HomeMy WebLinkAboutSUS508IN STREAM FLOW RELATIONSHIPS REPORT
TECHNICAL REPORT NO. 2
PHYSICAL PROCESSES
MAY 1985
R&M CONSULTANTS, INC.
ENGINEERS D.Ql..QGISTS PL,.ANNEA8 8UR\I.YQR.
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ALASKA POWER AUTHORITY
~·
SUSITNA HYDROELECTRIC PROJECT
Federal Energy Regulatory Commission
Project Number 7114
I NSTREAM FLOW RELATIONSHIPS REPORT
TECHNICAL REPORT NO. 2
PHYSICAL PROCESSES
MAY 1985
DRAFT REPORT
Prepared By:
R&M CONSULANTS, INC.
WOODWARD-CLYDE CONSULTANTS, INC.
and
HARZA-EBASCO SUSITNA JOINT VENTURE
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Section/Title
List of Tables
List of Figures
Acknowledgments
Preface
1. INTRODUCTION
1.1 Purpose
1.2 Organization
TABLE OF CONTENTS
1.3 Impacts at Other Projects
1 . 4 Data Sources
2. RESERVOIR SEDIMENTATION
Page
ii
v
ix
X
1-1
1-3
1-3
1-7
2.1 Factors Affecting Reservior Sedimentation
2. 2 Reservoir Sedimentation
2-1
2-4
3.
4.
5.
6.
CHANNEL STABILITY
3. 1 Introduction
3.2 Factors Affecting Channel Stability
3.3 General Analytical Approach
3.4 Analysis of Natural Conditions
3.5 With-Project Conditions
SLOUGH HYDROLOGY
4.1 Introduction
4.2 Factors Affecting Upwelling
4.3 Local Surface Runoff
4.4 Field Studies
4. 5 With-Project Changes
SUMMARY
REFERENCES
3-1
3-3
3-6
3-10
3-11
4-1
4-1
4-5
4-5
4-1 0.
5-l
6-1
ARLIS
Alaska Resources
Library & Information Servtces
Anchorage. Alaska
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LIST OF TABLES
Number/Title
1.1
1. 2
1.3
2.1
2.2
2.3
2.4
3. 1
3.2
3.3
3.4
3.5
3.6
Streamflow and sediment data, Susitna River basin.
Mean flows and floods, Susitna River basin.
Size distribution of bedload and bed material,
1982 data.
Comparison of trap efficiencies estimated by Brune's
curves, Churchill's curve, and sedimentation model.
Reservoir trap efficiency by Brune's curves.
Reservoir trap efficiency by Churchill's curves.
Particle size distribution of suspended sediment.
Characteristics of study sites on Middle Susitna
River.
Hydraulic parameters for main stem sites.
Hydraulic parameters for side channels and sloughs.
Representative bed material size distribution for
selected sloughs, side channel and mainstem sites.
Transportable bed material sizes in selected sloughs,
side channels and main stem sites.
Potential degradation at selected sloughs, side
channels and main stem sites.
ii
Page
1-9
1-10
1-11
2-9
2-10
2-11
2-12
3-16
3-17
3-18
3-20
3-21
3-22
-
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LIST OF TABLES (Continued)
Number/Title
3. 7 Natural and with project average weekly flows of
Susitna River at Gold Creek (1950-1983).
3.8 Maximum natural and with-project weekly flows of
Susitna River at Gold Creek.
3. 9 Susitna tributary stability analysis, summary of
semi-quantitative assessment.
Page
3-23
3-24
3-25
4.1 Linear regresssion equations for slough discharge 4-19
vs. main stem discharge ( 1982-83).
4. 2 Regression equations for slough discharge vs. main stem 4-20
discharge (1984).
4.3 Linear regression equations for slough discharge vs. 4-21
mainstem stage (1982-83).
4. 4 Linear regression equations for the main stem component 4-22
of groundwater upwelling to sloughs as a function
of mainstem stage (1984).
4.5 Storm runoff analyses, Slough 9 tributary. 4-23
4.6 1984 monthly water balances, Sloughs 8A and 11. 4-24
4. 7 1984 monthly water balance, Slough 9, Tributary 9B. 4-25
4. 8 Precipitation coefficients for transfer of recorded 4-26
data.
iii
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LIST OF TABLES (Continued)
Number /Title
4.9 Falling head test results, Slough 9 -boreholes.
4.10 Estimated daily runoff, Slough 8A, high rainfall
pattern.
Page
4-27
4-28
4.11 Estimated daily runoff, Slough 8A, moderate rainfall 4-29
pattern.
4. '12 Estimated daily runoff, Slough 8A, low rainfall
pattern.
4.13 Estimated daily runoff, Slough 9, moderate
rainfall pattern.
4. '14 Estimated daily runoff, Slough 9, low rainfall
pattern.
iv
-----------·--···
4-30
4-31
4-32
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LIST OF FIGURES
Number/Title
1.1 Susitna River Streamgage Locations.
1. 2 Typical River Bed Material.
2.1 !so-turbidity vs. time, Eklutna Lake at Station 9,
1984.
2.2 Suspended sediment rating curve, Susitna River
near Cantwell (Vee Canyon).
2.3 Annual flow duration curves, Susitna River near
Cantwell (Vee Canyon).
2.4 Suspended sediment rating curve, Susitna River
at Gold Creek.
2.5 Seasonal flow duration curves, Susitna River
at Gold Creek.
4.1 Approximate locations of slough study sites and
data collection points -stage recorders and
seepage meters.
4.2 Slough 8A upwelling/seepage, 1982.
4.3 Slough 8A ice-free areas, winter 1982-83.
4.4 Slough 9 upwelling/seepage, 1982.
4.5 Slough 9 ice-free areas, winter 1982-83.
4.6 Slough 11 upwelling/seepage, 1982.
4. 7 Slough 11 ice-free areas, winfer 1982-83.
v
-----------------
Page
1-12
1-13
2-13
2-14
2-15
2-16
2-17
4-33
4-34
4-35
4-36
4-37
4-38
4-39
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LIST OF FIGURES (Continued)
Number/Title
4.S Slough 21 upwelling/seepage, 19S2.
4.9 Slough 21 ice-free areas, winter 19S2-S3.
4.10 Groundwater contours, Susitna River at Slough SA
(QGC = 24,000 cfs). _
4.11 Groundwater contours, Susitna River at Slough SA
(QGC = S,300 cfs).
4.12 Groundwater contours, Susitna River at Slough SA
(ice-covered main stem).
4.13 Groundwater contours, Susitna River at Slough 9
(QGC = 25,000 cfs).
4.14 Groundwater contours, Susitna River at Slough 9
(QGC = S,4SO cfs).
4.15 Groundwater contours, Susitna River at Slough 9
(ice-covered mainstem).
Page
4-40
4-41
4-42
4-43
4-44
4-45
4-46
4-47
4.16 Slough SA water temperatures, 19S2. 4-4S
4.17 Slough SA water temperatures, 19S3. 4-49
4.1S Mean daily surface and intragravel water temperatures 4-50
recorded at Lower Slough SA -Site 3 (RM 125.6) and
Upper Slough SA -Site 3 (RM 126.6) during 1983-S4
winter season.
vi
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LIST OF FIGURES (Continued)
Number/Title Page
~
4.19 Slough 9 water temperatures, 19~. 4-51
4.20 Mean daily surface and intragravel water temperatures 4-52
recorded at Slough 9-Site 3 (RM 128.6) during
the 1983-84 winter season.
4.21 Slough 9 water temperatures, 1983.
4.22 Slough 11 water temperatures, 1983.
2
4.23 Upper Slough /1 water temperatures, 1983.
4.24 Lower Slough 21 water temperatures, 1983.
4.25 Seepage rate vs. mainstem discharge, seepage
meter 8-1.
4.26 Seepage rate vs. mainstem discharge, seepage
meter 8-2.
4.27 Seepage rate vs. mainstem discharge, seepage
meter 9-1.
4.28 Seepage rate vs. mainstem discharge, seepage
meter 9-2.
4. 29 Seepage rate vs. mai nstem discharge, seepage
meter 9-3.
4.30 Seepage rate vs. msinstem discharge, seepage
meter 11-1.
vii
-----------------· ..
4-53
4-54
4-55
4-56
4-57
4-58
4-59
4-60
4-61
4-62
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LIST OF FIGURES (Continued)
Number/Title
4.31 Seepage rate vs. mainstem discharge, seepage
meter 11-2.
4.32 Seepage rate vs. mainstem discharge, seepage
meter 21-1.
4.33 Seepage rate vs. mainstem discharge, seepage
meter 21-2.
4.34 Response of mainstem and Slough 8A discharges
to September 1983 storm.
4.35 Response of mainstem and Slough 9 discharges to
September 1983 storm.
4.36 Response of mainstem and Slough 11 discharges to
September 1983 storm.
viii
Page
4-63
4-64
4-65
4-66
4-67
4-68
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ACKNOWLEDGMENTS
This report was prepared by Jeff Coffin and Stephen Bredthauer of R&M
Consultants and Howard Teas of Woodward-Clyde Consultants, under the
direction of Wayne Dyok of Harza Ebasco Susitna Joint Venture. Guidance
and review were also provided by Woody Trihey of E. Woody Trihey and
Associates.
ix
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PREFACE
This report represents a volume of the lnstream Flow Relationships Study
technical report series prepared for the Susitna Hydroelectric Project.
The primary purpose of the I nstream Flow Relationships Report and its
associated technical report series is to present technical information and
data to facilitate the settlement process. These reports are specifically
intended to identify the relative importance of interactions among the
primary physical and biological components of aquatic habitat. The
presentation is primarily limited to the Middle Susitna River, the reach
from the mouth of Devil Canyon downstream to the confluence with the
Chulitna River. This section of the river is also referred to herein as
"the middle reach". It encompasses river miles (RM) 151 to 99, the
downstream section of river in which the aquatic habitat will be most
affected by construction and operation of the Susitna Hydroelectric Proj
ect. Discussion is also presented for sedimentation that would occur in
the Watana and Devil Canyon Reservoirs. The two reservoirs constitute
the impoundment zone and extend from RM 151 to RM 230.
The I nstream Flow Relationships Report and its associated technical report
series are not intended to be an impact assessment. However, these
reports present a variety of natural and with-project relationships that
provide a quantitative basis to compare alternative streamflow regimes,
conduct impact analyses, and prepare mitigation plans.
The technical report series is based on the data and findings presented in
a variety of baseline data reports. The I nstream Flow Relationships Re-
port and its associated technical report series provide the methodology and
appropriate technical information for use by those deciding how best to
operate the proposed Susitna Hydroelectric Project for the benefit of both
power production and downstream fish resources. The technical report
series is described below.
X
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Technical Report No 1. Fish Resources and Habitats in the Middle
Susitna River. This report consolidates information on the fish resources
and habitats in the Talkeetna-to-Devil Canyon reach of the Susitna basin
available through June 1984 that is currently dispersed throughout
numerous reports.
Technical Report No 2. Physical Processes Report. This report describes
naturally occurring physical processes within the Talkeetna-to-Devil Can
yon river reach pertinent to evaluating project effects on riverine fish
habitat.
Technical Report No 3. Water Quality/Limnology Report. This report
consolidates existing information on water quality in the Susitna basin and
provides technical discussions of the potential for with-project
bioaccumulation of mercury, influences on nitrogen gas supersaturation,
changes in downstream nutrients and changes in turbidity and suspended
sediments. This report is based principally on data and information that
are available through June 1984.
Technical Report No 4. I nstream Temperature Report. This report
consists of three principal components: (1) reservoir and in stream tem-
perature modelling; (2) selection of temperature criteria for Susitna River
fish stocks by species and life stage; and (3) evaluation of the influences
of with-project stream temperatures on existing fish habitats and natural
ice processes.
Technical Report No 5. Aquatic Habitat Report. This report describes the
availability of various types of aquatic habitat in the Talkeetna-to-Devil
Canyon river reach as a function of mainstem discharge.
Technical Report No. 6, Ice Processes Report. This report describes the
naturally-occurring ice processes in the middle river, anticipated changes
in those processes due to project construction and operation, and
xi
R24/3 13
discusses effects of naturally occurring and with-project ice conditions on
fish habitat.
xii
R24/3 14
1.0 INTRODUCTION
1.1 Purpose
This report was designed to bring together the available information on
sedimentation, stream channel stability and slough hydrology that has been
collected in the Middle Reach of the Susitna River. The Middle Reach
encompasses the river from Talkeetna, at river mile (RM) 99, to the outlet
of Devil Canyon at RM 151. This is the section of the river that will be
most affected by the construction and operation of the Susitna Hyd roelec-
tric Project. Also included in this report is discussion of reservoir
sedimentation within Watana and Devil Canyon Reservoirs, which extend
from RM 230 to RM 151.
The river downstream of the damsites is of particular concern, and will be
dealt with in the greatest detail. There is concern that detrimental effects
on fish resources in the Middle Reach may be caused by the changes in
mainstem flow that will occur with the project. With project flows will be
much more stable than at present. With-project summer flows will be lower
than under natural conditions, while with-project winter flows will be
higher. The regulated flows will also have a lower mean annual flood than
under natural conditions.
The suspended sediment regime will be altered by construction of the
project due to trapping of all bedload and most suspended sediment load in
the reservoirs. This reduction in sediment load may alter the physical
features of the river. However, reduced summer flows will limit the size
and volume of streambed materials that can be moved by the river. The
reduced level of the mean annual flood in the main stem will cause some
downstream tributaries to degrade their bed levels, while others will
remain perched above the mainstem.
The alteration of river flow 1s likely to affect groundwater upwelling.
Lower summer flows will tend to reduce the upwelling component from the
1-1
-
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mainstem. Winter flows will be greater than under natural conditions, but
changes in the ice regime will also alter the mainstem stages, altering the
winter groundwater upwelling.
Five species of Pacific salmon use the middle river for reproduction and
rearing of young. All five species use the Middle Reach for access to
spawning areas. Coho and pink salmon generally use clear water tributary
streams for spawning. The primary project impact on these species would
be from effects on access into the spawning streams. Changes in or at
tributary mouths and reduced water surface levels are discussed in this
context.
The fish resource of greatest concern in the Middle Reach are chinook and
chum salmon (APA 1984a). Chinook salmon spawn in clear water
tributaries. However, main stem side channel, and slough habitats, along
with the tributaries themselves, are required year-round for juvenile
rearing. Chum salmon primarily use the tributaries for reproduction and
some rearing, but they also use the mainstem, side channel and side
slough habitats (ADF&G 1984a). Changes in flow, depth, substrate size
distribution and groundwater upwelling caused by project operation may
have a serious effect on these species. These effects could come from
changes to less acceptable substrate size for spawning or rearing, or to
decrease in groundwater upwelling, leading to problems with access to
spawning sites and egg dessication and freezing.
Sockeye salmon would likely be affected in a similar manner to chum. The
lower numbers of sockeye salmon and the similarity in spawning habitat
requirements allow concerns for chum salmon to cover this species as well.
Rearing of juveniles, especially of chinook, may also be affected.
Sufficient rearing habitat must be maintained. Changes in mainstem
morphology and upwelling in sloughs may affect the areas.
I
('
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1. 2 Organization
Following a brief review of environmental effects downstream of other large
hydropower projects in the Introduction, the next three sections of the
report each review pertinent Susitna Hydroelectric Project studies to date
on specific types of physical watershed processes. They discuss the
effects of those processes on the aquatic habitat in the Susitna River.
Section 2 addresses sedimentation processes in the reservoir, Section 3
deals with stability of channels in the Middle Reach downstream of the
project, and Section 4 discusses groundwater upwelling and local surface
runoff as related to aquatic habitat in sloughs downstream of the project.
Section 5 presents a summary of the three types of processes and ranks
them in importance as concerns in the Middle Susitna River. References
are listed in Section 6.
1 .3 Impacts at Other Projects
Construction of dams at Watana and Devil Canyon would affect the
terrestrial and aquatic habitat downstream of Devil Canyon, with possible
effects on fish, riparian vegetation, and wildlife. The effects on the
physical processes of sedimentation (reservoir and stream channel) and
groundwater upwellings are the focus of this report. The following
descriptions of environmental impacts downstream of similar projects
introduce the subject of downstream effects of dams on these processes.
Kellerhals and Gill (1973), Petts (1977), Taylor (1978) and Baxter and
Glaude (1980) have summarized channel response to flow regulation.
Operation of reservoirs significantly alters the flow regime. There is often
an increase in the diurnal variation of flow due to the variation in the
amount of water passing the turbines in order to follow the load demand.
Annual peak discharges are reduced not only due to storage, which allows
no overflow over the spillway, but also due to the surcharge storage
provided by the rise in water level above the spillway crest. Routing
through a reservoir with no available storage may reduce some flood peaks
1-3
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by over 50% (Moore, 1969), depending on the characteristics of the
spillway, reservoir, and flood hydrograph. The magnitude of the mean
annual flood of the Colorado River below Hoover Dam has been reduced by
60% (Dolan, Howard, and Gallenson, 1974). The total volume of flow may
be reduced due to the increase in time during which seepage and evapo-
ration losses may occur. Base flow tends to be increased due to seepage
and to minimum releases to the channel below the dam.
Reservoirs with a large storage capacity may trap and store over 95% of
the sediment load transported by the river (Leopold, Wolman, and Miller,
1964). Although reservoir shape, reservoir operation, and sediment
characteristics have some influence (Gottschalk, 1964), the actual
percentage depends primarily on the storage capacity-inflow ratio (Brune,
1953).
The effect of dams on the sediment load must be considered but in relation
to changes in river sediment transport capacity, flow regime, channel
morphometry, and tributary inflow. Tributaries which transport large
quantities of sediment into a regulated stream with reduced capacity to
flush away sediments may stimulate mainstem aggradation, an increase in
bed slope of the tributary, and trenching of the deposit to form a channel
that is in quasi-equilibrium with the flow regime (King, 1961; Kellerhals,
Church and Davies, 1977). A reduced water-surface elevation in the
mainstem also produces an increased hydraulic gradient at the tributary
mouth. The increased gradient results in increased velocities, bank
instability, possible major changes in the geomorphic character of the
tributary stream, and increased local scour (Simons and Senturk, 1976).
All of the bedload entering a reservoir is deposited in the reservoir. This
reduction in sediment supply is usually greater than the reduction in sedi-
ment-transport capacity. This deficit in sediment transport generally
results in erosion downstream of the dam, except where an armor layer or
an outcrop of bedrock occurs (Petts, 1977). Degradation will occur where
the regulated flow has sufficient tractive force to initiate sediment
1-4
R24/3 18
movement in the channel (Gottschalk, 1964). Once the channel bed has
been stabilized, either by~ armoring or by the exposure of bedrock, then
the banks, which usually consist of finer material than the bed, begin to
fail and the channel will widen. Where armoring or bedrock occur across
the width of the channel, a simple adjustment wi II occur where streamflow
is accommodated in the existing channel.
The sediment load plays an important role in the process of meander
migration across alluvial plains by forming point bars from bed load depo-
sition on the inside bank. These point bars are then aggraded to flood-
plain levels due to the deposition of suspended sediment in the emerging
vegetation during peak flows. The reduction in sediment load may disrupt
this process, with at least local ecological changes. Widening of channels
at meander bends and lateral instability may also be expected (Kellerhals
and G iII, 1973) .
Maximum degradation normally occurs in the tailwater of the dam, but may
extend downstream. Rates of degradation up to 15 em per year have been
observed both in the United States (Leopold, Wolman, and Miller, 1964)
and in Europe (Shulits, 1934), but in sand-bed rivers. Channel
adjustment to bed degradation and the associated reduction in slope was
observed for nearly 250 km below Elephant Butte Dam (Stabler, 1925), also
involving silt and sand size bed material. When an armored condition
occurs where the river is unable to recharge itself to capacity, the river
may pick up additional material downstream, as was observed on the
Colorado River below Hoover Dam (Stanley, 1951). The Susitna River,
however, is a gravel-bed river and more resistant to bed degradation.
