HomeMy WebLinkAboutSUS520PRELIMINARY DRAFT
IMPACT ASSESSNENT TECHNICAL MEMORANDUN
INSTREAM: ICE
Prepared By:
Arctic Environmental Information and Data Center
University of Alaska-Fairbanks
707 11 A" Street
Anchorage, Alaska 99501
Submitted to:
Harza-Ebasco Susitna Joint Venture
711 11 H" Street
Anchorage, Alaska 99501
1985
TABLE OF CONTENTS
INTRODUCTION •
PURPOSE .
STATEMENT OF THE PROBLEM •
OVERVIEW OF ENVIRONMENTAL ASSESSMENT TECHNIQUES.
METHODS AND PROCEDURES
FISH RESOURCE.
IMPOUNDMENT ZONE •
MIDDLE RIVER •
LOWER RIVER
THE WITH-PROJECT ICE REGIME.
ANALYSIS
ANTICIPATED NEGATIVE EFFECTS
Watana Reservior •
Devil Canyon Reservoir •
Middle River
Lower River.
SUMMARY
REFERENCES
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INTRODUCTION
PURPOSE
Impoundment of the upper Susitna River would cause a change in the
natural pattern of instream ice formation and breakup.This document is a
comprehensive assessment of the effect of the with-project ice regime on fish
associated with the proposed upper Susitna River basin hydroelectric
development.Since Instream ice and breakup phenology are important variables
affecting habitat for Susitna River drainage fish.studies were initiated in
the beginning phases of Susitna environmental investigations to identify
potential adverse or beneficial with-project effects of the expected
alteration.
This report is one in a series on aquatic impact issues associated with
the Susitna Hydroelectric Proj ect.These issues instream temperature.
water quality.turbidity,instream ice,and bedload are examined separately
in five separate technical memoranda.Following review they will be
integrated into a single draft impact assessment report.The Alaska Power
Authority and Harza-Ebasco intends to utilize the final impact assessment
technical memorandum to discuss issues with agencies and intervenors in the
Susitna licensing process.
Impact issues addressed in this series of reports were defined in the
course of the Susitna licensing process.Following Federal Energy Regulatory
Commission (FERC)review of the original license application,the Alaska Power
Authority corrected noted deficiencies and provided supplemental information.
The license application was subsequently ruled acceptable.FERC then
proceeded with the preparation of an Environmental Impact Statement (EIS).
This decision set in motion a chain of events in accordance with Council on
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Environmental Quality mandates on EIS preparation (Vide 40 CFR 1500).
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Significant issues to be analyzed in depth in the EIS were identified during
scoping meetings.Twelve fishery were identified to this process;of these,
Issues F-3 and F-5,addressed with-project ice related phenomena on salmon and
resident fish habitats and populations.
APA commissioned a series of environmental field investigations and
analyses of existing published and unpublished information to provide accurate
statements of expected impact of the Susitna project on the natural ice regime-
-and subsequently,on fish resources.Over the years the data base and
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statements of anticipated effects have been scrutinized by agency and
intervenor representatives in a series of workshops and discussions.This
process has refined the data base and impact statements based on it.
This document is intended to serve as a discussion document and as an aid
to decision-making.It contains a presentation of the instream ice issue,a
brief synopsis of the relevant information base,the ramifications of ice
related phenomena to aquatic habitats and fish,and the projected effects on
fish due to various modes of Susitna project operation.It does not contain
voluminous data and analyses of ice related issues.Statements of effect or
of no effect and the confidence with which those statements are made ar~
provided.
STATEMENT OF THE PROBLEM
The proposed project is sited in the upper Susitna River drainage basin
and consists of two dams to be constructed over a period of about 15 years.
The first dam,known as the Watana Dam,would be completed near RM 184 at a
site three miles upstream from Tsusena Creek.It would include an underground
powerhouse and an 885 ft high earthfill dam and a reservoir approximately 50
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miles in length..This reservoir would have a surface area of 38,000 acres and
a usable storage capacity of 3.7 million acre-feet (maO.The second dam,
named Devil Canyon,would be built near RM 152 at a site 33 miles downstream
of the Watana dam site.It would be 645 ft high and would impound a
26-mile-Iong reservoir,having a surface area of 7,800 acres and a usable
storage capacity of 0.36 maf (Acres American,1983).
Construction and subsequent operation of the two Susitna hydroelectric
dams is expected to alter the normal ice regime of the river,thereby
influencing fish and their habitats.With both dams .on-line,the area between
Devil Canyon (RM 152)and the Oshetna River (RM 235)would be converted from a
lotic tp a lentic system.After impoundment,these reservoirs would resemble
naturally occurring,deep,glacial lakes (Acres 1983).
Winter reservoir drawdown would cause ice to fracture and drape over
exposed banks,thereby destablizing nearshore environments.In the
with-proj ect middle river,formation timing of a contiguous river ice cover
would be delayed;an extensive reach of ice-free water would occur below Devil
Canyon;winter river flow volumes would be four to five times greater than
natural;and ice meltout would occur earlier than normal.Portions of the
river near the ice front would be subject to freezeup staging,a natural
phenomena which often leads to overtopping of slough berms.With-project,
however,staging would be of shorter duration than occurs naturally.
With-project increased winter flows relative to natural could lower the
temperature of upwelled water in sloughs;natural upwelled water temperature
is believed to be an important variable of salmon incubation habitat.Breakup
would no longer occur in springtime with-project because of higher than normal
water temperatures and steadier stream flows.Ice would instead melt
gradually in place;this would lower the potential for ice jam formation.
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OVERVIEW OF ENVIRONMENTAL ASSESSMENT TECHNIQUES
Over the past 30 or so years,a variety of methods have been developed
for use in evaluating environmental impacts.The impetus behind this effort
was,and remains,federal resource management law.Prominent federal
environmental acts (table 1)were reviewed to identify fish and wildlife
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impact assessment requirements.Four broad areas of public interest form
common themes in environmental law:species-populations,biological
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integrity,environmental values,and habitat.Common methods of addressing
these themes are reviewed below,as is the methodology used in this analysis.
The first class of environmental assessment techniques examined is that
addressing the theme of species-populations.Notable federal acts calling for
this approach include the Endangered Species Act,the Federal Nonnuclear
Energy Research and Development Act,the Surface Mining Control and
Reclamation Act,and the Federal Water Pollution Control Act (table 1).
Many and diverse schemes exist for estimating population numbers and
density.The simplest technique,and possibly the one in widest use by
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managers,is the index.Population assessment indices are of two distinctly
different types.The first is a count of animals made in a manner which does
not allow direct population estimation by application of sampling theory •
This technique employs a sample survey in the absence of known sampling
probabilities.Many ADF&G fish escapement surveys are of this type.The
second kind of index is one based on complete counts of some known portion of
a population,e.g .•salmon on redds in a given reach of river.This approach
allows one to conduct a relatively intensive and statistically valid analysis
by incoporating basic knowledge of a species life history with the count data.
Multiple regression analysis is the most frequently used tool in this regard.
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Table 1.Federal acts which independently and collectively establish minimum
standards for environment impact assessment.
Archeological and Historic Preservation Act,16 U.S.C.469,et seq.
Clean Air Act,as amended,42 U.S.C.7401,~seq.
Coastal Zone Management Act,16 U.S.C.1451,et seq.
Endangered Species Act,16 U.S.C 1531,et seq.---
Estuary Protection Act,16 U.S.C.1221,et ~.
Federal Land Policy and Management Act,43 U.S.C.1701,et seq.
Federal Nonnuclear Energy Research and Development Act,42 U.S.C.5901 ~seq.
Federal Water Pollution Control Act,33 U.S.C.1251,et seq.
Federal Water Project Recreation Act,16 U.S.C.460-(ITi)~et seq.
Fish and Wildlife Coordination Act,16 U.S.C.661,et seq.-----
Forest and Rangeland Renewable Resources Planning Act,~U.S.C.1601,et seq.
Land and Water Conservation Fund Act,16 U.S.C.4601 -4601-11,et seq.
Marine Protection,Research and Sanctuary Act,33 U.S.C.1401,et seq.
National Environmental Policy Act,42 U.S.C.4321m et seq,
National Historic Preservation Act,16 U.S.C.470a,et seq.
National Forest Management Act,16 U.S.C.472,et seq.
Rivers and Harbors Act,33 U.S.C.403,~~.-----
Soil and Water Resources Conservation Act,16 U.S.C.2001,et seq.
Surface Mining Control and Reclamation Act,30 U.S.C.1201,et seq.
Water Resources Planning Act,42 U.S.C.1962,et seq.
Watershed Protection and Flood Prevention Act,-Y6~S.C.1001,et sea.-------'-
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More involved methods of population assessment include direct counts and
variants of the mark,release,and sub sequent recapture technique.Direct
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counts are best in terms of validity,but naturally turbid conditions in the
Susitna drainage hamper its use there.Over the last decade,the ADF&G and
the USFWS have expended much effort in improving electronic fish counters for
use in turbid conditions.This work has greatly influenced census work in
many glacially-moderated systems.
Mark-recapture techniques have a relatively long history of use in the
United States.~~ile widely used and under continual evolution,none of them
produce overly satisfying results in a statistical sense.This is because all
mark-recapture techniques rely on a range of assumptions which are difficult
to meet in the wild (e.g.,one common assumption is that there exists a well
defined population of animals;another is that the average probability of
observing a marked animal is equal to the average probability of observing an
unmarked animal).
