
I
().Relative elevation fro~arbitrary benc:h mark
-17-
figure 6.(Continued).
Sloughs with observed ooen
water all winter (upwelling
gfound.:ater influecce)
1983-84
8A
6.011/~6)
8.:0,26)
6.9(1/26)
10.4(1126)
10.6(1/26)
5.3(1/26)
5.2(11::7)
UnknOIoIn7
8A
I.
I I
19HZ-B3
2.9(2/4)
1.9(21"')
1.6(214)
:.5(2/4)
2.4(2/4}
4.l0/ll)
linknOlJn
J.SO/l)}
4.2(l/1l)
Unknown
1981-32
2.1o{)/5}
2.9(2/27)
J,O(J/S)
J.7(3/)
2.7(2/27)
1980-81
Unknown
Unknown
(date)thlckne ....ft
RH 98.6
RJ1 10J.3
Rh 108
RH 113.0
RM 120.6
RM 123,4
RM 126.2
RM 128.5
!l.H 130.9
RM 136.6
RM 1411.9
Curry
Sherr:;.:m
(;oid Creek
Portage Creek
l.:atana
Average tee
Conf Iuence
Sloughs breache~at
fr~ezeup
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~
SRf.MUP ~lay 8 M:l)'IO-1S ~lay 10
) •Relatlv~elevation from arbitrary b~nch =ark
I Historical breakup datelil for the r:.iddle SUSill:oil ki>'er as observed by ,\laska RallrC';I,d
personnel lR&:1 CO;'l$ultants,Inc.1980-81).
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1975
1976
1977
1978
1979
1980
M8)·15
Hay 1.
May 16
Hay 8-9
May 8
Hay 12-13
-18-
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The iee front progression rate decreases ••the ice lfont moves upriver.
In 1982,the plogressie"rate sloved to O.O~!:liles per day by the lillie it
r~ac:hed Gold Creek.This 1s probably due to the increase In gradient IIlOving
upriver and co the reduction in fra:!1 lee generation In the upper river .s it
develops a continuous ice cover.The upper river frce.:es over by border ice
grovth and brideing hefore the advancing leading edge ha.an opportunity to
reach there.
'''hen slaging Is sufficiently high as che lead in!~dge pallu in the
vicinity of a side t~nnel or slough.water may rise high enough to flow over
intervening benlls,gravel rises that separate the malnstelll iroQ the upper en<!s
of side channels and sloughs.t!hen these berms are chus overtopped,wnter and
slush ice are allowed to flow into the side area.Leading edge progression is
slowed during an overtopping event because flow relief into the ~id~area
prevents a low-velocity b.ckwater area fro~foraing.However.the ice tront
progression resumes when the side channel or slough becomes filled with water
and ice.Ioportant sloughs and side chann~ls in this r~;lch are indicated 1n
FlgUfC 7.
Local grounuwater levels .rc often raised when the leading edge approach-
es.This is probably due to staging effects raising the Ioiater level in the
mainstem,which then is propagated through the permeable riv~r sediments into
surrounding sloughs and side channels.
Many slough$that do not become Inunuateo by aainsteo water and ice {ail
to fora a continuous ice cover all wtnter due to upwelling of 1('J8tively wara
(l-)C)groundwater.However,ice does fora along slough margins,restricting
-19-
Arell
Figure 7.l~portant slough ~nd side chQnnel
areas in micdle Susitna River
(Harza-Eb.sco Susit~Joint Venture.
River HEe
Luc3tion
1984.1)
Threshold
Elev,1tion
Whiskers Slough
Side Channel ~t Head of Cash Creek
Slough 6A
Slough 8
Side Channel tlS11
Sid ...Channel t1SIl
Curry Slough
Hoose Slough
Slough 8A West Channel
Slough SA -EaSt Channel
Slough 9
Side Cnannel Upstteam oC Slough 9
Side Channel Upstream oC 4th Jul,Creek
Slough 9A
Side Channel Upstream of Slough 10
~ide Channel Downstream of Slough II
Slough 11
Slough 17
Slough 20
~lough 21 -Entrance A6
Slough 21
Slough 22
J67
Unkno ..'Tl
U
476
482
487
Unkno\,/ft
UnknO!Jn
m
5.2
60'
U1'lknolotn
Unkno",,"
6"
6"
Unkno\l1l
6.7
Unknown
730
'"155
7.8
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l
H Indicated location r ?resents the head of the slough or channel
M Indicated location represents the mouth of the slough or channel
U "Upland"slough \lith no upStrelln head or berm
-2l>-
•
•
the open water area to a narrow,open lead.Some sloughs that do fonn ice
covers after being inundated with mainstea water and ice late:r:elt out be-
cause of the groundwater the~l influence.These leads often then rem&in
open all winter.
AS slush ice accumulates against the leading edge,it consolidates from
time to time through ~ompression and thickening.Staging accompanies this
proteS6,which sometimes lifts the ice cover and ai10ws it lateral movement.
often extending the ice from bank to bank.
Water flo.....in8 under the ice cover throughout the .....il"ter often .::auseli
frictionnl erosion of the cnderside of the ice,opening l~ad$in the cover.