The channel properties of gravel-bed rivers such as the mainstem of the
Peace River in Alberta appear to be controlled by floods with a recurrence
interval of 1.5 to 2 years (Bray, 1972). Regulation reduces these flows,
effectively reducing the size of the gravel-bed river without immediately
changing the channel, but certain channel properties will adjust to the
channel regime over a longer period of time. On the Peace River, the
1-5
R24/3 19
entrenched layer of the channel, the proximity of bedrock, and the resis-
tant bed material preclude significant changes in width and depth relation-
ships or in the slope (except near tributary junctions), but deep scour
holes at bends will fill to some degree, and gravel bars exposed above the
new high water mark will have emerging vegetation (Kellerhals and Gill,
1973).
Vegetation encroachment on the higher elevations of the gravel bars down-
stream of a dam can be expected due to the reduced summer streamflows
and the lower flood peaks, and in time could encroach on present high
water channels (Tutt, 1979; Kellerhals, Church and Davies, 1977). The
effect of the additional vegetation would be to increase the channel rough-
ness, thus decreasing the channel water conveyance. The channel size
and capacity could gradually decrease due to vegetation encroachment,
deposition of suspended load in the newly vegetated areas, accumulation of
material from the valley walls and deposition of sediment brought in by the
tributaries. During periods of high flow, higher river stages could be
expected.
The W.A.C. Bennett Dam on the Peace River had a dramatic unplanned
impact on the Peace-Athabasca Delta (Baxter and Glaude, 1980). The
delta is a series of marshes interspersed with lakes and ponds of various
sizes. Before the dam was built, the delta was maintained in this state
due to almost annual flooding, which prevented vegetation typical of drier
ground from being able to establish itself. The hydrological situation
itself was complex. The Peace River, passing to the north of the delta,
contributed little to the actual flooding, but its flood waters blocked the
exit of the Athabasca River, which entered from the south and caused the
actual flooding. After construction of Bennett Dam, the delta started
drying up, with dry-ground vegetation establishing itself. The effect of
the dam was initially obscured due to lower than normal precipitation for
some years previously, but it was eventually concluded that the dam was
at least a contributing factor, as flood levels on the Peace River were
1-6
R24/3 20
lowered, resulting 1n the Peace River no longer blocking the exit of the
Athabasca River.
1.4 Data Sources
1.4.1 Streamflow
Streamflow records are available from the U.S. Geological Survey
(U.S. G. S.) for various stations on the river and its tributaries. The
periods of available records are shown in Table 1 .1. The stream
gaging locations are shown in Figure 1. 1. The mean annual and
seasonal flows and floods of selected recurrence intervals are shown
in Table 1.2.
1.4.2 Suspended Sediment
Suspended sediment data are available from the USGS at ten sampling
stations and are also shown in Table 1.1.
The mean annual suspended loads are about 5, 710,000, 7,300,000 and
14,000,000 tons respectively for the Susitna River near Cantwell, at
Gold Creek and at Sunshine, 7,400,000 tons for the Chulitna River
near Talkeetna and 1,600,000 tons for the Talkeetna River near
Talkeetna.
The suspended sediment concentration for the Susitna River upstream
from the confluence with the Chulitna River ranges from essentially
zero milligram per liter (mg/1) in winter to nearly 1,000 mg/1 during
summer floods. The Chulitna River, with 27 percent of its basin
covered by glaciers, has recorded suspended concentrations up to
4,690 mg/1.
1-7
R24/3 21
1.4.3 Bedload and Bed Material
Limited bed load discharge data are available from the U.S. G. S. as
are also shown 1n Table 1. 1. Typical size distributions of the
bedload are shown in Table 1 .3.
A total of 48 bed material samples were collected from the mainstem
and side chan nels of the Susitna River between the mouth of Devil
Canyon (RM 150) and the confluence between the Susitna and
Chulitna Rivers (RM 98.6). These samples were used to determine
the size distributions by sieve analysis. Bed material size
distribution had also been estimated in an earlier study (R&M
Consultants, Inc. 1982b) by grid sampling techniques. Figures 1.2a
and 1.2b show some examples of typical bed material. Average size
distributions are shown in Table 1.3.
1.4.4 River Cross Sections
Cross sections of the Susitna River have been surveyed at 106
locations between RM 84.0 near Talkeetna and RM 150.2, about 1.3
miles upstream from the confluence with Portage Creek (R&M, 1981a;
1982c, 1984a) Cross sections at 23 locations also are available between
RM 162.1 at Devil Creek and RM 186.8 at Deadman Creek (R&M,
1981a), all 23 of which are in the impoundment zone.
1-8
Table 1.1 -Streanflow and Sediment Data,
Susitna River Basin
USGS
Gaging Station Gage No.
Susitna River
near Cantwell 152 91500
Drainage 2 Area,~mi
(km 2
4,140
(10,720)
Streamflow
Period of
Record
5/61-9/72
5/80-Pres.
at Gold Creek 15292000 6,160 8/49-Pres.
near Talkeetna 15292100
right channel
below Chulitna 15292439
R. near Talkeetna
left channel 15292440
below Chulitna R.
near Talkeetna
(15,950)
at Sunshine 15292780 11,100
(28,750)
5/81-Pres.
at Susitna 15294350 19,400 10/74-Pres.
(50,250)
Chulitna River 15292400
near Talkeetna
below canyon 15292410
near Talkeetna
Talkeetna River 15292700
near Talkeetna
2,570
(6,656)
2/58-9/72,
5 /80-Pres.
2,006 10/74-Pres.
(5,196)
Suspended Sediment
Number Period
of of
Samples
43
375
27
5
5
53
Record
62-72,82
49,51-58,62
67-68,74-83
6/82-10/83
5/83-10/83
5/83-10/83
71,7 7, Rl-~4
44 -75-83
53
13
133
58-59,67-72,
80-83
83
66:-83
Bedload
Number Period
of of
Samples Record
3 7/81-9/81
29 6/82-2/84
7 5/83-2/84
7 5/83-2/84
34 7/81-2/84
18 7/81-9/82
15 3/83-2/84
33 7/81-2/84
SOURCE: Table reproduced from Wang, Bredthauer, and Marchegiani (1985)
1-9
-------------------------------
Table 1.2 -Hean Flows and Floods
Susitna River Basin
Periods of
records used 3 Mean Ft~ws, cfs 2 ~m /sec) Max. Floods, cfs
Gaging Station in analysis Summer-Winter-Annual 2-year 10-year
Susitna River 1962-72 11 '900 1,000 6,400 32,000 54,000
near Cantwell 81-83 (337) (28) (181) (906) (1530)
at Gold Creek 1950-83 17,800 1,600 9, 720 48,000 73,700
(504) (4 5) (275) (1,360) (2, 090)
at Sunshine 1982-83 45,600 4,500 25,100 142,000 182,000
(1 ,290) (127) (710) (4,020) (5,150)
Chulitna River 1959-72 16,200 1,400 8,800 42,000 62,000
near Talkeetna 81-83 (459) (40) (249) ( 1 , 190) (1, 7 60)
Talkeetna River 1965-83 7,300 700 4,000 27,500 49,000
near Talkeetna (207) (20) (113) (780) (1390)
1/ Hay through October
2/ November through April
?OuRCE: Wang, Bredthauer, and Marchegiani (1985)
1-10
~
::; I ) m ,sec
SO-year
65,000
(1840)
97,700
(2 '770)
212,000
(6,000)
87,000
(2,460)
61,000
(1730)
Table 1.3 -Size Distribution of Bedload and
Bed Material, 1982 Data
Size Distribution of Particles %
Bedload Bed l-1aterial
Gage Sand Gravel Cobble Sand Gravel CobbJe
Susitna River near Talkeetna 78 16 6 0 30 70
Chulitna River near Talkeetna 41 58 1 26 64 10
Talkeetna River near Talkeetna 75 23 2 5 52 43
Susi tna River at Sunshine 56 42 2 5 66 29
Source: Knott and Lipscomb (1983)
Harza-Ebasco Susitna Joint Venture (1984)
(Table reproduced from: Wang, Bredthauer, and !'1archegiani (1985))
1-ll
-----------~------
,;.a ... '·-'
COOK INLET
17
C•~
SOURCE: Modified from
(EWT & A and WCC, 1985)
+Proposed Dams i te
D. Streamgage (a 11 USGS except
Watana, which is R & M)
t 10 R1v11rmile lncromenls
Scale , .. , 16milu
' LOCATION MAP FIG. 1.1 SUSITNA RIVER STREAMGAGE LOCATIONS
(a) On a gravel bar near the Confluence of
the Susitna and Chulitna Rivers
. --. -~-
(b) The Susitna River near Talkeetna River bed
under 1 ft. (0.3m) of water
Fig. 1.2 -Typical River Bed Material
SOURCE: wang, Bredthauer, and Marchegiani (1985)
1-13
R24/3 22
2.0 RESERVOIR SEDIMENTATION
2.1 Factors Affecting Reservoir Sedimentation
The effect of the project on sediment transport in the Susitna River is of
concern as it relates to aquatic habitat. This section briefly describes the
processes of reservoir sedimentation and details the factors which affect
trap efficiency. Trap efficiency is the percentage of incoming sediment
which is retained in the reservoir. Section 3 discusses downstream project
effects on channel stability, which are derived from changes to the flow
and sediment regimes of the river. Changes to the sediment regime resu It
from trapping all the bedload sediment and a large proportion of the
suspended sediment which enters the reservoir, thus substantially
reducing the sediment supply downstream. Sediment effects on water
quality are addressed in Report Number 3, the Water Quality/Limnology
Report.
Trap efficiency of a reservoir depends on fall velocity of the sediment
particles and on residence time of the sediment within the reservoir. Fall
velocity is determined by a number of factors, including particle size and
shape, particle density, sediment chemical composition, water temperature,
water viscosity and sediment concentration ( R&M 1982d; PN &D and
Hutchison 1982; Jokela, Bredthauer and Coffin 1983). The chemical
composition may cause electrochemical interactions which lead to particle
aggregation or dispersion. Small particles may aggregate into clusters
which have settling properties similar to larger particles and fall more
rapidly (R&M 1982d). A review of data from glacial lakes (R&M 1982d)
indicated that particle sizes of 2 microns (0.002 mm) and less would pass
through the reservoir.
Another report ( PN &D and Hutchison, 1982) concluded that particles
smaller than 3 to 4 microns would likely remain in suspension, and that
wind mixing would be significant in retaining particles of diameter
12-micron and less in suspension above the 50-foot depth. Strong
2-1
R24/3 23
windstorms would cause re-entrainment of sediment, resulting in short-term
increases in suspended sediment at the reservoir edges.
Data collected at Eklutna Lake (R&M 1982a, 1985b), approximately 100 miles
south of the Watana damsite, indicate that the mean particle s1ze of
sediment carried through the lake is 3 to 4 microns equivalent diameter,
with larger particles being deposited most rapidly and forming a delta.
Residence time of sediment within the reservoir is determined by the
capacity-inflow ratio, by the reservoir geometry (plan shape and depth),
and by size and location of reservoir outlets. Capacity-inflow ratio is the
major factor, but it may be modified by "short-circuiting" of sediment-
laden inflow to the outlet if little mixing occurs. Shallow, open lakes are
more conducive to formation of internal currents (due to winds) than are
deep, confined lakes. These internal currents slow down the settling
processes, especially for fine, slowly-falling particles. Deep reservoirs
with large surface areas are almost continuously subjected to mixing
processes generated by climatic influences (wind and surface energy
transfer) and by inflowing and outflowing currents. This mixing creates a
substantial amount of turbulence which tends to keep the fine sediments in
suspension (PN&D and Hutchison 1982). Location and size of reservoir
outlets also affects trap efficiency, with bottom outlets more effective in
removing the higher sediment concentrations near the bottom (R&M 1982d).
Short-circuiting of inflow may occur if hydraulic conditions in the reser-
voir are such that the inflow plume travels to the dam outlet and is dis-
charged with little interaction having taken place with the ambient water.
The plume may travel through the reservoir as overflow, underflow or
interflow, depending on whether it follows a top, bottom, or middle layer
in the reservoir depth. The flow depth is determined by the relative den-
sities of the stream water and the lake water, the equilibrium depth being
that where densities of the two are the same. Density is primarily a
function of temperature and suspended-sediment concentration and to some
extent of dissolved-solids concentration. Frequency, duration, and
2-2
R24/3 24
intensity of underflows and interflows have also been attributed to lake
bathymetry, especially near the stream mouth (R&M 1982d). Illustrations
of the variation of turbidity (and thus of suspended sediment
concentration) versus depth and time are shown for Eklutna Lake for 1984
in Figure 2.1.
Another process which can affect sediment levels in a reservoir is slope
failure and deposition from the surrounding banks. Soil stability is
reduced by the reservoir raising the ground water table, especially when
it also acts to thaw permafrost that had been binding the soil. The
primary types of slope failure and subsequent erosion that are expected in
the Watana Reservoir are shallow rotational slides and other shallow slides,
mainly skin and bimodal flows (Acres American 1982). Devil Canyon
Reservoir slopes are expected to be stable after impounding due to shallow
overburden materials and stable bedrock.
Rotational slides are landslides with well-defined, curved shear surfaces,
concave upward in cross-section. Skin flows are detachments of a thin
veneer of vegetation and mineral soil, with subsequent movement over a
planar, inclined surface. In the reservoir impoundment area, this usually
indicates thawing of fine-grained overburden over permafrost. Bimodal
flows along the reservoir shore are slides that consist of steep headwalls
containing ice or ice-rich sediment. The ice-rich sediment retreats
retrogressively through melting to form a debris flow which slides down
the face of the headwall to its base (Acres American 1982).
The Alaska Power Authority (1983) made quantitative estimates of the
increases in suspended sediments expected from skin slides, bimodal flows,
and shallow rotational slides in the two reservoirs, including where they
were likely to occur. A "worst case" scenario was assumed, in which
2x108 cubic meters of unconsolidated materials would slide into the
reservoirs. It was assumed that all particles less than or equal to 10
microns would become suspended in the water. This resulted in an
estimate of 35 percent (by dry weight) of the material being suspended.
2-3
-~-------~------------
R24/3 25
Seventy-five percent of this suspended material was assumed to be trapped
in the reservoir. This reduced to an estimated maximum yield of 33 million
metric tons of suspended particulates which could pass through the
reservoirs and on downstream. Most of this activity would probably occur
during the first five years of reservoir operation.
2. 2 Reservoir Sedimentation
2.2.1 General Approach
Suspended sediment loads at the Watana and Devil Canyon dam sites
were estimated by interpolating the loads at the Cantwell (Vee
Canyon) and Gold Creek gages on the Susitna River. Sediment trap
efficiencies of the reservoirs were estimated by the Brune and
Churchill curves (Harza Ebasco, 1984c). Sediment deposits in Devil
Canyon Reservoir were estimated for with and without-Watana
Reservoir conditions.
Bedloads were estimated as percentages of suspended sediment loads
using available data at the Gold Creek, Talkeetna, and Sunshine
gages on the Susitna River. All bedloads were assumed to be
trapped by the reservoirs. Bedloads at Devil Canyon Reservoir were
computed for with-and without-Watana Reservoir conditions.
2.2.2 Sediment Load
Sediment discharges at the Cantwell (Vee Canyon) and Gold Creek
gages were computed by the sediment rating flow duration curves
method. Suspended sediment discharges and the corresponding water
discharges for the Cantwell (Vee Canyon) gage are shown in Figure
2.2. The data for the Cantwell (Vee Canyon) gage were grouped into
three groups, each corresponding to the period from June to October,
November to April, and May. Only one sample was available for the
2-4
R24/3 26
November-Apri I period and two samples for the May period. These
data were insufficient to develop separate curves. Therefore, one
sediment rating curve was fitted visually to all data points. Using
this suspended sediment rating curve and the flow-duration curve for
Vee Canyon on Figure 2.3, the mean annual suspended sediment
discharge at the Cantwell (Vee Canyon) gage was computed to be
about 5,660,000 tons/year.
Suspended sediment discharges and the corresponding water
discharges for the Gold Creek gage are shown on Figure 2.4. The
data for the Gold Creek gage, collected in the period from 1949 to
1982, were divided into three groups corresponding to June-October,
November-April, and May periods. The points for the June-October
and May periods indicated separate trend lines and were fitted with
two curves. Limited data points were available for the low-flow
period of November-April. These points appeared to be fitting the
lower part of the May curve. Therefore, the May curve was used for
the November-April period. The daily flow duration curves for the
Gold Creek gage for the June-October and November-May periods
were derived using the 1950-1982 flow data and are shown on Figure
2.5. The mean annual suspended sediment discharge at the Gold
Creek gage was computed to be about 7,260,000 tons/year.
2. 2. 3 Reservoir Sediment Inflow
Suspended-sediment inflows to Watana and Devil Canyon Reservoir
were computed by transposing sediment discharges at the Cantwell
(Vee Canyon) and Gold Creek gages, whose locations bracket the two
reservoirs. Sediment discharges at the two gages were assumed to
follow the following exponential relationship (Vanoni; 1975):
2-5
R24/3 27
in which:
qsl == sediment discharge per unit drainage area (unit sediment
discharge) at point 1
qs 2 == unit sediment discharge at point 2
A 1 == drainage area for point 1
A2 == drainage area for point 2
n == exponent
Using the unit sediment discharges at the Cantwell (Vee Canyon) and
Gold Creek gages, exponent "n'' in the above equation was computed
to be -0.376. Thus, suspended-sediment discharge at the Watana
damsite was computed to be 6,530,000 tons/year for the drainage area
of 5,180 square miles. Assuming no Watana Reservoir, the
suspended sediment discharge at the Devil Canyon was computed to
be 7,030,000 tons/year using a drainage area of 5,810 square miles.
Bedload discharge was estimated to be three percent of
suspended-sediment discharge, based on the following analysis.
Bedload and suspended sediment discharges for the Susitna River
near Talkeetna were estimated to be 43,400 and 2,610,000 tons/year,
respectively, as presented later in this report. Thus, the bedload
discharge is about 1. 6 percent of suspended sediment discharge. For
the Sunshine gage, this percentage is about 3. 2 based on the bedload
and suspended sediment discharges of 423,000 and 13,330,000
tons/year, respectively. A value of 3 percent was used in the
analysis.
2-6
R24/3 28
2.2.4 Sediment Trap Efficiency
Sediment trap efficiencies of Watana and Devil Canyon Reservoirs were
estimated by the Brune's and Churchill's curves (U.S. Bureau of
Reclamation, 1977). The trap efficiency of Watana was also estimated
by PN&D and Hutchison (1982) using a sedimentation model. Similar
modeling is not available for Devil Canyon Reservoir.
A comparison of the trap efficiencies of Watana and Devil Canyon
Reservoirs estimated by the three methods is shown in Table 2.1.
The Watana trap efficiency ranges from 96 to 100 percent based on
Brune's curves. The trap efficiency is about 100 percent based on
the Churchill's curves for local silt. The trap efficiency computed by
a reservoir sedimentation model, DEPOSITS, ranges from 78 to 96
percent depending on reservoir mixing and dead storage volume.
The trap efficiency of Devil Canyon Reservoir ranges from 86 to 98
percent based on the Brune's curves. The trap efficiency estimated
with the Churchill's curves is 95 percent for local silt and 88 percent
for fine silt, the latter case being for sediment discharged from an
upstream reservoir. Tables 2.2 and 2.3 show the estimation of the
trap efficiencies by Brune's curves and Churchill's curves.
2.2.5 Sediment Deposition
Based on the estimated trap efficiencies shown in Table 2.1, Watana
Reservoir was assumed conservatively to trap all sediment inflow to
the reservoir. The resulting sediment deposition over a 50-and
100-year period will be about 210,000 and 410,000 acre-feet. The
gross reservoir volume is about 9,470,000 acre-feet at a normal
maximum pool elevation of 2,185 feet, of which 5, 730,000 acre-feet is
the dead storage (APA, 1983a). The 100-year sediment deposit is
only about 7 percent of the dead storage volume.
2-7
----------·---~-"'
R24/3 29
Without Watana Reservoir, the 50-and 100-year sediment deposits in
Devil Canyon Reservoir would be about 226,000 and 442,000 acre-feet,
respectively, also assuming a trap efficiency of 100 percent. The
gross reservoir volume of Devil Canyon Reservoir is about 1,090,000
acre-feet at a normal maximum pool elevation of 1,455 feet, of which
about 740,000 acre-feet is dead storage. The 100-year sediment
deposit is about 60 percent of the dead storage volume.
