HomeMy WebLinkAboutAPA2332FINAL REPORT
OCTOBER 1984
DOCUMENT No.2332
Ar;A~KA R'F~~OURC1~1S LmRlH~Y
ljL~DEI~1'~C~l?
INTERIM MITIGATION PLAN
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FOR CHUM SPAWNING HABITAT
IN SIDE SLOUGHS
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OF THE MIDDLE SUSITNA RIVER
,!ezg~=~~~®~@
'4A JOINT VENTURE
:CONTRACT TO
WOODWARD-CL YDE
~~'ULTANTS
FEDERAL ENERGY REGULATORY COMMISSION
PROJECT No.7114
SUSIT~A
HYDROELECTRIC PROJECT
__ALASKAPOW.ER AUTHORITY_--I
D::::~3 1 1984
AIa.!ltA RF~otmc~~LTff"l'LU'1:
'fJ"s.DE1~1'..OF Il\rr~:I~IOR
SUSITNA HYDROELECTRIC PROJECT
DocuJlBnt No.
Susitna File No.
Tf-.
I W~S2332.'
4.2.2.1 "S~
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INTERIM MITIGATION PLAN FOR CHUM SPAWNING HABITAT
IN SIDE SLOUGHS OF THE MIDDLE SUSITNA RIVER
Report by
Woodward-Clyde Consultants
Under Contract to
Harza-Ebasco Susitna Joint Venture
Prepared for
Alaska Power Authority
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Final Report
October 1984
ARLIS
.Alaska Resources
LIbrary &InfonnatJon S',eIVJCes
Anchorage,Alaska
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TABLE OF CONTENTS
1 -APPROACH TO MITIGATION
2 -SCOPE
3 -SUSITNA RIVER MITIGATION PLAN
1
2
3.1 -Impact Assessment 2
3.1.1 Spawning Habitat Utilization in Sloughs
and Side Channels 4
3.1.2 Project Related Physical Changes in Sloughs
and Side Channels 6
3.1.3 Relationship Between Physical Changes and
Available Habitat in Sloughs and Side Channels 11
3.2 Mitigation Options 13
3.2.1 Flow Release 13
3.2.2 Habitat Modification 15
3.2.3 Artificial Propagation 42
APPENDIX A Passage Reach Flow Evaluation
APPENDIX B Detailed Mitigation Costs
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Table 1
Table 2
Table 3
Table 4
Table 5
Table 6
LIST OF TABLES
Area spawned within Slough 8A backwater zones and areas
between passage reaches for 1982,1983 and 1984.
Area spawned within Slough 9 backwater zones and areas
between passage reaches for 1982,1983 and 1984.
Area spawned within Slough 9A backwater zones and areas
between passage reaches for 1982,1983 and 1984
Area spawned within Slough 11 backwater zones and areas
between passage reaches for 1982,1983 and 1984
Area spawned within Slough 21 backwater zones and areas
between passage reaches for 1982,1983 and 1984.
Area spawned within Lower Side Channel 21 backwater zones
and areas between passage reaches for 1982,1983 adn 1984
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Table 7 Mean monthly discharges at Gold Creek for natural
conditions,Case PI and Case EVI predicted project flows
based on Case PI (maximum power generation),and predicted
project flows based on Case EVI instream flow requirements.
Table 8 Minimum and maximum weekly instream flow requirements for
Case EVI flows at Gold Creek
Table 9 Relationship between mitigation alternatives and the impacts
for which they are applicable
Table 10 Condition which provides successful passage most frequently
and approximate percent of time that passage is successful
during the period 20 August -20 September at Slough 8A
Table 11 Condition which provides successful passage most frequently
and approximate percent of time that passage is successful
during the period 20 August -20 September at Slough 9
Table 12 Condition which provides successful passage most frequently
and approximate percent of time that passage is successful
during the period 20 August -20 September at Slough 9A
Table 13 Condition which provides successful passage most frequently
and approximate percent of time that passage is successful
during the period 20 August -20 September at Slough 11
Table 14 Condition which provides successful passage most frequently
and approximate percent of time that passage is successful
during the period 20 August -20 September at Slough 21
Table 15 Condition which provides successful passage most frequently
and approximate percent of time that passage is successful
during the period 20 August -20 September at Side
Channel 21
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LIST OF FIGURES
Figure 1 Mean monthly discharges for natural,Case Pi and Case EVI
conditions and minimum and maximum mean weekly discharges
for Case EVI flows.
Figure 2 Shore ice buildup without overtopping
Figure 3 Predicted winter mainstem stages for natural and proejct
flows near the head of Slough 8A
Figure 4 Predicted winter mainstem stages for natural and project
flows near the head of Slough 9
Figure 5 Predicted winter mainstem stages for natural and project
flows near the head of Slough 9A
Figure 6 Predicted winter mainstem stages for natural and project
flows near the head of Slough 11
Figure 7 Predicted winter mainstem stages for natural and project
flows near the head of Slough 21
Figure 8 Wing deflector
Figure 9 Typical passage reach of slough along middle section of the
Susitna River
Figure 10 Rock Gabion Channel
Figure 11 Gabion barrier,highway curb barrier,pool and weir
structure
Figure 12 Collector tank at Slough 9
Figure 13 Thalweg profile of Slough 9
Figure 14 Thalweg profile of Slough 11
Figure 15 Thalweg profile of Slough 21
Figure 16 Induced upwelling using tributary water supply
Figure 17 Weir to increase spawning habitat
Figure 18 Timber post weir
Figure 19 Rock gab ion weir
Figure 20 Rock weir
Figure 21 Berm design to prevent overtopping of sloughs
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1-APPROACH TO MITIGATION
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1 -APPROACH TO MITIGATION
The objective of fisheries mitigation planning for the Susitna Hydro-
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electric Proj ect is to maintain existing habitat or provide
replacement habitat of sufficient quality and quantity to maintain
natural reproducing populations (Acres Am.1983).This is consistent
with the mitigation goals of the USFWS and the ADF&G (Alaska Power
Authority 1982,ADF&G 1982a,USFWS 1981).In order to accomplish this
objective,the Alaska Power Authority will avoid,minimize,or rectify
impacts.Where it is not feasible to mitigate the impacts in this
manner,the Power Authority will compensate for the impact with
propagation facilities.
Mitigation measures proposed for the Susitna Hydroelectric Project may
be classified within two broad categories:
Modifications to design,construction,or operation of the
project;and
Resource management strategies.
The first type of mitigation measure is project specific and
emphasizes the avoidance,minimization,rectification,or reduction of
adverse impacts,according to priorities in the Fish and Wildlife
Mitigation Policy established by the'Power Authority (1982)and
coordinating agencies (ADF&G 1982a,USFWS 1981).These measures are
implemented first to minimize adverse impacts.They involve adjusting
or adding project features during design and planning so that
mitigation becomes a built-in component of project actions.
When impacts cannot be fully avoided,reduction or compensation
measures are justified.This type of mitigation can involve
management of the resource rather than adjustments to the project,and
will require concurrence of resource management boards or agencies
with jurisdiction over resources within the project area.
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Mitigation planning for the Susitna Hydroelectric Project has
emphasized both approaches.The sequence of options from avoidance
through compensation has been applied to each impact issue.If full
mitigation can be achieved at a high priority option,lower options
may not be considered.In the resulting mitigation plans,measures to
avoid,minimize,or rectify potential impacts are treated in greatest
detail.Specifications for facility siting and design,special
mitigation facilities,construction procedures,and scheduling of
project actions to mitigate adverse effects on the biota are
presented.
Monitoring and maintenance of mitigation features to reduce impacts
over time are recognized as integral parts of the mitigation process.
The monitoring program will be developed during detailed engineering
design and construction planning and be applied to fishery resources
and their habitat.
2
2-SCOPE
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2 -SCOPE
This report refines the interim mitigation plan proposed in the
License Application to mitigate impacts on chum salmon spawning
habitat in the Talkeetna to Devil Canyon reach of the Susitna River
(middle Susitna River).The mitigation plans presented for selected
sloughs are applicable to other sloughs in the middle SusitnaRiver.
since the types of physical impacts are similar in all sloughs and
side channels.The sloughs selected for detailed analysis in this
report are the sloughs most heavily utilized by spawning salmon during
the 1981-1984 study period.Impacts to chinook rearing habitat in the
middle Susitna River are mitigated primarily through the proposed flow
regime.The mitigation plans for other species/life stages and other
regions affected by the project (e.g.impoundment)and the
applicability of proposed mitigation plans to other phases of the
project (e.g.Watana filling)are subjects of upcoming reports.
The mitigation plan examines two chum salmon spawning mitigation
strategies:(1)structural modification to presently utilized side
sloughs to maintain semi-natural spawning and (2)artificial
propagation with stream-side egg boxes to compensate for losses.As
stated in the License Application (Acres Am.1983).full mitigation
can be achieved with either strategy.Final decisions on the strategy
to be implemented will be made through discussions with resource
managers •
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3-SUSITNA RIVER MITIGATION PLAN
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3 -SUSITNA RIVER MITIGATION PLAN
It is expected that the distribution and abundance of fish species
downstream of the proposed Susitna Hydroelectric Project will change
as a result of project operation.The impact assessments presented in
this report were developed for the maximum power flows,Case PI,and
the proposed project flows,Case EVI (Figure 1);further discussion of
the development of these flow regimes are provided in Harza-Ebasco
(1984b).The impact assessments link predicted physical changes with
habitat utilization to provide a qualitative statement of impacts
likely to result from the Susitna Hydroelectric Project.Impact
issues have been identified and ranked by procedures established by
the Susitna Hydroelectric Project Fish and Wildlife Mitigation Policy
(Acres Am.1982).
3.1 -Impact Assessment
3.1.1 Spawning Habitat Utilization in Sloughs and Side Channels
The area of spawning habitat utilized within selected sloughs
and side channels was estimated by integrating the actual areas
spawned during the 1982,1983 and 1984 spawning seasons as
outlined by ADF&G (unpublished maps of spawning areas).The
areas outlined by ADF&G indicate general areas of spawning,not
the actual redds excavated by spawning fish.For example,a
circumscribed area of 10,000 square feet may have had 50
spawning pairs of fish widely distributed,while a similar area
elsewhere may have accommodated several hundred spawning fish
over the course of the season.The 1981 data were not used
because the high flows and poor visibility during the spawning
season precluded definition of spawning ares.The areas spawned
for all three years were classified as composite or total area.
Composite areas were obtained by superimposing maps of spawned
areas for each year and measuring the area spawned one or more
times.Total area was the sum of the area spawned in each year.
The ratio of the composite areas spawned to the total area used
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over the three years is presented in Tables 1 through 6 for
Sloughs BA,9,9A,11 and 21 and Side Channel 21 (ADF&G 1984c).
The ratio of the composite area to total area serves as an index
of the amount of area repeatedly spawned during the three years.
If the same area was used each of the three years the ratio
would be .33.Greater values indicate less consistent use of
spawning habitat.A value of 1.0 indicates use of the same area
in only one of the three years.
The composite areas spawned can be considered representative of
the potential spawning habitat within the sloughs and side
channels evaluated if the following conditions are satisfied:
1)Sufficient numbers of fish annually escaped to the sloughs
and side channels to occupy generalized areas of available
spawning habitat.
2)
3)
Flows during the 1982,1983,and 1984 spawning periods
provided average access and passage conditions to spawning
habitat that were representative of the conditions the long
term flow record has provided.
The periods in which access and passage conditions were
provided by the 1982-1984 flows coincided with the
availability of spawning fish.
Further evaluation of the above conditions will be undertaken
when the flow and escapement records for the 1984 season become
available.The fortuitous occurrence of a high 1984 escapement
and a period of high flow coincident with the historical
beginning of the peak spawning period during the 1984 season
should provide a valuable data base for evaluation of conditions
that allowed access to and utilization of most of the potential
slough and side channel spawning habitat in the middle Susitna
River.
5
3.1.2 Project Related Physical Changes in Sloughs and Side
Channels
Operation of the Susitna Hydroelectric Project will modify the
annual flow and temperature regime of the l?usitna River,thus
causing physical changes in sloughs and side channels in the
middle reach.In general,flows during project operation will
be less than natural flows during June,July,August,and
September and higher than natural flows in the remaining months
as the reservoir is drawn down.Project flows will be
relatively constant throughout the year as compared with the
natural variability of flows.Susitna River discharges
presented in this report are flows at the Gold Creek gage
maintained by the USGS.
-(a)Backwater
A backwater area forms at the mouth of a slough or side
channel if the stage in the mainstem is greater than the
stage of the flow in the slough or side channel at its
mouth.If the mainstem stage rises with no change in flow
in the slough or side channel,the level of the backwater
increases and the aerial extent of backwater influence
moves upstream in the slough or side channel.If the
mainstem stage drops,then the backwater level also drops
and its length is shortened.The drop in mainstem stage
can be sufficient to eliminate the backwater completely;
the stage and corresponding mainstem discharge at which
this occurs varies from site to site.The stage of the
backwater ~ay be defined by the mainstem discharge that
forms the backwater.Project operation will generally
cause decreased backwater area and stage during June
through September.
6
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(b)Breaching
A slough or side channel breaches when the flow overtops
the upstream end,or head,of the channel.Breaching is
directly related to mainstem discharges;as the discharge
increases.the stage increases and when stage exceeds the
elevation of the top of the b~rm at the head of the slough
or side channel,flow is diverted through the channel.
Further increase in stage will cause additional flow to
pass through the slough or side channel.Project operation
will generally cause a significant decrease in the amount
of time that a slough or side channel breaches.
(c)Groundwater Upwelling
Groundwater flows out of (upwells from)the bed of a slough
or side channel when the elevation of the bed is less than
that of the local groundwater level.Studies have been
conducted to relate the flow and temperature of the
mainstem to upwelling quantity and temperature in sloughs
and side channels (Alaska Power Authority (APA)1984).
Although a complete evaluation of the sources of
groundwater was not conducted,the apparent groundwater
upwelling component of slough flow was isolated from the
surface inflow component and related to mainstem discharge
at Sloughs BA,9,and 11.At these three sites,variations
~in the inferred upwelling components ranged from 0.0001 to
0.00035 of corresponding·variations in mainstem discharge
measured at Gold Creek (APA 1984).Relationships were
developed in the form of regression equations for inferred
upwelling component as a function of mainstem flows;these
were used in making a preliminary analysis of proj ect
related changes in the groundwater upwelling component of
slough discharge as described in Appendix A.
The temperature of the groundwater upwelling appears to
remain relatively constant at a value approximately equal
7
to the mean annual river temperature (APA 1984).A mean
.-annual increase resulting from projecttemperature
operation will probably be reflected as a slight increase
-in the temperature of groundwater upwelling flow (APA
1984).