This usually occurs rapidly after the initial stablli:l:ation of a slush ice
cover.These leads usually slowly free~e over .....ith a secondary tce cover,and
mOllt leAds are closed by Hardl.
The slu!lh ice front progression from the ~usitna/Chulitna confluence
generally ter~inates in the vicinity of Gold Creek ,about 35 to 40 ciles
upstream from the confluence,by December or early January.ICECAL codel
simulations of the progress of the ice front are shO'-'T1 in Appendix S.Dif-
ferent freezeup processes dominate the river above Gold Creek.
GOLD CReEK TO DEVIL CANYON (MIDDLE RIVER)
freezeup occurs grsdually in the reach froc Gold Creek to Devil Canyon,
with a complete ice cover in place much later than in the reach below Gold
Creek,usually not until March.The ice front doell not generall)'progress
-21-
beyond ~he vicinity of Cold Creek because or the lack of frazil ice input
after the upper ri\er freezes over.Also,ice is late in fo~ing here because
of the relatively high velocities in chis reach,caused by the steeper iradi-
enl ..~single-channel characteri5tics of the reach.
Wide border ice layers build out from shore throughout the freezeup sea-
son,narrawing the ~pen water channel in the mainstem and frequently forming
ice bridges across the river,separated by open leads.lr.the open water
areas,frazil ice adheres ~asily to any object it contacts within the ri~er
flow,such as rocks and gravel on the channel bot toe.forming anchor ice.
Anchor lee cay form into low dams in the stream bed,especially in areas nar-
rowed by border ice,increasing local water turbulence which cay increase
frazii generation.Slight back~ater areas ar~sometimes induced due to a gen-
eral raising of the effective channel bottom.affecting flow distrib'ltion
between channels and causing overflow onto border ice.Within the backwater
area,slush ice may freeze in a thin layer from bank to bank.
Little staging occurs in this reach during freezeup,and sloughs and side
Channels are generally not breached at their upper ends.They usually remain
open all winter due to groundwater inflow.Open leads occur in the mainstem ,
especially in high velocity areas between ice bridges,but few new leads open
after the fonnation of the initial ice cover.There 1s minilllal ice cover sag
1n this reach.
DEVIL CANYON AND ABOVE (UPPER RIVER)
in Devil Canyon.slush ice forming in this tutbulent,~igh velocity reach
is often the first to form on the entire Susitna River but is usually
-22-
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unstable,c.ontinually alternating between ac.cumulation and disintegration.
This process fo~s massive ice shelv~s in the canyon,as muc.h as 2)feet high.
The reach above Devil Canyon to Denali develops wid~shore ice by building
successive layers of slush.The c.hann~l finally becomes so narrow that flow-
ing slush is entrapped,eventually freezing into an ic.e c.over.However.this
proc.ess does not occ.ur simultaneously over this reach,causing a discontinuous
ic.e cover to exist with many open leads.Usually.by early ~:arch most of
these leads freeze over.
ICE COVER AT THE PEAK OF DEVELOPMENT
Once the inltL.1l.1 ice cover forms it rer.lains quit~dynamic,either thick-
ening or eroding.Slush ice adher~s to the underside of the ice cover in low
velocity areas and becom~s bonded by low temperatures.The ice cover beco~es
most stable at its height of maturity.generally in Marth.The only open
water at that time is in the numerous leads that persist over turbulent areas
and areas of groundwater upwelling.and little frazlI slush i'l generated.
River flows are generally at their minleun,restricted to a shallow,
narrllw thalweg channel.In the winter of 1982-83,low flows Ot Gold Creek
were about 1,500 cfa by the end of March.The ite tover h~s usually settled
and bctome grounded,and has an undulating surface.Tile ice cover is a foma-
tion of rigid layers at randol:J levels.separated by unc:onsolidated layers of
s~~'lo,crystals.The rigid layers represent zones fotl!led during eXlre:llely told
periods as the saturated sluail ice slowly drained.
-23-
8REAKUP
Obser"ed natural river ice breakup dates for 1981-81;for the lower river
are summarized in Figure 4.and for the ~lddle river in Figure 6.Additior.al-
ly,historical river breakup dates for the years 1975-1980 for the ~iddle
river are shown In Figure 4.
Under natural conditions,the SUiIlitna River ice cover disintegrates in
the spring by a progresston beginning "'ith a 51"",.gradual deterioration of
the ice and ending ",ith a dramatic breakup urive accompanied by ice jams,
flooding,and erosion.The duration of the bre~kup p~riod depends on the in-
tensity of solar rsoiation,air temper~rures,and precipitation.
A pre-breakup period occur.,as snowmelt begins in the area,usually by
early April.Snowmelt l-egins first at the Im.:",r elevations near the Susltna
River fIlouth and slo",ly works northward up the rlver.8y lIIte April.snow has
usually disappeared on the river south of Talkeetna and sn04~elt Is proceeding
into the reach above the Susitna/Chulitna confluence.Tributl1ries to the lower
river have nsually broken out in their lower elevations.and open water exists
at their confluences with ch~Susitna River.Increased flows fron the tribu-
taries erode the Susitna ice cover for considerable distances d04~strean frc~
their conflu~nces.