With Watana Reservoir, the 50-and 100-year sediment deposits in
Devil Canyon Reservoir would be abut 16,100 and 31,400 acre-feet,
respectively, or about 2 and 4 percent, respectively, of the dead
storage volume, assuming 100 percent trap efficiency for sediments
from the intervening drainage area. Any fine suspended sediment
passed through Watana Reservoir was assumed to also pass through
Devil Canyon Reservoir.
The sediment volumes presented above were computed using the
procedures of the U.S. Bureau of Reclamation (1977). Percentages of
clay, silt, and sand of the incoming suspended sediment were
estimated to be 20, 38 and 42, respectively, using sediment data for
the Cantwell (Vee Canyon)and Gold Creek gages (Table 2.4). Using
unit weights for clay, silt and sand of 26, 70 and 97 lb/fe,
respectively, the unit weights of the sediment deposits after 50 and
100 years were estimated to be about 80 and 82 lbs/fe, respectively.
The unit weight of bedload was estimated to be 120 lb/fe.
2-8
Table 2.1 COMPARISON OF TRAP EFFICIENCIES ESTIMATED BY
BRUNE'S CURVES, CHURCHILL'S CURVE, AND SEDIMENTATION HODEL
Method Tra:e Efficiencx 2 %
Watana Devil Canyon
Brune's Curves
Coarse Sediment 100 98
Median Curve 99 94
Fine Sediment 96 86
Churchill's Curve
Local Silt 100 95
Fine Silt 88
DEPOSITS Hodel
Quiescent 94 to 96*
Minimum Mixing 86 to 93*
Maximum Mixing 78 to 90*
* Corresponding to dead storage volumes from 5,340,000 acre-feet to
900,000 acre-feet (reservoir capacity = 9,470,000 acre-feet at normal
maximum pool).
SOL"RCE: Harza-Ebasco (1984c)
2-9
•
•
•
•
•
•
J
J -J
J
J
-J
J
J
J
·-J
-J
Table 2 .2
RESERVOIR TRAP EFFICIENCY
BY BRUNE'S CURVES
Reservoir
Storage
Capacity
af
Average
Annual
Inflow
af
Capacity
-:-Inflow
Trap Efficiency
Max. Median Min.
Watana
Devil Canyon
9,47o,ooo!/5,780,oood/ 1.&4
1,090,00o116,580,00~ 0.17
100 99
98 94
1J At normal maximum pool elevaton 2185 feet above mean sea
level. From License Application, Exhibit E, Chapter 2,
page E-2-55 (11).
96
86
11 At normal maximum pool elevation 1455 feet above mean sea
level. From License Application, Exhibit E, Chapter 2,
page E-2-55 (11).
1/ Converted from average annual flow of 7990 cfs at Watana, as
shown in License Application, Exhibit E, Chapter 2,
Table E.2.4 (11).
~ Converted from average annual flow of 9080 cfs, as shown in
License Application, Exhibit E, Chapter 2, Table E.2.4 (11).
SQ{JRCE: Harza-Ebasco (1984c)
2-10
N
I
1-'
1-'
Table .2.3
RESERVOIR TRAP EFFICIENCY
BY CHURCHILL 1 S CURVES
(1) (2) (3) (4) (5) (6)
Average2../
(7) (8)
Cross-Retention
Storage lf AveragelJ Retention11 Reservoir.i/ Sectional MeanW Period -:-
Reservoir Capacity Inflow Period Length Area Velocity Velocity
ft3 cfs sec ft ft2 • ft/sec sec2/ft
Watana 4.13xl011 7990 5.17xl07 2. 75xl05 1.50xl06 0.53xlo-2 9.70xl09
Devil Canyon
(local
silt) 0.48xloll 9080 0.52xl07 1.69xl05 0.28x1o6 3.23xlo-2 o.16xlo9
Devil Canyon
(fine
silt)
At normal maximum pool elevation 2185 ft for Watana and 1455 ft for Devil Canyon.
From License Application, Exhibit E, Chapter 2, page E-2-55.
From License Application, Exhibit E, Chapter 2, Table E.2.4.
Col. (2) -:-Col. (3).
(9)
% of
Silt
Passing
< 0.1
5
12
Converted from 52 reservoir miles for Watana and 32 reservoir miles for Devil Canyon.
Col. (2) -:-Col. ( 5).
Col. (3) -:-Col. (6).
SOu~: Harza-Ebasco {1984c)
I I
(lO)
Trap
Effi-
ciency
%
100
~s
88
\_t '-' '-' L..l '-' 1...1 '-' 1.....1 L-1 1...1 ·'-' 1-1 1-• L..' ._,--._i"-L..i-._*-L;-
Table 2.4
PARTICLE SIZE DISTRIBUTION OF SUSPENDED SEDIMENT
No. Particle Size (mm)
Stream Gaging of Y .002 .004 .008 .016 .031 .062 .125 .250 .500 1.000
Station Samele --percent Finer Than.Y
Susitna River 34 12 16 23 31 41 53 64 81 96 100
nr. Denali
Susitna River 27 12 18 25 33 43 54 67 86 97 100
nr. Cantwell
Susitna River 24 15 19 27 35 47 61 75 86 98 100
at Gold Creek
Susitna River 13 29 35 53 72 79 90 100
nr. Talkeetna
tV Chulitna River 36 21 31 37 46 55 62 72 85 99 100
I nr. Talkeetna i-'
tV Talkeetna River 16 9 16 22 31 41 53 65 85 99 100
nr. Talkeetna
Susitna River 17 22 33 43 53 62 67 79 90 100
at Sunshine
Susitna River 9 16 23 33 43 52 60 82 94 100
at Susitna Station
1/ Samples for which full range of size distributions were analyzed.
2/ The percentages given are the median values from a range of oberved percentages for various sizes.
S()t]"OCE: .Harza-Ebasco (l984d)
..... e .....
::t: ....
a.
w
Q
w !\) :.:: I
i-' <C
w ..J
2 2
(SAMPLE FREQUENCY ~Typ. )J 3 3 2
50
40
5
20
30 10
\
20
10
10
0~----~------~------~~--~------~------~~~~~----~--~~~~~--~~--~------~ JAN FEB MARCH APRIL MAY JUNE JULY AUG
FIG. 2.1 ISO-TURBIDITY vs. TIME
EKLUTNA LAKE at STATION 9
1984
SEPT OCT NOV DEC
SOURCE: Figure reproduced
from(R & M 1985b)
850
BOO
r
)>
" fTl
750
JTI
r
JTI < )>
-i
0 :z
.--':""
700
4-
. I.
5 6 7 4 5 6 7
4
' 10,~~{1
5 6 7 8 9 '
I 4
i
6 7
' " '
,/
;
;
;
/
-! L.!
' I
Figure 2. 2 Suspended Sed-___ .
irocmt rC!:ting curve , Susi tna __i
river near Cantwell. · -
! (Vee canyon}
' I
r 7 B
SOURCE: Harza-Ebasco {1984c}
1100,000 • •
9.
)'~.1.>-i' -v X OS~'-'.;:._;::--·,
"'. ( ~-' ,, ~-.... .. ,,__ .. ' • ·-• su
. '· .. t--: -. -----r_:_-
8
l 7
!j_
---·-:_-:-1 FIGURE 2.3 ANNUA.:.·~FLOW DURAT-ION
CURVE, SUSITNA RIVER NEAR CANTWELL
(VEE CANYON) -~
5
I 4 4
l 3 3
l
l
l
!
l
l
l ~
I
L
!
-,.
----,-----T-"'""~------· -----··---;------··-·i
j
l 1,000
l
!
I
L ..:
I
-1
.SOURCE: GRAPH RE-PLOTTED FROM (HARZA-EBASCO, 1984C)
PERIOD OF RECORD: 1962-1972, 1980-1982
~
PERCENTAGE OF TIME DISCHARGE IS EQUALLED OR EXCEEDED
-----·l---~-:
SOu"R:E: Harza-Ebasco (l984c)
2-16
l • • " •. ! ___ ·-:-P~Oe.AS!! ,-y '( 2' :_:_.:.'
>'.£~ ,., • " ""~~..,~~ .-:::-• • • 100.000
L
6
L
l
.;·.:· l
2
3
L~ ~
t :
SOURCE: GRAPHS RE-PLOTTED FROM HARZA-EBASCO (1984c)
PERIOD OF RECORD: 1950-1982
PERCENTAGE OF TIME DISCHARGE IS EQUALLED OR EXCEEDED
R24/3 30
3.0 CHANNEL STABILITY
3. 1 Introduction
The Susitna River between Devil Canyon and the confluence of the Susitna
and Chulitna Rivers has a single-channel or a split-channel configuration.
A number of barren gravel bars or moderately-to-heavily vegetated islands
exist in the river. The mid-channel gravel bars appear to be mobile
during moderate to high floods (R&M, 1982e). A number of tributaries,
including Portage Creek, Indian River, 4th of July Creek, and Lane
Creek, join the main river in this reach. Almost every tributary has built
an alluvial fan into the river valley. Due to relatively steep gradients of
some of these tributaries, the deposited material is somewhat coarser than
that normally carried by the Susitna River.
Vegetated islands generally separate the main channel from side channels
and sloughs. These sloughs and side channels exist on one bank of the
river at locations where the main river channel is confined towards the
opposite bank. The flows enter into these sloughs and side channels,
depending upon the elevations of the berms at their heads relative to the
mainstem river stages (Table 3.1). Coarser bed materials are generally
found at the heads of sloughs and side channels, as the flow entering
these sloughs and side channels is from the upper layer of the flow in the
main channel and does not carry coarse material. This relatively sediment-
free flow picks up finer bed material at the heads, thereby leaving coarser
material.
Evaluation of morphological changes between 1949-1951 and 1977-1980
(AEIDC, 1984) indicates that some sloughs have come into existence since
1949-51, some have changed character and/or type significantly, and
others have not yet changed enough to be noticeable. Many sloughs have
evolved from side channels to side sloughs or from side sloughs to upland
sloughs (definitions of slough types and other habitat types may be found
in (EWT&A and WCC, 1985)). Thus, they are now higher in elevation
3-1
R24/3 31
relative to the water surface in the mainstem at a given discharge. The
perching of the sloughs and increased exposure of gravel bars above the
water surface are indicative of river degradation over the 35-year period.
However, the photographs presented in the report also show significant
increase in the number and/or size of barren gravel bars, which indicates
that depositions also have occurred. Therefore, both aggradation and
degradation can be expected to occur in the Susitna River under natural
conditions, depending upon the flows and sediment loads.
Under with project conditions, the flow regime of the Susitna River will be
modified, and the reservoirs will trap most sediment except the smaller
particle sizes of fine silt and clay size material. The river will strive to
adjust itself to a new equilibrium. The main channel will have the
tendency to be more confined with a narrower channel. This may cause
the main channel to recede from the heads of some sloughs and side
channels.
Of major concern are potential aggradation or degradation in the sloughs
and side channels at their entrances, and at sites in the main channel.
Also of concern are intrusion of fine sediment into the gravel bed and its
subsequent entrapment. In case of fine sediment deposition on the gravel
bed, appropriate measures may be necessary to flush out the sediments so
that the bed can be kept clean.
Another concern is the potential change in hydraulic conditions at the
mouths of tributaries due to lower main stem water levels. Of special
interest are Indian River and Portage Creek, which receive the majority of
the escapement of chinook and chum salmon entering tributaries upstream
of the Chulitna River confluence. Potential perching of these and other
tributaries above the mainstem, the decrease or elimination of the
backwater area at the mouth, and increased velocities could restrict fish
access to spawning areas (Trihey, 1983). Conversely, excessive
degradation at some tributaries could potentially cause maintenance
problems at stream crossings of the Alaska Railroad (R&M, 1982f).
3-2
R24/3 32
This segment of the report discusses the analyses of sedimentation
processes conducted by Harza-Ebasco (1985), R&M (1982e,f) and Trihey
(1983) in order to evaluate stream channel stability under natural and
with-project conditions for study sites in the mainstem, in selected sloughs
and side channels, and in significant tributaries. For these analyses, a
stable channel means that its shape, slope and bed material size
distribution do not change significantly with time. Thus, these physical
parameters are relatively constant, although there may actually be
exchange of soil particle~ in the bed from time to time. Major items
discussed in this section are:
1. Evaluation of sedimentation processes under natural conditions;
2. Evaluation of potential degradation or aggradation under with-project
conditions;
3. Determination of discharge rates at which the mainstem flows are
likely to overtop the entrances of the sloughs and side channels
under natural and with-project conditions;
4. Estimation of discharge rates for the sloughs and side channels at
which their beds will be unstable, and also estimation of the rates
required to flush out fine sediment deposits; and
5. Estimation of changes in tributary mouth conditions at significant
tributaries.
3.2 Factors Affecting Channel Stability
To provide some background for analyzing the specific problems under
study, a brief description of sediment transport in a river is given below.
Sediment particles are transported by the flow as bedload and suspended
load. The bedload consists of wash load and bed-material load. In large
rivers, the amount of bedload generally varies between about 3 and 25
percent of the suspended load. Although the amount of bedload is
generally small compared to the suspended load, it is important because it
shapes the bed and affects the channel stability.
3-3
R24/3 33
The amount of material transported or deposited in a stream under a given
set of conditions depends upon the interaction between variables
representing the characteristics of the sediment being transported and the
capacity of the stream to transport the sediment. A list of these variables
is given below (Simons, Li and Associates, 1982).
Sediment Characteristics:
Quality: Size, settling velocity, specific gravity, shape, resistance
to wear, state of dispersion and cohesiveness.
Quantity: Geology and topography of watershed; magnitude, intensity,
duration, distribution and season of rainfall; soil condition;
vegetal cover; cultivation and grazing; surface erosion; and
bank cutting.
Capacity of Stream:
Geometric shape: Depth, width, form and alignment.
Hydraulic Properties: Slope, roughness, hydraulic radius,
discharge, velocity, velocity distribution, turbulence,
tractive force, fluid properties and uniformity of
discharge.
The above variables are not independent, and in some cases the effect of a
variable is not definitely known. However, the responses of channel
pattern and longitudinal gradient to variation of the variables have been
studied by various investigators, including Lane (1955), Leopold and
Maddock (1953), Schumm (1971) and Santos Cayudo and Simons (1972).
The studies by these investigators support the following general
relationships (Simons and Senturk, 1977):
3-4
R24/3 34
(i) depth of flow is directly proportional to the cube root of water
discharge;
(ii) channel width is directly proportional to sediment discharge and
to the square root of water discharge;
(iii) channel shape expressed as width to depth ratio is directly
related to sediment discharge;
(iv) channel slope is inversely proportional to water discharge and
directly proportional to both sediment discharge and grain size;
(v) sinuosity is dir~ctly proportional to valley slope and inversely
proportional to sediment discharge; and
(vi) transport of bed material is directly related to streampower
(defined as product of bed shear and cross-sectional average
velocity), and to concentration of fine material, and inversely
related to bed material sizes.
Because of the complexity of interaction between various variables, the
river response to natural or man-made changes is generally studied by
(i) qualitative analysis, involving morphological concepts; (ii) quantitative
analysis involving application of morphological concepts and various
empirical or experimental relationships; and (iii) quantitative analysis using
mathematical models. The insight to the problems obtained through the
qualitative approach provides understanding of the methods required to
quantify the changes in the system. Mathematical modeling can help to
study many factors simultaneously. Recent work by Simons and Li (1978)
and others indicate that physical process computer modeling provides a
reliable methodology for analyzing the impacts and developing solutions to
complex problems of aggradation, degradation and river response to
engineering activities.
For river channels of non-cohesive sediment, qualitative predictions of
river response have been made using Lane's relationship (Lane, 1955):
os-G d s s
3-5
R24/3 35
in which
Q = stream discharge
S = longitudinal slope of stream channel
G bed material discharge s
ds = particle size of bed material, generally represented by d 50 (median
diameter)
The use of the above relationship to predict potential responses of the
Susitna River under natural and with-project conditions is discussed in
Section 3.5.1.
Prediction of quantitative changes in a river system requires geomorphic
and hydraulic data or information which are generally not readily available.
Considerable effort, time and money are required to collect such
information. The data of primary needs include hydrological and
topographic maps and charts, large scale aerial and other photos of the
river and surrounding terrain, existing river conditions (roughness
coefficient, aggradation, degradation, local scour near structures),
discharge and stage data (under natural and with-project conditions),
existing channel geometry (main channel, side channels, islands), sediment
data (suspended load and bed-load, size distribution of bank and bed
material and suspended sediment), and size and operation of anticipated
reservoir(s) on the river system.
Because the available data did not permit meaningful mathematical modeling
using computer techniques, the morphological concepts and empirical
relationships were used to predict potential aggradation or degradation at
the study sites.
3.3 General Analytical Approach
Harza Ebasco (1985) evaluated the sedimentation processes of degradation
and aggradation under natural and with-project conditions in the Susitna
3-6
R24/3 36
River at the study sites (Table 3.1), using the approaches discussed
below.
3.3.1 Degradation
Generally, river bed degradation occurs downstream of newly
constructed diversion and storage structures. The rate of
degradation is rapid at the beginning, but is checked by either the
development of a stable channel slope or by the formation of an armor
layer if sufficient coarse sediment particles are available in the bed.
The important variables affecting the degradation process are:
1. Characteristics of the flow released from the reservoir,
2. Sediment concentration of the flow released from the reservoir,
3. Characteristics of the bed material,
4. Irregularities in the river bed,
5. Geometric and hydraulic characteristics of the river channel; and
6. Existence and location of controls in the downstream channel.
The assumptions used in the analysis of degradation include:
1. Bedload is completely trapped by the reservoir, but suspended
sediment particles of .004 mm and less in diameter will remain in
suspension and pass through the reservoir ( PN &0, 1982). The
sediment passing through the reservoir would be about 18
percent of the sediment inflow (Harza-Ebasco, 1984d);
2. 1 rregularities in the river and channel configurations remain
unchanged;
3-7
R24/3 37
3. Sediment supply due to bank erosion is negligible;
4. Sediment eroded from the river bed is carried downstream as
bedload;
5. Sediment injections by tributaries are carried downstream without
significant deposition;
6. Size distribution of bed material is constant throughout the
depth at each study site; and
7. Sufficient coarse material exists in the river bed to form an
armoring layer which prevents further degradation.
The size of transportable bed material was estimated using (i) the
competent bottom velocity concept of Mavis and Laushey (1948) and
U.S. Bureau of Reclamation (1977); (ii) the tractive force versus
transportable size relationship derived by Lane (1953); (iii) the
Meyer-Peter, Muller formula (U.S. Bureau of Reclamation, 1977);
(iv) the Schoklitsch formula (U.S. Bureau of Reclamation, 1977); and
(v) Shields criteria (Simons, and Li and Associates, 1982).
The depth of degradation or the depth from original streambed to top
of the armoring layer was computed by the following relationship
given in (U.S. Bureau of Reclamation, 1977):
y = y ( 1 -1) d a -
~p
in which:
Y d = depth of degradation, feet
Y = thickness of armoring layer, assumed as 3 times transportable a
size or 0.5 feet, whichever is smaller
Ap = decimal percentage of material larger than the size
3-8
R24/3 38
The transportable size for a given discharge was the average of the
five sizes estimated by using the five methods mentioned above.
3.3.2 Aggradation
Potential aggradation at the entrances of sloughs and side channels
was estimated by comparing the transportable size for the flow in the
mainstem before diversion into the slough or side channel and the
transportable size for the remaining flow in the main channel a'fter
diversion into side channel or slough. If the two sizes were
significantly different, it was concluded that some of the bedload
being transported would be deposited near the entrance.