Proj ect operation during winter would affect upwelling in
the sloughs.The higher project flows in conjunction with
increased water temperatures will change the ice processes
in the middle Susitna River.As the mainstem forms an ice
cover,the stage increases because of backwater effects
from frazil ice particles and pans jamming in constricted
areas or building up on downstream jams.Thus river stage
with an ice cover at low flow may approximate the stage of
a much larger flow in the open channel conditions of summer
flows.
Under project operation,the upstream edge of the ice cover
will vary from RM 125 to RM 142 depending on meteorological
conditions and the elevation (and thus temperature)at
which water is withdrawn from the reservoir (Harza-Ebasco
1984a).Upstream of an ice cover,the stage in the river
would decrease relative to natural stage experienced under
an ice cover.According to preliminary upwelling studies,
this will result in decreased groundwater upwelling in
sloughs and side channels throughout the winter.
(d)Flow Depth
During the open water season,the depth at any location in
a slough or side channel is a function of the cumulative
effect of backwater,breaching,and local flow in the
channel.Local flow is generated by surface inflow
(surface runoff and tributary inflow)and groundwater
upwelling.
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The influence of mainstem discharge on backwater,
breaching,and groundwater upwelling was introduced in the
previous sections.Variations in surface inflow are not
dependent on the mainstem discharge directly,even though
there is some correlation through their mutual dependence
on precipitation.Thus,a consideration of project effects
on flow depth must address changes in backwater.breaching,
and groundwater upwelling,and add unchanged surface inflow
to these parameters.
Decrease in slough or side channel depth resulting from
project operation is dependent on the location within the
slough or side channel.Relative changes in depth
generally decrease in the downstream direction for a given
channel configuration and will also be greater for riffle
configurations than for pool configurations.For example.
if a pool is 3 feet deep and the adj acent riffle is 0.5
feet deep,then a 0.25-foot reduction in both will have a
much greater effect in the riffle than the pool.Thus,the
depth of flow in riffle reaches are more significantly
influenced by project operation than those of pools.Flow
depths in the upstream riffle reaches of a channel are more
affected than reaches near the mouth since surface inflow
and groundwater upwellirig generally accumulate through the
site.
Another way to define the relative impacts of proj ect
operation on flow depth is to identify how often a certain
depth occurs under natural and proj ect conditions.For
example,a rift"le reach located near the mouth of a slough
may reach or exceed a specified depth 80 percent of the
time due to backwater only,20 percent of the time due to
breaching only,10 percent of the time if only groundwater
upwelling is available,and 40 percent of the time if an
average groundwater were supplemented by surface inflow.
Since backwater,breaching,and groundwater upwelling are
9
(e)
functions of mainstem discharge,the frequency of a certain
depth being equalled or exceeded can be obtained from the
flow duration curve for the period of interest.An
approximation of the frequency of surface flow can be
obtained from a precipitation duration curve,which is
related to th~surface flow through a runoff coefficient.
If it is assumed to be conservative,that the backwater,
breaching,and precipitation events are coincident,then in
the example above,the frequency that the specified depth
is equalled or exceeded is 80 percent,corresponding with
the frequency due to backwater.The evaluations of project
effects can address the frequencies corresponding to
project operation,which may be 0 percent of the time due
to backwater only,0 percent of the time due to breaching
only,5 percent of the time due to groundwater only and 35
percent of the time if average groundwater were
supplemented by the unaffected surface inflow.Thus,the
effects of the project for this example riffle reach is to
reduce the percent of time that a specified depth is
equalled or exceeded from 80 percent to 35 percent.This
relative change is fairly typical of the change that may
occur to a riffle near the mouth of a slough or side
channel,while a change from 10 percent to 8 percent may be
more typical of a riffle reach located farther upstream in
the site.Analyses in Appendix A provide results
indicating project influence on selected riffle reaches in
selected sloughs and side channels of the middle Susitna
River.
Winter Overtopping
The stage increase during ice cover formation (winter
staging)was described briefly in a previous section in
relation to the reduced upwelling at locations upstream
from the ice front.With project flows higher than natural
flows during winter,the staging effect will be higher
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during project operation downstream from the ice front.
Thus.the probability of breaching caused by ice staging at
and downstream from the ice front is also greater.Under
natural conditions,the staging effects occasionally cause
slough and side channel overtopping.An ice cover
prediction model uti1izin~weather data for the 82-83
winter predicted that the stage would be suff,icient to
overtop the berm at the head of Slough 8A continuously from
December to April (Harza-Ebasco 19844);however.Slough 8A
was overtopped by slush ice for five days in December
(ADF&G 1983b).When an ice cover forms.shore ice develops
causing flow channelization (R&M Consultants,Inc.1983).
The shore ice may act as a barrier to contain the flow and
prevent the mainstem from.overtopping the slough berms
(Figure 2).However.under higher mainstem discharges,the
probability of overtopping will increase.Figures 3
through 7 may be used to predict possible overtopping
events under natural and project winter flow regimes at
Sloughs 8A,9,9A,11 and 21 but do not identi fy the
probability or duration of actual events which are
dependent on other factors besides mainstem stage.(See R&M
1984 -for frequency information).
3.1.3 Relationship Between Physical Changes and Available
Habitat in Sloughs and Side Channels
Project flows reduce the amount of spawning and incubation
habitat available to chum salmon in sloughs.Reduction in the
quality and quantity of these habitats would result from the
following physi~a1 changes:
Reduced backwater effects
Elimination of breaching flows
Reduced groundwaterupwe11ing
Reduced Flow depth
Increased winter flows
11
(a)Reduced Backwater Effects
Backwater effects in the area of the slough mouth under
natural conditions provide greater depths in the affected
zone than would be provided by local slough flow.Project
flows will substantially reduce the backwater zone
resulting in a decrease in the surface area with suitable
spawning depths and a loss of spawning habitat.The degree
of loss is dependent on the relative spatial distribution
of available spawning habitat under natural and proj ect
conditions.
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(b)Elimination of Breaching Flows
Breaching flows provide access to spawning habitat within
the slough and side channels by increasing the amount of
area with suitable spawning depths over the amount present
under unbreached conditions.Project flows will eliminate
breaching flows and thus decrease the potential spawning
habitat.The amount of habitat lost is dependent on the
site specific frequency of breaching flows under natural
conditions.Spawning habitat provided by sites with
relatively high breaching discharges (low frequency of
occurrence)at breached conditions is generally of
insufficient duration for fish to effectively utilize~The
additional spawning habitat provided by channels with
relatively low breaching discharges (high frequency of
occurrence)under breached conditions is generally utilized
such that unbreached conditions under project flows will
result in a loss of spawning habitat.
(c)Reduced Upwelling
Reduced mainstem flows during the spawning season would
also decrease the amount of upwelling in the slough that is
.-utilized by spawning chum salmon.The reduction in the
12
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(d)
(e)
rate and aerial extent of upwelling reduces the available
spawning habitat.Winter flows,although higher than
natural,would result in reduced upwelling in sloughs
upstream of the ice cover because the staging effects
during ice formation will no longer occur.A decrease in
the areal extent and rate of upwelling in winter may
decrease the quality of incubation habitat.
Reduced Flow Depth
Access into and passage within the sloughs by returning
adult salmon is dependent on backwater effects of the
mainstem,the flow in the slough and the channel geometry.
Proj ect mainstem discharges during the August-September
spawning season will reduce backwater effects and the
groundwater and breaching contribution to slough flow,thus
resulting in restricted passage of adult fish into the
sloughs.
A reduction in fish entry into sloughs through passage
reaches will result in the loss of spawning habitat
available to the fish.Data collection and analysis are
currently underway·for low mainstem discharges to allow
more detailed incremental quantification of the total
impact.
Increaseq Winter Flows
Proj ect winter flows would be higher than flows under-
natural conditions.Thus,the probability of breaching
caused by ice staging at,and downstream from,the ice
front is also greater.Under natural conditions,the
staging effects occasionally cause slough overtopping.
For those sloughs which are overtopped,the influx of near
freezing water and subsequent ice formation will result in
embryo mortality (ADF&G 1983b).
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3.2 -Mitigation Options
3.2.1 -Flow Release
For the middle section of the Susitna River,altered flows would
affect the fish population.Under natural conditions,mainstem
discharges are high in late May,June,July,August,and early
September and decrease during September and October to low flows
throughout the winter (Figure 1).Hydroelectric power is
desired primarily during winter and water is retained during
summer to fill the reservoir.Flows under proj ect operation
would be much more uniform throughout the year and thus would
necessarily be higher in the winter and lower in the summer than
natural flows.
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(a)Impact Issue
The hydroelectric development on the Susitna River is
proposed for power production.To maximize power,benefits
the discharge downstream of the dams would follow Case PI,
presented in Table 7 (Harza-Ebasco 1984b).This schedule
of flows varies greatly from the natural mean monthly flows
recorded at Gold Creek (Figure 1).
The comparatively low flows during the August and September
would restrict movement of adult salmon into and within
~sloughs.At a mainstem discharge of 6,000 cfs under Case
PI,backwater effects at the slough mouths would be
negligible,breaching of the sloughs would rarely occur,-and local flow will be less due to reduced upwelling
component.Proj ect flows would also reduce the spawning
habitat available due to reduced backwater,breaching,and
groundwater upwelling effects.Project flow during winter
can cause reduced upwelling upstream of the ice front and
increased potential for overtopping downstream of the ice
front.
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(b)Mitigation
A mitigation flow schedule,designated Case EVI is proposed
(Tables 7 and 8)to reduce the adverse impacts of Case Pl.
The Case EVI flows are selected primarily to reduce loss of
chinook rearing habitat.
Under Case EVI,minimum flows during the critical period of
chum salmon migration and spawning in August and September
will be increased above the Case PI proj ected flows of
6,000 cfs to 9,000 cfs.
For Sloughs 9 and 11,a mainstem discharge increase from
6,000 cfs to 9,000 cfs is predicted to increase slough flow
1 cfs,based .on currently available analyses (APA 1984).
Sloughs 8A,9A and 21 the Case EVI flows are anticipated
also increase the local flow •.
The higher mainstem.flows will increase the di scharge in-the sloughs through increased groundwater contributions to
local flow and will increase fish passage efficiency.The
-higher Case EVI flows will have a neglibi ble effect on the
backwater at the slough mouths and the flows will not be
high enough to breach the sloughs of primary importance to-fish production (sloughs 8A,9,9A,11 and 21).
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Case EVI mainstem discharges are less than the natural
discharges during the summer and fall.The lack of
breaching flows and backwater effects will still lower the
efficiency of fish passage in sloughs.Local flow in the
sloughs will also remain lower than natural conditions.
Case EVI will have lesser impacts on chum salmon than Case
PI and will minimize impacts on chinook rearing habitat,
nevertheless,adverse impacts on side slough spawning and
incubation will occur.Mitigation in addition to flow
release will be necessary for the late summer and fall.
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3.2.2 -Habitat Modification
(a)Impact Issue
Case EVI will reduce from natural conditions the amount of
spawning and incubation habitat available to chum salmon in
sloughs and side channels of the middle Susitna River.
Partial or complete loss of these habitats will result
from:
·Reduced backwater effects
•Elimination of breaching flows
Reduced upwelling during spawning and incubation
•Passage restriction
•Increased winter flows
(b)Mitig~tion Measures
A number of mitigation measures are presented in this
section that can be used singly or in combination to
minimize identified impacts.Table 9 shows the
relationship between the mitigation measures and the impact
for which they are designed •
(i)Channel Width Modifications
Channeling slough flow will improve fish access
through passage reaches by contracting the width of
the channel and deepening the channel.This
technique is especially useful in drowning short
passage reaches or ameliorating wide passage
reaches.Wing deflectors extending out from the
channel bank or rock gabions restructuring the cross
section of the natural channel may be used to
contract the flow width (Bell 1973).
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In determining the modified width for the channel,a
maximum velocity criteria of 8 fps was used to
permit fish access through the reach.(Bell 1973)•
-Wing Deflectors
Wing deflectors are used to divert the flow in a
channel.Two wing deflectors placed on opposite
banks will funnel the flow from a wider to a
narrower cross section as shown in Figure 8.The
narrowed channel is designed to provide fish
passage at the minimum flow.At higher flows,the
wing deflectors are inundated;fill between the
banks and the wing deflector walls is sized to
prevent scouring at higher discharges.Fill will
typically be composed of large cobbles available
at the sloughs.
Wing deflector walls are constructed either of
rock or gabions formed of wire mesh and filled
with cobbles.Another alternative is the use of
12 inches in diameter timbers,anchored to the
banks and channel bed.A wing deflector costs
$31,000 when constructed of rock,approximately
$24,000 when constructed with gabions,and $22,400
if timber logs available on site are used.For
sites where timber is not available,a log wing
deflector would cost $23,200.Estimates are based
on a typical passage reach for a slough on the
middle Susitna River (Figure 9).
-Rock Gabion Channel
Reshaping the original cross section of the
channel with rock gabions is an alternative method
of channelizing the slough flow.The channel is
17
excavated and gab ions are used to reshape the
.....original configuration.The new channel shape is
designed to maximize depth at minimum flows;at
higher discharges,the gab ions prevent scouring of
the channel banks.Figure 10 illustrates a
typical cross section for a reshaped passage
reach.For long passage reaches.?resting areas
are created by widening the channel between the
rock gab ions forming the minimum discharge
channel.The gabions are provided throughout the
length of the passage reach and protected upstream
by riprap or wing wall gabions.The gab ion banks
.....extend higher than the height of the maximum
slough discharge to prevent collapse from erosion.
....
.....
(ii)
The gab ions composing the channel banks prevent
scouring of the banks;the channel will be more
stable than a similar channel modified by wing
deflectors.For passage reaches with greatly
varying discharges,the added stability of the
rock gabion channel is an advantage.The cost of
constructing the gabion channel is approximately
$60,000 for a typical passage reach.
Channel Barriers
Fish access through passage reaches is also improved
by creating a series of pools on the slope.
Barriers are placed to break the flow on long,steep
passage reaches and create pools between obstacles.
Fish passage over the obstacles is accomplished-if
sections of decreased barrier height are provided
(Bell 1973).
Channel barriers are used on long slopes to create
fish resting pools,as shown in Figure 11.These
18
-
,....
-
barriers with heights of 10 inches to 14 inches act
as weirs,with a section of decreased height to
improve fish passage between pools.The barriers
are constructed of various materials.Concrete
highway curbs anchored to the bed with rebar (Figure
11)or cobbles and boulders placed to create a sill
may be used.Logs may also be attached to the banks
and anchored securely to the bed to prevent movement
at high discharges.Gabions shaped as shown in
Figure 11 may also be used (Lister et al.1980).
