HomeMy WebLinkAboutSUS10032USING TIME SERIES STREAMFLOW DATA
TO DETERMINE PROJECT EFFECTS
ON PHYSICAL HABITAT FOR SPAWNING AND
INCUBATING PINK SALMONl
E. Woody Trihey2
Abstract.--The incremental method of instream flow
assessment was applied to identify effects of a proposed
hydroelectric project on pink salmon in the Terror River,
Kodiak, Alaska. Time series streamflow data are used to
compare spawning and incubation conditions for 27 years of
simulated pre-and postproject streamflows. This paper
demonstrates that an evaluation of project effects based
only on a comparison of long-term average monthly stream-
flows overlooks the dynamic nature of riverine habitat and
is likely to have lead the analysts to erroneous conclusions
regarding effects of the proposed project streamflows on
spawning and incubating pink salmon.
INTRODUCTION
Traditionally, instream flow assessments have
arrived at a single valued streamflow requirement
to protect the fishery resource --"a minimum
flow." Such an instream flow recommendation,
often determined solely from cursory review of
streamflow records, overlooks the seasonal and
annual variability of instream habitat conditions
and provides limited opportunity for negotiation.
Furthermore, such an approach promotes the mis-
taken assumption that only streamflows below this
"minimum" are detrimental to instream use and/or
resources.
As a result of the inflexibility and
fallacies associated with such traditional
approaches, a new methodology is emerging, capable
of displaying the dynamic response of instream
habitat conditions to seasonal and annual changes
in streamflow, yet also compatible with the deci-
sion-making processes of water planners and
managers. This methodology utilizes time series
streamflow data in association with physical
habitat simulation modeling. The U.S. Fish and
Wildlife Service 1 s Cooperative In stream Flow
Service Group (IFG) , Fort Collins, Colorado was
instrumental in pioneering and promoting the
Incremental Methodology (Bovee and Milhous 1978,
Stalnaker 1978, Trihey 1979).
lpaper presented at the Western Division of
the American Fisheries Society Symposium on the
Acquisition and Utilization of Aquatic Habitat
Inventory Information, Portland, Oregon, October
28-30, 1981.
232
The incremental methodology is based on the
theory that the availability and relative value of
riverine habitat conditions can be estimated by
evaluating the behavioral response of a species/
life stage to such streamflow-dependent variables
as depth, velocity, water temperature, and channel
structure. Thus, this methodology is intended for
use in situations where the streamflow regime and
channel structure are the principal factors
controlling the fishery resource and where field
conditions are compatible with the underpinning
theories and assumptions of the methodology. This
methodology is particularly well suited for
displaying effects of proposed water developments
or streamflow alterations on riverine fish
habitat.
The primary purpose for using hydraulic
simulation modeling is to make the most efficient
use of limited field data to describe the
occurrence of depths and velocities with respect
to stream temperature and substrate conditions
over a broad range of unobserved streamflows. The
availability and quality of fish habitat are
reflected as changes in a habitat ·index value
called weighted usable area (WUA). Calculation of
WUA does not totally describe the actual quantity
or quality of available fish habitat. It does,
however, provide a structured analytical approach
for using streamflow-dependent ·variables to
2E. Woody Trihey, Hydraulic Engineer, Arctic
Environmental Information and Data Center, Uni-
versity of Alaska, Anchorage.
describe selected physical aspects of fish habitat
in riverine environments. Thus, a change in the
WUA index can generally be accepted as a good
indicator of the effect a change in streamflow
would have on the availability of riverine habitat
for the species/life stage being evaluated.
This modeling process, utilizing the incre-
mental method, was applied by the Arctic Environ-
mental Information and Data Center (AEIDC) to
quantify effects of the proposed Terror Lake
Hydroelectric Project on existing fishery
resources in the Terror and Kizhuyak Rivers,
Kodiak Island, Alaska (Wilson, et al. 1981). For
the purposes of this paper, the discussion will be
limited to the "Terror Gage" study reach.
This 560-ft study reach was established to
characterize project effects on pink salmon
spawning habitat in the lower Terror River.