The second class of environemtal assessment techniques examined addresses
the theme of biological (i.e.ecological)integrity.The chief pieces of
legislation calling for this approach are the Federal Water Pollution Control
Act and the National Environmental Policy Act (table 1).If fully applied,
such an approach would document energy flow through the system allowing one to
precisely predict overall effects of change.In practice this is never done
because it is very labor intensive and,thus too costly.Instead,it is
common for a "few representative species and/or relationships to be singled out
for study,thereby narrowing its scope.Field study is typically undertaken
to document seasonal numbers of target species in the study (often without
regard to their relationship to local or regional populations),their habits
(e.g.,special use areas),and food resources.Biologically based assessments
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have increasingly made use of models (some elaborate,some not)to predict
with-project effects.Two factors limit the veracity of conclusions reached
by this approach.First,a given model's ability to predict the future
depends heavily on whether it is multidimensional or not and on the
-assumptions used.Most models used are one dimensional limiting their
utility.Second,conclusions reached in this approach are subjectively
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applied ad hoc to the system as a whole.
Consideration of economic and environmental values (the third of the four
areas of public interest addressed by federal law)is the essence of the
National Environmental Policy Act.This approach to impact assessment usually
entails estimating the monetary and nonmonetary values of the resources to be
affected.Implementation of a values approach to impact assessment is (and
will continue to be)limited by the difficulty (some would say the
impossibility)of setting values on often intangible environmental components
such as aesthetics.
The fourth approach to environmental impact assessment recognized by
federal law is habitat analysis.The principal laws legitimizing this
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approach are the Federal Land Policy and Management Act,the Fish and Wildlife
Coordination Act,the Forest and Rangeland Renewable Resources Planning Act,
the Endangered Species Act,and the Surface Mining Control and Reclamation Act
(table 1).Various techniques are available for characterizing habitat
"""quality.For example,species diversity is often used as an index of habitat
quality.This type of index accounts for both numbers of species and numbers
of individuals of each species in each habitat type.The approach has been
challenged on a number of grounds.For example Wiens (1978)points out that
it is insensitive to which species are present (i.e.,it treats rare and
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common species alike),while Inhaber (1976)notes the absence of a standard of
comparison (a problem of all biological indices).
Another habitat based impact assessment approach is the U.S.Fish and
Wildlife Service's Habitat Evaluation Procedures (HEP).HEP is a
species-habitat approach;habitat quality being denoted through use of an
index derived by evaluating the ability of key habitat components to supply
the life requisites of the subject species.Its chief limitation is that
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predictions made are applicable only for the species being evaluated,i.e.,it
does not directly relate that species to other ecosystem components.
The U.S.Fish and Wildlife Service's Instream Flow Incremental
Methodology (IFIM),another habitat based approach,is closely related to HEP
in logic.It too focuses on target species relationships with their habitat,
defined as Weighted Usable Area (WUA).Water depth,velocity,and substrate
data are coupled with habitat suitability curves to compute WUA.The chief
limitation of this approach is that it fails to take into account the effects
of with-project change on factors such as growth,competition,mortality,and
movement.These limitations are at the heart of a recent benchmark judicial
ruling (Energy Management 1984)against use of the IFIM and in favor of a less
rigorous,more qualitative,approach.
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METHODS AND PROCEDURES
The existing Susitna River Information base consists of a mix of
quantitative and qualitative data and model results:some is compatible,some
with-project environmental parameters are well known,as are
responses of aquatic organisms to changes of the types predicted.
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is not.It is strongly biased towards habitat descriptors.Natural and
the likely
Given this,
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a habitat based impact assessment is the logical technique of choice for the
Susitna River study.
This analysis was accomplished by comparing predictions of the
with-project environment with information on fish distribution,abundance,and
habits and on known fish and invertebrate response to perturbations of the
types predicted.Professional judgement was used as necessary to interpret
the relationship between various data base components,1.e.t the relative
comparability and utility of quantitative information vs.qualitative
information vs.model runs.
To assess effects of with-project changes in the ice regime on instream
biota t AEIDC first reviewed the information base on how ice related phenomena
affects aquatic organisms.Next,information on Susitna River fish stocks was
assembled and synthesized.Following this t estimates of with-project
environmental changes (and the information and procedures used in deriving
them)were reviewed.These changes are based on ICECAL simulations,DYRESM
reservoir ice simulations,groundwater analysis t intragravel fow and
temperature analysis,and sediment transport studies.
These three steps (determining how various life forms are affected by
different ice conditions,compiling information on the fish resource,and
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reviewing project ice studies)provided the basis for predicting effects of
the with-project ice regime on aquatic organisms.
Both the information base on fish stocks and that on the with-project ice
regime are adequate for use in an effects analysis.Available information is
sufficient to address ice effects on 13 of the 19 fish species present in the
project area.These are all five salmon species,eulachon,Bering cisco,
burbot,round and humpback whitefish,rainbow trout,Arctic grayling,and lake
trout.
This analysis was constrained by a number of factors.Chief among these
was that the models used were designed primarily to address physical process
~se,rather than the effects of icing on animals and their habitat.
Second,extant Susitna River basin data on fish distribution,abundance,and
habitats focus on salmon and are temporally and spatially limited.Third,
knowledge of the effects of various winter conditions on fish mortality rates
is particularly scant.
The veracity of conclusions reached varies by species and by river reach
in consequence of differences in available information quantity and type.
FISH RESOURCE
Judged against criteria for EIS preparation (40 CFR 1500),existing
information on Susitna River fish resources is generally adequate for an
assessment of with-project effects.(An EIS is simply an accounting tool
whose chief purpose is to ensure that all elements deemed significant by the
scoping process are considered in decision making.)Available information on
open water season salmon-life stage activities (distribution,abundance,
spawning timing and location,rearing,and migration)is quite complete;the
overwinter salmon data base is much less so.Nonetheless,it is sufficient
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for the purposes used.Tables 2 ,and 3 respectively provide an overview of
basinwide salmon escapements and the time of occurrence of their major life
phases.As with salmon,information on resident species is much more complete
for the open water season than it is for winter.Unlike salmon,however,it
is heavily weighted towards selected species.It,too,is sufficient for EIS
preparation purposes.Information on rainbow trout,burbot,and Arctic
grayling in the open water season is more complete than for other residents.
With the exception of limited winter radio-tagging data for rainbow trout and
burbot,little is known of the life histories of resident fish at this season.
A synopsis of available fish resource information follows.
IMPOUNDMENT ZONE
The principal source of information on fish distribution,abundance.
habitat use,and life history in the impoundment zone is ADF&G 1981a and
1983d.Impoundment study area investigations were conducted in 1981 and 1982
by ADF&G Su-Hydro during the open water field season (May-October).These
studies concentrated on Arctic grayling,making data on this species the most
complete.Data on overwintering activities in this area is particularly
scarce for all species.The major objectives of this study were to~
1)determine the seasonal distribution and abundance of fish populations in
the proposed impoundment area;2)identify spawning and rearing areas;and
3)determine the physical and chemical characteristics of these habitats
(ADF&G 1981a.1983d).More specific tasks dealt with determining the
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distribution,abundance,and migratory habits of Arctic grayling;determining
the distribution and relative abundance of selected resident fish species;
determining the abundance of lake trout and Arctic grayling in Sally Lake;
recording biological information on selected resident fish populations to
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Table 2.Susitna River Salmon Escapement Estimates~1981-1984.
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Chinook Sockeye 1 Pink Chum Coho 2YearTotal
1981 272,500 85,600 282,700 36,800 677 ,600
1982 265,200 890,500 458,200 79,800 1,693,700
.....1983 176,200 101,300 276,800 24,100 578,400
1984 250,000 605,800 3~629,900 812,700 190,100 5,488,500
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1 Second run sockeye only.
2 The 1984 drainage wide escapement estimates.Escapement counts for 1981
through 1983 do not include chinooks or any escapements into tributaries
downstream of RM 77,with the exception of those into the Yentna River.
Source:ADF&G 1983a;Barrett,Thompson,and Wick 1984, 1985.
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Table 3.Susitna River Salmon Phenology.
(cont'd)
DATE
HABITAT RANGE PEAK
Spawning Middle River Tributaries Jul 27 -Oct 01 Aug 05 -Sep 10
Middle River Sloughs Aug 05 -Oct 11 Aug 20 -Sep 25
Middle River Mainstem Sep 02 -Sep 19
Lower River Tributaries Jul 27 -Sep 09 Aug 06 -Aug 14
SOCKEYE (RED)SALMON 2
Adult Inmigration Cook Inlet -Talkeetna Jul 04 -Aug 08 Jul 18 -Jul 27
Talkeetna -D.C.Jul 16 -Sep 18 Jul 31 -Aug 05
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Juvenile Migration Niddle River 1&3 Jun 22 -Jul 17Nay18-Oct 11
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"-t-o .Spawning Middle River Sloughs Aug 05 -Oct 11 Aug 25 -Sep 25
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I PINK (HUMPBACK)SALMON
....._,.Adult Inmigration Cook Inlet -Talkeetna Jun 28 -Sep 10 Jul 26 -Aug 03
\...lJ Talkeetna -D.C.JulIO -Aug 30 Aug 01 -Aug 08
Niddle River Tributaries Jul 27 -Aug 23
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Middle River Sloughs Aug 04 -Aug 17
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1;Juvenile Migration Niddle River May 18 -Jul 24 May 29 -Jun 08
Spawning Middle River Tributaries Jul 27 -Aug 30 Aug 10 -Aug 25
Hiddle River Sloughs Aug 04 -Aug 30 Aug 15 -Aug 30
Lower River Tributaries Jul 27 -Sep 09 Aug 06 -Aug 09
~All migration (includes migration to and between habitat.not just outmigratibn).
3 Second run sockeye only.
No data available for pre-breakup movement;earlier date of given range refers to initiation of outmigrant
trap operation.
Source:Barrett,Thompson and Wick 1984.1985;Schmidt et a1.1984;ADF&G 1983a,c.