As water levels in the river begin to rise and fluctuate with spring
snowmelt and precipitat1Jn,overflow often occurs onto the ice ,ince the rigid
and impenneable ice cove':faUs to respond quickly enough to these changes.
Standing water appears In s~gs and depre~8ions on the ice Cover.This standing
water reduces the albedo,or refleCtivity,of the ice lIurface,and open leads
-24-
•
qul~kly appear in these depressiona.As the ~ater l.~el rilel an~erod~~the
i~e ~over,i~e be~ome$under~ut and ~ollapsel into the o~~"l ..ad5.dri(t1,.ng :0
their downstrealll ends and s~~uaulating 1n 811:all i~e jalllS.In this ~ay,leads
becOEe steadily wider and longer.This proc"ss is ..spe~ially nouble in the
re.llch frOlll T.alke",tna to DevIl Canyon;in the \lide,low-gradient river bela,",
Talkeetna oren lead,occur less frequently and cKcensiv ..OVcrflo~of ~instec
\later onto the ice cover Is the fir~t indicator of rising water levels.
the disintecratlon of the ice cover into individual fragcents or floes
and the drift of these floea dO\lnstrcttm and out of the river i8 called the
~reakup drive.The natur~l spri~g breakup drive is largely associated with
rapid flow iocreasell.due to precipitation and snotJlllelt.that lift and frac-
ture the ice surface.\i':l(ln the river discharge b ...~o=es high enough to break
and ltOve the ice ,heet.the br...akup drIve begtns.lts intensity i9 dependent
upon meterologi~al conditions durin8 the pre-breakup period.for eltalllple,in
1981 a lIIinta.l snowpack aod light pre~ipitatlon during ~pring cau~ed i~suffi
ci..nt increase in flow 1'0 devf!lop strong forces on the ice cover.and the ice
tended to slowly disintegrate in pllce,produCing f~\l 61toificant ite ja~!ng
events.Conversely,1n 1982 a heavy sno~psck \lith cool carly spring tempera-
tures prevented the ice cover frail deteriorating slgnificantiy during the
pre-breakup pertod,the ice re~ined strong into the later period of normal
spring tellperatures and rising flows,and the tover broke drnutlci!ll1)',pro-
duting severa I large ice jails.
Kajar ice jald generally occur io 51'1.11110\1 reachell ~!th a n.arro'J confining
thalwog tha~nel along one bank.or at sharp riv~r benda.for exalllple.during
tae breQkup o~i,83,staDle ice jams occurred at the follO\llng locations:
-25-
Lane Creek at 1M 11].2
Curry at ~~120.5 and iM 119.S
Slough 9 at RH 129
Shec.an Creek at RH 131.4
Slough II at ilK i34.5
Slough 21 at 1M 141.8
Kajor jalllS are cOllllllOnly found adjacent to side channO!.ls or slouGhs,and a:ay
have played a part in foraing then through catastrophic overflov and scouring
at s~t~in the past.This is known to have h~pp~ned at slough II in 19,0,
as reported by local residents in the area,...hen a brge ice ja::a overflo,",
event altered a previously-existing small upland slough Into a aajor side
slough.
Ilrcakup ice jams cOllll:lonly cause rapid,local stage increali~s thilt contin-
ue rising until either the ja~releases or the adjac~nt sloughs or siue chan-
neb becollle flooded.Il:lilc the jalll holds,flow and larGe amQU:'ltS 01 ice are
diverted into side channel.or .louahs,rapidly erodina away larl~sections of
riverbank and often pushing ice well up into the trees.010 ice .ears can be
.een on trees in some areas up to 10 feet above the bank top.SloUlhs and
other channele between Ta.lkeetna and De.vil Canyon that au reaularly influ-
enced by ice-induced flooding during breakup are shown in Figure 8.
Generally,the final destrucflon of the:ice cover occurs in early to
mid-Hay wh.m a series of ice jams bl'eaio.In louceessl0n,adding their ClaSS and
_entull to the next ja.:ll.downstream.This continu""until the river is swept
clean of ice except for stranded ice flews along shore.ICt!that h ••been
-26-
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Figure 8.Si4e channels an4 sloughs reguL5rly influenced
by 1ce-10duce4 flo041ng 4urir.g breakup (R&M
Cooaultanta.Inc.1983)
Slough 22
Slough 21 fros RH 142.2 to L~141
Slough II fro:.L'1 136.5 to 134.5
Side channels froo L'1 133.5 to 131.5
Side channels frolll RH 130.7 to 129.5
Slough 9
Slough 8A and 8
Slough 7
-27-
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pushed lJell up onto banks above the water level _y last for sO!vecal lo/eeks
before aeltins away In place.
EFFECTS OF YITH-PROJECT l~ST1l.EAM TE!iPERATI'RES
ON 5USITNA M1VF.R ICE PROCESSES
ICECAL I:lOdeling runs show chat operation of the Susltna River Hydro-
electric Project lJould have sl&nl!i~ant effeCts on the lee procc~scs of che
Susitna River,especially in the ralkeetna to Devil Canyon reach,due to
c.hans"s In flOlols and water temperature'in r~.river below the da,C9.C,eneral-
ly.lJinter flOOls "'ould be several tl~s greater tban they are under natu~al
winter c:onditiona (see Appendix A),and "tnter ..·.ter telllperatures \louhl be 0.4
C to 6.4 C where they are normally 0 C icmedlacely below the daas ~Alaska.