3.3.3 Stability of Tributary Mouths
The regulation of floods by reservoir operation results in a decrease
in stage during mean annual floods of from 3.2 to 7.6 feet at the
mouths of tributaries between Devil Canyon and the Chulitna River
confluence. Similarly, the decrease in average summer flows results
in average reductions in water levels of 1-4 feet. Material
transported to the tributaries' mouths will no longer be readily
transported downstream (although such transport is assumed in the
degradation analysis). Consequently, alluvial fans will increase in
size at the mouth of affected tributaries. Also, the reduced summer
water levels may result in headcutting and scour at the tributaries.
Field data were collected at nineteen tributaries. A qualitative
analysis was conducted to determine if the above problems were likely
to occur. A semi-quantitative analysis (R&M, 1982f) was done on six
creeks, and considered channel slope, the sediment discharge rate,
the bed material size distribution and the decrease in stage expected
at the tributary mouth. Due to their importance to chinook and chum
3-9
R24/3 39
salmon spawning, Indian River and Portage Creek were analyzed in
more detail for changes in hydraulic conditions due to project
operation, including bed changes and average velocities (Tri hey,
1983).
3.4 Analysis of Natural Conditions
The basic data used in this study were taken from various reports
prepared for Alaska Power Authority by the Alaska Department of Fish and
Game, Susitna Hydro Aquatic Studies Team (ADF&G); R&M Consultants,
Inc. (R&M); and Harza-Ebasco Susitna Joint Venture (H-E). Discharge
and sediment data also were taken from the publications of the U.S.
Geological Survey, Water Resources Division (USGS) in co-operation with
the Alaska Power Authority (Knott and Lipscomb, 1983, 1985).
Hydraulic parameters such as stage-discharge relationships, channel
widths, average channel depths, measured velocities and bed slopes of
selected side channels and sloughs, were taken from various reports of
R&M (R&M, 1982 b, c, f, g) and ADF&G (ADF&G, 1983b, 1984b). The
hydraulic parameters for the main channel reaches were derived from the
data given in (Harza Ebasco, 1984b). Some unpublished data were
obtained from USGS, R&M and ADF&G through correspondence. The site
characteristics and hydraulic parameters for study sites in the mainstem,
side channels and sloughs are shown in Tables 3. 1, 3.2 and 3.3.
The Manning's roughness coefficients for various main channel reaches,
side channels and sloughs (Table 3.1) were estimated based on field
reconnaissances made in 1983 and 1984 and on the analysis presented by
Harza Ebasco (1984b).
The representative bed material size distribution for each site was derived
from the analysis of the bed material samples collected by Harza Ebasco.
In the mainstem of the Susitna River, the surface material is generally
coarser than the sub-surface material. The bed material samples collected
3-10
R24/3 40
in the sloughs and side channels, however, did not show any distinct
difference between the surface and sub-surface materials. The surface
and sub-surface samples at a given site were combined to determine the
s1ze distribution. The adopted size distributions are given in Table 3.4.
These are considered only indicative of the bed material at the specific
sites because many additional samples would be required to determine a
representative size distribution for the whole length of the study reach.
The sizes of transportable bed material corresponding to a selected range
of discharges (Table 3. 5) were estimated as the average of the five sizes
computed using the methods of competent bottom velocity; tractive force;
Meyer-Peter, Muller formula; Schoklitsch formula; and Shields criteria. A
comparison of median bed material size and the transportable size at each
site indicated that under natural conditions, most of the selected sites are
subject to temporary scour and/or deposition, depending upon the
magnitude and characteristics of the sediment load and high flows caused
by floods or breaching of ice jams.
About 56 percent of the suspended sediment load carried by the river
under natural conditions is finer than 0.5 millimeter (medium to fine sand,
silt and clay). This fine sediment has been observed to deposit in side
channels and sloughs. However, many of these deposits are re-suspended
and removed during high flows, probably because of disturbances of the
surface bed material layer.
3.5 With-Project Conditions
3. 5. 1 River Morphology
The construction of the Susitna Hydroelectric Project will change the
streamflow pattern and sediment regime. The essentially sediment-
free flows from the reservoirs wi II have the tendency to pick up bed
material and cause degradation. The modified discharges downstream
from the dams, however, will have reduced competence to transport
3-11
R24/3 41
sediment, especially that brought by the tributaries. These two
factors tend to compensate each other, resulting in the overall effects
discussed below.
The Lane relationship discussed in Section 3.2 is based on an
equilibrium concept, that is, if any change occurs in one or two
parameters of the water and sediment discharge relationships, the
river will strive to compensate the other parameters so that a new
equilibrium is attaine<:L In the case of the Susitna River, both water
discharge and bed load discharge will be modified by the reservoirs.
Therefore, adjustments will occur in the river channel and particle
sizes of the bed material. A number of studies (Hey, et al 1982)
have indicated that the new median diameter under with-project
conditions may correspond to the o 90 or o95 of the original bed
material.
The potential morphological changes of the Susitna River also were
addressed qualitatively by R&IV1 (1982e). It was argued that the
Susitna River between Devil Canyon and the confluence of the Susitna
and Chulitna Rivers would tend to become more defined with a
narrower channel. The main channel river pattern will strive for a
tighter, better defined meander pattern within the existing banks.
A trend of channel width reduction by encroachment of vegetation and
sediment deposition near the banks would be expected.
3. 5. 2 Channel Stability
Potential degradation at the selected sites was estimated for various
discharges using the discussed procedure. The potential degradation
at each site estimated from these relationships is listed in Table 3.6.
These estimates are based on the assumptions that there would not be
a significant supply of coarse sediments by the tributaries and that
there would not be redeposition of bed material eroded from the
upstream channel.
3-12
R24/3 42
Table 3. 7 shows average weekly flows at Gold Creek for four project
operation scenarios and for natural conditions (Harza Ebasco, 1985).
These data indicate about 50 percent reduction in flows during the
May through September period and about 3 to 4 times increase in
flows during the October through April period. Table 3.8 shows
annual maximum weekly flow at Gold Creek for natural and
with-project conditions. Under with-project conditions, the maximum
weekly flows occur under 2002 load conditions for almost every year.
Using the average of these annual maximum weekly flows as the
dominant discharge (about 30,000 cfs), the potential degradation at
the main channel sites would be in the range of about 1.0 to 1.5 feet.
In the sloughs and side channels, the degradation would be about 0
to 0.5 feet. These estimates, however, are based on the assumptions
that there will not be significant injection of bedload by the
tributaries and that there would not be redeposition of sediment
eroded from the upstream channel. In actual situations, there will be
sediments carried down by the tributaries, of which some will be
deposited in the main river. Redeposition of some sediment eroded
from the upstream channel will also occur. Therefore, actual
degradation at the main channel sites would be less than that
estimated.
Table 3.3 shows that bifurcation of flow at the heads of the sloughs
and side channels will not significantly reduce the discharge rates in
the main channel. Therefore, the competence of flow to transport
bed material will not be affected due to bifurcation of flow and little
aggradation should be expected in the main channel near the
entrances to the sloughs and side channels.
It is not possible to accurately estimate the actual degradation since
there are many unquantifiable parameters. These include bed material
transport from tributaries and bank erosion, the degree of armoring
by the present bed, and the actual streamflows and floods which will
occur for the first few years of Devil Canyon operation. However,
3-13
R24/3 43
based on many samples of bed material and visual inspection, it is
believed that on the average, degradation in the main channel will not
exceed approximately one foot. The amount of this degradation may
be greatest near the Devil Canyon Dam face, decreasing with distance
downstream.
When the system energy demand increases (as in 2010), and less flow
is discharged in July and August, the armoring layer developed
earlier will be stable, more so than under natural conditions.
However, infrequent high flood events will not be controlled to as
great an extent as will smaller floods, and will still have the ability to
remove the armor layer and cause bed degradation. Reservoir
operation studies indicate that floods up to the 50-year event will be
controlled for project energy demands in 2002. Control of infrequent
flood events will be improved as energy demand increases, and the
potential for bed degradation will therefore be reduced.
Because of degradation in the mainstem, discharges higher than those
under natural conditions would be required to overtop the berms at
the heads of the sloughs and side chan nels. Assuming that the river
bed at the entrances would be lowered by about one foot due to
degradation, the with -project discharges that would overtop the
sloughs and side channels were estimated to be between 4,000 and
12,000 cfs higher than those under natural conditions, with an
average increase of approximately 8, 000 cfs.
3. 5.3 Intrusion of Fine Sediments
As previously discussed, the reservoir will trap all sediment except
for particles sizes of .004 mm and less, which constitute about 18
percent of the suspended load. The velocities at the study sites
(Tables 3.2 and 3.3) would be sufficiently high to carry these fine
particles in suspension, and the substrate would generally be cleaner.
However, some coarse silt and fine sand might be picked up from the
3-14
R24/3 44
river bed. These fine materials would have the tendency to settle
out in pools and backwater areas. Therefore, some deposition of
such silt and sand in the sloughs and side channels is possible, and
it may be desirable to operate the project such that the sloughs and
side channels are overtopped at least for a few days each year,
unless other means such as "Gravel Gerties" are employed to flush
out the fine sediment deposition.
3.5.4 Tributary Stability
The semi-quantitative assessment of the nineteen tributaries (R&M,
1982f) indicated that three creeks (Jack Long, Sherman and
Deadhorse) are estimated to aggrade and to likely restrict access by
fish. The tributaries at RM 127.3, RM 110.1, and Skull Creek are
estimated to degrade and to possibly affect the railroad bridges. The
other tributaries studied will either degrade or aggrade, but without
effects on fish access or railroad. The assessment is summarized in
Table 3.9.
The analysis of hydraulic conditions at Portage Creek and Indian
River indicates that fish access has not been a problem and is
unlikely to be a problem under with-project conditions (Trihey,
1983). These creeks will adjust their streambed gradients and will
re-establish entrance conditions similar to those under natural
conditions.
3-15
---------·----····"
, , , , ,
1 , , , , , , ,
jJ
Table 3.1
CHARACTERISTICS OF STUDY SITES
ON MIDDLE SUSITNA RIVER!.'
Approx.
River
Miles
OVerall Overall Observed Estimated
Slope of Slope of Overtopping Bed Elev.
Study Reach Hain River Discharge.V at Head
Main Channel Nr. River
Cross Section 4
Main Channel Between
River Cross Sec-
tions 12 and 13
Main Channel Upstream
from Lane Creek.
Mainstem 2 Side Channels
at River Cross
Section 18.2
NW Channel
NE Channel
Slough 8A (main channel)
NW Channel
NE Channel
Slough 9
99.0 to
100.0
108.5 to
110.0
113.6 to
114.2
114.4
115.5
126.2
126.7
128.3
Main Channel Upstream From 131.2 to
the 4th of July Creek. 132.2
Side Channel 10 134.2
Lower Side Channel 11 135.0
Slough 11 135.4
Upper Side Channel 11 136.2
Hain Channel Between 136.9 to
Cross Sections 46 and 48 137.4
Side Channel 21
Downstream from A5 140.6
Upstream from A5 141.9
Slough 21
NW Channel 142.2
NE Channel 142.3
.0017
.0012
.0017
.0030
.0020
.0024
.0024
.0024
.0024
.0026
.0015
.0039
.0024
.0029
.0045
.0017
.0030
.0043
.0017
.0012
.0017
.0017
.0017
.0017
.0017
.0017
.0017
.0016
.0015
.1017
.0020
.0020
.0020
.0017
.0032
.0023
1/ Data taken from various reports of H-E; ADF&G and R&M.
2/ Discharges at Gold Creek Station
3/ Not applicable.
SOt..JIO::: Harza-Ebasco (1985)
3-16
NA
NA
12,000
12,000
23,000
26,000
26,000
33,000
16,000
NA
19,000
5,000
42,000
1l,OOO
NA
12,000
20,000
23,000
26,000
NA
NA
NA
476.3
476.3
484.6
576.5
604.6
NA
656.6
684.6
684.3
NA
753.8
756.9
Estimated
~nning~s
Roughness
.030
.035
.035
.035
.035
.035
.032
.032
.032
.032
.035
.035
.035
.032
.035
.035
.030
.030
.030
.,
l
Table 3.2
l HYDRAULIC PARAMETERS FOR MAINSTEM SITES
Location Gold Creek Discharge ( cfs)
1 3,000 5,000 7,000 9,700 13,400 17 zOOO 23,400 341500 52,000
Near River Cross Section 4
Discharge, cfs 3,090 5,150 7,210 9, 990 13,800 17' 500 24,100 35,500 53,600
1 Width, ft 650 750 860 1,010 1,200 1,380 1,640 2,060 2,680
Depth, ft 2.9 3.4 3.9 4.6 s.s 6.3 7.3 8.9 10.6
Velocity, ft/sec 2.7 3.4 3.8 4.4 4.4 4.3 4.2 4.6 4.9
1 Jl~f;.~• ....
River Cross Sections
12 and 13
Discharge, cfs 3,090 5,150 7,210 9,990 13,800 17,500 24,100 35,500 53,600
Width, ft 380 410 425 445 460 473 495 518 545
1 Depth, ft 5.6 6.6 7.6 8.0 9.2 9.9 11.2 13.1 16.0
Velocity, ft/sec 2.3 3.0 3.4 4.2 4.7 5.3 6.1 7.0 7.7
1
Upstream from Lane Creek
Discharge, cfs 3,090 5,150 7,210 9, 990 13,800 17,500 24,100 35,500 53,600
Width, ft 850 960 1,020 1,110 1,350 1,680 1,790 1,860 1,900
Depth, ft 5.9 6.8 7.4 8.2 8.5 9.3 10.0 11.0 12.9
1 Velocity, ft/sec 1.7 2.2 2.6 3.1 4.1 4.3 5.2 6.7 7.5
Upstream from 4th of
July Creek
1 Discharge, cfs 3,000 5,000 7,000 9, 700 13,400 17,000 23,400 34,500 52,000
Width, ft 250 340 430 580 800 970 1,150 1,250 1,380
Depth, ft 6.3 7.2 7.7 8.3 9.0 9.3 10.1 10.6 11.6
Velocity, ft/sec 2.1 2.7 3.3 4.0 4.9 5.8 6.2 7.4 8.8
1 Between River Cross Sections
46 and 48
Discharge, cfs 3,000 5,000 7,000 9, 700 13,400 17,000 23,400 34,500 52,000
1 Width, ft 305 385 465 545 600 650 710 800 920
Depth, ft 5.1 6.2 6.9 8.1 9.0 9.7 10.6 12.0 14.1
Velocity, ft/sec 3.6 4.1 4.6 4.9 5.7 6.4 6.8 8.2 9.4
1 SOlJFCE: Harza-Eba.sco (1985)
'1
I
i
1
~
• I
3-17
----·~·· -~.,.,., .......... ,..~.~~--·
"1
'1 Table 3.3
HYDRAULIC PARAMETERS FOR SIDE CHANNELS
l AND SLOUGHS
Slough/Side
1 Gold Creek Channel Slough/Side Channel
Location Discharge Discharge Width Depth Ve1ocit;t:
(c fs) (Tt) (ft) (ft/sec)
(1) (2) (3) (4) (5) (6)
1 M.ainstem 2 Side Channel
Northwest Channel 17,000 150 112 1.0 1.39
1 23,400 940 117 1.9 2.78
34,500 2,940 228 2.5 5.20
52,000 6,700 264 2.9 8. 75
1 Northeast Channel 34,500 650 111 3.4 1. 71
52,000 2, 900 124 3.8 6.09
Main Channel Below
1 Confluence 17,000 150 128 0.5 2. 31
23,400 940 250 1.4 3.78
34,500 3,590 341 2.7 3. 89
52,000 9,600 366 4.4 6.00
1 Slough SA
Northwest Channel 30,000 19 45 0.7 0.62
1 35,000 47 45 0.9 1.18
40,000 98 45 1.0 2.21
45,000 183 45 1.1 3.75
52,000 383 46 1.3 6.58
1 Northeast Channel 30,000 17 70 1.0 .4 2
35,000 26 71 1.1 .51
40,000 37 73 1.2 .59
1 45,000 51 75 1.4 .6 7
52,000 74 78 1.6 .77
Main Channel Below
1 Conflu ... nce 30,000 36 62 0.8 .7 2
35,000 73 66 1.0 1.14
40,000 135 70 1.1 1.74
45,000 234 72 1.2 2.68
1 52,000 457 78 1.5 3.96
Slough 9 23,400 80 73 1.3 0.82
34,500 580 151 2.2 2.34 1 45,000 1,600 156 3.0 4.03
52,000 2,650 160 3.2 5.30
1
1
1
1
3-18
J
J Table 3.3 (con't)
HYDRAULIC PARAMETERS FOR SIDE CHANNELS
J AND SLOUGHS
Slough/ Side
J Gold Creek Channel Sloush/Side Channel
Location Discharge Discharse Width Depth Velocity
(cfs) (ft) (f t) (ft/sec.)
(1) (2) ( 3) (4) (5) (6)
J Side Channel 10 21,000 30 38 0.8 1.00
25,000 150 83 1.5 1.25
30,000 430 102 2.1 2.05
J 34,500 860 108 2.6 3.07
45,000 2,800 119 3.7 6.36
52,000 4,900 127 4.4 8.75
J Lower Side Channel 1 7,000 520 275 0.9 1.75
9,700 862 280 1.3 2.27
13,400 1,420 285 1.8 2.96
17.000 2,053 290 2.3 3.60
J 23,400 3,365 295 3.2 4.64
34,500 6,133 300 4.8 6.46
45,000 9,248 300 6.3 7.87
52,000 11,565 300 7.5 8.90
J Upper Side Channel 11 17,000 38 101 0.5 • 75
23,400 170 117 1.0 1. 52
34,500 1,060 146 2.2 3.30
J 45,000 3,900 155 4.0 6. 70
52,000 7,800 170 5.2 8.80
Slough 11 44,000 21 24 0.5 1.65 J 46,000 33 30 0.6 1.80
48,000 94 49 0.9 2.25
50,000 176 64 1.1 2.60
52,000 332 84 1.3 3.00 J Side Channel 21 12,000 67 77 1.0 0.87
16,000 205 105 1.4 1.40
20,000 420 130 1.7 1.90 J 25,000 810 162 2.0 2.50
30,000 1,350 189 2.3 3.10
40,000 2,900 260 2.7 4.15
52,000 5,600 298 3.3 5.70 J Slough 21 25,000 13 52 0.5 0.50
30,000 39 72 0.9 0.60
35,000 105 94 1.4 0.80 J 40,000 235 98 2.0 1.20
45,000 500 99 2.8 1.80
50,000 970 99 3.9 2.52
J
SOURCE: Har:za-Ebasco (1985)
J
J
J 3-19
,----· --~·-----'---
)
)
-I
~J
~I
l
-I
-J
-I
-I
1
1
Table 3.4
REPRESENTATIVE BED MATERIAL SIZE DISTRIBUTION
FOR SELECTED SLOUGil.S, SIDE CHANNEL AND MAINSTEM SITES
Particle Size, mm Bed Material
.062 .125 .250 .500 1.00 2.00 4.00 8.00 16.0 32.0 64.0
--Percent Finer Than
Sizes (mm) For
Given Percentage
Main Channel near
Cross Section 4-!1
Main Channel between
Cross Sections 12 and 131.1
Main Channel upstream from
Lane Creekl 1
Msinstem 2 Side Channels at
Cross Section 18. 2.!1
Slough W 1
Slough 9..§.1
Msin Channel upstream
from 4th of July Creek11
Side Channel 101l.1
Lover Side Channel 11, down-
stream from Slough 111 1
Slough 1illl
Upperside Channel 11, up-
stream from Slough 1ill1
Msin Channel between Cross
Sectio-n 46 and 4all1
Side Channel 21, downstream
from Slough 2111 1
Slough 2111 1
2
1
2
3
2
1
1
0
0
3
2
3
5
3
2
4
3
2
2
2
2
0
0
7 10 l3 16
3 5 8 12
5 7 9 10
7 10 13 17
6 10 12 l3
7 15 18 20
6 8 11 14
6 12 17 20
5 7 10 14
5 8 12 15
5 a 12 15
3 7 10 13
1 4 6 8
1 4 6 8
~1 Based on 6 samples taken at three locations near cross section 4.
1:.1 Based on 2 samples taken near river miles 109.3.