Transects 1 through 3 crossed a relatively deep,
high-velocity run, and transects 4 through 7 were
placed across an upstream pool area. Depth,
velocity, and substrate measurements were made
approximately every 2 feet along each transect at
three streamflow levels (94, 251, and 425 cfs).
Both right-and left-bank water surface elevations
were surveyed at each transect for each of the
three streamflows. Water surface elevation and
depth-velocity data were used to calibrate
hydraulic models, which were then used to predict
depth and velocity values for discharges between
50 and 120 cfs.
A comparison between total surface area and
weighted usable area for pink salmon spawning
habitat was developed for a range of streamflows
from 50 to 1200 cfs (Figure 1). This plot
90000 c--------------------=-~·
80000
70000
~ 60000
~
; 50000
8 ... 40000
~
4
~ 30000
.20000
1()()00
(
I
/
/
/
/
--/
-----\_
/ ·rotalsurfac•araa
Weighted ~~blearea
~~~~~~~~~~~~~~~~~.LL-~
100 200 300 400 500 600 700 800 900 1000 1100 1200
Streamflow leis)
Figure 1.--Total surface area and weighted usable
area as a function of streamflow at the
Terror Gage study site.
233
illustrates the reach specific response of total
surface area and WUA to incremental changes in
streamflow. These curves were used throughout the
remainder of the analysis as the primary
description of the availability of pink salmon
spawning habitat in the lower Terror River as a
function of streamflow.
A comparison was made between WUA indices for
simulated long-term average monthly pre-and
postproject streamflows for the pink salmon
spawning period (Table 1). From late July through
early September, streamflows would be decreased by
approximately 30%. WUA for spawning pink salmon
would increase approximately 7% in July while
decreasing 3 to 4% during August and September.
Overall this represents less than a 5% net change
in WUA for the pink salmon spawning period.
Table 1. --Comparison of long-term average monthly
pre-and postproject streamflowE and corre-
sponding \.JUA indices throughout the pink
salmon spawning period.
Honth
July
August
September
Average
Preproject
cfs WUA
579
374
375
23,280
24,610
24,610
24,610
Postproject
cfs \WA
346
261
245
24,800
23,850
23,530
24,060
The project sponsor proposed to stabilize
Terror River winter flows near 60 cfs. Thus, the
simulated long-term average monthly December
streamflow would decrease from 80 to 66 cfs, while
Harch flows would increase from 50 to 62 cfs.
Changes of this magnitude imply that the proposed
postproj ect streamflows would have a negligible
effect on altering preproject levels of redd
dewatering and the associated overwinter survival
of incubating eggs and alevins.
Solely by comparing simulated long-term
average monthly streamflows and corresponding
WUA indices, one would conclude that project
effects on the availability of spawning habitat
for adult pink salmon and the dewatering of
incubating eggs and alevins are inconsequential.
However, extremes in seasonal and annual stream-
flow conditions resulting from regional weather
patterns cause notable fluctuations in Terror
River fish stocks. Fall storms cause high
streamflows, which scour eggs and alevins from
streambed gravels. Low streamflows during
August and September concentrate spawners into
confined areas and cause redd superimposition.
Low streamflows during winter months often
dewater redds and contribute to the freezing of
exposed streambed gravels and the developing
embryos buried therein.
Therefore, a more rigorous examination would
be required of project effects on the annual and
seasonal variability of streamflow and the
associated WUA indices before project effects on
spawning pink salmon could be objectively dis-
cussed with any degree of confidence.
STREAMFLOW ANALYSIS
A flow frequency analysis was undertaken to
determine the validity of using average monthly
streamflow values as a basis for evaluating
project effects on fish habitat. These analyses
were based on 6 years of average daily streamflow
record at the Terror Lake outlet gage (USGS No.
15295600) and 4 years of average daily data at the
Terror River gage (USGS No. 15295700).
The 1-, 7-and 30-day high and low flows were
determined for each year of record. The ratios of
the 1-day to 30-day and 7-day to 30-day flows were
also determined to provide an indication of how
well monthly streamflow values might represent
extremes in seasonal and annual habitat con-
ditions. It was determined that the 30-day low
flow closely approximates the average daily low
flow (Table 2) while the high-flow statistics
indicate that peak daily flows are often two to
three times greater than the 30-day high flow
(Table 3).