Un!v,"[IOC 1984}.The ICECAL co=puter lI:odel de\Ocloped by lIana-Ebasco
5usitna Joint Venturc was used to simulate river ice conditions under various
scen~rios of project operations,with Wacana operating alone and ln conjunc-
tion with Devil Canyon dam,under varying po..-er demand situations.ana ""ith
differing ~llmatic conditions (flgure 3)(Har%a-Ebasco SUiitr-a Joint Venture
19843).The cesults of these simulations are genenilly summari~ed here,with
lIIore specific details in Figures 9 to l~o
WlTlI·PROJECT SanItATIONS,FREEZEUP
FU%ll ice that is generated in the up"er rlver aua.prinCipally ln the
Vee Canyon and Denali attlas.nona.ally drifts dO\ffistrealll lnto lhe 10W'er and
Diddle reachcH of the SUlitnn River and provides the source for initial ice
-28-
-
Start ice front 11-40 days later than natural
progression,Susitna-
Chulitna confluence
Years cOQpared.:
1971-72,cold
1976-77 .....anll
1981-82,cold
1982-8],average
Figure 9.Ieeeal Simulations
WaCana Alone,1996 Energy Oc~nd
Inflow Hatching Releases
(HlIrz&-f.basco Susiena Joint Venture.1984a)
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~
I,
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Maximu[;l upstream ice
~xtent
~lelt out
Most severe ice
conditions &staging
~llldest ice
conditions &stnging
RM 127-140
(mid-December -!;lce March)
]1-51 days earli~r than natural
Thickness 1s statlat to lI;leural
dO\iTlstr~ac of ice front
MaK.stages )-7 feet higher than natural
Thickness is si:D.ilar to natur.11
dOlomstrealll of ite iront
Max.stages 2-5 feet higher than n.Hurs!
-29-
2R.A-OOI
Figure 10.Icecal Si~ulations
Wauna Alone,1996
Warm,I.C Rel€oilses"
(Harza-Ebasco Susitna Joint Ventulc,1984a)
lear compared:
1971-72,colu
Start ice tront 42 days later than natur<ll
progression,Susitna-
Chulitna confluence
19 days lat.r than Inflow
=tchins
Maximum upstrea~
iee extent
~Ielt out
Most severe ice
conditions &staging
RM 127
(I'!d-Jaoua ry)
Thicknesl'l as I:lllch as l>feCI
less than natural
Max.stages as ~uch as 5 feet
higher than natural
13 milCh shortc~than
inflolol r'...Itchlng
49 d:i)'s earlter than inflo..·
matching
Thickness as eucn a~..feet
less chan Inilo~~aeching
Max.stages .-7 feee IO\,ler
chan lnflo..·maechinli
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"Thi~"cenario.with warm waeer releases,was run as a s"nsltivit::
test,and is compared here with both natural conditions,and
inflow matching releases.
-30-
Figure 11.lcecal Sillluilltions
Watana Alone,2001 Energy Demand
InflolO'Matching Releases
(Harza-Ebasco Susitn<l Joint V~nture,1984a)
Years co~p<lred:
197[-72.cold
[982-83.averabt"
Start ice front
prQgressiOll,Susitna
Chulitna confluence
l-laxiculll upstrenc
Ice extent
Melt ...ut
Nost severe ice
conditions !staging
Average ice conditions
to staging
23-44 days later than n.Hural
KM 124-[42
(late January -late Fo,lbruar)-)
Up to 5S days earlier thar.natural
Thickness is siDil"r to narural
dovnstre<lm of ice front
Max_staging 2-6 feet higher than natlil-il
Thickness is slDilar to n.ltllral
downstreal:l of lee front
}lax_,;raging [-11 feet higher than n.H'Hal
-3 [-
I
2RA-OO 10....
Figur~l2.Ieeeal Sigulations
W~tan3 and Devil Canyon.2002 Energy Oe~nd
InflOll ~:atC"hing Reh3ses
(a.u.a-Ebasco Susitna Joint Venture.198401)
Years cOI:lpared:
1971-,2.cold
1970-77 .....3rll
1981-82.cold
1982-83.average
I
I
I
I
Start ice iront
progression.Susi tna-
ChulltnA confluence
Maximum upstream
ice extent
Melt out
Host severe ice
conditions &staging
Hildest iel\!conditions
6 staging
:7-47 dars later tllall n.)tural
Rl'1I:>1-117
(mid-January -:Hd-~arch)
51-59 days later than natural
Thlc~ncss as much as 7 feet less than
n..tural.:-tax.stages liS l::uch as 4 teet
higher than natural
Thickness siailar ~o natur~l
dO'.llstrealll ot ice front.I'Iax.stag~s as
much as 6 feet higher than natural
-32-
••
•..
•••
2R,\-OOI,;v
Hgure lJ.