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provide information on survival and growth;and identifying Arctic grayling
spawning and rearing locations within and adjacent to the with-project
impoundment areas (ADF&G 1983d).
Prior to initiation of the 1981 ADF&G Su-Hydro studies,fish resource
data for this area were collected by the U.S.Fish &Wildlife Service (1952,
1954,1957,1959a,1959b,1960,1965)and ADF&G (1978).These studies were
preliminary Susitna environmental assessments designed primarily to define
species composition.They also highlighted selected habitat locations of
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particular interest.Additional information on the f.ish resource in this area
is found in the transmission corridor studies of Schmidt et al.1984c.
The natural environment between Devil Canyon and the upstream-end of the
proposed Watana Reservoir provides habitats for nine fish species (ADF&G
1983d);eight are year-round residents and one (chinook salmon)is anadromous
(Figure 1).Within Devil Canyon,Fog Creek (RM 176.7)marks the upstream
limit of salmon migration in the mainstem Susitna River.Only three streams,
(Cheechako,Chinook,and Fog creeks)had,in total,fewer than 100 chinook
salmon observed using them for spawning (Barrett,Thompson and Wick 1985).
Arctic grayling are the most widely'distributed and abundant species
utilizing habitats above the canyon.The total 1982 Arctic grayling
population above 15 em in length in eight of the impoundment zone streams was
estimated to be over 16,000 (ADF&G 1983b).Mainstem areas above the canyon
provide essential overwintering habitat for Arctic grayling,which move into
tributaries to spawn following breakup in late Mayor early June (ADF&G
1983d)•Arctic grayling migrate out of natal tributaries in September as
water levels and temperatures begin to drop.They overwinter in mainstem
environments which become less turbid following freeze-up (ADF&G 1983d).
-in the canyon had salmon observed in them during 1984.These streams,
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Except for documentation of their presence,little is known of the
relative abundance of other species resident in the environments of the
proposed impoundment zone.Based on limited capture data,it seems that both
burbot and longnose sucker are relatively common there (ADF&G 1983d).
Elsewhere in the Susitna River,burbot spawn under the ice in tributaries
(such as the Deshka River)over gravel substrates from January to February,
and radio tagged fish data suggests they also spawn in the mainstem (ADF&G
1983b).During the rest of the year,they apparently distribute themselves
throughout the deeper portions of aquatic environments.Susitna River long-
nose sucker are spring spawners which move from overwinter habitats in the
mainstem to tributary natal areas from late May to early June (ADF&G 1983d).
Small numbers of round and humpback whitefish have been captured (at two loca-
tions)within the impoundment areas,but there are no estimates of their rela-
tive abundances (ADF&G 1983d).If they behave similarly to lower river and
middle river whitefish,they also overwinter in mainstem environments.Al-
though available information is scant,it appears that these two white fish
species spawn in early October i.n clearwater tributary streams.
Although not currently present in mainstem areas,some lake trout might
gain access to the reservoirs as a result of the project.Sally Lake,which
supports a lake trout population of undetermined number,would be inundated by
the Watana Reservoir (ADF&G 1983d).Lake trout generally spawn from August
through December and require stable lake shore gravel substrates for
reproduction.High lake (located immediately north of Devil Canyon)is a
tributary system to Devil Creek which has a resident population of rainbow
trout.Should the project be completed,it is possible that some rainbows
might gain access to the Devil Canyon reservoir by outmigrating down Devil
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Figure 1!.•Fish of the impound~ent zone.
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SUSITNA RIVER DRAINAGE BASIN
Fi~h Species Present
lower River:1201 ArClic grayling,Arctic lamprey,BOling elsea,burbol,chinook
salmon,chum salmon,COho salmon,Dolly Varden,oulachon,
humpback wllllCfl~h,lake Iroul,lonon050 sucker,norHlern piko,
pink salmun,rawlbo'll/!fout,round wtlilellsh,s.llrny sculpin,
sucl-.p.ye salmon,lhreesplno stickleback,and nlnosplne
stickleback.
MlddlO Ai ...or:(161 Arcllc grayling.Arcllc lamprey,burbal.chInook salmon,chum
salmon,coho salmon,Dolly Varden,humpback whllcllsh,lake
Irolll,IOflgnose ~uc"er.pInk salmon,rlJinbow trout,round
whitefish,slimy sculpin,sockeyo salmon,and Ihroosplne
stickleback.
Impoundmenl Zone:(91 Arellc grayling,burbol,Dolly Varden,humpback whllellsh,lake
trout,long nose sucl-.er,round whitefish,slimy sculpin,and
chinook salmon.
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Creek.Elsewhere in the basin.rainbow trout typically overwinter in lakes
and mainstem habitats,returning in the spring following breakup to spawn in
tributary streams.Most rainbow trout spawn in clearwater streams whose beds
are covered with relatively small cobbles and have relatively moderate
velocities (ADF&G 1983b).
MIDDLE RIVER
Fish and aquatic habitat investigations have been conducted on the
Susitna River since the 1950's to evaluate the proposed hydroelectric project
(U.S.Fish and Wildlife Service 1952,1954,1957,1959a,1959b,1960,1965;
Barrett 1974;ADF&G 1976,1978.1981a,1983a,1983b,1983c,1985~;Barrett.
Thompson,and Wick 1984,1985;Riis 1977;Schmidt et al.1984a,1984b;and
Wangaard and Burger 1983).In 1980,the Susitna Hydroelectric Aquatic Studies
Program was initiated to collect data on the fish and aquatic habitat
resources of the basin.
Extant Susitna River basin data on fish distribution,abundance,and
habitat use focuses on salmon and are temporally and spatially limited.The
studies,and therefore the information available,is more complete for the
open water season and for the area upstream of the Chulitna River confluence.
A summary of ADF&G's Su-Hydro studies of the fish resources downstream of
Devil Canyon is available in a report by Woodward Clyde Consultants and Entrix
(1985).ADF&G's Su-Hydro studies have documented migration timing of salmon
runs in the Susitna River;estimated the population size and relative
abundance of salmon in various sub-basins of the Susitna River;estimated the
total salmon escapements into sloughs and tributaries upstream of RM 98.6;
quantified selected biological characteristics of Susitna River salmon stocks
(e.g.,sex ratio,fecundity,length at age);identified important spawning
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areas for some resident species;documented timing and estimated the relative
utilization of macrohabitat types by juvenile and adult salmon and some
resident species;developed habitat suitability criteria for adult and
juvenile salmon,eulachon,Bering cisco,and some resident species;estimated
population size and survival for juvenile chum and sockeye;documented
outmigration timing of juvenile salmon;collected baseline physical and
chemical water quality data in identified macrohabitat types;developed
understanding of site-specific habitat responses to various mainstem
discharges;evaluated the capability of adult salmon to pass into selected
sloughs;and confirmed the importance of groundwater upwelling for salmon
spawning in sloughs.
Above the Chulitna River confluence (RM 98.5)salmon spawn in a variety
of tributaries,sloughs,and a few mainstem sites.In this river reach,coho
and chinook have only been found to spawn in tributary stream environments;
pink salmon primarily in tributary streams (with a small number utilizing
slough habitats);chum salmon in tributary,slough,and mainstem environ-
ments;and sockeye almost exclusively in sloughs (Barrett,Thompson and Wick
1985).Over 90%of salmon spawning in this reach occurs in tributaries
(Barrett,Thompson &Wick 1985).
At least eighteen tributary streams in the middle river provide salmon
spawning habitats (table 4).Over 96%of the total chinook escapement above
the Chulitna confluence spawn in two streams;Portage Creek (RM 148.9)and
Indian River (RM 138.6)(table 4).In 1984,these two streams had a combined
escapement of over 13,000 fish which represented a little over 5%of the
basin's total chinook resource (Barrett,Thompson and Wick 1985).Only about
10%of Susitna River coho salmon spawn above the Chulitna confluence;they
apparently spawn only in tributaries in this reach (Barrett,Thompson and Wick
33RD4-005 -19 -
I "j I j J )J J J J )j J J J J )Ij
~
Table 4.Peak Salmon Survey Count.Above Talkeetna for Su.itna River Tributary Stream••
SURVEY
STREAM DISTANCE Coho Chinook
1974 1976 1981 1982 1983 1984 1975 1976 1977 1978 1979 1981 1982 1983 1984---
\o.'hiskers 0.25 27 70 176 115 301 22 8 3 67
Creek (RM 101.4)
Chase 0.25 40 80 36 12 239 15 3
Creek (RM 106.9)
Slash 0.75
Creek (RM 111.2)
Gash 1.0 141 74 19 234
Creek (RM 111.6)
Lane 0.5 3 5 2 24 40 47 12 23
Creek (1m 113.6)
Lower 1.5 56 133 18 24
McKenzie (RM 116.2)
McKenzie 0.25
Creek (1m 116.7)
Little 0.25 8
Portage (RM 117.7)
Fi fth 0.25 3 17
N of .July (RM 123.7)~
Skull 0.25
Creek (RM 124.71
Sherm.:m 0.25 3
Creek (RM 130.8)
Fourth 0.25 26 17 1 4 3 8 1 14 56 6 92
of July (RM 131.0)
Gold 0.25 1 21 23 23
Creek (RM 136.7)
lnd ian 15.0 64 30 85 101 53 465 10 537 393 114 285 422 1,053 1,193 1,456
River (RM 138.6)
Jack 0.25 1 1 6 2 6
Long (RM 144.5)
Portage 15.0 150 100 22 88 15 128 29 702 374 140 140 659 1,253 3,140 5,446
Creek (RM 148.9)
Cheechako 3.0 16 25 29
Creek (RM 152.5)
Chinook 2.0 4 8 15
Creek (RM 156.8)
---
TOTAL 307 147 458 633 240 1,434 62 1,261 767 254 425 1,121 2,473 4,416 7,178
33RCl!005a!1
J 1 JI J }}J J }J ,J J ~J I J
~
Table 4.Peak Salmon Survey Counts Above Talkeetna for Susitna River Tributary Streams.