22
18
14
22
15
23
20
25
19
20
20
17
12
12
~~ Based on 2 samples taken in main channel upstream from Lane Creek •
.!i 1 Based on 4 samples taken in the Ha.instem 2 side channel, at four
locations.
i 1 Based on 6 samples taken near the slough in the main channel at
RM 125.6 •
.i1 Based on 5 samples taken near the slough in the main channel at
RM 128,7.
2 1 Based on 3 samples taken in the main and side channels near
29 42
24 32
21 32
29 37
18 28
30 41
27 36
34 44
30 41
27 35
27 35
24 33
17 23
17 23
~~ \i~e~fo~u2ys~~f~s taken in Slough 10.
1 1 Based on 2 samples taken in Side Channel 11, downstream from Slough 11 •
.!.9.1 Based on one sample taken in Slough 11.
~~ Based on 2 samples taken between cross sections 46 and 48 •
.!.Y Based on one sample taken near the upstream end of side channel.
SOUR:E: Harza-E:tasco (1985)
3-20
016 °so Dgo
70 89 1. 7 20 65
50 77 3.0 34 78
48 77 5.0 35 84
53 73 1. 7 30 110
47 83 4.3 35 70
63 93 0.5 22 58
55 78 2.5 28 85
62 82 0.8 20 80
58 84 2. 6 25 72
50 68 2.2 32 100
50 68 2.2 32 100
53 72 3.3 30 100
40 62 7.5 46 96
40 62 7.5 46 96
------------------· -~---... --
.t
Table 3.5
~ TRANSPORTABLE BED MATERIAL SIZES IN SELECTED
SLOUGHS, SIDE CHANNELS AND MAINSTEM SITES
~ Location Discharge at Gold Creek (cfs)
5,000 7,000 10,000 15,000 20,000 25,000 30,000 35 ,ooo 40,000 45,000 55 ,ooo
TransEortable Bed Material Size (mm)
.I Main Channel near 18 21 24 29 33 36 38 41 43 44 48
Cross Section 4
Main Channel between
j Cross Sections 12 & 13 21 25 28 37 44 48 53 57 60 65 76
Main Channel upstream 25 28 32 37 44 48 52 56 60 64 72
from Lane Creek
-' Mainstem 2 Side
Channel at Cross
Section 18.2
.I Main Channel 6 11 18 25 31 37 43 56
North-east Fork 5 9 13 16 18 21 24 29
North-west Fork 5 9 13 16 17 19 21 24
Slough BA 4 6 8 9 12
.I Slough 9 9 13 17 20 24 31
Main ,Channel upstream 27 31 35 40 45 50 54 51 61 64 71
.I from 4th of July Creek
Side Channel 10 5 13 22 29 37 45 60
Lower Side Channel 11 5 9 16 22 28 34 39 45 50 61
.I Slough 11 5 17
Upper Side Channel 11 7 13 20 30 44 57 84
tl Main Channel between 30 35 41 49 56 62 68 73 79 84 94
Cross Sections
46 and 48
.I Side Channel 21 6 10 15 18 22 25 28 31 37
Slough 21 3 5 9 14 21 30 58
.I
SOr.JRCE: Harza-Ebasco (1985)
..1
..1
.I
.I
..1
.I 3-21
•
Table 3.6
• POTENTIAL DEGRADATION AT SELECTED SLOUGHS,
SIDE CHANNELS AND H.AINSTEM SITES
~ Location Discha~ge at Gold C~eek (cfs)
5,000 7,000 10,000 15 ,000 20,000 25,000 30,000 35,000 liJ ,000 45 ,000 55,000
j Estimated Deg~adation, ft
Main Channel nea~ 0.1 0.2 0.3 0.6 0.8 1.1 1.3 1.5 1.7 1.9 2.4
C~oss Section 4
J Main Channel between
C~o!IS Sections 12 & 13 0.1 0.2 0.3 0.4 0.6 0.8 1.1 1.3 1.8 2.4 3.7
Main Channel upst~eam 0.2 0.2 0.3 0.4 0.6 0.8 1.0 1.2 1.5 1.8 2.5
J f~om Lane C~eek
Mainstem 2 Side
Channel at C~oss
J Section 18.2
Main Channel 0 0 0 0 0 0.1 0.2 0.3 0.5 0.7 1.2
North-east Fo~k 0 0 0 0 0 0 0 0.1 0.1 0.2 0.2
North-'llest Fo~k. 0 0 0 0 0 0 0 0.1 0.1 0.2 0.2
J Slough 8A 0 0 0 0 0 0 0 0 0 0 0
Slough 9 () 0 0 0 0 0 0 0.1 0.2 0.3 o.s
J Main Channel upst~eam 0.3 0.3 0.4 0.6 0.8 1.1 1.3 1.5 1.7 2.0 2.5
from 4th of July Creek
Side Channel 10 0 0 0 0 0 0.1 0.2 0.4 0.6 1.0 2.0
J Lower Side Channel 11 0 0 0 0.1 0.2 0.3 o.s 0.7 1.0 1.3 2.1
Slough 11 0 0 0 0 0 0 0 0 0 0 o. 1
J Upper Side Channel 11 0 0 0 0 0 0.1 0.2 0.3 0.6 0.9 1.8
Main Channel between 0.3 0.4 0.6 0.9 1.2 1.4 1.7 1.9 2.1 2.4 2.8
Cross Sections
J 46 and 48
Side Channel 21 0 0 0 0 0 0 0.1 0.1 0.2 0.2 0.3
-Slough 21 0 0 0 0 0 0 0 0 0.1 0.2 0.5 _I
-.J SOU~: Harza-El::asco (1985)
)
)
)
)
:t.
3-22
·---~-·
J
J
Table 3.7
J NATURAL AND WITH-PROJECT AVERAGE WEEKLY FL~S
OF SUSITNA RIVER AT GOLD CREEK
(1950-1983)
"-J With-ProJect Flowsl'
1996 2001 2002 2020
Natural Load Load Load Load Jl ..,
') Weekl.1 Flow Condit ions.ll Conditions.ll Conditions..'!' Condito· ... s
{1) (2) (3) ( 4) (5) -(6)-
1 1607 9552 9695 7027 10323
J 2 1554 9540 9679 6997 10300
3 1512 9526 9655 6965 10285
4 1494 9537 9666 6936 10201
5 1427 9518 9639 6897 10225
6 1354 9561 9789 6903 10262
J 7 1390 9603 9775 6851 10141
8 1258 9502 9669 6802 10082
9 1204 9357 9521 6709 9957
10 1152 8711 8971 6376 9448
J 11 1149 8338 8486 6167 9117
12 1157 7953 8093 5959 8781
13 1167 7715 7852 5840 8581
14 1216 7593 7682 5832 8500
) 15 1240 7260 7303 5670 8245
16 1408 7028 7028 5543 8000
17 1667 6765 6765 5534 7644
18 3654 6912 6875 5481 7532
) 19 7914 7449 7559 5910 7932
20 13466 8886 9001 6780 9067
21 18715 10440 10521 7434 9896
22 23556 11910 11953 8115 10782
J 23 27284 11367 11438 9014 10252
24 29369 11679 11741 8960 10452
25 27860 11415 11539 10227 10322
26 26313 10974 11142 11773 10112
] 27 23987 10006 10161 13951 9317
28 24491 10124 10254 16950 9383
29 24708 10153 10275 19797 9460
30 24031 10013 10204 20915 9355
31 25294 11002 11103 22285 9613
J 32 23320 10470 10629 21810 9415
33 22387 11770 11072 21224 10756
34 20411 12367 12177 20478 11875
35 18377 12280 11929 18366 11281
_I 36 15621 12685 12088 15756 11772
37 14039 11783 11100 14030 10998
38 12871 11269 10790 12790 10211
39 10663 10304 10033 10750 9649
~~ 40 8102 8990 8726 8297 8812
41 6782 8384 8266 7258 8695
42 5348 8543 8374 6443 8557
43 4303 8636 8456 6531 8514
~I 44 3332 8440 8345 6620 8461
45 2861 8792 8691 6824 8908
46 2562 9215 9165 7032 9554
47 2358 9727 9698 7255 10122
~I 48 2204 10196 10195 7476 10603
49 1978 10892 11025 7775 11108
50 1886 11162 11312 7918 11474
51 1785 10796 10915 7675 11162
52
~I
1739 10080 10142 7263 10590
1/ F1 rst week is the first week of month of January.
~ I; Based on enviroTIIIlenta1 constraints, E-6.
3; Watana Operation.
4/ Watana -Devil Canyon operation.
{"1r'\f' 1TV""T' + • t.I-. ,.-._-. ~T"'1-.-. _......,,...., f1()0L:\ 3-23
]
-I
Table 3.8 ,_I
MAXIMUM NATURAL AND WITH-PROJECT WEEKLY
FLOWS OF SUSITNA RIVER AT GOLD CREEK ,_1
1996 2001 2002 2020
-1 Natural Load Load Load Load
Year Flow Conditions Conditions Conditions Conditions
1950 26171 10092 11534 21157 10327 -I 51 30057 15024 11374 30057 11856
52 38114 14216 14216 37243 12721
53 35114 14356 15779 25643 11771
~I 54 31143 13975 13975 31143 12664
55 37243 22402 19671 35236 18572
56 43543 25394 22429 32000 26000
-I 57 37443 20071 19275 25943 13414
58 38686 12426 12426 37485 11817
59 44171 28700 16498 41415 14829
60 32043 13342 13914 28943 12203 -I 61 38714 15622 15622 26000 13787
62 58743 26057 26057 35557 23571
63 40257 19900 19543 38549 22106
-I 64 75029 18410 18410 29834 14941
65 33643 21913 21913 28514 19812
66 47686 17098 17098 28014 14719
67 54871 41459 29071 41589 30600 ,_I 68 37343 14439 15125 29429 12551
69 18114 9861 8000 8000 10228
70 26429 9211 9409 8126 10226 -I 71 4 7186 22857 22857 37427 22857
72 44243 18029 19488 33149 18029
73 36443 11756 11756 23171 10293
~ 74 31357 11846 11846 16614 10828
75 36400 19886 18629 29900 19886
76 29843 11965 11965 25844 11530
77 46300 15438 15438 25514 14420 --78 22786 11800 11921 20214 11685
79 32457 12955 13558 32457 12927
80 33557 13106 13264 33557 13304
-~ 81 46729 37029 37029 39966 37029
82 28857 12141 12145 27500 11895
83 27343 12683 13481 26586 12875
"1 SOURCE: Harza-Ebasco (1985}
"1
"1
---3-24
No.
1
2
3
4
w 5 I
N 6 ln
7
8
9
10
11
12
13
14
15
16
17
18
19
1
2
3
4
Q 1
Name (cfs)
Portage 1680
Jack Long 181
Indian 786
, Gold 260
132.0 17
4th of July 187
Sherman 72
128.5 14
127.3 28
Skull 51
123.9 67
Dead horse 51
121.0 16
L. Portage 23
McKenzie 21
Lane 117
Gash 4
110.1 21
Whiskers 114
52
TABLE 3.9
SUSITNA TRIBUTARY STABILITY ANALYSIS
SUMMARY OF SEMI-QUANTITATIVE ASSESSMENT
D 3 ~E4 Reason Response
for to Increased
(ft/ft) <'*~) (ft) Concern Slope at Mouth
.0158 33 7.6 fish degrade
.0276 6.1 fish perch
.0150 50 ··5,5 fish degrade
.0194 36 5.2 fish degrade
.1280 3.2 RR perch
.0219 25 6.1 fish degrade
.0403 30 4.4 RR, fish perch
.0607 I 4,0 RR perch
.0597 3.6 RR degrade
.0159~ '20 4.2 RR degrade
.0230 5.0 fish perch
... 0344 19 4.4 fish, RR perch
.0483 20 4.4 fish degrade
.0048 26 5.0 RR perch
.0316 18 6.2 fish degrade
.0214 13 5.0 fish degrade
N/A 5.2 fish degrade
.0757 7.0 RR degrade
.0011 3.5 fish perch (but
backwater)
Impacts Foreseen
possible restriction of fish access
possible restriction of fish access
possible limited scour at RR bridgE
possible limited scour at RR bridgE
possible restriction of fish access
possible limited scour at RR bridge
SOURCE: R & M (1982f)
Mean annual flood, from Table 4.4.
Average channel slope, from Table 4.1.
Median bed particle size, from Table 4.2.
Decrease in Susitna River stage at mouth, from Table 4.3.
I
R24/3 45
4.0 SLOUGH HYDROLOGY
4. 1 Introduction
Flow into side-channel and upland sloughs comes from overtopping of
upstream berms by mainstem flow, from local surface tributaries, and from
groundwater upwelling. Slough discharges and hydraulic conditions when
the upstream berms are overtopped are dominated by mainstem flow. The
relationship between mainstem flow and slough flow for overtopped
conditions has been previously shown in Table 3. 3. Under with -project
conditions, the upstream berms will be overtopped much less frequently.
Consequently, groundwater upwelling and local surface runoff will control
slough hydrology. This section of the report describes these two aspects
of slough hydrology.
During non-overtopped conditions, sufficient local runoff and upwelling are
required to provide sufficient flow to allow access to spawning areas in the
side sloughs for chum and sockeye salmon (ADF&G 1983a). Upwelling also
provides water which both keeps incubating embryos from freezing and
supplies them with oxygen. Much of this upwelling water is at 2° to 4°C
throughout the winter. This warmer water keeps developing embryos alive
during early incubation and maintains development at a level elevated
above that which would occur in the mainstem at 0°C (Wangaard and
Burger, 1983).
4.2 Factors Affecting Upwelling
4.2.1 Sources of Groundwater
Groundwater sources for the Middle Reach can be separated into
mainstem and local upland sources. The origin of groundwater is
surface flow. Sources controlled by the mainstem originate at an
undefined point upstream. During the summer, upstream precipitation
events and glacial melt supply the surface water, which percolates
4-1
-------·----·----~-·
R24/3 46
into the groundwater. Much of the winter flow is maintained by
water stored during the summer in the broad gravel floodplains below
the glaciers at the headwaters of the basin. Alluvial fans at the
bases of upstream slopes and tributaries add to the volume. This is
considered to be the basic source of groundwater in the system
(Acres American 1983).
The upland component of groundwater upwelling comes from
precipitation falling on the slopes above the river. After reaching
the earth's surface, precipitation and/or snowmelt move as surface
runoff or go into soil storage or groundwater. Recent precipitation
and snowmelt history determine the amounts of each which occur.
Large precipitation events are usually required to contribute much
water into the groundwater system. Upland sources are independent
of mainstem discharge levels, since local events drive the system.
These local events also are unpredictable. The effects of upland
sources on upwelling are most pronounced for steeper, higher and
closer valley walls.
4.2.2 Aquifer Conditions
An aquifer is generally considered to be a geological formation that is
porous enough to hold significant quantities of water and also
permeable enough to readily transmit it horizontally. The material of
the floodplain aquifer in the Middle Reach typically consists of a thin
layer of topsoil overlying 2 to 6 feet of sandy silt. Below this is a
heterogeneous alluvium of silt, sand, gravel, cobbles, and boulders.
Non-stationary streambed deposition is believed to be responsible for
the heterogeneous pattern. The heterogeneous nature of the material
results in variable hydraulic conductivities, both laterally and
vertically (Acres American 1983). Depth through this material to
bedrock is approximately 100 feet at the abutments to the Alaska
Railroad bridge at Gold Creek (Prince 1964).
4-2
R24/3 47
Groundwater flow through an aquifer may be confined or unconfined,
depending on the location. Unconfined aquifers are similar to
underground lakes in porous materials. There is no restricting
material at the top of the aquifer, so the groundwater levels are free
to rise and fall. The top of the unconfined aquifer is the water
table. Below the water table the aquifer is saturated, while above
the water table it is only partially saturated. Much of the sand,
gravel and cobble alluvium underlying the Susitna River's bed is an
unconfined aquifer. This unconfined aquifer is bounded by bedrock
on the sides and bottom. Groundwater flow through the system is
downhill, running parallel to the valley walls and following the
general course of the surface river, but at a much slower rate.
Conditions in unconfined aquifiers are such that changes in mainstem
stage have a delayed and minimal effect on water table elevation.
This is caused by the large volume of aquifer that must be filled to
raise the water table by a given amount.
A confined aquifer is a layer of saturated, porous material located
between two layers of much less permeable material. If these
confining layers are essentially impermeable, they are called
aquicludes. If the layers are permeable enough to transmit water
vertically to or from the confined aquifer, but not permeable enough
to laterally transport water as an aquifer, they are called aquitards.
A confined aquifer bounded by one or two aquitards is called a leaky
or semiconfined aquifer. Aquitards consisting of layers of fine silt
often bound the highly permeable sand and gravel alluvium, creating
piping zones where groundwater is easily transmitted. Along the
Susitna River, such piping zones are believed to be sources of
shallow lateral flow to the upwelling areas. These piping zones would
be most likely to rapidly respond to changes in mainstem stage,
because such changes would be transmitted into the aquifer as
pressure effects rather than by filling or draining the pore space of
the aquifer. A regional confined aquifer may be providing water to
4-3
R24/3 48
the sloughs and mainstem. However, the preponderance of
near-surface bedrock along the valley walls and nearby mountains
minimizes the likelihood of a confined regional aquifer being a
significant water source, although some local springs and seeps may
occur at faults in the bedrock. According to APA (1984b), neither
regional flow from the valley walls into the alluvium nor downriver
flow through the alluvium appears to be sufficient to provide all of
the apparent groundwater upwelling to the side sloughs.
Ice processes have a dramatic effect on lateral flow during the win-
ter.
level
As an ice cover forms on the river, the effective water surface
(WSL) in the mainstem rises dramatically. Flow becomes
confined by the ice at the water surface. Friction caused by
movement against the stationary ice cover slows the velocity of the
river water. Water level rises as the velocity drops. The ice cover
also acts directly to increase the WSL by floating on the surface.
The increased pressure supplied by the floating ice increases the
effective WSL to near the top of the ice cover. In the Middle Reach,
confined 2,000-cfs flow may have the same effective WSL as 20,000 cfs
with no ice cover present. The result of this increase in stage is a
much higher hydraulic head, increasing lateral flow from the mainstem
into the groundwater system and, presumably, resulting in increased
upwelling in the side channels and sloughs.
Groundwater temperatures are buffered from seasonal climatic
variations by the heat storage in the aquifer. As groundwater moves
through the system, it adds to or removes heat from the surrounding
material. Heat transfer during groundwater movement can occur by
both conduction and convention. The groundwater temperature
approaches that of the surrounding material, and remains stable
through the year. The net energy balance is such that groundwater
temperature in the Middle Reach stabilizes at about 2-4°C,
approximating the mean annual (time-weighted) mainstem temperature.
4-4
R24/3 49
The temperature of the groundwater is a function of time. This
becomes important when considering groundwater temperatures in
areas of confined flow. The response of flow can be very rapid since
changes are caused by pressure waves. Actual time of flow is much
greater. Therefore, groundwater temperatures in these areas are
similar to areas of unconfined flow. The distance through the
alluvium that is travelled is much more important on the moderating
effect on the groundwater.
4.3 Local Surface Runoff
Runoff from a drainage basin is influenced both by climatic factors and
physiographic factors (Chow, 1964). Climatic factors include the forms
and types of precipitation, interception, evaporation, and transpiration, all
of which exhibit seasonal variations. Physiographic factors are further
classified into basin characteristics and channel characteristics. Basin
characteristics include such factors as size, shape, and slope of drainage
areas, permeability and capacity of groundwater formations, presence of
lakes and wetlands in the basin, and land use. Channel characteristics
are primarily related to the hydraulic properties of the channel which
govern the movement of streamflows and determine channel storage
capacity.
Many of the above factors are interdependent to a certain extent, and can
be highly variable in nearby basins. The general basin characteristics of
each of the study sloughs are described in the following section.
4.4 Field Studies
4.4.1 Study Sloughs
Four sloughs have been chosen for intensive sampling. These four,
8A, 9, 11 and 21, were chosen because they are the most important
side sloughs for salmon spawning and incubation (ADF&G 1 984c).
4-5
R24/3 50
They also encompass a wide range of physical variables, allowing a
better understanding of the general upwelling conditions in the Middle
Reach. The relative locations of each of the study sloughs are shown
in Figure 4.1.