Start icc front
progression,Susitna-
Chulitna confluence
11axh:lum upstrellc
ic~El'tent
Melt out
Most severe ice
conditions &staging
,\Vl<f.nge ice
conditions &st<lging
Icecal Simulations
Watana and Devil Canyon,202U Enersy Demand
Inflov Matching Releases
(Harza-f.basco Susitau Jo1:lt Ve:lcure,1984<1)
Y~ar~compared:
197t-12,cold
1982-83,<lv{'rage
28-39 days later than n.ltural
RM 127-133
(mid-January -late .J<lnuary)
Up to 59 days sooner thlln natural
Thickn~ss as much as 0 ieet Jess
than naLural
Mal',stage"as I:luch as 4 ieet higher
than n.ltur.ll
Thickness 2-4 tece less th;'11 n3Lur.ll
Max.stagcs as ~uch as 4 ~ce[higher
thun natural
-])-
••••••••••••••
•
bridging and subsequent ice cover formation for =Olt of the those reaches.
With \iatana dtll::and reservoir in place,this frBtU would be rr:lpped in the
reservoir and be prev..nted frolll reaching its norCl81 destinatior.s.Consequent-
ly,freezeup of the river below the dam 'oIould be deloiyed.Later,with the
cOnstruction of Devil Canyon dan and reservoir,t:IOSt of the fratil-generating
rapids within Devil Canyon ~ould be inund:lted,further r~duclng trazil produc-
tion reaching the middle and lower river reaches,and further delaying river
freezeup.
Arrival of the icc frunt at the Yentna River =outh usually occu~s 1n late
October or early Novecber under natural conditions.This tiaing 1s not ex-
pect~d to be significantly altered ~ith-project in spite of the reduced frazil
input from the upper Susitr.a Riv~r because the ice contributions fore the
Yentna River and other ~jor tributaries would re~in the sace.Based on this,
November 1 was useJ by IC~CAL as a representative date for the passage of the
ice front by the Yentna River .cuth.Ho~ever,reduced irati I input would sl~
the advance nte of the leading edge.These effects ',ould cocbine with the
higher winter flows and warmer water tecperatures to produce a delay of ini-
tial freezeup at the Susitna/Chulitna confluence ranging fro~about 2 t~5
weeks with Wat~na op~rating alone to 4 to 6 weeks with Wat3na and Dev11 Canyon
operating together (F1gure 14).
Ttl/!wormer water tC'llperstures released from the dams would not cool to
the freezing level for B number of miles (Figures 9 to I)and would prevent
iCll frOIll fOfllling nIl "'inter thllle,except for some border ice attached to
shore.The maximum upriver extent of ice cover progression below the project.
with "'stana operating alone,>;ould vary £rolll RJol 124 to lUi 142 depending on
-)4-
Starting Date Maxlmu:l
at Chulitna Helt-Out l'pst I"fO:(Io.
Confluence Date Extent
(River Mile)Natural Conditions
137 N1971-72 Nov.,
1976-77 Dec.•137~
1981-82 Nov.I'H.y 10ilSB 137~1982-83 Nov.,H.y 10 Il7 S
W'atana Only -1996 Deman.J
II'1911-72 Nov.28 H,y 1401976-17 Dec."Ma~'3~1)7
1981-82 Dec.28 Aprll 3 1)7
1982-83....Dec.12 Hat.20 1271971-72 Dec.17 Har.21 127
W'lItana Only -2001 Dc::oand
"1971-72 Nov."Hay 15-141
1982-83 Dec.19 Harch 16 124
Both Dams -2002 Deliland
"1971-72 Dec.2 Hay 3-1)7
1976-77 Jan.10 Apr II 20 116
1981-82 Dec.30 Har.12 124
1982-83 Dec.22 Har.20 12r
Both Dams -2020 Demand
1971-72 Dec.3 "prO I'1331982-83 Dec.14 Hu.12 127
•••••••••••••••••••
Legend;
Notes:
Flgurc 14
lCEC,\L simulated ice front progression and t·leltout dates
(Harza -Ebasco Susl.tna Joint Venture,198'.tI)
B Ob.:erved natural break-up.
E Helt-out date is extrapolated froQ results when occurring beyo~d
Aprll ]0.
N Ice cover for natural conditlons elttends Upstrealll of Gold Creek
(River Mlll1!137)by 1lI11!ans of lateral lee brldglng.
I COlllputed ice front prog:esslon upstrealll of Gold Creek (River
Mlle 137)15 approxilllation only.Observations indicate closur~
of river by lateral ice ln this reach for natural conditions.
1.~Case CH instrea:n flo\'!requirements are assuced for with-project
Sltlulatlons.
2.1971~72\.1 sta:ulation Ilssu=es ""arm,4·C reservoir releaJ'es.All
other ""lth-project shlUlatlons IlSSUllle an "tnflo\'!-oatehing~
temperature polley.