Channels are constrained in width to form effective
pools.For a wide channel,channel widths are
modified where a pool and weir structure is desired.
Estimates of costs per barrier on the basis of a two
barrier system are listed belo~.Each slope will
require more than one barrier to create a series of
pools.As more barriers are built on a site,the
cost per barrier will decrease because of the
economies of scale;the major cost involved in the
construction of the barrier is the cost of
transporting the equipment needed.
(iii)
Barrier
Concrete highway curbs
Rock sill
Gab ions
Anchored logs available on site
Anchored logs not available on site
Passage Through Flow Augmentation
Cost/Barrier
$12,000
$16,000
$12,000
$11,000
$12,000
I"'"'"
I,
I
-
With lower mainstem discharges,less groundwater may
percolate into the sloughs,resulting in decreased
slough discharge (APA 1984).Passage reaches
19
negotiable at natural flows might become impassable
under project conditions.In order to augment the
slough flow,a piping system can be designed to
transport water from the mainstem or other sources
to affected passage reaches.
The sloughs of primary interest,including 8A,9,
9A.11.and 21.were considered in evaluating the
~feasibility of piping at mainstemasystema
discharge of 9.000 cfs.This corresponds to the-
-
minimum spawning period mainstem discharge for Case
EVI flows.Computational details are provided in
Appendix B.
corresponding to the site-specific overtopping
discharges are necessary to produce the required
head for flow.
For Sloughs 8A and 9A.the mainstem elevation at
9.000 cfs produced insufficient head between the
mainstem stage and the critical passage reaches to-
-!
!
!
provide flow adequate for passage.Flows
....
-
At Slough 9.a 9.000 cfs mainstem discharge would
provide sufficient head for 1 cfs through a piped
system.A collection tank (Figure 12)20 feet from
the main channel would collect mainstem water
screened by the intervening gravels and use a
I-foot-diameter corrugated metal pipe to deliver the
water 2.800 feet to the upstream end of Passage
Reach (PR)V,as shown in Figure 13.The system
would provide a maximum of 3 cfs prior to berm
overtopping.For Slough II,a mainstem discharge of
9,000 cfs could provide sufficient head for a flow
of 1 cfs through a I-foot-diameter pipe for delivery
3.200 feet from the slough head given an
18-foot-Iong collection system (Figure 14).A
20
...-
I
....mainstem discharge of 9,000 cfs would be necessary
at Slough 21 for a local flow of 1 cfs from a
similar sized collector through a 1,700-foot-Iong,-0.75-foot-diameter pipe (Figure 15);a maximum of
2 cfs would flow through the system just prior to
overtopping.The collector was designed to be
~
located 20 feet from the mainstem in order to
.....
....
.....
(iv)
provide erosional protection and a filtration system
for the water.
Estimated construction costs total $120,000 for the
backhoe installation of the collector and piping
system in Slough 9,$120,000 for the system in
Slough 11 and $134,000 for the system in Slough 21.
Upwelling Augmentation
A system providing supplementary upwelling would
maintain or increase spawning habitat in the sloughs
during low mainstem discharges.The mainstem and
nearby tributaries were evaluated as possible
sources of upwelling water.The mainstem as an
upwelltng water source could not be used at numerous
sites because of the low hydraulic head at low
mainstem flows.
For sloughs with tributaries,the tributary could
provide the water and the hydraulic head for an
upwelling system,as shown in Figure 16.The....
critical period for induced upwelling would be
during the proj ect's projected low mainstem-discharge period in August and September.Under
natural conditions,it is assumed,based on the
....
i
relationships provided in APA (1984),that upwelling
increases during this period because of the high
mainstem discharges.Selection of spawning sites
21
....
..-
I
.....
has been shown to be related to the presence of
upwelling at a site;therefore,upwelling needs to
be maintained under project flows to maintain
spawning habitat •
Under natural conditions,the mainstem stage and
upwelling decrease from September until ice
formation in November to December.Similarly,a
tributary supplied upwelling system would also have
decreasing discharges during this period.Reduction
in a piped water supply would not become significant
until mid-October,when project discharges increase.
Upwelling under proj ect operation is likely to be
greater than upwelling under natural conditions from
September to December.
Upwelling during winter (December to March)will
decrease for sloughs upstream of the ice cover and
increase for sloughs downstream of the ice front,
relative to the natural conditions.
In the spring,tributary flows increase with the
melting of snow and ice.By April,the tributary
flows would be sufficient to provide upwelling from
the piping system.Upwelling thus would be provided
continuously throughout the year.Under natural
conditions,upwelling is greatest from June through
September and December through April.
Temperatures of the upwelling flows from the piped
system would correspond to the temperatures of the
tributary flows.Water will flow through the system
as long as the water temperatures are above DOC.
Freezing water will not be released in the spawning
gravels,as flow will cease in the system at
freezing temperatures •
22
......
......
-
......
-
An upwelling system supplied by tributaries would be
feasible for Sloughs 8A,9,and 9A.Estimated cost
of each system is $210,000 for a 300-foot main pipe
and 200-foot reaches of cross pipe,spaced at 5-foot
intervals for upwelling.A system with a longer
main pipe could be built to tap Gold Creek water for
Slough 11.
(v)Slough Excavation
Mechanical excavation of certain reaches of sloughs
would improve fish access and fish habitat within
the sloughs.At slough mouths,excavation would
provide fish access when backwaters are negligible
during low mainstem discharges.Mechanical
excavation can be used to facilitate passage within
sloughs by channelizing the flow or deepening the
thalweg profile at the passage reach.
On a larger scale,mechanical excavation to lower
the profile of the entire slough could increase the
amount of upwelling in the slough.A greater head
between the mainstem and the slough bed would result
in additional local flow in the slough •
An additional benefit of the excavation process
would be the opportunity to improve the substrate in
the slough.Replacement of poor substrate with
suitable spawning gravels would provide additional
spawning habitat.The excavation process would be
designed to develop additional spawning and rearing
habitat.
An estimate of the cost to excavate a typical slough
mouth in the middle portion of the Susitna River is
$26,000.
23
(vi)Development of New Spawning Habitat
In order to provide the conditions that chum salmon
prefer for spawning,existing pools in sloughs would
be modified.Chum salmon prefer to spawn at
upwelling sites (ADF&G 1983a).A weir structure
that is permeable at the base and impermeable
elsewhere could be erected in a pool to produce a
head difference between the upstream and downstream
sides.Such a weir would cause water to flow
through the spawning gravels placed at the base of
the structure (Figure 17).
A notch in the top of the structure facilitates fish
passage between pools.The notch is designed for a
minimum slough discharge of 2 cfs;this discharge
corresponds to a typical low discharge in the
sloughs along the middle section of the Susitna
River.
The structure is securely embedded,anchored to the
channel walls and bed,and riprapped to prevent
erosion during high flows.
The weir can be constructed of timber posts
10 inches in diameter,reinforced with 2 x 4 inch
cross bracing and faced with impermeable material,
as in Figure 18.Gravel materials are piled on each
side of.the weir;the gravel provides stability to
the structure in addition to providing spawning
habitat.Only fine silts present in the gravel base
will be eroded by the 2 fps water velocities over
the weir.The spawning gravels would have a maximum
angle of 100 with the channel bed to prevent
downstream displacement caused by females digging
redds during spawning.
24
Rock gab ions can also be used to construct the weir
shown in Figure 19.Sheets of plywood in the center
of the structure impede flow through the gabions.
Spawning gravels provide habitat at the base of the
structure.A notch is provided for fish passage at
low flows.
~
I
A rock structure with an impermeable core can be
built as in Figure 20.Plywood sheets anchored with
reinforcing rebars are adequate for use as a core.
The decision as to the materials used for the weir
structure will be made during the design phase of
the project based on the cost,durability,and
aesthetics of the various structures.-
The cost of the three structures is estimated
assuming a 20-foot channel width and a 3-foot
natural pool depth.Economies of scale are
considerable if more than one structure is built at
a site.
.-
I
Structure
Timber pile weir
Rock gab ion weir
Rock weir
(vii)Prevention of Slough Overtopping
Cost/Weir
$32,000
$32,000
$45,000
Proj ect flows are higher than natural discharges 'in
the winter.Ice staging at these discharges will.....
result in an increase in mainstem stage and increase
the probability of overtopping of sloughs downstream
of the ice cover front.
-25
,....
An influx of cold mainstem water into the incubating
area of the Slough 8A in 1982 caused high embryo
mortality (ADF&G 1983b).To prevent overtopping.
the height of the slough berms is increased as shown
in Figure 21.
Cost estimates per berm total $150.000 initially and
$7.500 average yearly maintenance.Maintenance may
be required in 3 to 5 year intervals.
(c)Site Specific Impacts and Mitigations
(i)Slough 8A
During the 1981-1983 studies.the mean peak counts
of chum salmon and sockeye salmon in Slough 8A were
331 (range:37-620)and 104 (range:67-177).The
mean estimated total escapements to the slough were
553 chum (range:112-1062)and 152 sockeye (range:
131-195)(ADF&G 1984a).
-Impact Issue
•Passage Restrictions
Under project flows.the frequency of successful
passage conditions will decrease at passage
reaches {PR's}I and II from natural levels of
79 and 48 percent to project levels of 25 and 16
percent.For PR's III to IV the decrease will
range from 1 to 3 percent (Table 10).These
decreases in frequencies of successful passage
may.over time.result in a loss of potential
spawning habitat.Historically spawned areas
are presented in Table 1.
26
....•Backwater
Spawning habitat tha.t is dependent on backwater
effects for providing suitable spawning depths
would be lost because of project effects.An
estimated spawning area of 103.000 square feet
is affected by the backwater zone of natural
flows and a portion of this area would become
unsuitable at project flows.
•Breaching
The exceedence probabilities associated with
natural breaching flows are 7 percent for the
left channel and 2 percent for the right
channel.These relatively low probabilities
indicate that the importance of breaching lies
in providing successful passage rather than
increasing the potential spawning habitat by
increasing the area with suitable spawning
depths.
•Winter Flows
Overtopping of Slough 8A is predicted for
several combinations of year specific
climatological data"operational regimes.and
demand schedules (Harza-Ebasco 1984a)•The
influx of near freezing water.even for periods
of short duration.may result in substantial
mortality to incubat:ing embryos.
Mitigation
Passage through PR's I and II is provided under
natural conditions by backwater effects from a
27
.....
.....
.....
.-
.....
high mainstem discharge.With Case EVI flows.
access through these passage reaches will be
provided in an alternative manner to maintain the
103.000 square feet fish habitat available within
the slough.
The maximum channel bed elevation of the PR I will
be reduced to ease fish passage into the slough.
Flow in PR II will be:channeled to increase the
depth at the expected lower slough flow.Adding
wing deflectors to narrow the channel and remove
boulders from the channel will improve passage
through PR II.Other passage reaches may be
improved by excavating a deeper channel through
the reach •
Slough 8A has five tributaries suitable for use as
sources of upwelling water.Upwelling will
potentially be reduced between PR's IV and V and
PR's VII and VIII neal:two of these tributaries .
Two upwelling systems are proposed for Slough 8A .
Winter overtopping occurs at Slough 8A under
natural conditions (R&M Consultants 1983).Under
Case EVI.the frequency of winter overtopping is
predicted to increase (Harza-Ebasco 1984a).
Increasing the elevation of the berm at the head
of each fork·of the slough will prevent
overtopping by near-freezing waters.The height
of the east fork berm ~,ill be increased by 9 feet;
approximately 250 feet of berm is required.The
west fork berm will be increased four feet for a
length of 250 feet.
The costs associated T,01ith each of the mitigation
measures for Slough 8A are shown below:
28
.....
....
Mitigation Measure
Number
Proposed
Capital
Costs
Annual
Operating &
Maint.Costs
Upwe 11 i ng systems 2
Slough mouth excavation 1
Wing deflector 1
Excavate passage reaches 7
Protective slough berms 2
Total
(ii)Slough 9
$415,000
26,000
24,000
11,000
295,000
$771,000
$15,000
5,000
1,500
2,000
15,000
$70,000
During the 1981-1983 studies,the·mean peak counts
of chum salmon and s,ockeye salmon in Slough 9
(including 9B)were 295 (range:175-358)and 33
(range:2-91).The mean estimated total escapements
to the slough were 563 c:hum (range:430-645)and 81
sockeye (range:0-230)C~F&G 1984a).
-Impact Issue
•Passage Restrictions
Based on the slough flow analysis in APA (1984),
Project flows will result in reductions in the
frequency of successful passage conditions at
PR's III,IV and V.At PR's III and IV,passage
under natural conditions is assured 100 percent
of the time as compared to 34 percent and 29
percent under project flows (Table 11).At PR
V,natural occurrenclas of 29 percent will change
to 0 percent passagl:!under project flows.The
general area of spa1ming above PR V that will
become inaccessible amounts to approximately
5300 square feet (Table 2).The reduction in
opportunities for passage at PR's III and IV may
also result in loss ()f some spawning habitats.
29
.-
-
-
....
....
•Winter Flows
The upstream extent of the ice cover is
proj ected to progress beyond Slough 9 for
several combinations of selected meteorological
data.operation regimes and demand schedules.
Based on the simulations completed to date,
there is a modera:te probability of annual
overtopping of the slough (Harza-Ebasco 1984a).
•Breaching
The exceedance probability associated with
breaching discharge:s of 19,000 ds is 29
percent.It is probable that the breaching
flows are providing the depth required for
spawning in some areas and that these areas
would become unspawnable at project flows.
However,the extent of these areas appear
minimal when the wetted perimeter boundaries at
a flow of 9.000 cfs are overlaid on outlines of
spawned areas from 1982-1983.
•Backwater
Backwater effects provided spawning area during
the study period 19182-1984 and that area was
spawned only in 1983.,The lower portion of this
slough has since silted in and the channel has
changed its course.thus precluding spawning in
this area •
-Mitigation
Passage through the do~mstream section of Slough 9
is currently difficult because of silt deposited
30
.....
-
-
-I
during the 1983-1984 season.Removal of this silt
will expose the spawni~g gravels and increase the
habitat in the downstream region of the slough.
Based on the relationship between mainstem flow
and slough flow presented in APA (1984),PR's III
and IV are greatly affected by a reduction in
natural discharges.At discharges.corresponding
to Case EVI the frequency of pas.sage through these
reaches will be increased by excavating a deeper
channel and channelizing the available local flow.
Larger cobbles and boulders will be removed from
the channel to improve the spawning habitat.
Upstream from PR V,spawning habitat is available
r-.
under natural conditions.Under project
conditions,based on the currently available
slough flow analysis,fish would not be able reach
this habitat.A piped water supply system will
provide mainstem flow,to the upstream end of PR
V;this flow when chan.nelized,will increase the
frequency of passage through this reach.A pool
and weir structure will be constructed to enable
fish to access the natural pool habitat available
upstream of PR V.A series of 20 weirs composed
of anchored logs will allow salmon to access an
additional 1000 ft of Slough 9.