Slough 8A, located at RM 125, is a side slough on the east side of
the river. The two-mile long slough is relatively straight with two
upstream channels connecting it to the mainstem (Figures 4.2, 4.3).
Overtopping of the .northwest channel at RM 126.2 occurs at about
26,000 cfs, while overtopping of the northeast channel at RM 126.7
occurs at 33,000 cfs. The substrate in the upper slough is primarily
cobble and boulders, and in the lower slough is gravel and cobble.
At present, several beaver dams, some of them armored with cobble
are located along the slough. Surface water input is supplied by 6 to
8 streams coming down from steep slopes adjacent to the slough with
shallow or exposed bedrock.
Slough 9 is a 1.2 mile-long S-shaped side slough on the east side of
the river at RM 128 (Figures 4.4, 4.5). The upper slough has a
fairly steep slope and cobble/boulder substrate. The lower slough
has a low gradient and smaller substrate consisting of gravel/cobble.
Overtopping discharge of the berm at the upper end of the slough is
about 16,000 cfs. A major water source during non-overtopped
conditions is slough 9B (Figure 4.4). This small slough drains a
marshy area near the head of the slough. A small tributary
(Tributary 9B) with a drainage area of about 1.5 square miles enters
the slough further down.
Slough 11, at RM 135, is another side slough on the east bank of the
river. This mile-long slough was formed in 1976 as an overflow
channel when an ice jam blocked the river during breakup. The
steeper upper slough has a cobble/boulder substrate while the lower
slough is less steep and has a mostly gravel/cobble substrate. The
slough overtops at approximately 42,000 cfs. There are no
4-6
R24/3 51
tributaries into the slough. Non-overtopped flow in the slough comes
from seepage and upwelling in the lower two-thirds of the slough
(Figures 4. 6, 4. 7).
Slough 21 is located at RM 149, on the east side of the river, and is
about one-half mile long. The upper one-half of the slough is
divided into two channels, with overtopping flows of 23,000 and
26,000 cfs. There are no tributaries conveying surface runoff to this
slough. Groundwater upwelling is very obvious, as large areas of
strong upwelling and springs occur throughout the slough (Figures
4. 8, 4. 9). A large upland a rea may provide considerable input into
the local groundwater.
4.4.2 Field Investigations
In order to explain the relationship between the mainstem and
upwelling in the sloughs, several studies were conducted in the study
sloughs described in the following section. Slough discharges were
recorded in Sloughs 8A, 9, 11 and 21. Daily mainstem flow or stage
measurements have been compared with slough flow using linear
regression analysis, with slough flow as the dependent variable
(Tables 4.1 and 4.2) (R&M 1982, 1985a; Acres American 1983; APA
1984b, Beaver, 1985). Analysis was complicated by frequent
overtopping of the upstream berms in Sloughs 8A and 9 during much
of the summer. Data collected in 1984 were particularly useful in
investigating groundwater upwelling to the sloughs because a
significant portion of the 1984 open-water data are for very low
mainstem discharge rates, thus minimizing complicating effects such as
surface runoff and overtopping of berms. Correlations between
weekly average slough discharge and weekly average mainstem stage
are given on Table 4.4. Correlation with mainstem stage, rather than
mainstem discharge, makes it easier to estimate groundwater upwelling
for various with project scenarios, particularly winter conditions when
ice staging effects have been simulated. Similarly, the use of weekly
4-7
R24/3 52
rather than daily averages makes it easier to apply the results of
with-project simulations, which are generally expressed as weekly
average mainstem stage or discharge values.
Additional data were obtained by monitoring groundwater surface
levels in shallow wells dug in the vicinities of sloughs 8A and 9 (R&M
1982g, APA 1984b). The data allow groundwater flow direction to be
determined in the areas immediately around sloughs 8A and 9.
Comparison of the plots for different dates and mainstem flows shows
the temporal variability of flow patterns in the groundwater system
(Figures 4.10-4.15).
Mainstem, groundwater, intragravel and slough water temperatures
have been continuously recorded (ADF&G 1983a, b; 1984 b, c, d).
These data show the range in variations for different locations
(Figures 4.16 -4.24).
Seepage meter data were obtained at upwelling sites in several
sloughs (APA 1984b). The data serve as another indicator of flow
rate through the groundwater system. Relationships between
mainstem discharge and upwelling rates are illustrated in Figures
4.25-4.33.
In 1984, the water balance in the sloughs was investigated (R&M
1985a). Studies focused on quantifying the local upland input into
sloughs 8A, 9 and 11. Continuous flow measurements of tributary
flow into Slough 9 were made. Storm runoff analyses and monthly
water balances are shown in Tables 4.5, 4.6 and 4. 7. The spatial
variability of precipitation along the Middle Susitna River was also
investigated. Coefficients to adjust recorded rainfall for other
locations along the Middle River are shown in Table 4.8.
4-8
R24/3 53
4.4.3 Results
a. Slough SA
Slough discharge at Slough SA is moderately well correlated to
mainstem discharge and stage (Tables 4.1 through 4.4). Local
runoff from the adjacent steep, rocky hillslopes causes some
disruption of the relationship. Linear regression equations have
been developed from several data bases. In order to minimize
the disrupting effects of overtopping flow and local runoff on
the relationship, data from 1983 were separated into a subset
where all data pairs were eliminated in which either flow at Gold
Creek exceeded 30,000 cfs or flow in Slough SA exceeded 3 cfs.
Data from 1984 were subdivided in a similar manner, using flows
at Gold Creek of 27,900 cfs and 12,500 cfs as the upper limits
for the equation. These regression equations are shown an
Table 4. 1. The coefficient of determination ( R 2 ) improves for
the lower flow range. The low flow regression equation is for a
period of relatively little local precipitation, so little local runoff
would be expected.
Beaver (1985), using weekly flows, shows an improvement in the
determination coefficient over the same data using daily
averages, and also over low flow periods in 1983. Precipitation
in 19S4, especially after September 1, was generally lower than
during the two previous years (R&M 19S5a). The lower
precipitation resulted in less local runoff in 19S4, and resulted
in the high R 2 values obtained for non-overtopped conditions.
Seepage data were collected at two sites near the head of Slough
8A in 1983. The seepage rates are plotted against mainstem
discharge in Figures 4.25 and 4.26. Data from the site nearest
the upstream berm, located in the channel, showed the higher
correlation to mainstem discharge (R 2 =0.62). The other site,
4-9
R24/3 54
located in a small channel adjacent to a steep bank, had a
relatively poor correlation (R 2 =0.3S).
Water surface elevation data collected in 19S3 from wells and
boreholes indicate the general downvalley movement of
groundwater in the vegetated island separating Slough SA from
the mainstem. Data collected with an ice cover on the mainstem
(Figure 4.12) show a definite trend of groundwater flow down
valley and from the mainstem towards the side-channel. The
trend was also evident during the open-water period (Figure
4. 10). When streamflow is dropping, groundwater levels in the
island may be higher than the water surface in either the slough
or the mainstem (Figure 4.11).
Intra-gravel water temperature in the slough rose from -0.1°C
during the winter (ADF&G 19S3a) to 5. 5°C in August (ADF&G
19S4a) of 19S3. During the same period mainstem surface water
ranged from 0.2°C in May to 15.S°C in July (ADF&G 19S4a)
(Figures 4.16-4.1S).
A monthly water balance study of Slough 8A conducted in 19S4
(R&M, 19S4a) determined that 62%-73% of available precipitation
falling on the Slough SA watershed ran off as surface water
(Table 4. 6). Higher percentages of runoff may occur with large
storms, as the soil layer on the slopes above the river is
relatively thin.
Analysis of local precipitation data for 27 September to 7 October
19S3 (Bredthauer 19S4) shows an immediate response in slough
discharge to a major rainstorm (Figure 4.34). The event
occurred after a fairly long dry period (over one month). It
was an intense storm, with 1.12 inches of rain falling in
Talkeetna on 29 September. This amount of precipitation
apparently was sufficient to saturate the groundwater table and
produce a rapid response.
4-10
R24/3 55
The daily surface runoff pattern into Slough 8A was estimated
for high, moderate, and low monthly precipitation (Tables 4. 10,
4.11, 4. 12). The recorded slough discharges for August 1984
(high precipitation), September 1983 (moderate precipitation),
and September 1984 (low precipitation) were separated into
surface runoff and groundwater flow. Groundwater flow was
estimated using the regression equation for slough discharge and
the average daily flows for the Susitna River at Gold Creek.
The estimated groundwater flow was then subtracted from the
recorded value. (When the groundwater flow estimate from the
regression equation exceeded the recorded value, groundwater
flow was reduced to the recorded value.) Surface runoff was
assumed to be the difference between the recorded discharge and
the estimated groundwater flow.
Although the estimates for surface runoff are not precise, Tables
4.10 through 4.12 do indicate that there are long periods when
little surface runoff is contributed to Slough 8A, even in months
when precipittation is well above average. In Table 4. 10, a
13-day period of zero surface runoff is indicated, even though
the monthly precipitation is exceeded only 20 percentof the time
in August. Similar periods of zero surface runoff were indicated
for the low rainfall month (September 1984). Surface runoff
contributed an estimated 57%, 64%, and 15% for the high,
moderate and low precipitation patterns illustrated in Tables 4.10
through 4.12.
The data in Table 4.10 also indicate that the runoff period
extends for several days after a major precipitation event.
Apparently, there is sufficient shallow subsurface flow on the
valley slopes to maintain the flow for several days.
The sources of water to flow in Slough 8A are complex. When
the upstream berm is overtopped, mainstem flow dominates the
4-11
R24/3 56
discharge. When the berm is not overtopped, groundwater flow
dominates the discharge during periods of low precipitation and
during the winter. Good correlation exists between mainstem
discharge and slough discharge for periods of low precipitation
and little surface runoff. Local surface runoff may be high
during periods of high precipitation, with subsurface flow
maintaining the local flow for several days after a major
precipitation event.
b. Slough 9
Due to the relatively low flow (16,000 cfs) required to overtop
the upstream berm, hydraulic conditions in Slough 9 are
dominated by mainstem flow for much of the summer. Upwelling
occurs in the slough, contributing flow throughout the year.
Upwelling sites can be observed during low flow conditions
(Figure 4.4). Linear regression equations for data collected in
1983 and 1984 during periods of non-overtopping are shown in
Tables 4.1 and 4. 2. The slopes of the equations for both the
1983 and the 1984 data are very similar.
Tables 4.3 and 4.4 give the linear regression equations for the
apparent mainstem related component of groundwater upwelling as
a function of mainstem stage. Table 4.!f__ presents the
relationship of slough flows to mainstem stage based on weekly
rather than daily averages. This technique shows no real
improvement in the relationship over the daily averages for
slough 9 (a good relationship already).
Results of groundwater surface elevation measurements show
movement from the side channel upstream of the slough toward
the upper reach of Slough 9 between its head and Tributary 98
(APA 1984). A subdued response was often seen even at well
9-3, away from the slough on the upland side. An analysis of
4-12
R24/3 57
lateral flow to the slough based on the Pinder curves showed
slough flow to be much less than expected (APA 1984). Major
variations in the results of falling head tests performed in 1984
( R&M 1985a) indicate semiconfined aquifer conditions (Table 4. 9).
Data from seepage meters in 1983 showed a higher correlation at
the downstream end of the slough than in a marshy area near
the head of the slough (APA 1984). The poor correlation in the
marshy area is likely due to water seeping into the groundwater
system from Trib~tary 9B.
I ntrag ravel water temperatures were very stable throughout the
study, at just over 3°C (Figures 4.19 and 4.20). Groundwater
temperatures from boreholes 9-1A and 9-5 show a limited rise
from 2°C in April to 4°C in September of 1983 (Figure 4.21)
(APA 1984). Temperature data from borehole 9-3 show no
variation related to the main stem. There appears to be a strong
inverse relationship between variations in temperature of the
groundwater and distance from the mainstem. Figures 4.19 and
4. 21 also show mai nstem temperature for comparative purposes.
Tributary 9B was gaged at 2 locations in 1984: (1) at the base
of the slope and (2) above its confluence with Slough 9. The
intervening area between these 2 gages is an alluvial fan with
meadows and beaver ponds. A significant portion of the water
measured at the base of the slope infiltrates into the ground
before reaching the slough. The data indicate that the amount
of infi It ration loss is controlled by the water table level, which
in turn is controlled by the stage in the mainstem (R&M, 1985a).
Runoff percentages for the 2 sites for the months of August -
October 1984 are shown in Table 4. 7. Runoff analyses for two
precipitation events in 1984 are shown in Table 4.5.
4-13
R24/3 58
Figure 4.3.5 shows the response of Slough 9 to a high
precipitation event during a period in 1983 when the upstream
berm was not overtopped. Slough 9 is dominated by overtopping
under natural summer conditions. Effects of overtopping likely
carry over into non-overtopped conditions, with a high level of
soil saturation being one of these. When not overtopped, effects
of both main stem and upland groundwater sources are seen.
Mainstem effects are evident in the seepage meter data from the
slough mouth, and in much of the groundwater data. As in
Slough 8A, groundwater dominates the low precipitation periods,
but high surface runoff may occur during periods of high
precipitation.
c. Slough 11
Slough 11 is the simplest of the sloughs studied, with no direct
surface tributaries. Since its upstream berm is overtopped only
at relatively high flows (42,000 cfs), no surface water
contributes to slough discharge for most of the year.
Consequently, streamflow is maintained by bank seepage and
upwelling throughout the year. Seepage and upwelling locations
are mapped on Figure 4.6, and winter open leads are shown in
Figure 4. 7 (ADF&G, 1983b).
The relationship between slough flow and the mainstem is shown
in Tables 4.1 through 4.4. The relationship is particularly good
for the relationship based on weekly averages. Seepage meters,
used to get an index of intragravel flow on the slough banks,
also showed a strong relationship to the mainstem at both the
lower (R 2 = 0.94) and upper (R 2 == 0.83) sites (APA 1984)
(Figures 4.30, 4.31).
There was little effect on slough discharge from precipitation
events. The analysis of the data from the September 1983 storm
4-14
R24/3 59
event {Figure 4.36) showed no immediate response in slough
discharge, and only a minimal response to the mainstem level.
The lack of response is in keeping with the lack of tributary
input and small drainage area for the slough. This is further
illustrated in the monthly water balances (Table 4.6). Flow was
stable through the summer, despite high precipitation in July
and August.
I ntragravel wate~ temperatures in the slough were very stable
year-round at about 3.6°C. Surface water temperatures were
less constant and did not show a pattern similar to that for
intragravel temperatures. Surface water temperatures were also
dissimilar to mainstem temperatures (Figure 4.22).
All of the above relationships tend to confirm that Slough 11 flow
is derived from mainstem recharge to the local groundwater
aquifer. Responses to changes in the mainstem are minimized
and delayed. The delay and buffering of the groundwater
system explains the high value for the coefficient of
determination for weekly averages in the slough mainstem
relationship. The longer time period allows much greater delays
to be taken into account. The delays and buffering also account
for a very stable intragravel temperature and minimal response
to the September 1983 storm.
d. Slough 21
The relationship between mainstem discharge and slough
discharge appears to be different at Slough 21 than at other
study sloughs. Seepage was negatively correlated to mainstem
flow at one site (seepage increased as main stem flow decreased),
while no correlation existed between seepage and mainstem flow
at a second site. The regression relationships between slough
discharge and mainstem discharge (Table 4.1) were poor when all
4-15
R24/3 60
data were used, but had a very good relationship for data
obtained late in 1982 (September 22 -October 22), when little
precipitation occurred.
Water temperature patterns were fairly complex (Figure 4. 23 and
4.24). The intragravel water temperature in the upper slough
ranged from a winter low of 2.0°C in October to a high of 8.6°C
during much of the summer (ADF&G 1984a). Higher
temperatures of ';JP to 13.1°C were also seen during overtopping
for short periods. Surface water temperature at the same
location ranged from 0. 7° to 9.2°C (with the same overtopping
exception). Generally, surface water temperatures closely
mirrored intrag ravel temperatures throughout the year. In the
lower slough, intragravel temperatures were about 3. 3°C in
March (ADF&G 1984a). Upwelling locations are shown in Figure
4.8.
The geologic structure of the area around the slough helps
explain the data. Above the east side of the slough there is a
bench of old alluvial material at least -!-mile wide. This bench
may act as a large groundwater reservoir. It is a potential
reason for the constant intragravel water temperature in the
lower slough. The measurements from the seepage meters
(Figures 4.32 and 4.33) may also be a function of local upland
flow. The intragravel and surface water temperatures from the
upper slough, on the other hand, seem to be more closely relat-
ed to mainstem temperatures. Slough 21 may show the effects of
different sources at different points along the slough.
4.5 With-Project Changes
Changes in flow through the Middle Reach, brought about by the
completion of the Watana and Devil Canyon Dams, are expected to have
some impacts on groundwater and upwelling. Project operations which
4-16
R24/3 61
change the mean annual temperature in the river are likely to change the
groundwater temperature by a similar amount (Acres American 19S3) as a
result of the temperature-stabilizing effects of the soil framework.
Upwelling is expected to change, but by a variable amount, depending on
the relative input of mainstem-influenced and upland groundwater sources.
Some sloughs, such as Slough 11, would respond fairly directly to changes
in mainstem discharge. Slough 11 has no tributary streams, and its
upstream berm is rarely overtopped. Most slough discharge is directly
correlated to mainstem discharge.
Groundwater upwelling in Slough 9 will be reduced because of the
reduction in mainstem discharge. However, significant surface runoff is
contributed from the nearby slopes. The small tributary (Tributary B)
flows across a large alluvial fan and meadow, losing flow to the
groundwater system when the water table is low. This water probably
appears further down the slough as upwelling.
Most sloughs are similar to Slough SA, with a complex relationship between
surface runoff and the mai nstem and upland sources of groundwater.
Slough discharge will be reduced due to the reduction 1n mainstem
discharge, but will have the same contributions of flow due to upland
groundwater and local surface runoff.
Where upland sources provide a substantial volume of the slough flow,
access to spawning areas may not be hindered, despite expected lower
groundwater input from the mainstem with project.
An analysis of estimated with project slough flows at sloughs SA and 9 was
performed by R&M Consultants (19S5a). The results (Tables 4.10 through
4.14) show the results of the analysis for dry (93% exceedance) normal
(61% exceedance), and wet (20% (exceedance) conditions. While these are
only estimates, they are of some help in analyzing the types of changes
that can be expected under with-project conditions. The results suggest
4-17
\~
R24/3 62
that access may be more limited to sloughs, but flow peaks from upland
sources would still provide access under most conditions.
More detailed predictions on with-project changes cannot be made. The
number of variations, both within and between sloughs, and the large
number of sloughs and other affected habitats, limit the predictions .
. Within these constraints, it appears that there will not be major impacts to
groundwater upwelling from changes in mainstem characteristics.
4-18
I
M19/49 1
Slough
8A
9
1 1
21
1983
1983
1983
1982
1982
TABLE 4.1 LINEAR REGRESSION EQUATIONS
FOR SLOUGH DISCHARGE VS. MAINSTEM DISCHARGE (1982-83)
Regression• Equation _R_2_ Comments
s -3.83 + 0.000526 G
s 5.10 + 0.0000377 G s 0.155 + 0.000117 G s -0.627 + 0.000128 G
s -149.7 + 0.010008 G s 2.94 + 0.000307 G s 1.97 + 0.000351 G
s 1. 51 + 0.000102 G
s 2.15 + 0.000104 G
s -7.62 + 0.00105 G s -0.570 + 0.000445 G s -2.71 + 0.000803 G
o. 103
0.001
0.086
0.631
0.264
0.089
0.805
0.766
0.504
0.543
0.405
0.916
A I I va 1 ues.
Excluding overtopping flows, G>30,000
June 6-August 7 only; excluding G>30,000
June 6-August 7 only; excluding G>30,000, S>3
All va I ues.
Exc I ud i ng overtopping f I ows, G > 16, 000
Exc I ud i ng G > 16, 000, S > 8
All va I ues.
All values.
All va I ues.