(cant-d)
SURVEY
SIREA1'I ~Chum Sockeye
----1974 1975 1976 1977 1981 1982 1983 1984 1974 1975 1976 1977 1981 1982 1983 1984
Whiskers 0.25 1
Creek (RH 101.4)
Chase 0.25 1 1
Creek (RH 106.9)
Slash 0.75
Creek (RH 111.2)
Gash 1.0
Creek (llH 111.6)
Lane 0.5 3 2 76 11 31
Creek (RH 113.6)
Lower 1.5 14 1 23 1
HcKenz ie (RH 116.2)
HcKenzie 0.25 46
Creek (1m 116.7)
Little 0.25 31 18
Portage (RH 117.7)
Fifth 0.25 6 2
"N of July (RH 123.7)
ro,".w,
~~..l Skull 0.25 10 1 4
Creek (RH 124.7)
Sherman 0.25 9 6
Creek (RH 130.8)
Fourth 0.25 594 78 11 90 191 148 193 1
of July (RH 131.0)
Gold 0.25
Creek (RH 136.7)
Indian 15.0 531 70 134 776 40 1,346 811 2,247 1 2 1 1 1
River (RH 138.6)
Jack 0.25 3 2 4
Long (RH 144.5)
Portage 15.0 276 300 153 526 1,285 12
Creek (RH 148.9)
Cheechako 3.0
Creek (RH 152.5)
Chinook 2.0
Creek (RH 156.8)
----
TOTAL 1,401 73 512 789 241 1,736 1,494 3,814 48 2 1 1 1 13
33RCl/005a/2
Source:Barrett 1974;Barrett,Thompson and Wlck 1984,1985;RUs 1977;ADF&G 1976,1978,1981,1983a.
33RC1!005a!3
1985).Indian River (RM 138.6)is the most important tributary for coho,
~
I
,-
providing a little over 30%of the reproductive habitat available here
(table 5).Portage and 4th of July (RM 131.1)creeks and Indian River provide
r~productive habitats for over 80%of middle river pink salmon;this repre-
sents about 1%of the total Susitna escapement for pink salmon (Barrett,
Thompson &Wick 1985).The same three streams provide over 98%of tributary
spawning habitat for chum salmon in this reach (Barrett,Thompson and Wick
1985).In 1984,these tributaries accounted for about 1%of the total Susitna
chum salmon escapement.
Based on escapement counts for 1984,34 middle river sloughs collectively
provided habitat for approximately 5.5%of all salmon migrating above
Talkeetna station (Barrett,Thompson and Wick 1985).These sloughs are of
particular importance to middle river chum and sockeye salmon.About 50%of
the chum and almost all of the sockeye spawning above the Chulitna confluence
occurs in sloughs.This represents about 2%of all chum and less than 0.5%of
all sockeye spawning in the Susitna drainage (Barrett,Thompson and Wick
1985).
Spawning habitat quality apparently varies greatly between sloughs as,in
the last four years,the majority (>88%)of chum salmon spawners counted were
in 10 of the 34 (tables 5 and 6).Three of these 10 (8A,11,21)have added
significance in that they also accommodated over 90%of all sockeye spawning
in the middle river (table 5).
33RD4-005 -23 -
J }J ~)~I -~l J --I 11 )j i ..~-~,-]JJ
~
Tllble 5.Peak Slough Escapement Count.Above Talkeetna.
CHUH SOCKEYE PINK
RIVER
SUlll(;1I NO.~lE!!.1975 1lli.l1Zl ~ill1 1983 1984 !21!t ~1976 1977 ~ill1 1983 ill!!.!ill l1Zl ~ill1 1983 ill!!.
1 99.6 6 12 10
2 100.4 27 49 17.9 7 2
3R 101.4 50 3 56 15 7 5 70 1 28
3A 10l.9 17 1 11 56
Talkeetna St.103.0
4 105.2
5 107.2 2 1 1 4
6 108.2 1
6A ll2.3 11 2 1 35
7 113.2
8 113.7 302 65 2 25 1
P.llshrod 117.8 90 10
CUTry St.120.0
80 121.8 23 49
8C 121,9 48 4 121 2 1
88 122.2 1 80 104 400 2 5 1 68
Moose 123.5 167 23 68 76 8 22 8 8 25
A'124.6 140 77 III 24
A 124.7 34 2 2 2
·N 8A 125.1 51 620 336 37 917 70 177 68 66 128 28 134
0\.8 126.3 58 7 108 8 2 9 32
9 128.3 511 181 36 260 300 169 350 8 6 10 5 2 6 12 1
98 129.2 90 5 73 81 1 7
9A 133.3 182 118 105 303 2 1 1
10 133.8 2 2 1 36 1
11 135.3 33 66 116 411 459 238 1,586 79 84 78 214 893 456 248 564 1 131 121
12 135.4
13 135.7 1 4 4 13
14 135.9 2 1
15 137.2 1 1 1 100 1 1 132 1 500
16 137.3 2 12 4 3 15 13
17 138.9 24 38 21 90 66 6 6 16 1
18 139.1 11
19 139.7 4 3 3 45 3 32 8 23 5 11 1 1
20 140.0 107 2 28 14 30 63 280 20 2 64 7 85
21 141.1 668 250 30 304 274 736 319 2,354 13 75 23 38 53 197 122 64 8
21A 145.5 10
22 144.5 8 114 151
TOTAL 1,352 495 98 541 2,596 2,244 1,458 7,547 103 194 134 300 1,241 607 555 926 1 13 28 507 9 1,069
Source:Barrett 1974;Barrett,Thompson and Wick 1984,1985;RHs,1977;ADF&G 1976,1978,1981,1983a.
,
33RCI/007b
Table 6.Chum Salmon Escapement for the Ten Most Productive Sloughs Above
I"'"RM 98.6.1981-84.
!
I""'"
Percent
River 4-Year of Total
Slough Mile 1981 1982 1983 1984 Average Escapement
-8 113.7 695 0 0 217 228 3.4
8B 122.2 0 99 261 860 305 4.5
Moose 123.5 222 59 86 284 163 2.4
~
AI 124.6 200 0 155 217 143 2.1
8A 125.1 480 1.062 112 2.383 1.009 14.9
9 128.3 368 603 430 304 426 6.3
9A 133.8 140 86 231 528 246 3.6
11 135.3 1,119 1.078 674 3,418 1.572 23.2
17 138.9 135 23 166 204 132 1.9
21 141.1 657 1,737 481 4.245 1,780 26.2
Source:Barrett.Thompson.and Wick.1984, 1985.
.....
--I 33RD4-005 -25 -
-
Relatively few salmon spawn in mainstem nonslough habitats;of those
which do,chum salmon predominate.Generally,spawning habitats within the
mainstem proper are small areally and widely distributed.In 1984,ADF&G made
a concerted effort to identify mainstem middle river spawning habitats;they
identified 36 spawning sites.Numbers of fish counted at each of these sites
varied from one to 131 with an average of 35 (Barrett,Thompson,and Wick
1985).The estimated total mainstem escapement was approximately 3,000 chum
salmon (Barrett,Thompson and Wick 1985).This is less than 0.5%of the total
Susitna escapement.
Four of the five salmon species (all but pink)use middle river waters
for rearing purposes (Schmidt et ale 1984b).At this time insufficient
""'"I
I
I
-
information exists to characterize the relative importance of mainstem rearing
habitats relative to each other.From May to September juvenile chinook rear
in tributary and side channel environments,coho mostly rear in tributary and
upland sloughs,and sockeye move from noted side sloughs to upland sloughs for
rearing.From May to July rearing chum juveniles are distributed throughout
side slough and tributary stream environments (Dugan,Sterritt,and Stratton
1984).
Of the five salmon species present,only chinook and coho were captured
in the middle river during the 1981-82 winter field season (ADF&G 1983c).
Preliminary studies indicate that significant numbers (perhaps 25 to 50%)of
chinook and coho juveniles reared in this zone overwinter in side slough and
tributary stream environments (ADF&G 1985a).Provisional capture data for the
1984-85 winter field season show that a few sockeye are also overwintering in
this area of the river (Crawford 1985).Preliminary evidence indicates that
few juvenile salmon utilize the mainstem proper for overwintering purposes
(ADF&G 1985a).
33RD4-005 -26 -
.....
.....
-
Of the 11 resident middle river fish species (figure 1),capture data
indicate that rainbow trout,Arctic grayling,round whitefish,longnose
sucker,and slimy sculpin are common (ADF&G 1983c).Dolly Varden,burbot,
humpback whitefish,threespine stickleback,and Arctic lamprey also occur,but
all appear to be more abundant in the lower river (Sundet and Wenger 1984).
Lake trout are found only in surrounding area lakes,none of which would be
influenced by the project.
Less is known about most resident fish species in the middle river than
about salmon.Rough population estimates made in 1983 showed there to be
about 4,000 adult rainbow trout in the middle river.Catch data from 1981-84
in the middle river show round whitefish to be the most abundant species and
that Arctic grayling and longnose sucker are more abundant than rainbow trout
which are more common than burbot (Sundet and Wenger 1984).Lakes in the
Portage Creek and Fourth of July drainages where rainbow trout are abundant
probably contribute heavily to middle river rainbow populations (Crawford,
Hale,and Schmidt 1985).