....
-
An upwelling system between PR's IV and V will
increase the amount of upwelling in this area.
Other efforts to iIilprove spawning habitat in the
pool region between PR's IV and V include
construction of a rock gabion weir to increase
spawning habitat available.
31
-
Slough 9 is expected to be overtopped more
frequently in winter by the increased ice stage
caused by project flows (Harza-Ebasco 1984a).An
overtopping-prevention berm 8 feet in height and
375 feet in width will be placed at the head of
the slough to maintain the suitability of
incubation habitat within the slough.
The costs associated with each of the mitigation
measures for Slough 9 are shown below:
Mitigation Measure
Number
Proposed
Capital
Costs
Annual
Operating &
Maint.Costs
.....
Upwelling system 1
Water supply system 1
Protective slough berm 1
Log barri ers 20
Passage reach excavation 1
Total
(iii)Slough 9A
$210,000
120,000
150,000
30,000
5,000
$515,000
7,000
10,000
7,500
6,000
1,000
$31,500
-I
..-
f
During the 1981-1983 studies,the mean peak count of
chum salmon in Slough 9A was 135 (range:105-182)
while the mean estimated total escapement to the
slough was 152 chum (range 86-231)(ADF&G 1984a).
-Impact Issue
•Passage Restrictions
Under natural condi.tions,PR's I-IX can be
successfully negotiated by chum salmon 100
percent of the time (Table 12).Five out of
these nine passage "reaches.are anticipated to
provide successful passage condition 3 to 32
percent of the time under project operation.Of
the five passage rea.ches,PR III is considered
32
.....
-
....
to be of greatest concern since access to
substantial amounts of historically spawned
areas can be achieved if passage through this
reach is facilitated (Table 3).
Breaching
The breaching discharge of 12,000 cfs has an
exceedance probabi1:Lty of 71 percent.Field
observations during September 1984 indicated
that the gravel sur·face·of some areas spawned
earlier in the season under breached conditions
were dewatered.Su:rvival from these areas is
unknown.Estimates of the spawning area lost
will be obtained by overlaying the boundaries of
the wetted surface area at 9,000 cfs onto the
spawned areas delineated for the 1982-1984
seasons.
•Backwater
because breaching
majority of the
.....
Evaluation of backwater
applicable to this slough
conditions prevail for the
spawning season.
•Winter Flows
effects are not
r-
i
Simulation of the upstream extent of ice cover
for several combinations of operating regimes.
demand schedules and meteorological conditions
for selected years indicated a moderate
probability of the slough overtopping on an
annual basis (Harza-J8basco 1984a).
33
,...
Mitigation
Spawning habitat in Slough 9A is primarily
accessed during brea(~hing flows under natural
conditions.Under Case EVI scheduled discharges,
the habitat will be retained by lowering the
slough profile until depths suitable for spawning
are obtained.
While the slough profile is being excavated,the
large cobbles and boulders will be removed to
improve access between the series of pools that
exist along the thah.l'eg.Removal of·the large
cobbles and boulders will provide additional
spawning habitat to that presently existing within
the side channels.
Slough 9A breaches at a relatively low natural
mainstem discharge mtd protection from winter
overtopping under prroject conditions.will be
supplied.The berm at the head of the slough will
be heightened 10 .feet for a length of 150 feet to
prevent winter overtopping if the ice front is
predicted to extend uprstream of this slough more
frequently than once every ten years.
The costs associated 'idth each of the mitigation
measures for Slough 9A are shown below:
"'""
Mitigation Measure
Protective slough berm
Excavation of slough
Total
34
Number
Proposed
Capital
Costs
$150,000
26,000
$176,000
Annual
Operating &
Mai nt.Costs
$7,500
5,000
$12,500
-
(iv)Slough 11
During the 1981-1983 studies,the mean peak counts
of chum salmon and sockE!ye salmon in Slough 11 were
369 (range:238-459)and 532 (range:248-893).The
mean estimated total escapements to the slough were
957 chum (range:674-1119)and 1128 sockeye (range:
564-1620)(ADF&G 1984a).
-Impact Issue
•Restricted Access
Under natural conditions,PR's I-III provide
successful passage 70,43 and 12 percent of the
time,principally through the groundwater
contribution to local slough flow (Table 13).
Passage reaches IV and V provide adequate
passage conditions only during infrequent
breaching conditions,which occur one percent of
the time.Based on currently available
information,project:flows of 9,000 cfs will
reduce the groundwater input to the extent that
passage will be restricted across all passage
reaches (APA 1984).The spawning areas that
will be affected are shown in Table 4.
•Breaching
The exceedance probabilities associated with
natural breaching discharges of 43,000 cfs is
one percent.Based on this low frequency of
occurrence,the contribution of breaching
conditions in providing access and passage or in
increasing the spawnablearea·within the slough
is negligible.
35
-
•Backwater
The backwater at the slough mouth affects
approximately 50,000 square feet of area that
I
has been spawned ill the past.Overlying the
boundaries of the wetted surface area at
9,000 cfs indicates that approximately 20
percent of that spaWll1ed area is dewatered during
project operations.For purposes of mitigation
this dewatered are~L will be considered lost
habitat.For purposes of mitigation it will be
considered lost h~~itat.Additional habitat
with the wetted perimeter at 9,000 cfs may be
unsuitable for spro~ing due to insufficient
depth and would also be considered lost habitat.
•Winter Flows
Simulations of iCE!cover progressing have
indicated that the front will proceed as far as
Slough 11 generally in the coldest years
(Harza-Ebasco 1984a).The probability of the
slough overtopping on a yearly basis is
therefore low.
-Mitigation
The passage reaches in Slough 11 will require
channelization in orde:r to increase the depth of
flow in the reaches and provide passage.
A channel will be eJrcavated through the silty
materials at the slough mouth and the banks of the
channel stabilized 1i1ith rock gabions.The
stabilized channel will extend 1,200 feet upstream
in the slough and mod:Lfy PR I s I and II.Passage
36
-
.....
-
.....
.....
r
through PR III will be facilitated by construction
of wing deflectors mad,e from rock gab ions.
A channel will be excavated at PR IV.A pool and
weir structure will be constructed in the
excavated channel which will improve fish passage
upstream.Fifteen weirs will be needed for
300 feet of slough channel.
Local flow lost becaus:e of the decreased mainstem
discharge will be replaced by piping water from
Gold Creek into Slough 11.The increase in local
flow will improve the ,ease of fish passage through
the reaches •
Under natural flows,backwater effects provide
50,000 square feet of fish spawning habitat at the
slough mouth.Under project conditions,this
spawning area will be lpartially replaced with rock
gabion weirs placed ill pools between PR's II and
III and PR's III and IV.
Under project conditions the slough may experience
winter overtopping.If further analysis of ice
processes indicates a high frequency of
overtopping,the berm at the head of the slough
will be heightened five feet for a length of
250 feet to prevent this occurrence.
The costs associated ldth each of the mitigation
measures for Slough 11 are shown below:
37
Mitigation Measure
Number
Proposed
Capital
Costs
Annual
Operating &
Maint.Costs
Tributary flow diversion 1
Weirs 2
Bank stabilization 1
Slough excavation 1
Log barriers 15
Total
(v)Slough 21
$380,000
61,000
25,000
26,000
24,000
$615~000
$40,000
6,000
3,000
5,000
5,000
$59,000
.....
I
During the 1981-1983 studies,the mean peak counts
of chum salmon and sockeye salmon in Slough 21 were
443 (range:274-736)and 96 (range 38-197).The
mean estimated total escapements to the slough were
958 chum (range:481-1737)and 148 sockeye (range:
63-294)(ADF&G 1984a).
-Impact Issue
•Restricted Access
PR's I,IlL,and IIR provide suitable passage
conditions 100,25 and 20 percent of the time
under natural flow.Project flows will reduce
the frequency at PR's I,IlL and IIR to 6,0,
and 1 percent,primarily as a result of reduced
groundwater flow (Table 14).The restriction at
PR IlL will eliminate the spawnable area above
this point (Table 5).Moreover,if passage is
facilitated,much of the historically spawned
area will not be of sufficient depth for use
under project flows.
•Breaching
The exceedance probably associated with the
natural breaching discharge of 25,000 cfs,for
38
....
r-
I
r
....
the left channel,is 10 percent.Breaching
provides access and passage within the slough,
but does not appreciably increase spawnable
area.
•Backwater
Spawning areas in the mouth of the slough do not
appear to be depend.ent on backwater and areas
that were spawned Illnder natural flows should
remain spawnable.
•Winter Flows
The ice front is prredicted as far as Slough 21
only during the coldest of years (Harza-Ebasco
1984a).The probability of the slough
overtopping is very low.
-Mitigation
Passage through Side Channel 21 is necessary prior
to entry into Slough 21.Mitigation of passages
reaches within Lower Side Channel 21 is needed to
permit fish access to the habitat in Slough 21.
Passage through PR I will be ameliorated by the
excavation of a ch"mnel through the reach.
Passage through reaches IlL and IIR will be
accomplished by remroving large cobbles and
boulders and channelizing the flow.A water
supply system will pipe 1 cfs from the mainstem
into PR IlL in order to increase the local flow
available for passage •
39
The large cobbles and boulders in the upper
portion of the slough will be removed and sorted
gravel provided to increase the available spawning
habitat above the level that is currently
available.
The flow will be channelized by excavating a
deeper channel through the reaches.Reaches with
erodible substrate will be stabilized with rock
gabions.
The costs associated lirith each of the mitigation
measures for Slough 21 are shown below:
-Mitigation Measure
Excavation of slough
Rock gabions
Water supply system
Total
(vi)Lower Side Channel 21
Impact Issue
•Restricted Access
Number
Proposed
1
2
1
Capital
Costs
$34,000
54,000
134,000
$222,000
Annual
Operating &
Maint.Costs
$7,000
6,000
12,000
$25,000
Under natural condi.tions the frequencies of
suitable passage conditions range from 71-100
percent for PR's I-X (Table 15).Under project
conditions,successful passage conditions will
be available about 30 percent of the time at
PR's I-IV and one percent or less at PR's V-IX,
based on current analysis.The majority of the
spawning occurs abovE,PR V and these areas would
have restricted access (Table 6).
40
--!
Breaching
A series of channels enter Lower Side Channel 21
(LSC2l)along its le.ngth and each breaches at a
different mainstem discharge.The uppermost
channel.A6.has a breaching discharge of
24.000 cfs with an associated frequency of
occurrence of 12.Spawning areas between the
entry point of this channel into LSC21 and next
downstream channel.AS are limited primarily by
the depth provided by local flow and not
breaching.
The exceedance probability of 71 percent
associated with breaching discharges of
12.000 cfs at the AS channel indicates that
mainstem flow into the side channel provide the
required depths for much of the spawned area
downstream from this point during the 1982-1984
seasons.This was confirmed by field
observations of the channel at unbreached
conditions in September.1984 in which areas
spawned in previously in the season were
dewatered.
•Backwater
Evaluation ofbackwa~ter effects on availability
of spawning habitat are not applicable in light
of the low breaching discharges.
•Winter Flows
Similar to Slough 2',1.the ice front is only
projected to reach Lower Side Channel 21 in the
coldest years.The probability of overtopping
41
-
.....
-I
-
.....
is low,although the side Channel would overtop
before the slough.
-Mitigation
At project flows,the lack of breaching flows will
impact fish passage wHhin Side Channel 21.The
frequency of fish passage will be increased by
channelizing the local flow.
Passage reaches I-V will be ameliorated by
excavating a channel through the most restrictive
sections of each passage reach.
Passage reaches upstream of PR V will be
channelized with rock gab ion wing deflectors at
the passage reaches.Large cobbles and boulders
will be removed to improve the frequency of fish
passage through the reaches.Marginal spawning
substrate in the upstream slough pools will be
replaced with sorted gravels to increase the
available spawning habitat.
Winter overtopping of the berms along the length
of Side Channel 21 is not anticipated since the
ice front on the Sus tina River is estimated to be
downstream (Harza-Ebasc:o 1984a).
The costs associated v;rith each of the mitigation
measures for Slough 21 are shown below:
Mitigation Measure
Excavation of channel
Wing deflectors for
bank stabilization
Total
42
Number
Proposed
7
Capital
Costs
$45,000
240,000
$285,000
Annual
Operating &
Maint.Costs
$9,000
35,000
$44,000
-
3.2.3 -Artificial Propagation
An alternative means to achieve the mitigation goal of
maintaining chum salmon production is through artificial
propagation.Mitigation by artificial propagation will be
considered if other mitigation measures are ineffective.The
artificial propagation method selected for mitigation for chum
salmon spawning habitat losses in the middle Susitna River is
stream-side egg incubation boxes.The emergent fry will be.
returned to the sloughs for rearing and/or migration.Egg boxes
with gravity fed water systems are 'well suited for remote-site
installation because they are cost effective and require little
maintenance.
-
!""'"
!
(a)Design and Operation of Egg Box
The egg box to be used is a str4:!am-side egg.incubation box.
The egg box is a 4 ft x 4 ft x 8 ft gravel-filled upwelling
box capable of incubating 500,000 eggs.This egg box is
used extensively in Washing1i:on State for artificial
propogation of chum salmon.The box will be insulated to
protect against freezing.
In each egg box 500,000 green E:ggS (those just-fertilized)
are placed on plastic mesh trays and incubated.At the
eyed stage,the eggs are shocked and the dead and blank
eggs are removed.At hatching the alevins fall through the
plastic mesh trays to the gravEd surface and migrate into
the gravel.Alevins reside i.n the gravel interstitial
spaces until the yolk-sac has been absorbed,at which time
they emerge from the gravel and leave the box.Survival
from eyed egg to emergent fry is typically greater than 90
percent (B.Snyder,Univ.Wash.I>pers.comm.,1984).
43
-
(b)Site Selection Criteria
The primary concern in sit~rrg the egg boxes is the
availability of a dependable water source.The water
should be sediment free.meet water quality standards and
be gravity-fed tel the egg boxes:.The latter is of primary
concern due to the low reliabilIty and high cost of pumping
water.Other criteria are access to the site and proximity
to a slough for juvenile release and adult return.Curry
Station (RM 120)appears to satisfy the above criteria for
site location.
(i)Water Supply
.....