Low-flow statistics (Table 2) indicate that
the 1-, 7-, and 30-day low flows are relatively
constant. Thus, a reasonably accurate evaluation
of project effects on overwintering habitat would
result from a comparison of 30-day (monthly)
streamflow values. A comparison of 7-day pre-and
postproject streamflow values would provide a
better portrayal of project effects on the natural
stress to which incubating eggs and alevins are
being subjected. However, in the case of the
Terror River project, insufficient data were
available on 7-day pre-or postproject streamflows
to justify using anything shorter than a 30-day
time step in the analysis, particularly when it
was evident that 7-day low flows of record did not
differ appreciably from the monthly values.
Midwinter streamflow records were also
reviewed to determine months that are most criti-
cal to incubation success. Low streamflows occur
between January and March but are most prevalent
during late February and early March. During this
4-to 5-week period, the mean monthly streamflow
was found to be a reasonable indicator of natur-
Table 2.--Low-flow statistics for the
Terror River drainage.
Water Annual low flow in
Year 1-DAY 7-DAY
1963 18. 19.3
1964 11. 11.7
1965 10. 10.1
1966 8. 8.
1967 9. 9.
1968 14. 14.6
MEAN 11.7 12. 1
Water Annual low flow in
Year 1-DAY 7-DAY
1965 28.0 29.1
1966 23.0 23.0
1967 19.0 20.4
1968 38.0 40.3
MEAN 25.2 28.2
TERROR LAKE OUTLET
USGS Gage 15295600
cfs
30-DAY Min. Month
for Year
23.4 23.4
12.4 12.5
11.1 11.3
9. 1 9.2
11.5 11.7
19.5 26.2
14.5 15.7
TERROR RIVER GAGE
USGS Gage 15295700
cfs
30-DAY Min. Month
for Year
32.5 33.6
26.9 27.4
26.6 27.1
54.8 75.7
35.2 41.0
234
Ratio
1-DAY
30-DAY
.77
.89
.90
.88
.78
.72
.81
Ratio
1-DAY
30-DAY
.86
.86
.71
.69
.72
7-DAY
30-DAY
.82
.94
.91
.88
.78
.75
.83
7-DAY
30-DAY
.90
.86
.77
.74
.80
Table 3.--High-flow statistics for the
Terror River drainage.
TERROR LAKE OUTLET
USGS Gage 15295600
Water Annual high flow in cfs Ratio
Year 1-DAY 7-DAY 30-DAY Max. Month 1-DAY 7-DAY
for Year 30-DAY 30-DAY
1963 3250 1168 452 270 7.2 2.6
1964 904 554 454 449 2.0 1.2
1965 1490 681 389 362 3.8 1.8
1966 1800 693 564 533 3.2 1.2
1967 1130 587 378 349 3.0 1.6
1968 1560 666 418 371 3.7 1.6
MEAN 1689 725 442 389 3.8 1.6
TERROR RIVER GAGE
USGS Gage 15295700
Water Annual high flow in cfs
Year 1-DAY 7-DAY 30-DAY
1965 1490 806 692
1966 2600 1416 1090
1967 1780 1232 708
1968 2000 968 797
MEAN 1968 1105 822
ally occurring low-flow conditions in two of three
winters for which continuous streamflow data were
available. However, simulated preproject monthly
midwinter flows were found to differ markedly from
observed monthly streamflows. It was also deter-
mined that naturally occurring monthly low flows
throughout the 3-year period of record were
considerably less than the simulated long-term
average monthly streamflows. Therefore, it is
reasonable to assume that incubating eggs and
alevins are subjected to a greater amount of
dewatering and subsequent desiccation and freezing
than the simulated long-term average monthly
preproject streamflows indicate.
High-flow statistics (Table 3) indicate peak
daily streamflows for the year often exceed the
30-day high flow by a factor of 2.5. Thus evalu-
ation of project effects on pink salmon spawning
habitat based only on monthly streamflows would
cause the potentially detrimental effects of these
naturally occurring peak streamflows on spawning
success to be overlooked.