Given the naturally reduced winter flow regimes of tributary streams,the
majority of resident fish (with the exception of lake trout)probably
overwinter somewhere in the mainstem.It is generally believed that most
.-.
resident fish which migrate to tributaries in the summer overwinter downstream
of their natal tributaries in the mainstem (Sundet and Wenger 1984).Of the
most common resident species,three (round whitefish,longnose sucker,and
slimy sculpin)can occur year-round in the mainstem.Rainbow trout and Arctic
grayling migrate out of tributaries by early October and most overwinter in
the mainstem slightly downstream of these tributaries (Crawford,Hale,and
Schmidt 1985)•
33RD4-005 -27 -
LOWER RIVER
At least 17 tributary streams and six sloughs provide salmon reproductive
habitats downstream of the Chulitna confluence.Tributary systems in this
reach support more than 99%of all spawning salmon.To date,no chinook,
.-
-
sockeye,or pink salmon have been observed spawning in lower river mainstem
waters;all apparently use tributary streams exclusively for this purpose
(Barrett,Thompson and Wick 1985).Small numbers of chum and coho salmon have
been seen spawning in 13 separate mainstem sites and six side sloughs;most
members of these two species also spawn in tributary environments.ADF&G
estimates that,in aggregate,the number of chum salmon spawning within
mainstem environments in this reach represents roughly 0.3%of-the 1984
basinwide escapement.The estimated number of spawning coho in the mainstem
represents roughly 0.2%of the 1984 escapement (Barrett,Thompson and Wick
1985).Chum salmon were the principal users of side slough spawning
environments,being present in five of the six sloughs used.Their estimated
numbers represent roughly 0.1%of the total 1984 escapement.Only six coho
were seen spawning in sloughs in 1984;all were in one slough (Barrett,
Thompson and Wick 1985).Thus,lower river sloughs are less important than
middle river sloughs for spawning purposes.
Less is known of salmon rearing and overwintering habitats in lower river
mainstem environments than in the middle river.Coho,chinook,chum and
-
-
sockeye juveniles primarily rear in tributaries;chinook,chum,and sockeye
juveniles also make use of side channels.Sloughs are limited in occurrence
and are not used heavily by any salmon species (Crawford,Hale,and Schmidt
1985).A few coho and chinook have been captured during winter in mainstem
environments in this river reach (ADF&G 1983c).
-33RD4-005 -28 -
Several million eulachon spawn in late May to early June in the lower 50
miles of the mainstem Susitna River.Most of these fish spawn below RM 29 in
main channel habitats near cut banks over loose sand and gravel substrates
(Barrett,Thompson and Wick 1984).Bering cisco return to the Susitna River
in late August and spawning takes place from September through October.In
1981 and 1982,spawning activity peaked in the second week of October.Bering
cisco are known to spawn only in main channel environments;the majority of
spawning apparently takes place between RM 75 and RM 85 (Barrett,Thompson and
Wick 1984).
Little is known about most resident fish life histories in the lower
river.The 13 resident fish species found in the lower river.-with the
exception of lake trout,northern pike,and ninespine stickleback,are
generally believed to be common (Sundet and Wenger 1984).As elsewhere in the
drainage rainbow trout,Arctic grayling,and Dolly Varden spend most of the
open water season in tributaries,using the mainstem principally for migration
and overwintering (ADF&G 1983b).These species move into tributaries to spawn
in the spring after breakup.Rainbow trout and Arctic grayling outmigrate
r
~,
from most eastside tributaries in September (Crawford,Hale,and Schmidt
1985).Burbot,whitefish,longnose sucker,sculpin,stickleback,and Arctic
lamprey are found in both the mainstem and tributaries during the open water
season.All of these species are believed to overwinter in the mainstem,but
only rainbow trout,burbot,and slimy sculpin were captured there during 1982
winter sampling (ADF&G 1983b).Round whitefish are believed to spawn in
October at either mainstem,tributary mouth,or tributary locations (Schmidt,
et al.1984b).Burbot spawning generally occurs between January and March
-
und,er the ice in areas influenced by the mainstem or in tributaries like the
Deshka.
33RD4-005 -29 -
r-
I
I
Based on ongoing radio telemetry studies,it appears that favored
mainstem overwinter habitats for adult rainbow trout and burbot differ
principally by depth and location (Crawford 1985).Tagged rainbows are most
frequently relocated in mainstem side channels,near tributaries,in waters
generally less than five feet in depth.Tagged burbot are frequently located
in winter in mainstem pools greater than six feet deep along river bends.
-
However,most of the tagged burbot were found in the Deshka River.
species seem to favor low velocity environments.
Both
33RD4-005 -30 -
.....
THE WITH PROJECT ICE REGIME
The following is a synopsis of selected aspects of the with-project
environment that have relevance to an effects analysis of the with-project ice
regime on fish.(A detailed description of with-proj ect ice processes is
found in R&M et at.1985.)The Watana Reservoir would inundate roughly 48
linear miles of the mainstem Susitna River and about 30 miles of tributary
stream environments,thereby converting them to a lentic system.The Watana
Reservoir would generally begin to freeze over sometime in mid-November,with
drawdown would cause nearshore ice to fracture and drape over exposed banks.
r
I
probable maximum ice thicknesses ranging from 3 to 5 ft.Winter reservoir
.....While on-line alone,the Watana reservoir's winter drawdown would average
about 90 ft.With both dams constructed drawdown in Watana would average
about 40 ft.In midwinter,grounded ice could form barricades at tributary
mouths.Based on observations of natural ice processes within the upper
basin,however,it is believed that tributary flows would downcut grounded ice
before reservoir ice meltout which would generally occur between May and early
June.
The Devil Canyon Reservoir would inundate a maximum of 32 linear miles of
mainstem Susitna River environments.Freeze-up times would be similar to
those of the Watana Reservoir,but probable maximum ice thickness would not
exceed 4 ft.Yearly winter reservoir drawdown would be slight if it occurred
at all.Consequently,less ice draping would occur than in the Watana
-
Reservoir.A few miles of open water may occur in the upper part of Devil
Canyon Reservoir due to the warm water released from the Watana Reservoir.
33RD4-005 -31 -
The with-project middle river ice environment would differ dramatically
-from natural conditions.Formation timing of a contiguous river ice cover
-
....
would be delayed,there would be an extensive reach of ice-free water below
Devil Canyon,winter river flows would be four to five times greater,and ice
meltout would occur earlier.These changes would occur as a consequence of
dam interception of mainstem frazil ice,increased winter flows due to the
reservoir's operating schedule(s),and warmer than normal instream winter
temperatures (the reservoirs would function as heat sinks).
During the winter,with-project water temperature is predicted to range
between 0.4 C to 5.6 C at the dam outlet (AEIDC 1984).Water temperatures are
predicted to decline relatively uniformly with increasing distance downstream,
until reaching 0 C.
Middle river freeze-up is predicted to be delayed between 2 to 6 weeks
with Watana Dam and 4 to 7 weeks with both dams in place.Depending on the
weather and with only Watana Dam on-line,the ice front is predicted to range
somewhere between RM 124 and RM 142 and ice thickness below the front would be
similar to or slightly thinner than natural.With both dams operating,the
ice front is expected to range between RM 123 to RM 137 and ice thickness is
expected to be less than for natural conditions.The ice front would likely
be dynamic,changing location in some winters more than others in response to
changes in weather conditions and with-project flows.Upstream of the ice
front,the river would not be completely ice covered,open water with
temperatures often above 0 C would occur throughout the winter.Between the
o C isotherm and the upstream edge of the ice front,a zone of anchor ice and
border ice formation would occur;neither anchor ice nor border ice would form
upstream of this zone.
-33RD4-005 -32 -
-
...,
Portions of the river near the ice front would be subject to freeze-up
staging.due to displacement by the developing ice cover and additional
friction at the rough bottom surface of the ice cover.When this happens.
water velocity slows and the water level rises.This would lead to periodic
flooding of sloughs and side channels.a phenomena seen naturally.Staging
can last all winter under natural conditions.However.there is a gradual
reduction in water levels as discharges drop and the cover erodes.Staging
would occur for a shorter period with-project since the ice cover would form
later and melt out earlier.There would.however.be much more flow in the
river with-project.
Intragravel temperatures in many sloughs and side channels du~ing winter
are believed to be moderated by groundwater flows,except for periods of
overtopping of upstream berms as a result of ice staging or ice breakup.The
mean annual mainstem temperature is not expected to change significantly
with-project,and the temperature of that component of groundwater flow which
is directly related to mainstem flows should not be changed.(Sloughs 8A and
21 appear to be more directly influenced by mainstem temperature variations
than others.The increased winter flows relative to natural conditions and
increased mainstem water levels resulting·from ice formation could produce
colder than natural upwelling groundwater and.thus,colder intragravel
temperatures here.)
Regardless of the final reservoir operation regime adopted,winter flow
rates would increase significantly with-proj ecL Consequently,the aquatic
instream environment would be substantially greater in extent (i.e.,the
wetted area would be increased).Because no ice staging would occur in the
open water reaches immediately below Devil Canyon.no winter flooding is
anticipated in this area.However,localized flooding would occur within
.-
33RD4-005 -33 -
~,
-
ice-mantled river reaches.since higher than natural flows would be coupled
with ice-induced staging.Higher flow rates might also increase the length of
open leads in ice-mantled areas downstream of the ice front.
The with-project springtime environment would differ from natural
conditions chiefly in breakup phenology.Predicted higher than normal stream
temperatures and steadier stream flows would cause a gradual in-place melting
of the ice cover and the potential for breakup ja~ing would be reduced.Ice
meltout is expected to occur four to seven weeks earlier than natural with the
Watana Dam and seven to eight weeks earlier with both dams operating.