-
-
-
Curry Station has an existing gravity-fed surface
water system.Using an existing system is more
economical than developing a new water system.The
system at Curry was built in the 1930 I S as a water
supply for the railway construction camp.It
consists of an impoundment structure and pipeline
which draws water at an estimated 5 cfs year round
(B.Barrett.ADF&G,pers ..comm ••1984).Temperature
and water quality appear to be within acceptable
limits (D.Seagren.MlF&G,pers.cornm ••1984);
however.before an egg box program is implemented.
detailed temperature and water quality data will be
obtained.Information em the temporal temperature
variation of the·water source will be used to
predict the emergence t:lming of fry and to select
the proper brood stock.
(ii)Slough Proximity
Another aspect of site location is the proximity to
a slough.The slough will be utilized in two ways.
First.emergent fry from the egg boxes will be
44
-
r
i"""
r
(iii)
released,directly into the slough for additional
rearing and/or migration.Second.the slough will
serve as an adult retUlm area and will facilitate
procurement of the brood stock.Curry Slough is
approximately 4000 ft downstream from Curry Station
and can be utilized.
Site Access
Curry Station is easily accessible by helicopter and
rail.The close proximity of the railway will
facilitate movement of materials and equipment to
the site.
,...
i
(b)Brood Stock
The initial selection of brood stock will depend on the
temperature profile of the wat,er source.It appears that
the existing water source is colder than intergravel
temperatures to which incubating eggs are exposed.This
may cause the fry produced frrom egg box to emerge later
than native fry.If this delay exceeds the natural
variation in emergence timing fror native fry.the tributary
spawning chum in the middle Susitna River,or another stock
of earlier-spawning chum,will be selected to allow the egg
box fish to emerge at approximately the same time as native
fry.
The donor stock will be utilizled for the first five years
of the project since Susitna cruJm predominantly return at 4
and 5 years of age.After the initial 5 year introduction
period the returning adults will serve as the brood stock.
To mitigate for the loss of 4200 chum.approximately
700.000 eggs (250 females)will be needed for mitigation.
This figure is based on maintaining the 4200 chum
escapement using the following assumption:1.1:1 male to
45
-
-
female ratio (ADF&G 1984a)a 15 percent egg-to-fry survival
(ADF&G 1984b),a fecundity of 2850 eggs per female,and a
0.7 percent fry to adult return (including harvest)
(Barrick et a!.1983).ExceSlS returns to the egg box
facility will be allowed to spawn naturally in the slough
or in adjacent sloughs.To insure genetic diversity of the
arti£ic~ally propogated stock,eggs from each female will
be fertilized with the gametes of several males.
(c)Alternatives for Development
There are two alternatives for the Curry Station egg box
site.The first is a plan to establish the egg box site at
Curry Slough and the second is a plan for development of
the egg box site at Curry Station.
-
.....
(i)Curry Slough Development
Establishing the egg b01l:site at Curry Slough will
require the water source presently at Curry Station
(approximately 4000 feet upstream)to be piped to
Curry Slough.This will entail burying (to
safeguard against free~:ing and physical damage)
approximately 4000 feet of 6-inch diameter pipe.
The egg boxes will be set:up near the downstream end
of Curry Slough and emergent fry will be released
directly into the slough from the egg boxes.The
slough will be appropriately sloped to facilitate
downstream mitigation of fry and to ensure that
returning adults have access to the slough.·The
advantage of.locating the boxes adj acent to the
slough,is that the emEtrgent fry can be released
without being handled.Fry will be released into
the slough to allow for acclimation and/or rearing
before seaward migration.Releasing newly emerged
fry directly into the m~linstem would not allow for
46
acclimation and orientation.The costs for this
option are outlined in Appendix B and summarized
below:
Number
Mitigation Measure Proposed
Artificial propagation 2
Total
(ii)Curry Station Developmen~
Capital
Costs
$450,000
$450,000
Annual
Operating &
Ma i nt.Costs
$50,000
$50,000
-
The Curry Station development consists of installing
the egg boxes near the outfall of the existing water
system.This will require a minimal amount of pipe,
which can be installed above ground if insulated
pipe is used.Newly emE!rgent fry will be collected
in two 18 foot diameter x 4 foot deep above-ground
rearing ponds.Fry will be transported daily to
Curry Slough and liberall:ed.This installation has
the disadvantage of extensive handling of fry.The
costs for this option arl:!outlined in Appendix Band
summarized below:
Number
Mitigation Measure Proposed
Artificial propagation 2
Total
47
Capital
Costs
$81,000
$81,000
Annual
Operating &
Maint.Costs
$35,000
$35,000
r-
i
i
REFERENCES
.....
REFERENCES
Acres American Incorporated.1982.Susitna Hydroelectric Project:
Fish and Wildlife Mitigation Policy.Alaska Power Authority_
Anchorage,AK.
Acres American Incorporated.1983.Application for license for major
project,Susitna Hydroelectric Projec1t,before the Federal Energy
Regulatory Commission.Vol.6A.Ex·h.ibit E,Chaps.3.Alaska
Power Authority.Susitna Hydroelectr:lc Project •
Air Photo Tech,Incorporated.1983.Aeria.l Photographs on October 8,
1983 •
.Alaska Department of Fish and Game.19tH.Susitna Hydro Aquatic
Studies -Phase I Final Species/Subj ec~t Report:Adult anadromous
fish study.Prepared for Acres Ameriean,Inc.Buffalo,NY.
ADF&G.1982a.Susitna Hydro Aquatic Studies -Phase
Aquatic Studies Program.Prepared for Acres
Incorporated,Buffalo,NY.
I Report:
American
......
..-
....
ADF&G 1982b.Susitna Hydro Aquatic Studies -Phase I Final Draft
Report:Aquatic Studies Program.Prepared for Acres American,
Incorporated,Buffalo,NY.
ADF&G 1983a.Susitna Hydro Aquatic Studies -Phase II Basic Data
Report,Volume 4:Aquatic Habitat and Instream Flow Studies.
1982 •
ADF&G 1983b.Susitna Hydro Aquatic Studies -Phase II Data Report.
Winter aquatic studies (October 1982 .~May 1983),Anchorage,AK.
ADF&G 1984a.Susitna Hydro Aquatic Studies,Report No.1:Adult
Anadromous Fish Investigations,May -October 1983.Prepared for
Alaska Power Authority,Anchorage,AK ..
ADF&G 1984b.Susitna Hydro Aquatic Studies,Report No.2:Resident
and juvenile anadromous fish investigations,May -October 1983.
Dana C.Schmidt,Stephan S.Hale,Drew L.Crawford,Paul M.
Suchanek (eds.).Prepared for APA,Anchorage,AK.
ADF&G.1984c.Susitna Hydro Aquatic Studies,Report No.3:Aquatic
Habitat and Instream Flow Investigations,May -October 1983
(Review Draft).Chapter 6:An evaluation of passage conditions
for adult salmon in sloughs and side channels of the Middle
Susitna River.Prepared for Alaska Power Authority,Anchorage,
AK.178 pp.
Alaska Power Authority.1984.Comments on the FERC Draft
Environmental Impact Statement Clf May 1984.Volume 9,
Appendix VII -Slough Geohydrology Studies.Anchorage,AK.
48
-
.....
....
-
-
Barrett.B.1984.Personal Communication"Alaska Dept.of Fish and
Game.
Barrick.L.et a1.1983.Upper Susitna River Salmon Enhancement Study
(Draft).Division of Fisheries Reha.bi1itation,Enhancement and
Development,Alaska Dept.of Fish &Game.Anchorage.AK.15 pp.
Bell.M.C.1973.Fisheries Handbook of Emgineering Requirements and
Biological Criteria (Revised 1980).Prepared for
Fisheries-Engineering Research Progr~n,Corps of Engineers,North
Pacific Division.Portland.Oregon.
Browning.R.1984.Personal Communicatio,n.U.S.Fish and Wildlife
Service.
Harza-Ebasco Joint Venture.1984a.Susitna Hydroelectric Project:
Instream Ice Simulation Study.Prepared for Alaska Power
Authority.Anchorage,AK •
Harza-Ebasco Joint Venture.1984b.Evaluation of Alternative Flow
Requirements.Anchorage.AK.
Lister.D.B.et a!'1980.St ream Enham~ement Guide.Province of
British Columbia.Ministry of Envirorunent,Vancouver.BC.Canada.
R&M Consultants.Inc.1982.Task 3 -Hydrology.Slough Hydrology
Preliminary Report.Prepared for Acrles American,Inc.New York.
R&M Consultants,Inc.1983.Susitna Hydroelectric Project:Susitna
River Ice Study (Task 4).Prepared for Harza/Ebasco Joint
Venture.Anchorage,AK.183 pp +map:s.
R&M Consultants.Inc.1984.Memorandum Report:Local Runoff into
Sloughs.Prepared for Harza-Ebasco Joint Venture.Anchorage,
AK.
Schmidt.D.1984.Personal Communication.Alaska Department of Fish &
Game.
Seagren.D.1984.Personal Communication.ADF&G.
Snyder.B.1984.Personal Communication.Th~iversity of Washington.
U.S.Fish &Wildlife Service.1982.Endangered and Threatened Wildlife
and Plants.Federal Register 50 CFR 17.11 and 17.12.January 1.
1982.
49
..-
.,
TABLES
Table 1 Area spawned within slough 8A backwater zones and areas
between passage reaches for 1982,1983 and 1984.The
ratio of the composite to the total area spawned for
all years is also shown •
.-
Area Spawned (£1:2 )Composite/
1982 1983 1984 Composite Total
Backwater Zone 19,700 17,900 93,700 103,400 .79
Passage Reaches
I -II 21,900 20,200 94,700 107,100 .78
II-III 4,100 2,900 29,200 31,800 .88
III-IV 5,900 12,400 70,800 72,700 .82
IV-V 0 0 10,400 10,400 1.0
..-V-VI 0 0 12,900 12,900 1.0
VI-VII 8,600 0 2,000 10,300 .97
VII-VIII 7,800 0 600 8,400 1.0
VIII-IX 0 0 5,200 5,200 1.0
IX-X 0 0 0 0 0
-_......._.--~-----------------,------------------
Table 2 Area spawned within slough 9 backwater zones and
between passage reaches for 1982,1983 and 1984.
ratio of the composite to thle total area spawned
all years is also shown.
areas
The
for
Area Spawned (ft2 )Composite!
1982 1983 1984 Composite Total-
Backwater Zone 0 1.200 0 a a
~/Illo Passage Reaches
I-II O'1.200 0 0 0
II-III 13.500 23.900 18,100 47.200 .85
III-IV 7,500 4.000 4.000 11 ,200 .79
IV-V 7.700 3.200 6,900 11,700 .76
V-VI 4,600 2.900 4,000 5,300 .46-
.-
Table 3 Area spawned within slough 9A backwater zones and areas
between passage reaches for ll982 J 1983 and 1984.The
ratio of the composite to the total area spawned for
all years is also shown.
Table 4 Area spawned within slough 11 backwater zones and areas
between passage reaches for 1982,1983 and 1984.The
ratio of the composite to the total area spawned for
all years is also shown.
~1J'miIl'I,
Area Spawned (ft 2 )Composite!
1982 1983 1984 Composite Total
Backwater Zone 13,100 25,800 35,000 50,200 .68
Passage Reaches
I-II 13,400 25,800 40,900 56,200 .70
II-III 4,100 0 9,700 9,700 .70
III-IV 15,200 7,300 38,200 46,200 .76
IV-V 5,000 0 3,500 5,200 .61
V-VI 2,900 3,600 4,000 5,800 .55
VI-VII 27,000 9,900 19,100 32,600 .58-
Table 5 Area spawned within slough 21 backwater zones and areas
between passage reaches for 1982.1983 and 1984.The
ratio of the composite to the total area spawned for
all years is also shown.
......Area Spawned (ft 2 ).Composite/
1982 1983 1984 Composite Total
.....Backwater Zone
Passage Reaches-I-II 3,400 12.100 10,000 19.100 .75
II-III 2.900 33.600 21.900 38.900 .67
-
.....
-
.-
Table 6 Area spawned within lower side channel 21 backwater
zones and areas between passlige reaches for 1982,1983
and 1984.The ratio of the composite to the total area
spawned for all years is alse,shown,.
Area Spawned (f1:2 )Composite/
1982 1983 1984 Composite Total
Backwater Zone 80,100 80,500 178,600 239,300 .71
r-
Passage Reaches
I-II 0 0 300 300 1.0
~II-III 0 6,300 9,000 9,000 .59
III-IV 0 3,600 2,200 3,700 .64
'IV-V 19,700 21,500 63,400 65,900 .63
V-VI 1,500 13,200 7,800 19,000 .84
VI-VII 3,300 0 600 3,900 1.0
VII-VIII 33.300 17,700 74,300 105,200 .84
VIII-IX 0 0 0 0 0
IX-X 0 0 0 0 0
X-XI 22,300 18,300 21,000 32,400 .53
.....
Table 7 Mean monthly discharges at Gold Creek for natural
conditions.predicted project flc)ws based on Case PI
(maximum power generation).and predicted pro1ect flows
based on Case EVI Instream flow requirements.
Natural Case PI Case EVI
Month (cfs)(cfs)(cfs)
January 1,440 10.900 10,700,-February 1,210 9,200 8,900
March 1.090 7,900 7,700
April 1,340 7.300 7,000
May 13,400 8,800 8,500
June 28,150 10,500 11 ,400
July 23,990 8.900 10,200
August 21,950 9,800 10,700
September 13.770 10,900 9,900
October 5,580 10,200 9.800
November 2,430 20,600 10,300
December 1,750 12.100 11.900
a Minimum and maximum instream flow requirelments are listed in
~Table 8!
-_._-._~--------------------------..-._----------------
Table 8 Minimum and maximum weekly instream flow
requirements for Case ID1I flows at Gold Creek
Week Mil1 (cfs)Max (cfs)
1 2,000 16,000
January 2 ""
3 ""
4 II "
1 2,000 16,000
February 2 ""
3 ""
4 ""
1 2,000 16,000
March 2 ""
3 ""
4 ""
1 2,000 16,000
April 2 "11
3 ""
4 ""
1 2,000 16,000
May 2 n "
3 ""
4 l.,OOO "
1 6,000 16,000
June 2 ""
3 ""
4 9,000 35,000
1 9,000 35,000
July 2 ""
3 ""
4 11 11
1 9,000 35,000
August 2 ""
3 ""
~4 ""
1 9,000 35,000
September 2 "h
3 8,000 "
4 7:.000 "
1 6,000 18,000
October 2 6,000 12,000
3 5,000 16,000
4 ~"OOO 16,000
1 3,000 16,000
November 2 ""-3 ""
4 11 "
1 31,000 16,000
December 2 2,000 "
3 ""
4 ""
,....