Further review of the U.S. Geological Survey
(USGS) streamflow records for the Terror River
235
Ratio
Max. Month 1-DAY 7-DAY
for Year 30-DAY 30-DAY
625 2.2 1.2
1066 2.4 1..3
708 2.5 1.7
660 2.5 1.2
765 2.4 1.3
gage indicates that maximum mean monthly stream-
flows are normally associated with the June-July
snowmelt period, while maximum daily streamflows
occur between late August and early October as the
result of intense rainstorms. Considerable
variation was observed among the monthly stream-
flow values of record. It was also determined
that peak daily flows range from 4. 7 5 to 9. 45
times greater than the long-term average monthly
streamflow for the months in which they occur.
Hence pink salmon that spavm in the Terror River
are subjected to a wide range of naturally
occurring streamflow conditions which, at times,
can be detrimental.
SPAWNING
Monthly Streamflows
To visualize the effects that the proposed
project flows might have on the natural vari-
ability of habitat conditions on the lower Terror
River during the pink salmon spawning period, WUA
indices were determined utilizing time series
streamflow data. The 27 years of simulated
monthly pre-and postproject streamflows used by
the engineering firm to determine reservoir
operational characteristics formed the basis for
this analysis. WUA indices were determined for
corresponding monthly streamflow values during the
pink salmon spawning period for the 27 years of
simulated streamflows (Figures 2a and b).
2500
2400
2300
2200
2100 Preproject
2500
I ~~~ 1!~. ~ ,,/{1 ! ~ 2400
2300 v ~ 0/ ~ ~ y IIV
Msan22,780 ~
2200
2100
2000
1900
Postrroject
1!l52 1956 1960 1964 1968 1972 1976
Figure 2. --Composition of time series WUA indices
for spawning pink salmon in the lower Terror
River for average monthly pre-and post-
project streamflows during the spawning
season.
The long-term pre-and postproj ect average
WUA indices for the 27 years of simulated values
are 23,380 and 22,780, respectively. A comparison
between these two averages indicates a net
reduction in WUA of 2.6 percent, a relatively
insignificant project impact. However, it is
quite apparent from a comparison of the time
series analyses that the proposed postproject
streamflows would notably reduce the WUA index in
8 of the 27 years. This is attributable to the
proposed withdrawal of water from the Terror River
for power production during naturally occurring
low-flow periods without regard for spawning
requirements. Such a practice, if allowed, would
amplify an already stressed situation and probably
cause losses beyond those that would have occurred
under natural conditions.
Daily Streamflows
Figures 3a and 3b illustrate the relationship
between average daily streamflows and their
respective WUA indices for spawning pink salmon.
August 1968 was chosen for this analysis because
the range of daily streamflows that occurred
during that month encompass a broad spectrum of
236
flow conditions that spawning pink salmon are
likely to encounter. The average monthly stream-
flow of 407 cfs is within 10% of the simulated
long-term average monthly flow of 374 cfs. Daily
flows vary between 129 and 2,000 cfs.
Peak flow events, which occurred on August 10
and 13, were associated with intense rainstorms
which frequent Kodiak Island during late summer
and fall. The 1,060 cfs streamflow which occurred
on August 13 reduced the WUA index for that day,
but only about one-eighth as much as the 2,000 cfs
event that occurred 3 days earlier. WUA values
peaked out between August 19 and 21, when stream-
flows were in the range of 300 cfs.
Construction of the proposed Terror Lake
reservoir is expected to reduce peak daily stream-
flows at the mouth of the Terror River during
August by approximately one-third. Thus, for
purposes of illustrating the general effect of the
project on the availability of spawning habitat on
a daily basis, it was assumed that daily stream-
flows for August 1968 would have been reduced by
30 percent and the corresponding daily WUA indices
plotted (Figure 3c). WUA indices during the
w
2050 r
1650
~ 1250
<( :z: u
"' Ci
3
25000 ::----...