-]5-
••••••••
I
••••••••••
~inter cliaate and operational scenario (Figures 9 to ll).Sl~11arly.~ith
both Warsoa and Devil Canyon operating,th~ma~loum ice cover extent ~~uld he
frol:\RM 12J to I>M 137 (figures 12 arod 13).The ice:front lOould reach its
~xl~um position between mid-December and late ~rch for ~atana alone and
mid-January co mld-!".arch for Wataoa ...nd Devil Can)'on together.but would fluc-
tuate considerably In position for the rest of th~wint.'!f rlependlng on pre-
vailing air temperatures (see Appendices C :0 G).
Under natural conditions.in :lome ye:>rs an ice bridge Coms at the
Susitna/Chulitna confluence before the icc front progressiun in the lower
river has reached there.Also,In se"'ercly cold ~erlods s",condary bridges
form above tho!confluence causing secondary l.,ading edge progressions.....ith
the project in place these conditions l:l.1y not occ"r,and ICr.':AL simulations
are baseJ onl~on the initiation of an ict hridge at the Su~itn3/Chulitn3
coni:lucncc after the lower river ice front has reached there.Further,lCECAL
assumes only one leading edge progres~ion above the confluence.
Increases lon winter discharges in the river below the dams would cause
staging levels during freezeup to be significantly higher than natural down-
stream from che ice front.In that reach,where the ice cover !o~s.staging
1~expected to be 2 to 7 f~et higher than noreal with ....atana operating alor.e
(Figures 9 to 11),"'hile with both dams operational,stages should be about
to 6 feet higher than nOI1Jl1l1 (Figures 12 and L3).Downstream frOQ the ice
front,more ~loughs and side channels would be overtopped,more frequently
n 19ures L5 tl'.7).
-36-
•..
•••
Occurrences l
'"O!arza -
Figure IS
....here 1Jlth-project m:l;dr.lul!!river stages
higher than natur~l conditions
Ebasco Susitnn Joint Venture.1984'1)
••••••••••••••
lJatana \Jatana and
Slough or River Only Dev!1 Cmyon
S.(de Channel Hile 0perattn\::Opel"at Ing
\.'hlskers 101.5 '/6 ./6
Cosh Creek H2.0 '/6 'I'OA 11203 ".5/6
8 111,.1 '/'./.
HSII 11~)'5 ./../.
HSI I 115.9 ./.'/'Curry 120.0 '1'3/'
!'1<'lose 12].5 '/''I'8A ;,rest 126.1 5/.,/.
SA East 127 . I 'I'2/.,129.]'I'2/.
9 uts 130.6 3/.0/.
"eh July DL8 3/6 2/6'A 133.7 3/.1/.
10 "I,134.3 'I'1/'
II dt.135.J 3/.0/.
II 136.5 'I'2/.
Notes:
I.For exa"-ple.4/6 Ille<lnli that 4 of the 6 with-project 61Clulaclons
resulted In a higher maximu.::l river Itage than the natural
conditions for correspon.:llng ...inters.
2.-Case e"Inlltrealll flow requirements and Minfle....-matching ..
reservoir relense temperatures are 3SlIllll:ed for \lIth-project
1II1all,llat tons.
-)7-
-• • • • •• • •• •• • • • •• • •
WA'M'ADNlY
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Sloo.th n .....,_,W"."'01"'<'.1>,.,...,~......no'...1
cond,,-..'",...«,"..'w'..........,n,,'
SIo.4>,_..,t....'w,oI <o,.,J,,_••
....,...,,_"""",o,oe'
"01E5
t '·C...c~,"'"._,,_w ""'".,,"~-'hH .."I.' •.-...,.....
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........;"'~,........n ,"H,_.,.,,.,•
Figure 16.ICECAL slmuln tions.Slough over topp log.
5u8ltna Joint Venture,1984'1)
(llano -Ebasco
o
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•,
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0-
"0'N=.~,-
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-39-
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Winter dtlehargeb would be hit~er than nor~l bur no free~eup sraging
would occur upstream fro=the ice front's ~ximum position and water level~in
that reach would be 1 to J feet 10000l!r ttan natural hee~.!lIp flta~tng l~\'els
with Uatana operating alone,and 1 to 5 teet h""er witn both dalll~op"rattng.
Thereiore.no sloughs should be oVertopped.HO'.Iever,lack of fr~ezeup staging
in this reach of the river may prevent or reduce grou~dwa~er upwelling In tte
sloughs.Natural freezeup staging causes ap?roxigately tho!s~ne hydraulic read
to exts~between the calnstee and adjacent sloughs as occurs during su~er.
\.:ith tbe project in place and no free~eup staging occurrtng,the hvdraul1c
bead would be reduced.
Since the tce edge would not ad'JOulce al far.or as rapldh·.during pro-
jl<Ct operations as during natural cor:ditions,~rt'"reas of open ,"'atet ...ould
exist.and they would reeltn longer than usual.This could cause lh..inci-
dence 01 lroOre anchor Ice during cold periods.This eight cau:.e the fon-..a.tion
of &llght backwater areas because of the geperol raising of th~channel bOl-
lOlll,posstbly ..ffecling flow distribution belveen channels lo'irh lolo'bel"Cl!l.
Where an ice cover forms.the oaxil:lul:l lotai tce thickne1JI lo'ith k'alolna
operating alone are expect~d to be generally sl=ilar to natural tee thickness.