Table 9 Relationship between mitigation alternatives and the
impacts for which they are applic~ble
Winter
Loss o:f Loss of overtopping
I""'"Mitigation alte~-Inadequate physical upwelling of slough
natives/impact issue passage habita'l:at habitat berm
channel width
modification P
channel barrier
construction P
Flow augmentation P P S
Upwelling augmentation S S P
~.Slough excavation P P S
creating spawning
habitat in pools P S
Increase berm height P
.....
..-p =primary effect
S =secondary effect
I""'"
Table 10.Condition which provides successful pa:ssage most frequently and
approximate percent of time that passal~e is successful during the
period 20 August -20 September at Slough 8A.
F"
Passage Natural Project 9 ,DOD cf's Project 8,000 ds
Reach Condo Occurrence Condo Occurrence Condo Occurrence
(%)(%)(%)
I BW 79 SW/GW 25 SW/GW 24
II BW 48 SW/GW 16 SW/GW 15
J'~
III SW/GW 19 SW/GW 16 SW/GW 15
.....IV SW/GW 10 SW/GW 7 SW/GW 7
V SW/GW 9 SW/GW 7 SW/GW 7,
VI SW/GW 12 SW/GW 9 SW/GW '9
VII SW/GW 11 SW/GW 9 SW/GW 9
~
VIII SW/GW 4 SW/GW 3 SW/GW 3
IX BR 2 0 0
_BW is backwater condition which neglects the effect:of local flow
BR is breaching condition which represents controlling discharge through the slough
..-
-
GW is groundwater condition as it appears to fluctuate with mainstem discharge
SW/GW is surface water and groundwater condition wjLth a median natural flow or
minimum project flow controlling groundwater levels and surface water related
to precipitation events.
Appendix B contains an explanation of the derivation of the percent exceedance values
Table 11 Condition which provides successful passage most frequently and
approximate percent of time that passage is successful during the
period 20 August -20 September at Sl~~gh 9.
Passage Natural Project '9.000 cfs Project 8.000 cfs.....Reach Condo Occurrence Condo Occurrence Condo Occurrence
(%)(%)(%)
....
I GW 100 GW 100 GW 100
II GW 100 GW 100 GW 100
III GW 100 SW!GW 34 SW!GW 29
IV GW 100 SW!GW 29 SW!GW 28
V BR 29 a a
BW is backwater condition which neglects the effec1t of local flow
.....
)l'i'JiIilWiII"
.....
BR is breaching condition which represents controlling discharge through the slough
GW is groundwater condition as it appears to fluctuate with mainstem discharge
SW!GW is surface water and groundwater condition with a median natural flow or
minimum project flow controlling groundwater levels and surface water related
to precipitation events.
Appendix B contains an explanation of the derivation of the percent exceedance values
Table 12.Condition which provides successful passage most frequently and
approximate percent of time that passage is successful during the period
20 August -20 September at Slough 9A.
Passage Natural Project 9.000 cfs Project 8.000 cfs
~,Reach Condo Occurrence Cond.Occurrence Cond.Occurrence
(%)(%)(%)
I GW 100 GW 100 GW 100
II GW 100 GW 100 SW/GW 41
-~
III GW 100 SW/GW 32 SW/GW 14
IV GW 100 GW 100 GW 100
V GW 100 GW 100 SW/GW 20.
VI GW 100 SW/GW 24 SW/GW 14
VII GW laO-sw/aw 10 SW/GW 7"
VIII GW 100 SW/CW 6 SW/GW 3
IX GW 100 SW/GW 3 SW/GW 2
~
X a a a
-
BW is backwater condition which neglects the effect:of local flow
BR is breaching condition which represents controlling discharge through the slough
GW is groundwater condition as it appears to fluctuate with mainstem discharge
SW/GW is surface water and groundwater condition with a median natural flow or
minimum project flow controlling groundwater levels and surface water related
to precipitation events.
Appendix B contains an explanation of the derivaticin of the percent exceedance values
Table 13.Condition which provides successful passage most frequently and
approximate percent of time that passage is successful during the
period 20 August -20 September at SlOtllgh 11.
Passage Natural Project 9,000 cis Project 8,000 cis
Reach Condo Occurrence Condo Occurrence Condo Occurrence
(%)(%)(%)
I GW 70 0 °
II GW 43 0 0
III GW 12 °0
-IV BR 1 °0
V BR 1 0 °
BW is backwater condition which neglects the effect:of local flow
BR is breaching condition which represents controlling discharge through the slough
GW is groundwater condition as it appears to fluctuate with mainstem discharge
SW/GW is surface water and groundwater condition with a median natural flow or
minimum project flow controlling groundwater levels and surface water related
to precipitation events.
Appendix B contains an explanation of the derivation of the percent exceedance values
.....,
Table 14.Condition which provides successful palasage most frequently and
approximate percent of time that passage is successful during the
period 20 August -20 September at Slough 21.
Passage Natural Project 9,000 cfs Project 8,000 cfs
Reach Condo Occurrence Condo Occurrence Condo Occurrence
(%)(%)(%)
I GW 100 SW!GW 6 SW!GW 4
IlL SW/GW 10 0 0
IIR SW!GW 4 SW/GW 1 SW!GW 1
BW is backwater condition which neglects the effeC1:of local flow
BR is breaching condition which represents controlJLing discharge through the slough
GW is groundwater condition as it appears to fluctuate with mainstem discharge
SW/GW is surface water and groundwater condition wjlth a median natural flow or
minimum project flow controlling groundwater levels and surface water related
to precipitation events.
Appendix B contains an explanation of the derivation of the percent exceedance values
Table 15.Condition which provides successful passage most frequently and
approximate percent of time that passage is successful during the period
20 August -20 September at Side Channel 21.
Passage Natural Project '9,000 cfs Project 8,000 cfs
Reach Condo Occurrence Condo Occurrence Condo Occurrence
(%)(%)(%)
I GW 100 SW/GW 28 SW/GW 24
II GW 100 SW/GW 28 SW/GW 24
III GW 100 SW/GW 31 SW/GW 26
IV GW 100 SW/GW 31 SW/GW 26
V BR 71 SW/GW 1 SW/GW 0•.5
~VI BR 71 SW/GW 0.5 '0
VII BR 71 SW/GW 0.5 a....
VIII BR 71 SW/GW 0.5 a
IX BR 71 SW/GW 0.5 a
i""'I
x GW 100 SW/GW 9 SW/GW 5
BW is backwater condition which neglects the effect:of local flow
BR is breaching condition which represents controlling discharge through the slough
GW is groundwater condition as it appears to flu~tuate with mainstem discharge
SW/GW is surface water and groundwater condition wi.th a median natural flow or
minimum project flow controlling groundwater levels and surface water related
to precipitation events.
Appendix B contains an explanation of the derivation of the percent exceedance values
I I
.-,
FIGURES
I
~
I J 1 1 ]1 ·~··--l ~....J
f j -1 i jj
I
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iCC:co
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SUSITNA RIVER A
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ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECTMEANMONTHLYDISCHARGESFORNATURAL»
P1 AND EVI CONDITIONS AND MINIMUM AND
MAXIMUM MEAN WEEKLY DISCHARGES FOR
EVI·FLOWS
FIGURE 1
\Noodward-~
Consultants "..
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-1 1 -1 1 I ,I 'I ')J i
SLOUGH
SLOUGH BERM AT LOWER
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MAINSTEM CHANNEL .....
SHORE ICE BUILDUP WITHOUT OVERTOPPING
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
FIGURE 2,
Woodward-Clyde
Consultants (I IXI£OOtz£~m(ID&~
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NOVEMBER DECEMBER JANUARY FEBRUARY MARCH APRIL
1871 1872
WEATHER PERIOD 1 NOV 71 -30 APR 72 (COLD WINTER)
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,1882 1883
WEATHER PERIOD 1 NOV 82 -30 APR 83 (AVERAGE WINTER)
LEGEND
-NATURAL FLOW AND WEATHER
._••WATANA 1888 FLOW AND NATURAL WEATHER
,REF:HARZA-EBASCO SUSITNA JOINT VENTURE.1884.INSTREAM A LAS KA POW ERA UTHO RITY
ICE SIMULATION STUDY.DRAFT REPORT PREPARED FOR ALASKA POWER
AUTHORITY FOR SUSITNA HYDROELECTRIC PROJECT.SEPTEMBER.SUSITNA HYDROELECTRIC PROJECT
PREDICTED WINTER MAINSTEM STAGES FOR NATURAL AND WoodwardoClyde
PROJECT FLOWS NEAR THE HEAD OF SLOUGH 8A Consultants ~.OO£OO~I::Im{IDCl~
IUIIY""JOINT YENYU''!
FIGURE 3
J !1 J J I 1
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/
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en .
~595..NOVEMBER DECEMBER JANUARY FEBRUARY MARCH APRIL
1871 1872
WEATHER PERIOD 1 NOV 71 -30 APR 72 (COLD WINTER)
620
6J5
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~605 "1&1 .---'-~-7 _......--_...-----~.~#-....._-_...,;--.--.--,------..-.._...;.....-.._.--~
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~1882 1883
WEATHER PERIOD 1 NOV 82 -30 APR 83 (AVERAGE WINTER)
LEGEND
-NATURAL FLOW AND WEATHER
.-••WATANA 1888 FLOW AND NATURAL WEATHER
REF::HARZA-EBASCO SUSITNA JOINT VENTURE.1884.INSTREAM ALA'SKA POWER AUTHORITYICESIMULATIONSTUDY.DRAFT REPORT PREPARED FOR ALASKA POWER
:AUTHORITY FOR aUSITNA HYDROELECTRIC PROJECT.SEPTEMBER.SUSITNA HYDROELECTRIC PROJECT
PREDICTED WINTER MAINSTEM STAGES FOR NATURALANC 'NoodwanI-CIyde OO£OO?Z£-~lID&~PROJECT FLOWS NEAR THE HEAD OF .SLOUGH 8
Consultants ".aUIITNA "'OINT YlNTU"l
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JANUARY I FEBRUARY I MARtJH
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!~_1'..I__~____u.!
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cd 64'_I
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LEGEND
-NATURAL FLOW AND WEATHER
••••WATANA 1'"FLOW AND NATURAL WEATHER
REF:HARZA-EIA8CO 8U81TNA JOINT VENTURE.1 ••4.INSTREAM
IC!SIMULATION STUDY.DRAFT REPORT PREPARED FOR ALASKA POWER
AUTHORITY FOR 8UIITNA HYDROELECTRIC PROJECT.SEPTEMBER.
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
PREDICTED WINTER MAINSTEM STAGES FOR NATURAL AND
PROJECT FLOW8 NEAR THE HEAD OF SLOUGH tA
FIGURE 5
\YoodwardoClyde
Consultants "
OO£f?J~~m~~
aUIITN4 JOINT YtNTu"r
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&&I 68
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1871 1872
WEATHER PERIOD 1 NOV 71 -30 APR 72 (COLD WINTER)
695
THRI SHOLD EL.V.
690
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(1$.7.~NOVEMBER DECEMBER JANUARY FEBRUARY MARCH APRIL
1882 1883
WEATHER PERIOD 1 NOV 82 -30 APR 83 (AVERAGE WINTER)
LEGEND
-NATURAL FLOW AND WEATHER
••••WATANA 1888 FLOW AND NATURAL WEATHER
REF:HARZA-EBASCO SUSITNA JOINT VENTURE.1884.INSTREAM ALASKA POWER AUTHORITYICESiMULATIONSTUDY.DRAFT REPORT PREPARED FOR ALASKA POWER
AUTHORITY FOR SU$ITNA HYDROELECTRIC PROJECT.SEPTEMBER.SUSITNA HYDROELECTRIC PROJECT
PREDICTED WINTER MAINSTEM STAGES FOR NATURAL AND Woodwaf'doClyde ~£(;J~-§~~PROJECT FLOWS NEAR.THE HEAD OF SLOUGH 11 .ConsuJtanb 'Q .IUI"H"JOIHT VEHlU".FIGURE 6
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~745 NOVEMBER DECEMBER JANUARY FEBRUARY MARCH APRIL
1871 1172
WEATHER PERIOD 1 NOV 71 -30 APR 72 (COLD WINTER)
765
760
f THRl8HOLD EL ~V.
755-'>."....,..--_....-_......--.....-.-_..~-'_._.-....IIIIl_-....~,...-...__#••__...--"--"'--"~-~~-"--'......-...-_.
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cd 745~NOVEMBER DECEMBER JANUARY FEBRUARY MARCH APRIL
I 1982 I 1883 I
WEATHER PERIOD 1 NOV 82 -30 APR 83 (AVERAGE WINTER)
LEGEND
-NATURAL FLOW AND WEATHER
••••WATANA 1888 FLOW AND NATURAL WEATHER
..,
REF:HARlA-EBASCO 8USITNA JOINT VENTURE.1884.INSTREAM j ALASKA POWER AUTHORITY'CE 81MULATION STUDY.DRAFT REPORT PREPARED FOR ALASKA POWER I
AUTHORITY FOR SUSITNA HYDROELECTRIC PROJECT.SEPTEMBER.SUSITNA HYDROELECTRIC PROJECT,
PREDICTED WINtER MAINSTEM STAGES FOR NATURAL AND Woodward-Clyde OO£OOtz£c.m~~PROJECT FLOWS NEAR THE HEAD OF SLOUGH 21 Consultants 41 IUIITNA oI0'NT V1NTU,.E
,'FIGURE 7,
Ie----ORIGINAL WIDTH -
...•LARGE COBBLE FILL
. .
.-r+--WING DEFLECTOR WALLS
STREA FLOW
T
PASSAGE
REACH
-
-
-
.....
WING DEFLECTOR
ALASKA POWER AUTHORITY
SUSITNi&.HYDROELECTRIC PROJECT
FIGURE 8
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"I ]1 1 !I .~J j 1 5 J 1 I ,]I J
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SIDE VIEW
POOL
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Q-
:a.FLOW
EXPOSED ROCKS
PLAN VIEW ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
TYPICAL PASSAGE REACH OF SLOUGH ALONG
MIDDLE SECTION OF THE SUSITNA RIVER FIGURE 9 .
WoodwatdoClyde
ConsuJtants Q IXJ£OO~ca~~®:OO
IUIITN4 JOINT VlNTU"(
1 1 ,1 1 i J I !I I I 1 1 1 1
HEIGHT OF MAXIMUM SLOUGH DISCHARGE
--ORIGINAL CHANNEL
I I·~7 ROCK GAB IONS
, , •EMBEDDED IN
CHANNEL BANKS
ROCK GABION CHANNEL
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
FIGURE 10
Woodward-Clyde
Consultants {I oo£oo~~rnfID&~
aUIITN4 JOIHT vtHTU"(
-
NOTCH TO PROVIDE EASE
"IN FISH PASSAGE
FLOW.--.-.-
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ANCHOR
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SZ
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~NATURAL DEPTH OF FLOW
-,.~TYPICAL SLOPE
POOL AND WEIR STRUCTURE CREATtoN OF POOI.S BETWEEN BARRIERS
ALASKA POWER AUTHORITY
SUSITN)~HYDROELECTRIC PROJECT
igBll:llil
GAB ION BARRIER
HIGHWA Y CURB BARRIER
POOL AND WEIR STRUCTURE
FIGURE 11
Woodward-Clyde
ConsuIt:!nts "
[XJ&OO~e=m(IDtt~
aUIITNA,.I01""T V[HTU~t
J I )))j 1 J I 1
MAINSTEtJf ELEVATION
AT 800 FT.