ICECAL simulations have not been run for the lower river because of the
complexity of the system;the following is based wholly on subj ective input
provided by the Harza-Ebasco ice modeling team.Ice would probably begin
forming with-project in early November about the same time as it does
naturally.Decreased ice contribution from the middle river is expected to
delay upstream movement of the ice front by 2 to 6 weeks with Watana Reservoir
and 4 to 7 weeks with both dams on-line.Increased winter flows might produce
somewhat more ice than now occurs.Overtopping of slough berms occurs
naturally in this reach and.as in the middle river.increased wi th-proj ect
water levels may increase the incidence of overtopping.Lower river ice
meltout could be advanced over natural conditions due to the expected earlier
than normal meltout of the middle river.The·beginning of the lower river
meltout would be closely coincidental to the completion of the middle river
meltout.The lower river breakup is expected to begin earlier and be somewhat
milder than natural.
33RD4-00S -34 -
ANALYSIS
ANTICIPATED WITH-PROJECT EFFECTS
WATANA RESERVOIR
Ice processes attendant to winter reservoir drawdown would affect
reservoir fish spawning and rearing habitat quality.The littoral habitat
would experience periodic dehydration,substrate freezing,and possibly some
ice gouging,and erosion.Reservoir drawdown,ice draping,and ice gouging
would preclude evolution of a stable littoral zone conducive to lake trout
(from Sally Lake)reproductive and rearing success.Lake trout reaching the
impoundment,however,would likely live out a normal life span.~he effects
on other salmonids would be less severe,because they can spawn in tributary
streams.Thus,only their rearing and overwintering life stages would be
affected.Rearing habitats for Arctic grayling and whitefish within the
impoundment would probably be less than ideal since lake drawdown,ice
draping,ice gouging,erosion,and associated effects would likely limit cover
these events would preclude
invertebrate productivity,and
Taken together
establishment of riparian vegetation,limit
dewater the habitat.
The effects of the Watana Reservoir ice regime on burbot are more
and food availability.
difficult to predict,because they have more generalized habitat requirements.
Burbot often inhabit deep,cold,and turbid environments.Burbot found in
lakes often utilize lake shore gravels for spawning,however,most of those
found in the Susitna River spawn in tributary stream environments.Due to the
.....disruptions :in the impoundment's littoral zone,
additional viable reproductive habitat because
it would not afford any
of its unstable nature.
Because of their ability to use either lake shoreline or tributary areas for
33RD4-005 -35 -
-
--
,....
-
spawning,available habitat would still remain for them in the tributaries to
the reservoir.Thus,the impoundment's ice regime probably would not exert
discernible negative effects on the burbot population.
Ice blockage of tributary stream mouths by stranded ice may be a problem
for fish in extremely cold years,when spring ice meltout is retarded.
However,if climatic conditions match long-term averages,the tributary mouths
should be ic,e free before late Mayor early June when Arctic grayling and
longnose sucker migrate to tributary stream spawning habitats.Blockage of
stream mouths by ice is very unlikely,as snowmelt runoff has to go somewhere,
and meltout in the tributaries should be similar to natural conditions.If
the spring meltout did not occur until after early June,both grayling and
longnose sucker could fail to access the tributaries and experience
reproductive failure for that year.From a fish population biology standpoint
loss of a single-year class is not particularly troubling unless the loss is
to a dominant year-class or the population is being simultaneously stressed by
other factors such as epidemics or sport fishing.In Alaska,some local fish
populations c.ommonly have certain year classes predominate while others are
absent or nearly so.
Once the Devil Canyon Dam lvas on-line,Hatana Reservoir operations could
have less influence on fish habitats because the expected drawdown would be
less.However,since predicted drawdown exceeds 40 ft.it would still
severely limit establishment of a stable littoral zone.
DEVIL CANYON RESERVOIR
Because of its smaller scale,winter drawdown of the Devil Canyon
Reservoir would be less influential on impoundment littoral zone habitats than
that predicted for the Watana Reservoir.Ice draping would be minimal (if it
33RD4-005 -36 -
-
r
,....
occurred at all)and ice gouging negligible given the bedrock substrate and
lack of ice fracturing from extensive drawdown.Perhaps importantly,
impoundment area geomorphology and geology are such that they naturally limit
the availability of potential lentic spawning habitat.The canyon's steep
side walls and bedrock substrate severely limits potential use by spawning
fish,and for this reason the reservoir would be an unproductive environment
for fish.
Arctic grayling,burbot,longnose sucker,and possibly rainbow trout
could access the Devil Canyon Reservoir and become residents.None depend
exclusively on lentic littoral zones for reproductive purposes.Lake trout
are not resident within the Devil Canyon impoundment area.They would have to
gain access from the Watana Reservoir either by passing through the turbines,
over the spillway,or through the gate valves.
With-project ice blockage of tributary stream mouths should not be a
problem in this reservoir.The two main tributaries capable of providing
reproductive habitats for the subject species,Fog Creek (RM 177)and Tsusena
Creek (RM 181)are located in the upper end of the reservoir where open water
is more likely.Normal spring tributary meltout in this area should easily
wash out ice allowing timely access to spawning and rearing habitats for all
reservoir residents.
MIDDLE RIVER
The chief ice related concerns in the middle river are over slough
incubation and rearing habitat quality.One deals with the potential
introduction of near-freezing water to slough incubation and rearing
environments through ice-induced overtopping.Another slough related issue
concerns the potential of with-project flows altering the character of
33RD4-005 -37 -
.-
.-
upwelling waters.Other issues in this vein pertain to the with-project end
of the natural cycle of breakup-induced flooding of slough habitats and the
amount of with-project anchor ice.Natural breakup-induced floods are
necessary to flush fines from slough spawning gravels.
There are few nonslough ice related concerns in the middle river.One
concerns a potential gain in primary productivity in the ice-free reach (as
more light penetrates the ice-free water surface).Another,is the potential
for there being more overwinter habitat with-project than naturally occurs (as
a result of higher than natural with-proj ect flows).The last non-slough
issue pertains to anchor ice;when anchor ice breaks up,melts,or otherwise
disperses,it dislodges considerable amounts of substrate which can be life
threatening to developing embryos.Each of these issues are addressed below.
Overtopping of slough berms occurs naturally during freeze-up as a result
of ice-induced
formation.It
staging and during breakup as a consequence of ice dam
can directly influence overwinter embryo mortality in the
-
middle river (ADF&G 1983d,1985b).Overtopping from freeze-up-induced staging
is the most troublesome to salmon,because it could introduce mainstem water
which is coldler than ambient groundwater to developing embryos,for relatively
long periods of times.
During the incubation period,embryo survival naturally varies greatly
and is dependlent on several factors.The principal natural phenomena inducing
embryo mortality are freezing of the spawning habitat,redd desiccation from
dropping water levels,changes in the thermal and chemical characteristics of
groundwater,and silting of redds (Buklis and Barton 1984,Canada Department
of Fisheries &Oceans 1984).Dewatering and freezing of salmon redds have
been identified as the principal natural factors inducing chum salmon embryo
mortality in the middle Susitna River (ADF&G 1985b).Natural mortality is
33RD4-00S -38 -
.-
.....
generally high during incubation;reported survival rates from North America
and Asia range between 1.5%to 30%(Buklis and Barton 1984;McNeil 1980).
Preliminary survival estimates for eggs deposited in 1985 in the middle
Susitna drainage averaged 30%,22%,and 16%for chinook,sockeye,and chum
salmon respectively (Roth and Stratton 1985).
Embryo It.emperature tolerance ranges are much narrower than those for
adults (Alabaster and Lloyd 1982).Generally,the lower and upper temperature
limits for successful initial incubation of Pacific salmon eggs fall between
4.5 C and 14.5 C (Reiser and Bjornn 1979).Salmon embryos are most vulnerable
to temperature stress in their early development stages,before closure of the
blastopore.Closure occurs at about 140 accumulated Celsius temperature units
(Combs 1965;Bams 1967).(A temperature unit is one degree above freezing
experienced by developing fish embryos per day).
Merrell (1962)suggested that pink salmon embryo survival in Sashin
Creek,southeastern Alaska,may be related to water temperature during
spawning.Embryos exposed to cooler spawning environmental temperatures have
been shown to experience greater incubation mortality than those which began
incubation at warmer temperatures (McNeil 1969).Bailey and Evans (1971)
.....
.....
reported an increase in pink salmon mortality when water temperatures were
held below 2 C during the initial incubation period.Laboratory experiments
with developing Susitna chum and sockeye salmon embryos resulted in increased
mortality and alevin abnormality when average temperatures were maintained at
a level less than 3.4 C (Wangaard and Burger 1983).However,these increases
were relatively slight.Following the period of initial sensitivity to low
temperatures,i.e.,after blastopore closure (approximately 30 days at 4.5 C),
embryos and alevins can survive temperatures near 0 C (McNeil and Bailey
1975),but their development is slowed.During the incubation period,mean
fMI1lIl
I
i 33RD4-005 -39 -
.....
,
intragravel w'ater temperatures in the primary middle river spawning sloughs
range from 2.0 C to 4.3 C (ADF&G 1983d).Since peak chum salmon spawning in
sloughs occurs between late August and September (table 11),it follows that
blastopore closure occurs by October.
Slough SA was naturally overtopped in late November 1982 by cold mainstem
water (near 0 C),providing some insight into potential effects of with-
project overtopping events.Slough SA intragrave1 water temperature ani.)'
dissolved oxygen were depressed during this event.Subsequently,embryo
development and emergence was delayed,and large numbers of dead embryos were
seen (ADF&G 1983d).This suggests that increased mortality occurred.
The significance of with-project overtopping to developing salmon varies
between sloughs,being more problematic in those downstream of the predicted
ice front.As noted above,the predicted ice front location with the Watana
Reservoir would occur between RM 124 and RM 142 (table 18).When it is at
RM 124 (the farthest downstream ice front location predicted with the Watana
Reservoir),sloughs upstream of this point would be subject to overtopping.