21000
<( 17000
:::> ;:
13000
9000
5000
A. Average daily stream flows August 1968.
9 11 13 15 17 19 21 23 25 27 29 31
8 Corresponding daily WUA for spawning pink salmon
Ll, I"-/ -----.._
I v MEAN 22,360
1 5 7 9 11 13 15 17 19 21 23 25 27 29 31
25000
21000
17000
<(
:::> ;: 13000
9000
5000
1 3 5 9 11 13 15 17 19 21 23 25 27 29 31
DAY
Figure 3. --Average daily streamflows and corre-
sponding pre-and postproject WUA indices for
spawning pink salmon in the lower Terror
River.
latter part of the month are depressed as a result
of the proposed streamflow withdrawals during the
low-flow period. The severity of adverse effects
from the peak daily flows are greatly diminished.
Such a change in daily WUA indices must be inter-
preted within the proper context. A marked 1-or
2-day change in the IVUA index such as discussed
here is far more important in alerting the analyst
to the biological (reduction of scour), rather
than the arithmetic significance of the change in
the monthly WUA index.
INCUBATION
In the Terror River, fertilized pink salmon
eggs incubate among streambed gravels from their
time of deposition through early April. High
streamflows during the August-October period are a
recurrent cause of streambed scour and associated
mortalities. Another major cause of incubation
mortality, redd dewatering, persistently occurs
during the January-March period. Therefore, to
adequately evaluate the effects of postproject
streamflows on the existing pink salmon resource
of the lower Terror River, a comparison must also
be made between the "survivability" of eggs under
pre-and postproject streamflow conditions.3
Streambed Scour
The following discussion is not intended to
serve as an analysis of stream channel stability,
but simply to provide a general understanding of
the probable effects that postproject streamflows
are likely to have on the potential for scouring
spawning areas in the lower mainstem of the Terror
River.
Streambed scour is principally a function of
channel gradient, discharge, and substrate
particle size. Particle size is also an important
influence on the suitability of streambed mate-
rials for spawning. Hence, to evaluate the
potential for spawning areas to be scoured, it is
necessary to know both the predominant sizes of
particles used by spawners and at what discharge
rate specific particle sizes are likely to begin
moving.
Particles used by spawning pink salmon in the
lower Terror River range from medium gravels to
cobbles (1 to 8 in). But the predominant par-
ticles found in most spawning areas are coarse
gravels and small cobbles (2 to 4 in). Threshold
velocities required to move the various sized sub-
3Thermal effects associated with the
altered flow regime are also recognized as an
essential component of incubation and were
evaluated in the Terror Lake study. However,
presentation of that assessment is outside of
the scope of this paper.
237
strate particles found in the lower Terror River
were determined through hydraulic analyses. Mean
column velocities in the range of 7 to 8 feet per
second were required before spawning areas in the
lower Terror River were likely to be scoured
(Simons et al. 1980).
Simulated mean column velocities at selected
transects within the Terror Gage study reach were
obtained for a range of streamflows between 400
and 1200 cfs directly from the hydraulic model
(Tables 4 and 5). Comparisons between these
simulated mean column velocities and the threshold
velocity required to move the predominant sub-
strate material at the Terror Gage study reach
Table 4.--Simulated mean column velocities for
selected streamflows at designated points
along transect 2 (within a riffle/run) at the
Terror Gage study reach.