SATURATED WATER
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.......--.....
........
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CONCRETE TANK
2'x 4'JC 18'
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3'
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1 CFS 1'"--=----TO PR V•
2'
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
COLLECTOR TANK AT SLOUGH 9
FIGURE 12
Woodward-Clyde
Consultants "
(XJ£OO~-~(ID&~
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1 1 1 1 }1 1 )1 )1
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OUTLET STRUCTURE OF
COARSE GRAVELS AND
COBBLES1'DEPTH
SLOUGH 9
PASSAOE REACH LOCATIONS
c::J SILT I UNO
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THALWEG PROFILE OF SLOUGH 9 ALA'SKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
FIGURE 13
WoodwardoCfyde
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STREAM8ED STATION
THALWEG PROFILE OF SLOUGH 11
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FIGURE 14
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SLOUGH 21 COMPLEX
PASSAGE REACH LOCATIONS
r:=J IILI'......
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THAL WEG PROFILE OF SLOUGH 21
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FIGURE 15
Y/oodwatd.CJyde
Consultants {I oo£r?J~t:2mOO&~
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SUSITNA HYDROELECTRIC PROJECT
"tI,,,
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SUSITNA RIVER FISHERY MITIGATION INDUCED
UPWELLING USING TRIBUTARY WATER SUPPLY
FIGURE 18
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LEVEL
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NOTCH FOR ISH PASSAGE
FLOW
41 IMPERMEABLE SECTiON
WEIR TO INCREASE SPAWNING HABITAT
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SUSITNA HYDROELECTRIC PROJECT
FIGURE 17
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TIMBER POST WEIR
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FIGURE 18
CiJ&~~CI~[ID£~
IVIITN",JOI"T V[HTU'I(
1 -I I ..1 J 1 >J I J J J 1 J ·1 "
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ROCK .GABIONS
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1..,.8 REBAR ANCHOR TYP
--1---i---I--;--rl--t
L_L_L~L'_L_
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FIRM STRUCTURE EMBEDMENT
...
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FLOW
~
ROCK GABION SIZES:3'X "x l'
&a'X ,'x 2'
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SUSITNA HYDROELECTRIC PROJECT
ROCK GABION WEIR
rFCGURE 19
Woodward-Clyde
ConauJtants {I lXJ£[fJ~~rnlID&~
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-
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3'
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EXCAVATION TO EMBED
STRUCTURE IN CHANNEL
~~'----ORIGINAL
CHANNEL
CROSS-SECTION
ROCK WEIR
ALASKA POWER AUTHORITY
SUSITNt~HYDROELECTRIC PROJECT
-FIGURE 20
-
........._---~
PLAN VIEW
L=LENGTH OF BERM
-
I~
Y
D
-IMPERMEABLE CORE
OFlIGINAL BERM __J
CROSS-SECTIONAL VIEW
D=DEPTH OF EXCAVATION FOR IMPERMEABLE COI:tE
Y=INCREASED HEIGHT ABOVE ORIGINAL BERM
BERM DESIGN TO PREVENT OVERTC)PPING OF SLOUGHS
ALASKA POWER AUTHORITY
SUSITNA HYDROELECTRIC PROJECT
FIGURE 21
Woocfward.ctyde
Consultants ~C=8&~~~rn(ID&~:
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---,.'~--_._~-----------------------------------
APPENDIX A
....
APPENDIX A
Passage Reach Flow Evaluation
-
r
I,
.-
A previous analysis assessed the required local flow for successful
fish passage through the passage reaches of the sloughs along the
middle section of the Susitna River (ADF&G 1984c)•In order to
evaluate the available local flow in sloughs SA,9,9A,11 and 21 in
comparison to the required local flows,an analysis of the local flow
sources for each slough was conducted.A primary source of local flow
for most of these sloughs is groundwater related to the mainstem
discharge (APA 1984).
The relationships developed for slough local flow at the R&M gage site
within the slough versus mainstem discharge measured at Gold Creek are"
listed below (APA 1984)•
Slough Regression Equation r 2
r-SA S =-.629 +.000128G .632
9 S =1.97 +.000351G .805
11 S =1.52 +.000102G .765
21 S =7.55 +.00105G .542
S =Slough Discharge
G =Mainstem Discharge at Gold Creek
-
.-
These relationships were used to estimate the amounts of local flow at
the R&M gage site in a slough given a mainstem discharge.In order to
obtain the local flow at other points within the slough,the amounts
of upwelling throughout the slough were estimated in terms of percent
of the gage flow using aerial photogrclphs,observations by R&M
personnel (R&M Consultants,Inc.1982),and measured upwelling values
(APA 1984 and WCC 1984).The percentage values were applied to the
calculated flow at the gage resulting in ,estimates of local flow at
points corresponding to passage reaches in the slough.For slough 9A,
measured upwelling values were correlated with mainstem discharge to
yield local flow at the passage reaches.
-,~...uP--_.....-__we~_---...:...,,_
F""
I
-
A comparison between required local flow andl estimated available local
flow was made.Tables BI to B5 present the required passage reach
discharges ~nd the calculated available passage reach discharges.
Other potential contributions to the flow through the passage reaches
were then considered.An evaluation was cOlnducted of how much of the
time the local flow requirements could be satisfied by groundwater
flow alone.The required local flow was input to the relationship
between slough flow and mainstem discharge to obtain the required
mainstem dsicharge.The flow duration curve for the mainstem
discharge was used to evaluate the percent Clccurrence of these flows.
A combination of surface water and groundwater sources was analyzed on
the basis of the assumption that groundwater was at a level
corresponding to typical mainstem flows.For natural slough flows,
the mainstem discharge of 50 percent occurrence equalling 15,000 cfs
was chosen as the basis for groundwater flows.The flow duration
curve developed for the period 20 August to 20 September (ADF&G 1984c)
was used for the natural flows.Project flows were assumed constant
at 9,000 cfs and 8,000 cfs.The percent of time that tributary inflow
was sufficient to supplement groundwater w~tS based on an estimate of
the contributing basin area,an assumed runoff percentage of 40
percent,and precipitation duration curve~s for Talkeetna for the
period of 1972 to 1981 (Tables BI to B5).The percent occurrence of
successful passage for passage reaches a.ffected by backwater and
breaching was previously analyzed (ADF&G 1984c).
The final value selected for each passage reach was the largest
percent successful passage occurrence value of those calculated.
Tables B6-BII were used for the identification of the maximum percent
occurrence given each contributing flow"These tables identify
passage reaches impacted by a decrease in mninstem flow.Any additive
effects of accumulation of percent occurrences were assumed
negligible.
;
I
1 1 1 J ~l 1 -I 1 I 1
Table Bl.Required and available passage reach discharges and percent exceedance of passage for the period
20 August -20 September at Slough 8a '
Passage Req1d Required Basin Amount ,Exceedance Based
Reach Flow a Base GW Flow (cfs)Surface Water (cfs)area Prec.Neeeded (in.)on Total Dai1X ppt
(PR),(cfs)Natll 9,000 '8,000 Nat '1 9.000 8,000 (mil e l )Nat'1 9,000 8.000 Nat 11 9.000 8.000
,
2 1.3 0.5 0.4 0.7 1.5 1.6 1.36 .01 .03 .03 32 25 24
II (4)1.3 0.5 0.4 2.7 3.5 3.6 1.36 .05 .06 .06 19 16 15
III 4 1.3 0.5 0.4 2.7 3.5 3.6 1.36 .05 .06 .06 19 16 15
IV (5)0.8 0.3 0.2 4.2 4.7 4.8 1.09 .09 .1 .1 9 7 7
V 5 0.7 0.3 0.2 4.3 4.7 4.8 1.09 .09 •1 •1 9 7 7
VI (4)0.6 0.2 0.2 3.4 3.8 3.8 .96 .08 .09 .09 12 9 9
VII (4)0.5 0.2 0.1 3.5 3.8 3.9 .96 .08 .09 .09 11 9 9
VIII 4 0.3 0.1 0.1 3.7 3.9 3.9 .55 .16 .17 .17 4 3 3
IX 4 0.2 0.1 0.1 3.8 3.9 3.9 0 b b b 0 0 0
a Numbers in parenthesis assume that required flow at upstream PR is sufficient for passage at downstream PRo
b Not possible;basin area is insufficient to provide surface runoff
I I 1 .1 I -1 1 )I ])J I J 1
~
Table B2.Required and available passage reach discharges and percent exceedance of passage for the period
20 August ~20 September at Slough 9
Passage Req'd Requi red Basin Amount \Exceedance Based
Reach Flow a Base GW Flow (cfs Surface Water (cfs)Area Precip Needed (in.)on Total Daily ppt
(PR)(cfs)Nat'l .9.000 8,000 Nat'l 9,000 8,000 (mil e Z )Nat'l 9,000 8,000 Nat '1 9,000 8,000 ..
2 8.9 6.3 5.9 0 0 0 2.99 0 °0 100 100 100
II 1 8.4 6.0 5.6 0 0 0 1.73 0 0 0 100 100 100
III 6 7.2 5.1 4.8 0 .9 1.2 1.73 0 .01 .02 100 34 29
IV (6)6.8 4.8 4.6 °1.2 1.4 1.73 0 .02 .02 100 29 28
V (6)5.5 3.9 3.7 .5 2.1 2.3 0 b b b 0 0 °
a Numbers in parenthesis assume that required flow at downstream PR is sufficient for passage at upstream PR
b Not possible;basin area is insufficient to provide surface runoff.
I J 1 ---.]J --1 ··-1 1 1 ]I I I !)J ]
8
Table B3.Required and available passage reach discharges and percent exceedance of passage for the period of
20 August -20 September at Slough 9A.
Passage Req'd Requi red Basin Amount \Exceedance Based
Reach Flow a Base GW Flow (cfs)Surface Water (cfs)Area Precip Needed (in.)on Total Oailf ppt
(PR)(cfs)Nat'l 9,000 8,000 Nat'1 9.000 8,000 (mf.le 2 )Nat'l 9.000 8,000 Nat'l 9.000 8,000
4.4 3.1 2.98 0 0 0 2.27 0 0 0 100 100 100
II 3 4.3 3.0 2.5 0 0 .5 2.27 0 0 .005 100 100 41
III 3 4.1 7.8 2.0 0 .2 1.0 .35 0 0.01 .07 100 32 14
IV 1 3.8 2.5 1.9 0 0 0 .35 0 0 0 100 100 100
V (2)3.3 2.0 1.6 0 0 .4 .21 0 0 .04 100 100 20
VI (2)3.1 1.8 1.53 0 .2 .47 .17 0 .03 .06 100 24 14
VII (2)2.8 1.5 1.3 0 .5 .7 .13 0 .09 .13 100 10 7
VIII (2)2.7 1.4 1.2 0 .6 .8 .10 0 .14 .19 100 6 3
IX 2 2;5 1.3 1.13 0 .7 .87 .08 0 .20 .25 100 3 2
X 3 0 0 0 3 3 3 .02 b b b b b b
a Numbers in parenthesis assume that required flow at upstream PR is sufficient for passage at downstream PR
b Not possible;basin area is insufficient to provide surface runoff
:;!
1 1 1 1 1 1 ]I
Table B4.Required and available passage reach discharges and percent exceedance of passage for the period of
20 August -20 September at Slough 11..
Requ~red
Passage b aReachFlow%Exceedance Base GW Flow (cfs)Surface Water (cfs)
(PR)(cfs)Nat'l 9.000 8.000 Nat'l 9.000 8.000 Nat'l 9.000 8.000
I 4 70 0 32 4.5 3.5 3.3 0 .5 .7
II 4 43 0 13 3.9 3.0 2.9 •1 1.0 1.1
III 4 12 0 0 3.2 2.4 2.3 .8 1.6 1.7
IV 8 0 0 0 3.0 2.3 2.2 5.0 5.7 5.8
V 4 0 0 0 2.0 1.6 1.5 2.0 3.4 3.5
a Surface water is not available due to lack of contributing drainage basin
b Percent exceedance to provide required flows from groundwater supplies only
1 )I 1 i 1 1 1 1 )1 1 I J I 1
Table B5.Required and available passage reach discharges and percent exceedance of passage for the period of
20 August -20 September at Slough 21 Complex.
Passage Req'd Basin Amount ,Exceedance Based
Reach flowa Base GW flow (cfs)Surface Water (cfs)Area Precip Neeeded (in.)on Total Daily ppt
(PR)(cfs)Nat'l 9,000 8,000 Nat'l 9,000 8,000 (mile 2 )Nat'l 9,000 8,000 Nat'l 9,000 8,000
Slou~
5 10.0 2.3 1.1 0 2.7 4.9 .52 0 .12 .22 100 6 4
ilL 5 2.9 0.7 .3 2.1 4.3 4.7 0 b b b 0
0 0
IIR 5 3.2 0.7 .4 1.8 4.3 4.6 .26 .16 .39 .41 4
Side channel 21
(8)18.1 4.2 2.0 0 3.8 6.0 5.03 0 .02 .03 100 28 24
II 8 18.0 4.2 2.0 0 3.8 6.0 5.03 0 .02 .03 100 28 24
III (7)17.5 4.1 1.9 0 2.9 5.1 5.03 0 .01 .02 100 31 26
IV 7 17.5 4.1 1.9 0 2.9 5.1 5.03 0 .01 .02 100 31 26
V 18 17.4 4.0 1.9 .6 14.0 16.1 .52 .03 .63 .73 24 1 .5
VI (20)17.2 4.0 1.9 2.8 16.0 18.1 .52 .13 .72 .81 7 .5 0
VII (20)16.8 3.9 1.8 3.2 16.1 18.2 .52 .14 .73 .82 6 .5 0
VIII (20)16.5 3.8 1.8 3.5 16.2 18.2 .52 .16 .73 .82 4 5 0
IX 20 16.4 3.8 1.8 3.6 16.2 18.2 .52 .16 .73 .82 4 .5 0
X (5)12.5 2.9 1.4 0 2.1 3.6 .52 0 .09 .16 100 9 5
a Numbers in parenthesis assume that required flow at upstream PR is sufficient for passage at downstreamPRbNotpossible;basin area is insufficient to provide surface runoff
I I I j -J I J "1 -1 ]I
Table B6.Percent exceedance of successful passage due to breaching flows.backwater effects.groundwater and
surface water discharges for the period of 20 August to 20 September at Slough 8A.