Excluding overtopping flows, G> 24,700
September 22 -Octob'er 22 only; exc I ud i ng G> 24,700
Notes: s = Slough discharge, cfs; G Mainstem discharge at Gold Creek, cfs
Source: Beaver ( 1984)
11::>
I
N
0
M19/49 2
Slough
8A
9
11
Source:
July 3 -October 30, 1984
(excl. 8/23-8/28)
September 1 -October 20,
September 8 -October 30,
June 1 -October 30, 1984
R&M ( 1985a)
TABLE 4.2
REGRESSION EQUATIONS FOR
SLOUGH DISCHARGE VS. MAINSTEM DISCHARGE (1984)
Regression Equation
Q8 -0.08 + .00017 QGC
log Q8 = -5.0 + 1.29 log QGC
1984 Q8 = -.67 + .00025 QGC
log Q8 = -7.13 + 1.85 log QGC
1984 Q9 = -.62 + .00039 QGC
log Q9 = -4.1 + 1. 15 log QGC
Q11 = 1. 3 + .000072 QGC
log Q11 = -1.5 + 0.45 log QGC
0.53
0.79
0.73
0.91
0.82
0.84
0.68
0.76
Points Comments
115 Flo~ range (2,200-
115 27,900 cfs)
61 Lo~ runoff period.
61 (2,200-12,500 cfs)
56 Flo~ range (2,200-
56 11, 400 c fs) .
153 Flo~ range (2,200-
153 40,600 cfs)
M19/49 3
TABLE 4.3
LINEAR REGRESSION EQUATIONS
FOR SLOUGH DISCHARGE VS. MAINSTEM STAGE (1982-83)
Slough Year Regression Eguation ~ comments
8A 1983 s -2149.8 + 3.698W1 0.065 All values
s -92.3 + 0.1683W1 0.000 Excluding overtopping flows, G)30,000
s -740.96 + 1.2737W1 0.626 June 6 -August 7 only; exc I ud i ng G > 30, 000, S) 3
9 1983 s -32801 + 54.380W2 0.228 All values s -769.1 + 1.2871W2 0.085 Excluding overtopping flows, G) 16, 000
s -877.21 + 1.4658W2 0.755 Exc I ud i ng G > 16, 000, S > 8
11 1983 s -367.04 + 0.54004W3 0.783 All values
1982 s -327.05 + 0.48278W3 0.531 All values
21 1982 s -4400.2 + 5.8554W4 0.491 All values
s -1810.6 + 2.4130W4 0.391 Excluding overtopping flows, G)24,700
s -3244.1 + 4.3212W4 0.938 September 22 -October 22 only; excluding G)24, 700
NOTE;:>: s = Slough discharge, cfs.
.s::.. G Mainstem discharge at Gold creek, cts •
I Wl Mains tern stage at RM 127 .1. ft. N
I-' W2 Mains tern stage at RM 129. 3. ft.
W3 = Mains tern stage at RM 136.68. ft.
W4 = Mains tern stage at RM 142.2. ft.
Source: Beaver (1984)
..,.
I
N
N
M19/55 1
Slough
8A
9
11
TABLE 4.4
LINEAR REGRESSION EQUATIONS FOR THE MAINSTEM COMPONENT OF
GROUNDWATER UPWELLING TO SLOUGHS AS A FUNCTION OF MAINSTEM STAGE (1984)
Regression Equation
1984 S ·368.211 + 0.6356W1
1984 S -171.8788 + 0.28892W2
1984 S ·335.39272 + 0.49209W3
21 No relationship
NOTES: Discharge and stage data are average weekly values.
S apparent maJnstem -related component of slough discharge .
W1 mainstem water-surface elevation (WSEL) at river mile (RM) 127. 1.
W2 WSEL at RM 129.3.
W3 WSEL at RM 136.68.
Source: Beaver ( 1985).
0.78
0.84
0.96
M15/12 4
Precipitation Period (1984)
Runoff Period
Tota I Precipitation ( Inches)
Max. Daily Precipitation (Inches)
Total Precipitation Volume
(mi II ion cubic feet)
Total Runoff Volume
(mi 1 lion cubic feet)
Baseflo'd Volume
(mi I lion cubic feet)
Storm Runoff Volume
(mi I I ion cubic feet)
% Runoff
Ground'dater Level,
We I I 9-3
Maximum Daily Flo'd
susitna River at Gold Creek
TABLE 4 • 5
STORM RUNOFF ANALYSES
SLOUGH 9 TRIBUTARY
Sl
08/17-08/25
08/17-09/06
6.46
2.05
10.96
6.468
1.034
5.434
50%
09/15-09/20
09/15-09/28
1. 40
0.61
2. 37
1. 081
0.798
0.283
12%
SOURCE: Table reproduced from R & M (1985a)
Slough 9. Tributary
Lo'de r Site
08/17-08/25 09/15-09/20
08/17-09/06 09/15-09/28
6.46 1. 40
2.05 0.61
21.91 4.75
12.181 0. 149
0.272 0.073
11.909 0.076
54% 1. 6%
606.8 604.8
31,700 11. 400
M15/12 5
TABLE 4.6
1984 MONTHLY WATER BALANCES
SLOUGHS 8A AND 11
June .JJ.U.:t: August September October
Slough 8A
Flow, Q ( cfs) 2.98 9.19 1. 70 0.63
(mi II ion cu. ft. ) 7.46 (3-31) 24.62 4.41 1.69
Precipitation, p (inches) 5.46 8.16 2.52 0. 78
(million cu. ft. ) 19. 14 28.61 8.85 2.72
Evaporation, E (inches) 2.02 2.49 0.80 0
(m iII ion cu. ft. ) 7.07 (3-31) 8.72 2.80 0
( P-E) 12.07 19.89 6.05 2.72
Q/(P-E) 0.62 1.24(1) 0.73 0.62
""'
slough 11
I
N F I ow, Q (cfs) 3.17 2.82 2.75
""'
2.44 1. 45
(million cu. ft.) 8.21 7.58 7.35 6.32 3.75
Precipitation, p (inches) 1.49 4.72 6. 78 2. 15 0.65
(million cu. ft.) 3.9~ 18.55 26.60 8.44 2.56
Evaporation, E (inches) 5.66 2.21 2.49 0.80 0
(million cu. ft. ) 22.14 8.68 9.76 3.13 0
( P-E) (m iII ion cu. ft. ) -18.21 9.87 16.84 5.31 2.56
Q/( P-E) -o. 11 0.77 0.44 1 • 19 1. 47
(1) Slough 8A likely overtopped in late August.
SOURCE: Table reproduced from R & M (1985a)
d::>
I
N
U1
M15/12 7
Slough 9 Tributary
___{_!Jp_2e r ~i._.t__,e'-'1 __
F I ow, Q ( c f s )
(mi II ion cu. ft.)
Precipitation, P (inches)
(million cu. ft.)
Evaporation, E (inches)
(million cu. ft.)
P-E, Precipitation-Evaporation
Q/ ( P;-E)
Slough 9 Tributary
~__{_bQwe r Site)
f I OW', Q ( c fs)
(million cu. ft.)
Precipitation, P (inches)
(million cu. ft.)
Evaporation, E (inches)
(million cu. ft.)
( P-E), Precipitation-Eva po ration
Q/(P-E)
1. 21
3.23
5.25
17.81
2.21
7.50
10.31
0.31
Table 4.7
1984 MONTHLY WATER BALANCE
SLOUGH 9, TRIBUTARY 96
August
2.62
7.02
7.44
12.62
2.49
11.21
8.41
0.83
4.97
1 3. 31
7.44
25.24
2.49
8.113
16.81
0.79
(1) Affected by runoff from storm in late August.
SOURCE: Table reproduced from R & M (l985a)
September October
0.91 (1) 0.50
2.54 1. 34
2.11 0.87
3.58 1. 48
0.80
1. 35 0
2.19 1.48
1.16 ( 1 ) 0.91
0.30 0.07
0.78 0. 19
2. 11 0.87
7. 16 2.95
0.80 0
2. 71 0
4.45 2.95
0.18 0.06
R23/3 44
Site
Curry
Slough 8A
Slough 9 (Sherman)
Gold Cr'eek
TABLE 4.8
PRECIPITATION COEFFICIENTS
FOR TRANSFER OF RECORDED DATA
Continuous Station
Talkeetna Sherman
1.5 1.2
1 .3 1.07
1.2 1. 0
1.07 0.9
Devil Canyon
1.7
1.4
1 .3
To obtain precipitation estimate for above sites, multiply precipitation at
the continuous station by the appropriate multiplier.
SOURCE: Table reproduced from R & M (1985a)
4-26
M19/55 2
TABLE 4.9
FALLING HEAD TEST RESULTS
SLOUGH 9 -BOREHOLES
Depth of
Well I.D. Screen Date Transmi ss ivi ty
Borehole ( ftl ( ft l of Test Ft 2 LDa;y: Comments
9-1 o. 11~6 24-27 07/17/84 3.5 Good curve f t
9-1 0.146 24-27 07/31/84 5.4 Good curve f t, retest
9-1 o. 146 24-27 08/15/84 3.4 Good curve f t, retest
9-1 0.063 9.4~10.7 08/15/84 0.2 Good curve fit
9-1 0.063 9.4-10.7 08/29/84 0.2 Good curve fit, retest
9-2 0.146 7-10 08/13/84 50 Sparse data, poor curve fit
9-2 0.146 7-10 08/15/84 92 Sparse data, poor curve fit, retest
9-2 0.146 7-10 08/29/84 12 Poor curve fit, retest
9-2 0.063 10.7-12.1 08/15/84 No curve fit
9-2 0.063 10.7-12.1 08/25/84 2.6 Poo r c u rve f i t, retest
9-3 o. 146 37-40 07/31/84 3.4 Good curve fit
9-3 0.146 37-40 08/14/84 3.6 Retest
.1::> 9-3 0.146 37-40 08/14/84 2.4 Retest after surging we I I. Value
I probably affected by previous N
...J testing .
9-4 0.063 11.7-13.1 08/13/84 No useable data
9-4 0.063 11.7-13.1 08/13/84 No useable data, retest
Source: R&M (1985a)
M19/55 3
Daily
Precipitation(2)
Qate (inches)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
0.4
.51
.55
0.7
1. 35
. 58
. 31
.06
.64
.37
2. 19
1. 33
20% exceedance probabi I ity
Measured
Flow( 3)
(cfs)
5.9
5.6
5.2
4.8
4.8
4.4
4.1
3.8
4.4
4. 1
3.6
3.2
2.6
2.4
2.2
2.0
1.7
2.6
4.1
4.8
5.2
5.9
8.0
34
65
44
17
11
8.0
5.9
4.8
TABLE 4.10
ESTIMATED DAILY RUNOFF, SLOUGH 8A
HIGH RAINFALL PATTERN(l)
Estimated
Estimated Estimated With-Project
G rou ndwa te r Surface Groundwater
Flow(4) Runoff Flow(5)
(cfs) {cfsl (cfs)
5.1 0.8 1.6
4.7 0.9 1.6
4.3 0.9 1.6
4.2 0.6 1.6
4.5 0.3 1.6
4.4 0 1.6
4. 1 0 1.6
3.8 0 1.6
4.4 0 1. 6
4.1 0 '1. 6
3.6 0 1. 6
3.2 0 1. 6
2.6 0 1.6
2.4 0 1. 6
2.2 0 1. 6
2.0 0 1. 6
1. 7 0 1. 6
2.6 0 1.6
3.6 0.5 1. 6
3.8 1. 0 1.6
4.2 1. 0 1.6
4.0 1.9 1.6
3.8 4.2 1.6
5.0 29 1.6
6.9 58 1. 6
7.3 37 1. 6
6.3 11 1.6
4. 7 6.3 1. 6
3.7 4.3 1.6
3. 3 2.6 1.6
2.7 2.1 1.6
( 1 )
( 2) August 1984 precipitation. Data are from Talkeetna through day 21, from Sherman after day 21.
AI I data are adjusted to Slough 8A.
( 3)
( 4)
( 5)
August 1984
Q8 -0.67 + 0.00025 QGC
Assumes flow at Gold Creek is 9,000 cfs
Source: R&M (1985a)
Estimated
With-Project
Slough Flaw
(cfs)
2.4
2.5
2.5
2.2
1. 9
1.6
1.6
1.6
1. 6
1.6
1. 6
1. 6
1.6
1. 6
1.6
1. 6
1. 6
1. 6
2. 1
2.6
2.6
3.5
5.8
3. 1
6.0
34
13
7.9
5.9
4.2
3.7
M19/55 4
TABLE 4.11
ESTIMATED DAILY RUNOFF, SLOUGH 8A
MODERATE RAINFALL PATTERN(1)
Estimated
Estimated Estimated With-Project Estimated
Daily Measured Groundwater surface G roundwa te r With-Project
Precipitation(2) Flow(3) Flow(4) Runoff Flow(5) Slough Flow
Date ( i nches_L_ (cfs) {cfs) lcfs) (cfs) (cfs)
1 .08 7.7 5.7 2.0 1. 6 3.6
2 20.8 5.7 15. 1 1. 6 16.7
3 17.0 5.2 11.8 1.6 13.4
4 15. 3 4.6 10.7 1. 6 12.3
5 11.6 3.9 7.7 1.6 9.3
6 9.3 3. 3 6.0 1.6 9.6
7 7.7 3.0 4.7 1.6 6.3
8 0.7 6.4 2.8 3.6 1. 6 5.2
9 . 39 6.0 2.6 3.4 1.6 5.0
10 .07 5.3 2.5 2.8 •1. 6 4.4
11 4.6 2.4 2.2 1.6 3.8
12 4.0 2.2 1.8 1. 6 3.4
1 3 3.3 2. 1 1.2 1.6 2.8
14 .39 3.3 2.0 1.3 1. 6 2.9
15 .74 3.0 2.0 1. 0 1.6 2.6
.!:> 16 2.8 2.0 0.8 1. 6 2.4
I l7 2.4 1. 8 0.6 1.6 2.2 (\)
I!) 18 2.2 1. 7 0.5 1.6 2. 1
19 2. 1 1.6 0.5 1.6 2. 1
20 2.2 1.7 0.5 1. 6 2.1
21 .04 2.8 2.0 0.8 1.6 2.4
22 .30 3.8 2.7 1 . 1 1.6 2.7
23 . 13 3.5 3.5 0 1.6 l . 6
24 2.1 2. l 0 1. 6 1.6
25 1. 6 1.6 0 1.6 1.6
26 1. 5 1.5 0 1.6 1.6
27 3.8 1.7 2.1 1.6 3.7
28 .21 19.8 1.6 18.2 1. 6 19.8
29 1. 46 25.3 1.7 23.6 1. 6 25.2
30 . 42 19.8 2.2 17.6 1.6 19.2
( 1 ) 61% exceedance probability,
( 2) September 1983 Talkeetna precipitation adjusted to Slough 8A.
( 3) September 1983
( 4) Q8 = -0.67 + 0.00025 QGC
( 5) Assumes flow at Gold creek is 9,000 cfs.
Source: R&M (1985a)
M19/55 5
TABLE 4.12
ESTIMATED DAILY RUNOFF, SLOUGH 8A
LOW RAINFALL PATTERN(1)
Estimated
Estimated Estimated With-Project Estimated
Daily Measured Groundwater surface G roundwa te r With-Project
Precipitation(2) Flow(3) Flow(4) Runoff Flow(5) Slough Flow
Date ( inchesl__ {cfs) (cfs) (cfs) {cfs) (cfs)
1 4. 1 2.5 1. 6 1. 6 3.2
2 3.2 2.3 0.9 1. 6 2.5
3 2.6 2. 1 0.5 1.6 2. 1
5 2.0 1.9 0. 1 1.6 1.7
6 1. 7 1. 7 0 1. 6 1.6
7 .11 1.5 1. 5 0 1. 6 1.6
8 1. 4 1.4 0 1.6 1. 6
9 1.2 1.2 0 1.6 1.6
10 1.2 1. 2 0 1.6 1. 6
11 1.0 1. 0 0 '1. 6 1.6
12 .24 1.0 1. 0 0 1.6 1.6
13 .18 1. 0 1.0 0 1.6 1. 6
14 0.9 0.9 0 1.6 1.6
15 .02 0.8 0.8 0 1. 6 1. 6
16 . .12 0.9 0.9 0 1. 6 1.6
.1::> 17 .04 0.9 0.9 0 1. 6 1. 6
I 18 . 61 1.2 1. 2 0 1.6 1.6 w
0 19 .65 1. 7 1.7 0 1.6 1.6
20 .05 2.2 1.9 0.3 1.6 1.9
21 2.2 2.2 0 1. 6 1.6
22 2.2 1. 9 0.3 1. 6 1.9
23 2.2 1. 6 0.6 1.6 2. 1
24 2.0 1.4 0.6 1.6 2.2
25 . 13 2.0 1.3 0.7 1.6 2.3
26 1. 7 1. 2 0.5 1.6 2.1
27 1. 5 1.2 0.3 1.6 1.9
28 1.5 1.1 0.4 1. 6 2.0
29 .02 1. 4 1 . 1 0.3 1.6 1. 9
30 .05 1. 4 1.2 0.2 1.6 1.8
(1) 93% exceedance probabi I ity
( 2) September 1984 Sherman percipitation, adjusted to Slough 8A
( 3) September 1984
( 4) Q8 = -0.67 + 0.00025 QGC
( 5) Assumes flow at Gold Creek is 9,000 cfs
Source: R&M (1985a)
ol:>.
I w
.......
M19/55 6
Date
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
Daily
Precipitation(2)
(inches}
(1) 61% exceedance probabi I ity
Measured
F I ow( 3)
(CfS)
8.3
7.8
7. 1
6.8
6.4
6. 1
5.7
5.5
5.3
5.5
5.3
5.3
5. 1
5. 1
5.5
5.7
6.1
6.6
7.3
6. 1
5.9
5.7
5.7
8. 1
14.2
TABLE 4.13
ESTIMATED DAILY RUNOFF, SLOUGH 9
MODERATE RAINFALL PATTERN(1)
Estimated
G roundwa te r
F I ow( 4)
(CfS)
5.6
5.2
4.7
4.5
4.3
4. 1
3.9
3.7
3.6
3.5
3.5
3.3
3.0
2.9
3.0
3.5
4.7
6.2
5.3
4. 1
3.5
3. 1
2.9
3.0
3.9
Estimated
Surface
Runoff
(cfsl
2.7
2.6
2.4
2.3
2.1
2.0
1.8
1.8
1. 7
2.0
1.8
2.0
1.9
2.2
2.5
2.2
1. 4
0.4
2.0
2.0
2. 1
2.6
2.8
5.1
10.3
(2) September 1984 Sherman percipitation,
(3) September 1984
adjusted to Slough 8A
(4) Q8 = -0.67 + 0.00025 QGC
(5) Assumes flow at Gold creek is 9,000 cfs
Source: R&M (1985a)
Estimated
With-Project
Groundwater
F I ow( 5)
(cfsl
2.9
2.9
3.9
2.9
'2.9
2.9
2.9
2.9
2.9
2.9
2.9
2.9
2.9
2.9
2.9
2.9
2.9
2.9
2.9
2.9
2.9
2.9
2.9
2.9
2.9
Estimated
With-Project
Slough Flow
(cfs)
5.6
5.5
5.3
5.2
5.0
4.9
4.7
4.7
4.6
4.9
4.7
4.9
4.8
5.1
5.4
5.1
4.3
3.3
4.4
4.9
5.3
5.5
5.7
8.0
13.2
M19/55 7
TABLE 4.14
ESTIMATED DAILY RUNOFF, SLOUGH 9
LOW RAINFALL PATTERN(1)
Estimated
Estimated Estimated With-Project Estimated
Daily Measured G roundwa te r Surface G roundwa te r With-Project
Precipitation(2) Flow(3) Flow(4) Runoff Flow(5) Slough Flow
Date (inches} {cfs} (cfsl (cfsl (cfsl (cfs)
1
2
3 11 3.7 7.3 2.9 10.2
4 9.5 3.6 5.9 2.9 8.8
5 7. 1 3.4 3.7 2.9 6.6
6 5.6 3.4 2.2 2.9 5. 1
7 .10 4.8 3.5 1 • 3 2.9 4.2
8 4.2 3.6 0.6 2.9 3.5
9 3.6 3.5 0. 1 2.9 3.0
10 3.2 3.2 0 2.9 2.9
11 3.8 3.0 0 2.9 2.9
12 .22 2.4 2.9 0 2.9 2.9
13 .17 2.4 2.9 0 2.9 2.9
14 2. 1 2.8 0 2.9 2.9
15 .02 2.1 2.7 0 2.9 2.9
"" 16 .11 2. 1 2.6 0 2.9 2.9 I 17 .04 2. 1 25 0 2.9 2.9 w
N 18 .57 2.7 2.6 0. 1 2.9 3.0
19 .61 3.2 3.0 0.2 2.9 3. 1
20 .05 3.6 3.4 0.2 2.9 3. 1
21 4.2 3.8 0.4 2.9 3. 3
22 3.6 3.4 0.2 2.9 3. 1
23 3.2 2.9 0.3 2.9 3.2
24 2.8 2.6 0.2 2.9 3. 1
25 .12 3. 3 2.5 0.8 2.9 3.7
26 3. 3 2.4 0.9 2.9 3.8
27 2.8 2.3 0.5 2.9 3.4
28 2.4 2.2 0.2 2.9 3. 1
29 .02 2.4 2.2 0.2 2.9 3. 1
30 0.5 2. 1 2.3 0 2.9 2.9 "
( 1 ) 93% exceedance probabi I ity
( 2) September 1984 Sherman percipitation, adjusted to Slough 8A
( 3 ) September 1984
(4) Q8 -0.67 + 0.00025 QGC
( 5) Assumes flow at Gold Creek is 9,000 cfs
Source: R&M ( 1985a l
J
j
-J
J
J
f]
SOURCE: MODIFIED FROM TRIHEY (11)
Direction
of
A ow
-..