Horiz. Velocitv (fps)
Dist. Q-400cfs Q-600cfs Q-800cfs Q-1200cfs
3.5 * 0.00 0.00 0.00
5.0 0.00 .23 .38 .57
6.0 .16 .19 .21 .24
7.4 .34 .48 .60 .83
7.5 .34 .48 .60 .83
8.0 .50 .65 .77 .99
10.0 1. 82 2.87 3.96 6.21
12.0 2.46 3.51 4.51 6.40
14.0 3.71 5.10 6.39 8.74**
16.0 3.84 4.99 6.01 7.78**
18.0 4. 17 5.25 6.18 7.74**
20.0 4.51 5.52 6.35 7.711:*
22.0 4.99 6.27 7.37** 9.23**
24.0 4.85 5.88 6.72 8 .lli<*
26.0 4.78 6.09 7.22** 9.15**
28.0 4.64 5.92 7.03** 8.94**
30.0 4.40 5.65 6.73 8. 60'"*
32.0 3.45 4. 15 4.72 5.63
34.0 3.34 4.14 4.80 5.91
36.0 3.16 3.94 4.60 5.70
38.0 3.18 4.19 5.09 6.67
40.0 3.16 4.20 5.12 6. 77
42.0 2.87 3.35 3.74 4.34
44.0 2.35 2.73 3.03 3.51
47.0 2.14 2.60 2.58 3.60
50.0 1. 68 2.59 3.52 5.41
52.0 1. 48 2.10 2.53 3.16
55.4 .99 1.56 1. 96 2.51
58.0 0.00 .34 .57 .89
69.0 0.00 0.00 0.00 0.00
90.0 0.00 o.oo 0.00 0.00
97.0 0.00 0.00 0.00 o.oo
107.5 .19 .33 .42 .54
113.5 .11 .27 .37 .50
119.8 0.00 .14 .23 .34
120.0 * 0.00 0.00 0.00
* No Flow
** Scour Likely
Table 5.--Simulated mean column velocities for
selected streamflows at designated points
along transect 5 (within a pool) at the
Terror Gage study reach.
Horiz.
Dist.
8.0
10.5
12.0
12.5
15.0
18.0
21.0
24.0
28.0
31.0
34.0
37.0
40.0
43.0
46.0
50.0
53.0
56.0
59.0
62.0
65.0
67.0
70.0
73.0
76.0
78.0
82.0
85.0
88.0
91.0
94.0
97.0
100.0
103.0
107.5
108.0
112.0
115.5
* No Flow
Q=400cfs
0.00
.43
1.06
1.55
2.18
2.43
2.46
2.53
2.41
2.94
2.96
2.77
3.16
3.06
2.88
3.23
2.94
2.89
2.83
2.49
2.47
1. 99
1. 75
1. 83
1. 62
1.45
1. 63
1. 50
1. 27
1. 37
1.17
.95
.83
.71
.59
0.00
* *
Velocity (fps)
Q-600cfs Q-800cfs Q-1200cfs
0.00
.68
1. 29
1.81
2.38
2.66
2.65
2.69
2.55
3.29
3.31
2.92
3.59
3.36
3.06
3. 71
3.43
3.52
3.25
3.29
3.36
2.81
1. 93
2.08
1. 98
1. 72
2.19
2.01
1. 75
1.84
1. 67
1.50
1.41
1. 32
1.10
.37
0.00
*
o.oo
.85
1.48
2.04
2.54
2.84
2.80
2.82
2.66
3.56
3.58
3.04
3.94
3.60
3.21
4.10
3.84
4.07
3.59
4.02
4.19
3.61
2.07
2.29
2.28
1. 96
2.60
2.39
2.11
2.18
2.03
1. 88
1.80
1. 72
1. 43
.78
0.00
*
0.00
1.11
1. 76
2.41
2.79
3.13
3.04
3.03
2.84
4.01
4.03
3.23
4.52
3.98
3.45
4.74
4.53
5.02
4.15
5.36
5.76
5.16
2.29
2.63
2.81
2.34
3.21
2.96
2.63
2. 70
2.57
2.43
2.36
2.30
1. 91
1. 27
.16
0.00
indicate that streambed scour is unlikely to occur
in pool areas, but local scour probably would
occur in runs and riffles when streamflows
approach 1,000 cfs. Scour probably would occur in
spawning areas throughout the lower mainstem
whenever streamflows exceed 1,500 cfs.
Knowledge of the seasonal occurrence and
frequency of such flows is of particular impor-
tance for evaluating the survivability of
deposited eggs. During 1965-1968 period of record
at the USGS Terror River gage (15295700), 12 daily
238
streamflows greater than 1,500 cfs and 47 greater
than 1, 000 cfs were recorded. Ten flows greater
than the former and 20 above the latter discharge
occurred between mid-July and early October.