BREACHING BACKWATER
Controlling Ground-Surface
Discharge %Successful %Water Water Total
PR Flow (cfs)Exceed Flow Exceed %Exceed %Exceed %Exceed
I Nat'l 27.000 7 <10.600 19 a 32 79
9.000 0 0 25 25
8.000 0 0 24 24
II Nat'l ,27.000 7 15.600 48 a 19 48
9.000 0 0 16 16
8.000 0 0 15 15
III Nat'l 27.000 7 b'a 19 19
9.000 0 16 16
8.000 0 15 15
IV Nat'l 33.000 2 b a 10 10
9.000 0 7 7
8.000 0 7 7
V Nat'l 33.000 2 b a 9 9
9.000 0 1 1
8.000 0 7 7
VI Nat'l 33.000 2 b a 12 12
9.000 0 9 9
8.000 0 9 9
VII Nat'l 33.000 2 b a 11 11
9.000 0 9 9
8.000 0 9 9
VIII Nat'l 33,000 2 b a 4 4
9.000 0 3 3
8.000 0 3 3
IX Nat'l 33,000 2 b a 0 2
9.000 0 0 0
8.000 0 0 0
ab Surface Water Needed to Supplement Groundwater
Breaching Occurs Prior to Backwater Effects
1 I I -I 1 1 }1 J !1 1
Table B7.Percent exceedance of successful passage due to breaching flows,backwater effects,groundwater and
surface water discharges for the period of 20 August -20 September at Slough 9.
BREACHING BACKWATER
Controlling Ground-Surface
Discharge %Successful %Water Water Totd
PR Flow (ds)Exceed Flow Exceed %Exceed %Exceed %Exceed
I Nat'l 19,000 29 <12,200 70 100 100
9,000 0 0 100 100
8,000·0 0 100 100
II Nat'l 19.000 29 b 100 100
9.000 0 100 100
8.000 0 100 100
III Nat'l 19,000 29 b 100 100
9.000 0 a 34 34
8,000 0 29 29
IV Nat'l 19,000 29 b 100 100
9,000 0 a 29 29
8,000 0 28 28
V Nat'l 19,000 29 b a c 29
9,000 0 0
8,000 0 0
a .
b Surface Water Needed to Supplement Groundwater
Breaching Occurs Prior to Backwater Effects
c Not Enough Drainage Area Exists to Provide Runoff
1 J 1 !I 1 I 1 i J I 1 J
Table B8.Percent exceedance of successful passage due to breaching flows,backwater effects,groundwater and
surface water discharges for the period 20 August -20 September at Slough 9.
BREACHING BACKWATER
Controlling Ground-Surface
Discharge %Successful %Water Water Tota!
PR Flow (cfs)Exceed Flow Exceed %Exceed %Exceed %Exceed
I Nat'l d d 100 100
9,000 100 100
8,000 100 100
II Nat'l d d 100 100
9,000 100 100
8,000 a 41 41
III Nat'!d d 100 100
9,000 a 32 32
8,000 14 14
IV Nat'!d d 100 100
9,000 100 100
8,000 100 100
V Nat'!d d 100 100
9,000 100 100
8,000 a 20 20
VI Nat'!d d 100 100
9,000 a 24 24
8,000 14 14
VII Nat'l d d 100 100
9,000 a 10 10
8,000 7 7
VIII Nat'!d d 100 100
9,000 a 6 6
8,000 3 3
Table B8 (Continued)
BACKWATER
j
1 1
PR
IX
X
1 I
Flow
Nat'l
9.000
8.000
Nat'l
9.000
8.000
BREACHING
Controlling
Discharge
(cfs)
d
d
1
%
Exceed
J 1
Successful
Flow
d
d
%
Exceed
-}1
Ground-
Water
%Exceed
100
a
100
a
i 1
Surface
Water
%Exceed
3
2
c
1
Total
%Exceed
100
3
2
100
o
o
J
ab Surface Water Needed to Supplement Groundwater
Breaching Occurs Prior to Backwater EffectscdNotEnoughDrainageAreaExiststoProvideRunoff
No Data Available
1 J J })j CJ I
Table B9.Percent exceedance of successful passage due to breaching flows,backwater effects,groundwater and
surface water discharges for the period of 20 August -20 September at Slough 11.
BREACHING BACKWATER
Controlling Ground-Surface
Discharge %Successful %Water Water Total
PR Flow (ds)Exceed Flow Exceed %Exceed %Exceed %Exceed
I Nat'l 42.000 1 16,200 44 70 e 70
9,000 0 0 0 0
8.000 0 0 0 0
II Nat'l 42.000 1 33,200 2 43 e 43
9,000 0 0 0 0
8,000 0 0 0 0
III Nat'l 42,000 1 39.600 .1 12 e 12
9,000 0 0 0 0
8,000 0 0 0 0
IV Nat'l 42,000 1 b 0 e 1
9,000 0 0 0
8,000 0 0 0
V Nat'l 42,000 1 b 0 e 1
9,000 0 0 0
8,000 0 0 0
b Breaching Occurs Prior to Backwater EffectseNoSurfaceWaterAvailable
I 1 I I I -,I )
1
I
1 -1 1 !-i 1
Table BI0.Percent exceedance of successful passage due to breaching flows,backwater effects,groundwater and
surface water discharges for the period of 20 August -20 September at Slough 21
BREACHING BACKWATER
Controlling Ground-Surface
Discharge %Successful %Water Water Total
PR Flow (ds)Exceed Flow Exceed %Exceed %Exceed %Exceed
I Nat'l 25,000 10 b 100 100
9,000 0 a 6 6
8,000 0 4 4
IlL Nat'l 25,000 10 b a c 10
9,000 0 0
8,000 0 0
IlR Nat'l d d a 4 4
9.000 1 1
8,000 1 1
:Surface Water Needed to Supplement Groundwater
Breaching Occurs Prior to Backwater EffectscdNotEnoughDrainageAreaExiststoProvideRunoff
No Data Available
J 1 1 1 )f -)l 1 I I 1 1 1 1 1
Table B11.Percent exceedance of successful passage due to breaching flows,backwater effects,groundwater and
surface water discharges for the period of 20 August -20 September at Side Channel 21
BREACHING BACKWATER
Controlling Ground-Surface
Discharge %Successful %Water Water Total
PR Flow (cfs)Exceed Flow Exceed %Exceed %Exceed %Exceed
I Nat'l 12,000 71 12,000 71 100 100
9,000 0 0 a 28 28
8,000 0 0 24 24
II Nat'l 12,000 71 b 100 100
9,000 0 a 28 28
8,000 0 24 24
III Nat'l 12,000 71 b 100 100
9,000 0 a 31 31
8,000 0 26 26
IV Nat'l 12,000 71 b 100 100
9,000 0 a 31 31
8,000 0 26 26
V Nat'l 12,000 71 b ,a 24 71
9,000 0 1 1
8,000 0 0.5 0.5
VI Nat'l 12,000 71 b a 7 71
9,000 0 0.5 0.5
8,000 0 0 0
VII Nat'l 12,000 71 b a 6 71
9,000 0.5 0.5
8,000 0 0
VIII Nat'l 12,000 71 b a 6 71
9,000 0 0.5 0.5
8,000 0 0 0
-iii
I J 1 J 1 )J 1 I 1 1
Table Bll (Continued)
Successful
FlowPR
IX
x
Flow
Nat'l
9,000
8,000
Nat'l
9,000
8,000
BREACHING
Controlling
Discharge
(cfs)
12,000
24,000
%
Exceed
71
o
o
12
o
o
b
b
BACKWATER
%
Exceed
Ground-
Water
%Exceed
a
100
a
Surface
Water Total
%Exceed %Exceed
4 71
0.5 0.5
0 0
100
9 9
5 5
:Surface Water Needed to Supplement Groundwater
Breaching Occurs Prior to Backwater Effects
APPENDIX B
.-
....
-
APPENDIX B
Detailed Mitigation Costs
Chapter 3 outlines mitigation proposals for several sloughs and a side
channel.This appendix presents the costs for the various mitigation
measures presented.
Costs for these proposals are preliminary an.d are based mostly on past
experience in different proj ects.A major IcOSt,and one difficult to
evaluate consists of mobilizing equipment,materials and men to the
sites.These costs are based on using the Alaska Railroad to
transport much of the equipment and materials.Details regarding
loading and unloading and delays with thla railroad have not been
evaluated completely.
Side Channel 21 and Slough 21 do not have access to the railroad or
other land transportation during the COI1lstruction season.Three
alternatives exist to mobilize equipment to this site.
1)Helicopter:Advantages in timing,
Disadvantages are very high cost
equipment size.
speed and scheduling.
and severe limit"of
....
--
2)
3)
Barge:Advantages in lower costs t some ability to schedule
and operate efficiently.Disadvantage of shallow draft in
river,equipment size may be limited.
Mobilizing during winter:AdvcLntage of getting large
equipment and supplies into work site by transport over
river ice.Disadvantages are posed by long lead time to
mobilize materials,tying up equipment for one year before
demobilization could be completed.
Costs in this section for Slough and Side Channel 21 are based on the
assumption that river conditions are such that barges may be operated
to the site.
.....,
Slough SA
~2 Upwelling Systems
Labor 70,000
Materials/Equipment 40,000
Cross Pipes 20,000
Piping,Intakes 60,000
Gravel Processing 160,000
Mobilization/Demobilization 25,000
Engineering/Management 40,000
Total $415,000
1 Slough Mouth Excavation
Labor 6,000
Equipment 8,000
Mobilization/Demobilization 7,000
Engineering/Management 5,000
Total $26,000
1 Wing Deflector
Labor 5,000
Equipment/Materials 9,000
Mobilization/Demobilization 5,000
Engineering/Management 5,000
Total $24,000
Excavation of 7 Passage Reaches-Labor 2,000
Equipment/Materials 4,000
Mobilization/Demobilization 2,000
Engineering/Management 3,000
Total $11,000
Buildup of 2 Slough Berms
Labor 120,000
Equipment 40,000
Mobilization/Demobilization 2,000
Engineering/Management 3,000
Total $295,000
TOTAL COSTS OF MITIGATION MEASURES FOR SLOUGH 8A $771,000
.....
-
-
-
Slough 9
1 Upwelling System
Labor
Materials/Equipment
Cross Pipes
Piping Intakes
Gravel Processing
Mobilization/Demobilization
Engineering/Management
Total
1 Water Supply System
Labor
Materials/Equipment
Piping
Mobilization/Demobilization
Engineering/Management
Total
1 Buildup of Slough Berm
Labor
Equipment
Mobilization/Demobilization
Gravel and Core Processing
Engineering/Management
Total
20 Log Barriers
Labor
Materials/Equipment
Mobilization/Demobilization
Engineering/Management
Total
Excavation of 1 Passage Reach
Labor
Materials/Equipment
Mobilization/Demobilization
Engineering/Management
Total
35,000
20,000
10,000
30,000
80,000
15,000
20,000
$210,000
50,000
25,000
18,000
12,000
15,000
$120,000
60,000
20,000
10,000
40,000
20,000
$150,000
20,000
2,000
2,000
6,000
$30,000
J,OOO
1,000
2,000
1,000
$5,000
-
TOTAL COSTS OF MITIGATION MEASURES FOR SLOUGH 9 $515,000
.....
Slough 9A
....
1 BUildup of Slough Berm
Labor
Equipment
Mobilization/Demobilization
Gravel and Core Processing
Engineering/Management
Total
Excavation of Entire Slough
Labor
Equipment/Materials
Mobilization/Demobilization
Gravel Processing
Engineering/Management
Total
60,000
20,000
10.000
40,000
20.000
6,000
7,000
5,000
5,000
3,000
$150,000
$26.000
TOTAL COSTS OF MITIGATION MEASURES FOR SLOUGH 9A $176,000
____1II!~;pI...__......•.~."""'-_
I""'"
Slough 11
~
Flow Diversion From Tributary (Gold Creek)
Labor 120,000
Equipment/Materials 50,000
Pipe 90,000
Gravel Processing 20,000
Mobilization/Demobilization 35,000
Engineering/Management 65,000
Total $380,000
2 Weirs..-Labor 18,000
Equipment/Materials 28,000
MObilization/Demobilization 8,000
Engineering/Management 7,000
Total $61,000
Bank Stabilization 1000 ft
Labor 8,000
Materials/Equipment 7,000
Mobilization/Demobilization 5,000
Engineering/Management 5,000
Total $25.000
Slough Excavation-Labor 6,000
Equipment/Materials 7,000
Mobilization/Demobilization 5,000
Gravel Processing 5,000
Engineering/Management 3,000
Total $26.000
15 Log Barriers
Labor 15,000
Materials/Equipment 2,000
Mobilization/Demobilization 2,000
Engineering/Management 5,000
Total $24,000-
TOTAL COSTS OF MITIGATION FOR SLOUGH 11 $·516,000
Side Channel 21
Excavation of Channel
Labor
Equipment/Materials
Mobilization/Demobilization
Gravel Processing
Engineering/Management
Total
7 Wing Deflectors Bank Stabilization
Labor
Materials/Equipment
Mobilization/Demobilization
Oversize Material Removal
Engineering/Management
Total
8,000
9,000
11 ,000
8,000
9,000
70,000
65,000
20,000
35,000
50,000
$45,000
$240,000
TOTAL COSTS OF MITIGATION MEASURES FOR SIDE CHANNEL 21 $285,000
....
Slough 21
Excavation of Slough
Labor
Equipment/Materials
Mobilization/Demobilization
Oversize Substrate Removal
Engineering/Management
Total
2 Rock Gabions
Labor
Equipment/Materials
Mobilization/Demobilization
Engineering/Management
Total
Water Supply System
Labor
Materials/Equipment
Piping
Mobilization/Demobilization
Engineering/Management
Total
5,000
6,000
5,000
10,000
8,000
$34,000
25,000
12,000
8,000
9,000
$54,000
55.000
30,000
9,000
20.000
20.000
$134,000
TOTAL COSTS OF MITIGATION MEASURES FOR SLOUGH 21 $222.000
..-Curry Slough Development
Propagation System
Labor
Equipment/Materials
Pipe
Gravel Processing
Mobilization/Demobilization
Engineering/Management
Total
Curry Station Development
Propagation System
Labor
Equipment Materials
Gravel Processing
MobilizationDemobilization
Engineering/Management
Total
135,000
80,000
100,000
30,000
35,000
70,000
15,000
35,000
8,000
10,000
13,000
$450,000
$81,000