~ith bOl~da~s operating,~~icuro total tce thickne~s should be about I to 2
feel le!:l~than natural ice thickness (Figures 18 and 1':1).
Simulations of 4 C releases froc the project,compared t~sil:lulntions of
"intl'Jw JIl{tchinK"release"(Figu!'e 10)show that l:<lntrol of reservoir lc!"ase
fclll ..crOtur~s may have :I.significant effect on river ice processes,Control of
release telllperntures h~s been used by so~e hydroelectric projects to control
-40-
•••'"•••••
SUSITNA HYDROELECTRIC PROJECT
TOTAL ICE TIUCKNESS
MAXIMUM SIMULATED VAlUES3
"A',IIlA,
COt.OOllUHJ
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(u ...,,_=....,
II.......$0<0 ....,....,
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011.''.."0_,1010<'.'1.'1......._to -'"I1.""~'ftl-,_...'u,.....1"'.
"'hl,'ft•••I .l Fig""...!CECAL .lm"'"I,""T",I 10.
SutlJtntl Joint Venture,19843)
thlckne»s.(Hlur.a -Ebotlco
J;Cl•,••6 ~->uo u-",0
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Eo ':;.~...::;;;..
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<><><>0,_____-=_::---:I --;l.. ..<> <><>°1
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-42-
ice conditions below the dams.especially ~hcre rivers~de towns or other de-
veloped areas have been threatened by project-relateu ir.~onditions.
WITR-PR01~~7 SIMULATIO~S,BREAKUP
5reakup processes ~re expected to be different in the Susitns River below
the project,esr::.cially in the Talkeetna to Devil Canyon reach.Since the
maxi~u~up~trea~extent of the ice cover below the daas would be .~me~here
b~twP~n RM 124 and aM 142,there would be no co~tinuou8 ice cover between this
~rea and the denaite,and consequently no breakup or meltout in thAt reach.
Any border ice attached to shore would probably slowly aelt away in place;
occasional pieces of border Ice might break away fra-shore and ~loat d~~
strea~.Ice in the river rench above the project woulu break up normally,but
would not drift Into this areu ;H'It normallr does becsu!!e it would be trapped
in the reservoirs.
The no:-o.al spring breakup dr~ve Is usually brought on by :'3rld flow in-
crealies that lift and fracture the ite cover.The proposed project reservoirs
wou·'regulate such seasonal flows,yielding a more steady flow regime and
resulting in a slow l:Ieltout of the ice cover in place.
The wa[1ller-than-no~1 water temperatures released from the project would
cause the upstream end of the ice cover to begin to decay earlier in the sea-
son than normal.Cradual spring meltout with Watana operating alone is
predicted to be 4 to 6 weeks earlIer than normal,and 7 to 8 weeks earlier
tt..'\n nomal with both d<ll:ls operating.By May.flow levels in the river would
be siln~[icantly reduced ••the project begins to store incomIng flow~from
upStream.Th('re6ult is expected ro be that breakup drive procelllles that ,101.'
-43-
normally occur in the middle river area ~ould be eff~ctiv~ly eliminated.
Instead.a slov and steady meltolJt Ot rJ.ver J.cc in Li.!.:t:.:!~"::'::~':;::::::::::1.-
occur.Since there would be nu extenSive voltme of broken ice flo.iting down-
streaa and accuculating against the unbroken ice cover.ice jall:lll.ing in the
middle river would usually not occur or would be substantially reduced in
severity.This ~ould elioinate or substantially reduce river staging and
flooding normally associated with ice jams.thereby el1al.natil'lg or greatly
reducil'lg t;le overtopping of bet1lls and the flooding of side sloughs.
In the lower river below the SU5icna!Chulitn3 confluence,breakup sev'!ri-
ty woula probably ailio be reduced due co the 10000er flows occurring in the
river during breakup.Ice thicknesses 1n thilJ rt!lIch,howeve!".may be sOl:lewhat
thicker than non:ml because of the higher ~inter floo.:!l frolll the project.
FURTHER STUDIES
Studies of l~tural ice proceSSl<S by R ,:1 Consultants,Inc.are continu-
ing on the Susitna River.Further ICECAl.oodel runs are being carried out by
Harza-Ebasco Susitna Joil'lt Venture.co address oth...r with-project scenarios.
Also.simulations may be produced for othcr project flov regines beside Case C
if'these are identified as deSlreable.The results of these observlltior.s and
s~ulation studies wIll be included in the report addressIng the effects of
altered river ice processes on aquatIc habitats and fIshery resourccs,to be
completed in the spring of 1985.
-44-
I
I
I
I
I
I
I
I
I
I
REFERE!;CES
Acres American,Inc.1983.Application for licenSe for llllljor project,
Suslcnn Il)'droelecttic Project.before the Federal Energy Regulatory
CommhisfOfl.Vol.5A.Exhibit E,"hap.2.Alaska Power Authority.
Susiena Hydroelectric Project.Vol.
Alaska University.Arctic Environmental Info=athm and Data Center.