Sherman Creek
Indian River
\ Talkeetna: 26 River Miles
LEGEND:
Devil Canyon: 7 River Miles
Direction
of
Flow
11-1
0
I
1
I
MILES
(APPROX. SCALE)
• STAGE. RECORDER
SEEPAGE METER
FIGURE 4. I APPROXIMATE LOCATIONS OF DATA COLLECTION POINTS -
STAGE RECORDERS AND SEEPAGE METERS.
{Figure reproduced.
from APA {l984b) )
4-33
Source: ADF & G(l983b)
• I .....
Figure 4.2 Slough 8A upwelling/seepage, 1982.
/
.SLOUGH SA
UPWELLING/ SEEPAGE
0 2000
fEET
IAI'f>ROII.$ULf)
• UPWElLING
.t>.
I w
V1
• • •
Source: ADF & G(l983b)
Figure 4.3 Slough 8A ice-free areas~ winter 1982-83 .
• • • • • • • • • •
SLOUGH 8A
ICE-FREE AREAS
0 1000
.NOIJIIU'Ib•r 18,t98t
Of•iwv•r 25,f90'
• --• -
LJ LJ L.i L_l L I I •
~~ SUSITNA RIVER--
Source: ADF & G(l983b)
Figure 4.4 Slough 9 upwelling/seepage, 1982.
SLOUGH 9
UPWELUNG/SEEPAGE
0 1000
ff£T
(APPRO:t SCAU)
• -UPWElLING
I I • •
--.
----SUS/ TNA
Source: ADF & G(1983b)
RIVER--
SLOUGH 9
ICE-FREE AREAS
0 1000
( Af'PROX ICAl(j
0Nov•mbtr t8.191C:
0Ftbtu<H1 23,UUn
Figure 4.5 Slough 9 ice-free areas, winter 1982-83.
-• -• • • • • • •• . ----
-1:>.
I w
CXl
I
I
Source: ADF & G(1983b)
Figure 4.6 Slough 11 upwelling/seepage, 1982.
---• -II II
e 156
Ill
SLOUGH II
UPWELLING/ SEEPAGE
0 1000
FEET
• UPWELLING
-II II -II -Ill
5 I rNA stJ
Source: ADF & G(l983b)
... '
Figure 4.7 Slough 11 ice-free areas, winter 1982-83.
. I -! I ...
SLOUGH II
ICE-FREE AREAS
(I 1000
FEET
(APPROX. IC:AU: t
ONovtmNr 18,198Z
[1)Febtuor1 23,1983
""' I
""' 0
SLOUGH Zl COliPl£)(
Source: ADF & G(l983b)
Figure 4.8 Slough 21 upwelling/seepage, 1982 .
. ~.~}11 ., 111 .•.• • "11 II 1111
e•••
lrll
SLOUGH 21
UPWELLING/ SEEPAGE
0
II
f[[T
fAPf'fi:OI. IC&\.l)
•·UPWELLING
II
1000
II II II' II'
/
SLOUGH ll: I COWPL£)(
-sustrNA
Source: ADF & G{l983b)
Figure 4.9 Slough 21 ice-free areas, winter 1982-83.
SLOUGH 21
ICE-FREE AREAS
0 1000
nn
(.u>PROM JUL.&)
0 Non~~nb•r fl.t982
0 Febtli!Cf(J 23,198-'
Preceeding
Pr·ecipitation
Date
9 14 19.0
9-15 19.8
9-1 G 11.2
9-17 9.4
9-18 10.0
9-19 18.6
9-20 6.0
0 cc ---
8.9 10,200
12.2 28,200
8.6 32,500
5.4 32,000
7.9 27,500
7.7 2-1, 100
7.5 24,000
FIG. 4.10
GROUNDWATER COr.JTOUnS
SUS.I'fNA RIVER AT SLOUGti SA
SCALE: I"= 1000'
---------·------·~.--------'----
Legend
• observation well
11 600 11 groundwater elevation
Date: 9-20-82
QGC: 24,000
Source: R & M (1982g)
Climatic
Precceding
Precipitation
Date
9-29 7.4
9-30 8.4
10-1
10-2
10-3
10-4
10-5
0 Gc
6.0 12,400
4.9 12,500
2.2 12,400
3.3 11,700
1.8 11,000
1.3 10,500
0. 1 9,800
FIG. 4.11
Legend
• observation well
"600" groundwater elevation
Dale: 10-5-82
QGC: 8,300
Source: R & M (l982g)
GROUNDWATER CONTOURS
SUSrrr·JA RIVER AT SLOUGU SA
SCALE: 1"= 1000'
..;.--.);~
. . . . . .
,
4-20
4-21
4-22
4-23
4-24
4-25
4-26
...
',:•. ·.··:.·
·. .;
·. ·!·:.:·J,.·:
:>; .
...... :·:
.; . _:-::=·-:·.; . ..-;,(;':::·:\: .... ~:-·
7.0 1. 7 Ice
0.0 1.5 Ice
0.0 1.2 Ice
0.0 0.1 Ice
1. 6 1.1 Ice
0.0 4.4 Ice
0.0 1.0 Ice
FIG. 4.12
cover
cover
cover
cover
cover
cover * cover
Date:
QGC:
Precip. and temp. data from .Devil Canyon
Climate Stations.
observation well
groundwater elevation
4-26-82
Ice Cover
Source: R & M (1982g)
GROUNDWATEH CONTOURS
SUSI'TNA RIVER AI SLOUGH SA
SCALE: 1"= 1000'
--------··-·---· .. -·-·-·-·--~-----·--~-----------·---------------
Climatic Summary for
. Preceeding 7-Day Period
Precipitation
Date (mm)
Temperature
(OC)
6-25
6-26
6-27
6-28
6-29
6-30
7-1
2.0
0.0
0.0
0.8
0.0
9.2
1.6
16.5
15.9
14.9
12.7
13.0
13.6
10.1
FIG 4.13
25,000
27,000
24,000
25,000
'·
GROUNDWATER CONTOURS
SUSITNA RIVER AT SLOUGH 9
SCALE: I II~ 1000'
Legend
•
11 600 11
observation well
groundwater elevation
Date: 7-1-82
QGC: 25,000
Source: R & M (l982g)
·----.. ·-·--....... --,·---·--··---,.---,..· .. ~---·-·----· ..... -... --............. ,._._. ..... _.._,_ ..... _ .. ________ _,... ____ _
Precipitation
Date QG
-
10-1 2.2 12,400
10-2 3.3 111700
10-3 2.8 11,000
10-4 1. 3 10,500
10-5 0. 1 9,800
10-6 2.3 8,960
10-7 0.5 8,480
FIG. 4.14
·---------------·-·------·---..
GROUNDWATER CONTOURS
SUSITNA RIVER AT SLOUGH 9
s c A L E : 1" = 1000 I
Legend
ll
11 600 11
Date:
Oc;r:.
Source:
observation well
groundwater elevation
10-7-82
8,480
R & M (l982g)
: ·---.. ·:.;.'>;
Date: 12-22-82
Note: Winter flow, Ice cover·
on mainstem
FIG. 4.15
{:::,::; ~-,-.~ : .. ;·:::·,'.: :-.:.:::: ·r.: : ... , ;. ~; t.: ,,,. 1. ~ ...... ~·:-:r;:::•.'·' ·: ·~<:;; ·.·~·
. ; : :·:::-: :·:-: :. ·.'•; .·.,·,·::-: •.::;-;::: ::.::·::. !:i:·>=::,: ==~ ~:,:: r: . < .608.16
606.50 ~
• G}cz,
GROUNDWATER CONTOURS
SUSITNA RIVER AT SLOUGH 9
•
11 600"
observation well
g;oundwater elevation
Source: R & M {1982g)
1982
AUG SEP OCT NOV DEC llUL J4--------~------~------~------~------~------~
J
-.10
..1
J
..1
-.J
]
LEGEND
0 MAINSTEM LRX 29·, SURFACE ~-lATER
A SLOUGH SA MOUTH, INTRAGRAVEL
• SLOUGH 8A.UPPER, INTRAGRAVEL
SOURCE: ADF&G (2}
JUL AUG SEF OCT NOV DEC
FIGURE 4.16 SLOUGR8A WATER TEMPERATURES, 1982. (Figure reproduced
fran APA (1984b) .)
4-48
JAl' FEB HAR APR MAY
14 -
JA:; FEB cL~R APR ~11\Y
SOURCES; ;\lJ[·\';\: ( J J as presented in AllF&i; PIWV I S!O~/,\L 198) DATA
1983
JllN JUL AUG
JUN JUL AUG
APA (1984b)
SEP
SEP
OCT NOV DEC
~
0 MAINSTEM LRX 29, SURFACE \.JATER
~ SLOUGH 8A UPPER, SURFACE WATER
e SLOUGH 8A UPPER, INTRAGRAVEL
OC:T NOV DF.C:
FIGURE 4 .17 SltlUCll 8,\ ~:.\TFII
Tr::JPt-:[~.XJTi, l:S, 1 ~-·0)
-0
0
w
0:
:::::)
i-
<(
a::
w
a_
~ ~ I
V1 w
0 i-
0: w
i-
<(
~
15
14
13
12
II
9
8
7-
6-
5-
4-
3-
2-
1-
0-
-1 -
-2-
-3-
-4-Source: ADF & G(l985)
MEAN DAILY SURFACE WAJER TfMPERATUR~
-----UPPER SLOUGH 8A ·SITE 3 ( RM 126.6)
•·•••••••• lOWER SLOUGH 8A ·SITE 3 (RM 125.6)
MEAN DAILY INTRAGRAVEL WATER TEMPERATURE
UPPER SLOUGH 8A·SITE 3 (RM 126.6)
_ .. _ •• _ LOWER SLOUGH 8A ·SITE 3 ( RM 125.6)
Figure 4.18 Mean daily surface and intragravel water temperatures recorded
at Lower Slough BA -Site 3 (RM 125.6) and Upper Slough BA -
Site 3 (RM 126.6) during the 1983-84 winter season.
1983
JAN FEB MAR APR MAY JUN
14
12
10
0
sou;,cEs: ADFI.G < J) J as presented in APA (l984b)
.\[)F&G PROVISIONAL 1983 DATA
JUL AUG SEP OCT NOV DEC
0 MAIN STEM LRX 29, SUHFACE WATf.R
0 SLOUGH 9, SURFACE WATEH
e SLOUGH 9, It\TRAGRA VEL
FIGURE 4 .19 SLOUGII 9
HATER TE~fl'ERI 1 ').S 3
15
13
12
-II-
0 10-0
9-
UJ
Q:: 8-
::::>
1-7-
<l
Q:: 6-
UJ 5-0..
~ 4-UJ
1-3-
Q:: 2-
.1:>. UJ I 1-1-U1
N <l
:J: 0-
-I-
-2-
-3-
-4-
. . . ~. I •
II II
.,~·: . ,
I
I
I • I
I
I
~
.. ..
" II
I I -· : .. . '• I II
Source: ADf & G(l985)
I
SEP
I
OCT
MEAN DAILY SURFACE WATER JCMP(RATURE
-----SLOUGH 9-SITE 3 (Rt.f 128.61
MEAN DAILY IHTRAGRAVEL WATER TEMPERATURE
--SLOUGH 9-SITE 3 (RM 128.61
! .. •• •• ••• ' • . .
• t I " .. ,.,., . '.: .., ' _: v '. :' • .. ,. ,., ' . . ,; .
l·.·~·t·:~
;., .: : ~ , ,
--
Figure 4.20 Mean daily surface and intragravel water temperatures recorded
at Slough 9 -Site 3 (RM 128.6) during the 1983-84 winter season .
••••••••••• •• •• • •••
ol:>
I
14
12
10
lJ1 8 w
0
JAN FEB MAR APR
~-------------A~··
.'\:'v"-"-"'o-------'"""'
.I i\~1 n:11 ~L\R APR
Sllti\CL~i: 1\ili·~.c (I)
DATA]
as
t\IJFSG ~'!{ft\' t;; l 0:4AL 1983 fJi\l'A
1(1,'·1 Ct >:;sur. r.\NT~ I'IWVTS!ONM. !983
1983
MAY JUN JUL AUG SEP OCT NOV DEC
LEGEND
0 MAINSTEM LRX 29, SURFACE WATER
e BOREHOLE 9-lA
0 BOREHOLE 9-3
t:. BOREHOLE 9-5
MAY JUN JUL AUG SEP OCT DEC
presented in APA (1984b) FIGURE 4.21 S\ ili;l;H \)
L',\ I'F!\ ! L'ii'U:_\ J t,J~I:S. l lJh)
I
!
I I
1983
I JAN FEB MAR APR MAY JUN JUL AUG SEP OCT
14
I
I LEGEND
12 L;. MAINSTEM AT SLOUGH 11, SURFACE FP,!ER
I 0 SLOUGH 11, SURFACE WATER
I 10 c SLOUGH 11, INTRA GRAVEL
• I! 8
.z:,.
I
oc
6
l I
I
4
I ~~
I
I
I 0 c;..:, ~
I JA!< FEB MAR APR Hl.Y JUN JUL AUG SEP OCT
I SOURCES: A!JF&G ( 3 ) ] as presented in APA (l984b) ADF&G PROVISIONAL !983 DATA
FIGURI::; 4.22 SLOL:CH 11 I h'A TER 1 E.\lP EK \ TL! ES • J%J
. -·-' :,i
14
12
t 10
(J1
(J1
8
6
4
z
•,,
JAN FEB
L _______ l __
JAN
SOUR.CES:
rr:u
\Ill-;,(: ( ) )
PI:II\'IS!Oc:.\L
MAR APR MAY JUN
HAR APR MAY JUN
1983 DATA1 as presented in APA (1984b)
1983
JUL AUG SEP
JUL AUG SEP
OCT NOV
LEGEND
0 MAINSTEM LRX 57, INTRAGRAVEL
• SLOUGH 21 UPPER, SURFACE WATER
1::. SLOUGH 21 UPPER, INTRAGRAVEL
ilCT
FIGURE 4.23
DEC
SLllUCII 2 l
TE>1PriP.TURES t 1983
~tAR
;\iJFSG ( 3 ) J
1\iH&C PI<UV l S [ON,\L 1983 DATA
APR HAY JUN
l.ll APA ( l984b) as presented .
JUL
NOV PEC
• MAINSTEH LRX 57 • SURFACE \!ATCR
0 MAlNSTEM LRX 57 • lNTRAGRAVEL
CJ SLOUGH 21 MOU TH, SURFACE \'ATER
0 SLOUGH 21 MOUTH • H;TRAGRAVEL
AU;G----~----~;-__ _l ___________ _jl
~ SEP OCT NOV OEC
FIGURE 4 .24
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FIGURE 4.25 SEEPAGE RATE VS. MAINSTEM DISCHARGE, SEEPAGE METER 8-1.
Source: APA (1984b)
4-57
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Source: APA (19B4b)
4-58
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4-64
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J===== Source:APA (1984b)
-_I 4-65
,...,....--
1
-~-o~-+3+o:::::: ......... H1H5:::::-_:-.:::::+F+-IHGriUR E 4. 3 4 RESPONSE 0 F MAINS T lj: '-' _AND S L 0 UGH J~ ~ ....,... ,., ~~0~1
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DISCHARGE-S--TOSEPTEMBER 1983 -STORM _____ -·
-mf 0 -~
---
-
-
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R24/3 63
5.0 SUMMARY
Construction and operation of the Susitna Hydroelectric Project will affect
several of the physical processes which produce and regulate the aquatic
habitats in the Middle Susitna River. Changes will occur in the river
sedimentation processes, in the channel stability, and in the groundwater
upwelling processes. The specific project effects are reviewed below, in
relation to their effect on habitat.
The river sedimentation processes will change from strictly river-type to
combined lake-type and river-type. A large proportion of the sediment
reaching the impoundment zone from upstream will be trapped in the
reservoirs, with only the fine suspended particles (smaller than about 3-4
microns) passing through to the river downstream. This will have some
direct effects on the stability of the river channel below the project.
The reservoir releases will be transporting less sediment than comparable
flows under natural conditions, and will consequently have capacity to
transport additional sediment. The flows will thus have a tendency to pick
up finer particles from the riverbed. However, with-project flows will also
be smaller than naturally-occurring summer flowsJ with reduced ability to
transport sediment. The net result of project construction and operation
is that the main stem in the Middle Reach is expected to degrade from zero
to 1 foot. The median size of particles in the mainstem is likely to
increase, making the channel more stable. The beds of sloughs and side
channels may degrade from zero to 0.5 foot.
Local aggradation in the mainstem, primarily due to bifurcation of the
streamflow between the mainstem and other channels, is not expected to be
significant. The side channels and sloughs will still require larger
mainstem flows to overtop them, on the order of 8,000 cfs higher than
naturally, due to degradation of the main river. Intrusion of fine
sediments into the gravel beds of sloughs and side channels may occur at
pools and backwater areas, potenially causing problems for spawning and
5-1
R24/3 64
incubation. As a mitigative measure, the project may release larger flows
to flush out the deposited fine sediments, or "Gravel Gerties" may be
used. Jack Long, Sherman, and Deadhorse Creeks, three tributaries used
by salmon1 are likely to aggrade, possibly restricting access.
Project effects on slough hydrology relate to likely changes in flow levels
and water temperatures. There is considerable variation between sloughs
as to the nature of their dependence on the mainstem. Sloughs similar to
Slough 11, whose flows are strongly related to the main stem water level,
are likely to experience a decrease in groundwater upwelling under
with project conditions. These sloughs may also have problems with fish
access or with environmental conditions for incubating embryos, including
freezing, shortage of oxygen, or change in development time. Mitigative
measures may be required in such cases. Other sloughs which derive
significant inflow from upland sources or from local surface flow will be
affected to a lesser extent. Flow peaks from the local sources will still
allow access under most conditions.
5-2
R24/3 65
6.0 REFERENCES
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Hydrogeology Report.
Anchorage, Alaska.
Susitna
Prepared
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Anchorage, Alaska.
6-1
R24/3 66
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6-2
R24/3 67
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6-3
R24/3 68
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6-4
R24/3 69
concentration. Draft report. Prepared for Alaska Power Authority.
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6-6
R24/3 71
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6-7
Prepared for Acres
Susitna Hydroelectric
R24/3 72
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R24/3 73
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