Of the most productive chum salmon sloughs in the middle river,only
sloughs 8,8B,and Moose are located downstream of RM 124 and would be subject
to overtopping.An average of 696 chum salmon spawned in these sloughf:;
between 1981 and 1984 (table 14).This represents approximately 10.4%of the
total chum salmon escapement to middle river sloughs for those four years
(table 14).At the other extreme,when the predicted ice front is RM 142,all
of the top c.hurn salmon producing sloughs would be subject to overtopping.
From 1981 to 1984,these sloughs supported an aggregate average of 6,004
spawning chum salmon,approximately 88.5%of those spawning in middle river
sloughs (tabl,e 14).
33RD4-005 -40 -
Predicted river freezeup dates with the Watana Reservoir only range from
-November 28 to December 30 (Harza-Ebasco Susitna Joint Venture 1984).Ice
-
formation in all model simulations is assumed to begin at the confluence of
the Chulitna and Susitna rivers and progress upstream from there.The
expected rate of ice front progression upstream from the Chulitna River
confluence varies annually due to climatic influence and temperature of the
outflow.With the Watana Reservoir on-line,ice front advance is predicted to
take up to six weeks (Harza-Ebasco Susitna Joint Venture 1984).
Given the predicted start of river freezeup (late November)and the
predicted rate of ice front advance,the earliest an overtopping event could
occur is early December,which is generally after blastopore closure.Most
model runs indicate that freeze-up start dates would be later,occurring in
mid to late December (table 18).Therefore,the majority of predicted
..-
I
overtopping events from ice staging could not occur before late December and
perhaps not until January.
According to ICECAL simulations,sloughs 8,8A,9,9A,and 11 would be
overtopped in some winters due to ice staging with Watana only (Harza-Ebasco
Susitna Joint Venture 1984).Together,these sloughs accounted for about 51%
of all chum and 79%of all sockeye salmon spawning in middle river sloughs
from 1981 to 1984 (table 13 and 14)•
Based OIl ICECAL simulations of river freezeup timing,subsequent ice
front advance,and what is known of the relationship between temperature and
chum salmon embryo development,some with-project ice-induced overtopping
events could lead to widespread embryo mortality in affected sloughs.While
the likelihood of any direct embryo mortality from thermal stress diminishes
after October following blastopore closure,some ICECAL simulations predict
that staging induced overtopping events could last until spring meltout.If
33RD4-005 -41 -
-
.this were to occur,indirect mortality could be significant given that cold
temperatures of this severity (near 0 C)and duration should delay embryo
development and fry emergence to such an extent that they would be unable to
complete their life cycle.This problem could be exacerbated in slough 8A
where a direct linkage between mainstem temperature and intragravel water
temperature has been posited.Staging,even in the absence of overtopping,
could lead to colder than natural upwelled water temperatures in slough
incubation environments (this temperature linkage is also believed to exist in
portions of slough 21,but should not produce a similar problem because of the
warmer with-project winter water temperatures there).
The envi.ronmental consequences of ice-staging overtopping events appear
to be less with both dams on-line.This is because initial freezeup dates are
predicted to be later,meltout dates are expected earlier,and ice thickness
would be less.Further,the predicted duration of overtopping events is
.-
shorter,and they would occur later in winter.
According to ICECAL simulations,only sloughs 8,8A,9,and 9A would be
overtopped in cold winters due to ice staging with two-dam scenarios
(Harza-Ebasco Susitna Joint Venture 1984).Together,these four sloughs
accounted for about 28%of all chum and 14%of all sockeye salmon spawning in
middle river sloughs from 1981 to 1984 (table 13 and 14).Importantly,only
the "cold winter"simulations,which represent environmental extremes,
predicted overtopping.
Overtopping of slough berms by colder mainstem waters could also affect
overwintering fish,as water temperature affects fish metabolism,growth,food
capture,swimming,and disease resistance (see temperature memorandum).
Juvenile salmonids are tolerant of a wider range of water temperatures than
embryos and can survive short exposures to temperatures which could ultimately
33RD4-005 -42 -
be lethal.They can live for long periods at relatively low temperatures,at
which time they abstain from feeding,are less active,and spend more time
resting in secluded habitats (Alabaster and Lloyd 1982;Chapman and Bj ornn
1969).For example,in Carnation Creek,British Columbia,fish stopped
feeding and u~ved into deeper water or closer to objects providing cover at
temperatures below 7 C (Bustard and Narver 1975).Similarly,in Grant Creek,
near Seward,Alaska,juvenile salmonids were inactive at water temperatures
between 1.0 C to 4.5 C and inhabited cover afforded by streambed cobbles
(AEIDC 1982).Regardless of whether one or two dams are on-line,some fish
overwintering in sloughs would be exposed to colder overflow waters.As
-
..-
mentioned above,the chief difference between the one and two-dam-options in
this regard lies in the number of sloughs subj ect to overtopping and the
duration of overtopping events.
Overwintering salmonids exposed to cold overflow waters (near 0 C)could
respond in one of two ways,given that a critical thermal minimum has not been
demonstrated short of actual freezing (AEIDC 1984).They conceivably might
simply seek cover within the slough,becoming relatively inactive until
temperatures once again rise following the end of the overtopping event •
Alternately,since they are mobile they might elect to leave or be forced out
by high velocities during large overtopping events.Given that overflow water
temperature would be identical to mainstem temperature,it is arguable whether
given a choice they would flee.If they did emigrate,their survival would
ultimately depend on availability of replacement habitat which appears limited
in this reach.
Overtopping of slough berms from breakup-driven ice jams is not expected
to be a with-project issue,given ICECAL predictions,as river ice would melt
33RD4-005 -43 -
-
....
I
in place rather than breakup.Thus.no ice jams are predicted to form at this
time and no flooding of slough environments would occur.
The second middle river addressed issue concerns the effect of
with-project ice-staging on upwelling rates in middle river spawning sloughs
(table 19).Maximum winter river stages upstream of the with-project ice
-I
I
front are predicted to be lower than corresponding natural conditions.because
freezeup staging would not occur (Harza-Ebasco Susitna Joint Venture 1984).
Since upwelling rates are believed to be a function of river flow volumes.
there is concern that this lower stage could reduce the amount of slough
upwelling.This should be of minimal concern since with-project winter flows
upstream of the ice front (with either dam scenario)are predicted to be
similar to those occurring naturally in September and higher than the minimum
with-project summer discharges.As upwelling is presently sufficient for
I"""
I
incubation purposes during natural September flows.one could assume that
with-project upwelling would also be sufficient.Downstream of the ice-front.
with-project river stages with both dams on-line are predicted to be higher
than natural.Consequently.concern over project effects on upwelling rates
are apparently moot in this zone.
The third issue examined deals with the potential effects of the with-
proj ect wintE!r open water zone below Devil Canyon on fish habitat quality
(table 19).Regardless of whether one or two dams are built.an ice-free zone
of open water would occur each winter below Devil Canyon.With Watana
Reservoir above.this (predicted by ICECAL)would be 10 to 28 miles long;with
both dams operational the zone would be between 15 to 29 miles long
(table 18).Conceivably.primary productivity could be enhanced in this area
because of warmer water temperatures and less snow and ice cover.Taken by
itself.ice removal would allow more light to penetrate the water column.
33RD4-005 -44 -
stimulating primary production.However.the question is complicated by the
fact that there is little sunlight here in the winter and released reservoir
waters ~.;ould be turbid,whereas natural winter flows are relatively clear
(Acres American 1983).An ongoing AEIDC study seeks to answer the
productivity question.At present.there is no reliable information to use to
describe the probable influences of the with-project open water area on winter
productivity.
Another aspect of the open water reach lies in its potential to become
overwintering habitat.Present juvenile salmon overwintering areas are
characterized by the presence of ice cover and by upwelling warmer than
ambient water (ADF&G 1985a).Little is known about most resident species
-
overwintering habitats,however,limited data from radio tagged rainbow trout
suggests that this species uses areas of upwelling for overwintering (Sundet
and Wenger 1984).Many resident species have been found to overwinter in
deeper mainstem pools and at tributary mouths (ADF&G 1983c).
The open water reach could conceivably provide some overwinter habitat
for juvenile salmon,since released reservoir waters (0.5 C to 5.6 C)would be
within the normal range of upwelling temperatures (0.8 C to 4.2 C)and cover
could be afforded by the turbid conditions.However,it is premature to
speculate on the effectiveness of this type of cover because of the broad
range of turbidities forecasted for this time of year (Acres 1983).The open
water area could provide more overwintering habitat for resident species than
now exists,chiefly because of the combined effects of higher with-project
flows (which could create favored deep pool environments)and the relatively
warmer temperatures.
The open water area could also provide additional salmon spawning and
incubation habitat.Chum salmon have been observed spawning in other mainstem
33RD4-005 -45 -
"'"
areas influenced by upwelling groundwater (ADF&G 1985b).Although
.....
.-
undocumented,it is possible that upwelled mainstem water temperatures at
these sites are similar to those seen in sloughs.Given that released water
temperatures are predicted to be in the range of upwelled slough water
temperatures,and given the proclivity of chum salmon for spawning in mainstem
environments,it is conceivable that this area of the middle river could
function as reproductive habitat provided that suitable substrate exists
there.
Another expressed ice-related concern in the middle river pertains to the
natural flushing of beaver dams as well as fines from slough spawning habitats
by breakup-induced flooding (table 19).Regardless of whether one or two dams
are built,ICECAL simulations predict that drastic breakup events would no
longer occur;the river ice cover would gradually melt in place and no large
flood flows would clean out the sloughs.