1984.Assessment of rhe effects of the propoi'led Susitna llydrolec-
eric Project on instrealll telllpCriltur~and fishery resources i.n ti:~
Watana to Talkeetnn reach.Drilft report ...mgusr.2 \'oJi'.
Ashton,D.1978.River ice.Annual Revie...."on Fluid Mechanics.
10:(J69-392)
Bilello,A.1980.A ....inter environmental data survey of the drainage
basin of the Upper Sl,Isitna River,Alaska.U.S.Army Corps of
Engineers,Hanover,NH.Special Report 80-19.
Har1.a-Eb~sco Susitna Joint Venture.(984a.lnstream ice simulation
study.Alaska Power Authority.Susitna Hydroelectric Project.
Draft report,Septelllber.Z vols.
Hana-Ebasco Susltna Joint '/encure.1984b.Instrealll ice calibration of
COClputer molicl.Final Report.Alaska PlllJer Authority.Suaitnll
Hydroelectric Project.APA Docucent IIZZ.1 vol.
-45-
I
I
I
I
I
,
,
I
Michel.1971.Winter regiml!of rivers and lakes.Cold Regions
Research lind Engineering Laboratory,U.S.Ar/;lY Corps of Engineers,
Hanover,~H.130 pp.
Osterkamp.T.E.1978.Frazll Ice Fonnation:a revie....Journal of
the)'Hydraulics Division of the Ai::erican Society of Civil
Engineers.IO'(N9):1239-1255.
R6l'1 Consultants.Inc.1981.Ice observations 1980-1981.Anchorage,
Alaska.Alaska Pl,Ner Authority.Susiena Hydroelectric Project.
Report for Acres A!:Ierican,[ne.1 voJ.
___1982.tce observations 1981-1982.Anchorage,Alaska.Alaska
Power Authority.Susitna llydroelectric Project.Report for Acres
Nllerlcan,Inc.vol.
~__198].Susiena River ice study 1982-1983.Anchorage,Alaska.
Alaska PO\ler l.uthority.Susien...Hydroelectric Projloct.Report for
Harza-Ebasco Susitna Joint Venture.1 vol.
___1984.Susitna River ice study 1983-1984.Draft:.Anchorage.
Alaska.Alaska Po:.rer Authority.Susitna Hydroelectric Project.
Report for llarza-Ebasco Susitna Joint Venture.1 vol.
2AA-OOlc
-46-
2RA-OOIb
APPENDlX A
Susitna Ril1er natural str"!amflowl',and
with-project reserlloir discharges.
-47-
oooo
~
III,,
;;Iz
~II',
I II,,IIII:,I
~~l
i :i: I '~~~ii,
,I II.,~r
I I i
I Irrr-~~
i i \'
'I 'I,-·~J:I I!i I
iii @g~~o--.!....---,-----------,----l
o 0 0~0 0~0N
It
r r r ..."....................
-----------
NOTE:Discharges shown are averages among the
1971-72, 1976-77,1981-82 and 1982-83
winter weather conditions simulated
Discharge
From
Reservoi r
Watana
Watand
Devil Canyon
Devil Cani'on
1996
2001
2002
2020
Energy
Demand
\
r i
J,iI
t-,f/\\l
"
LEGEND:
'\.-
"---\
I
-j-:--
6000
14 000
I ;-----'._-
:\
12000 -l r--/"I
..
/r ~
'I ~,~
10000 ...~
~
~
~
~
~
~
~
8000 ~~-'/----\0
~
~
/-/--
•000 -'I----,=--,-=;;--,--;c;-;;--...-:=-,--=;;--,--;c=--,t NOV.I DEC.I JAN.I FEll.I tolAR.I APR.I
DISCHARGE FROH :-ROJECT RESERVOlltS
2RA-GOlb
APPENDIX B
ICI::CAL Simulations of natural tee front
progression in the ciddle ~usitna River.
1971-72,1976-77.1981-82.19f12-83.19S3-8l..
(Harza-Ebasco Susitna Joint Venture.1984a)
•
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2RA-OOlb
APPENDIX C
tCECAL si~ulations of ite front progression,Watana
alone,1996,inflo\l matching releases,1971-72,1976-77,
1981-82,1982-83.(Harza-Ebasco Susitna Joint Venturt!,
1984a)
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2RA-OOlb
APPENDIX D
ICECAL simulations of ice front progression,
Watana alone,1996,4 C releases,1971-72
(Harza-Ebasco Susitna Joint Venture,1984a)
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2RA-OOlb
APPENDiX E
ICECAL simulations of ice front progression,
Watana alone,2001,inflol.l ~atching releases,
1971-72,1982-83 (Harza-Ebasco Susitna Joint
Venture,1984a)
i
I
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2RA-001b
APPE!';1HX F
lCECAL simulations of ice front ptogression.
Watana and Devil Canyon.2002.inflow CUltc:hing
releases.1971-72.1976-77.1981-8:!.1982-83
(Hana-Ebasc:o Susitna Joint Venture.1984a)
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2RA-001b
APPENDIX G
ICECAL s1roulations of ice front progression.
Watana and Devil Can~·on.2020.inilo....matching
releaSCd.1971-72.L982-83 (liana-Ebasco Susitna
Joint Venture,19848)
..
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