Because no sediment samples have been taken before and after breakup
floods,the issue remains founded on subj ective appraisal of environmental
conditions.While it is conceivable that breakup flooding is necessary for
the maintenanee of slough spawning substrates (at least in some locations),it
is also possible that hydraulic upwelling pressure (coupled with the actions
of redd building adults)is sufficient for this purpose.Given the lack of
information on the amount and size of intragravel fines before and after
floods,no clear conclusions can be drawn.
The last question analyzed concerns the effect of with-project anchor ice
on fish and their habitats (table 19).Mechanisms of anchor ice formation are
poorly understood,but it is known to form most often in supercooled reaches
over gravel substrates (Michel 1971;Mason 1958).While anchor ice is
33RD4-00S -46 -
relatively common in the mainstem middle river.none has been found to date in
either mainstem or slough upwelling areas.
Little is known about the influence of anchor ice on Susitna River fish
habitats.Benson (1955)studied anchor ice effects on trout stream ecology in
Michigan.!here.anchor ice was not found to affect trout eggs buried in the
gravel.However.trout fry were apparently vulnerable if they were emerging
at the same time as anchor ice was forming.In California.Needham and Jones
(1959)noticed that dispersing anchor ice dislodged substrates carrying away
considerable numbers of invertebrates.In the middle river.anchor ice can
carry gravel substrates away in a similar manner (R&M Consultants Inc.1984).
This could be a concern to fall and winter mainstem spawners like~urbot and
whitefish if they happen to be using areas subject to anchor ice formation.
Since little is known about the mechanics of anchor ice formation.it is
not simulated in the ICECAL model.However,the extent of anchor ice would be
limited to the reach between the 0 C isotherm and the ice front.It is
r
believed that there would be less anchor ice with-project in the middle river.
Upstream of the 0 C isotherm,in the open water lead below Devil Canyon,no
anchor ice formation is likely due to the influence of warmer than natural
released water.This could have a stabilizing effect on instream invertebrate
habitats.Anchor ice would form with-project between the upstream edge of the
ice-front and the 0 C isotherm in a manner similar to that seen naturally.
More anchor ice would form with the Watana Reservoir than with both dams
on-line because of the greater amount of open water at 0 C.It is probable
that no anchor ice would form in areas influenced by relatively warm upwelled
water.Thus,with-proj ect anchor ice should not influence those salmon
reproductive habitats in areas of upwelling.
33RD4-005 -47 -
LOWER RIVER
As indicated earlier,no ice modeling has been done for the lower river;
thus,conclusions presented are tentative.Two ice related issues are
apparent in t:he lower river.One relates to staging and the other to the
influence of :ice cover on primary production and on cover.
With regard to staging,it is thought likely that freezeup would occur
later than normal with either one or two dams operating.Subsequent
overtopping would also occur,but would likely be later than under natural
conditions.The consequence to the salmon resource as a whole from
..-
overtopping would be minimal.Even if 100%mortality occurred,lower river
slough reproductive habitats are severely limited in area and are utilized by
only a small number of chum salmon.Consequently,their collective
contribution to maintenance of Susitna River salmon stocks is very small.
As in the middle river,the question of ice-related effects on upwelling
pertains to salmon reproductive habitat quality.In essence,the question
rests with two points:the rate of upstream migration of the ice front and
the assumption that mainstem upwelling has a controlling influence on embryo
survival.Salmon spawning naturally occurs in the mainstem at a time when
river flow is decreasing.Successful salmon reproduction in the mainstem is
partly depend1ent on freezeup staging,which raises the water level and assures
that upwelling is not diminished.This concern is more acute near the
confluence of the Chulitna and Susitna rivers than.further downstream for two
reasons;it would take longer for the ice front to arrive and more fish spawn
in this area.
With the project ice front advance would be slower than natural but flows
would be greater than those now occurring.These two factors seem to offset
each other.If so,effects to incubating embryos would be minimal,because
33RD4-00S -48 -
r-
I
flows should be sufficient to maintain upwelling.However,it is important to
point out that,to date,there is no direct evidence that mainstem upwelling
in the lower river exerts a controlling influence on incubation environments
there.
The last lower river ice-related issue raised pertains to the question of
how the with-proj ect ice cover would affect primary productivity and the
amount of overwinter fish habitat (table 19).It is believed that regardless
of whether one or two dams is built,there would be more ice in the lower
river with-project than naturally.However,the exact morphology of the ice
cover is unknown.Provided that extensive lead systems did not develop,
....
.....,
instream primary production with-project should be reduced in rough-proportion
to the increase in ice cover seen.Due to the low gradient and high porosity
of the ice under with-project conditions,it is more likely that open leads
will occur in a manner similar to natural conditions.If this is true,then
an extensive system of open water leads would develop,and primary
productivity could increase.
It is possible that winter habitat availability could increase
with-project,given the combined effects of ice-induced staging and greater
flows.However,overwinter habitat is comprised of more components than just
water volume.Numerous other variables,such as bed morphology,water depth,
water velocity,temperature,and cover are at play.So,the belief that
.....
overwinter habitat might increase with-project is provisional.
33RD4-005 ..:.49 -
-
-
SUMMARY
Winter drawdown of the Watana Reservoir would have a destabilizing
influence on its littoral zone,making it unproductive for salmonids.Some
species would be more affected than others.In all likelihood,winter
.....
I
-
drawdown would preclude successful fall and winter reproduction.This could
effect lake trout,whitefish,and burbot spawning and if it took place at all,
eggs would desiccate or freeze.Ice draping,gouging,and associated erosion
would probably limit invertebrate productivity and cover availability,which
in turn would diminish rearing habitat quality for Arctic grayling and
whitefish.In some extremely cold years,ice blockage of tribu~ary stream
-
.-
mouths could delay Arctic grayling and longnose sucker natal migrations.At
such times,it is likely that reproductive failure could occur.This is not
considered unlikely and even if it occurred at all should not be a major
problem,since loss of a single year class is not overly threatening to
relatively long-lived and fecund organisms like fish.
The environment of the Devil Canyon impoundment would be much more
stable,given its winter .drawdown schedule.However,the canyon's
,~
geomorphology and substrate geology limit establishment of a productive
littoral zone.Fish reproductive habitats near the mouths of Fog and Tsusena
creeks may not be influenced by with-project icing events.Both are located
in the upper end of the reservoir where open water is more likely.
The chief ice concern with-project lies in potential altering of slough
incubation habitat quality.Ice staging downstream of the ice front could
cause overtopping of slough berms with colder than ambient mainstem water.
This would have consequence to natal habitats.
33RD4-005 -50 -
ICECAL simulations predict that all with-project ice-induced overtopping
events would occur after blastopore closure.Thus,there is little likelihood
that direct mortality of embryos would ensue.However,indirect mortality
would be significant given the predicted duration of most overtopping events
(.:.one month).This would delay development to such a degree that it is
unlikely that the embryos could complete their life cycles.Overtopping
.-
r
i
waters could also affect overwintering juvenile fish.Effects would be more
severe the longer the cold exposure lasted.Overtopping events would be more
frequent and severe with the Watana Reservoir alone than with both dams
on-line •
Concern has been raised that the absence of with-project ice-staging in
the area upstream of the ice front would alter slough upwelling rates.This
does not seem likely as with-project winter flows are forecast to be between
8,000 and 12,000 cfs.This is similar to flows occurring naturally in
September.Since September upwelling rates are apparently sufficient to
maintain salmon natal habitat quality,it seems likely that with-project
winter flows should also be adequate.The with-project 10 to 29 mile long
-open water zone in winter below Devil Canyon could enhance primary
productivity in the mainstem.Theoretically,more light would penetrate th~
open water column,thereby stimulating photosynthesis.However,there is
f'"
!
-
-
little light at this time of year and winter flows would be somewhat turbid
confounding the issue.
A more likely effect of this open water zone could be the creation of
additional overwinter habitat due to the combined influence of higher flows
and warmer than natural water temperatures.Higher flow volumes could create
deep pool overwinter habitats for resident species.Since released reservoir
waters are predicted to be about the same temperature as that of upwelled
33RD4-005 -51 -
-
......
.....
slough groundwater.this area might also provide some salmon overwinter and
spawning habitat.The with-project flow regime would eliminate
breakup-inducE:d flooding of slough habitats.This process may be necessary
for maintenance of slough natal habitats (through flushing of beaver dams and
fines from interstitial gravel spaces).Given present knowledge.it is
impossible to predict the long term consequences of elimination of
breakup-induced flooding on these habitats.
Anchor :ice has been shown to have a destabilizing influence on
invertebrate and fish embryo habitats by dislodging substrates during melting
or breakup.No anchor ice is expected to form with-project in the open water
lead upstream of the 0 C isotherm;however.it would form between the ice
front and thl:!0 C isotherm in a manner analogous to that seen naturally.
Cessation of anchor ice formation in the open water zone could stabilize
incubation habitats.
Less physical and biological information exists on the lower river than
for the other two reaches.No temperature or ice modeling has been attempted
for this reach,making evaluation of with-project effects completely
subjective.Overtopping is still expected to occur in the lower river
although some:what later than natural.Because of the very small number of
salmon spawning in the area its effect on the Susitna stocks should be minor.
With-project winter icing probably would not negatively influence upwelling
rates,given that the effects of the predicted slower than normal ice front
advance and the higher than natural flows would likely offset each other.
Higher with-project winter flows coupled with ice-induced staging could
increase the amount of overwinter fish habitat (since wetted area would be
....
increased)•
33RD4-005
Since overwinter habitat is comprised of more than just water
-52 -
....
""'"
volume,it is impossible to speculate on whether new wetted areas would be
utilized •
.....
33RD4-005 -53 -