Annual peak daily flows of record have always
occurred in association with rainstorms during
late summer and early fall. These peak stream-
flows are normally of short duration and represent
relatively small volumes of water. For example,
the September 10, 1965 discharge of 1,490 cfs was
preceded by more than a week of average daily
streamflows of between 150 and 250 cfs. The
September 18-19 and September 26-29, 1966, peak
flow periods of 1,000 to 2,200 cfs occurred within
a 15-day period when ambient streamflows were
between 200 and 450 cfs (USGS 1965 and 1966).
As a result of the project, the storage
capacity of Terror Lake would increase from
16,000 to 94,000 acre-feet, providing 78,000
acre-feet of active storage (R. W. Retherford and
International Engineering Company, Inc. 1978,
1979). The September 26-29, 1966, runoff (13,500
acre-feet) is the largest volume of water
attributable to a fall storm during the 1965-1968
period of record. The Terror Lake drainage area
comprises 15.1 mi2 of the 46 mi2 upstream of the
Terror River gage. If the rainstorm that caused
this 4-day peak flow event had been uniformly
distributed over the Terror River basin, approxi-
mately one-third of the 13,500 acre-feet of runoff
or 4,400 acre-feet would have originated above the
proposed Terror Lake dam. Seldom would the
proposed reservoir with 850 surface acres and
78,000 acre-feet of active storage be so full that
it could not temporarily store all the upper basin
runoff from such a storm.
Were peak daily streamflows in the lower
Terror River reduced by 30% as might result from
the proposed dam, only two streamflow events above
1,500 cfs and 11 above 1,000 cfs would have
occurred between the mid-July and early October
period. This contrasts with 10 flows above 1,500
cfs and 20 above 1,000 cfs for the 1965-68 period
of record. Thus, it may be concluded that the
frequency at which lower mainstem spawning areas
are scoured would be notably reduced but not
eliminated as a result of the project.
Dewatering of Redds
Another major factor influencing the survival
of fertilized pink salmon eggs is the potential of
low winter streamflows to ciewater redds. Stream-
flows during the spawning season provide salmon
easy access to spawning habitat along the stream-
bed margins and in riffle areas. However, mid-
winter water surface elevations often drop
appreciably below those present in these areas
during the spawning season. As a result, spawning
habitat along the stream margins and in riffle
areas can become dewatered, and flow through the
streambed gravels may be substantially reduced.
Terror Gage
8/27/80
X Pink salmon redd
PS Intense pink salmon spawning
Note: Left bank defined looking upstraam
so
7
Figure 4.--Redd map of the Terror Gage study
reach, August 1980.
16
14
12
10
8
6
4
2
CROSS SECTION NO.6
Streambed Elevation (f!) _
preproject water surface
postproject water surface
observed spawning area
o L. -----· ~--~----
0 10 20 30 40 50 60 70
Distance from Left Bank (ft)
CROSS SECTION No. 5
§~ambed g.!_evation (ft)
16
14
12
10
8
6
4
2
0
80 90 100
~; --\ ----~:
10 "<:.~----------~-...... ------=------~ ~~
8
6
4
2
0
16
14
12
10
8
6
0 10 20 30 40 50 60 70 80
Distance from Left Bank (ft)
CROSS SECTION No.2
Streambed Elevation (ft)
90 100
8
6
4
2
0
4 4
2 2
0 0
0 10 20 30 40 50 60 70 80 90 100
Distance from Left Bank (ft)
Figure 5.--Comparison of long-term average monthly
water surface elevations during August and
February in the lower Terror River.
239
Figures 4 and 5 present a redd map (field
sketch) and scale drawing of respective cross
sections denoting the locations of pink salmon
redds observed during August 1980. Transects 2,
5, and 6 collectively represent typical stream
channel cross sections for the study reach, hence
the remainder of the transects were deleted from
the analysis. To expedite analysis of project
effects on redd dewatering, August and February
were selected as index months. Figure 5 provides
a comparison between pre-and postproject water
surface elevations for long-term average August
and February streamflows. Postproject streamflows
would reduce the magnitude of the change between
average monthly water surface elevations for the
index months by approximately 0. 5 ft. The long-
term average postproject winter water surface
elevation would be approximately 0. 1 ft higher,
while during the spawning season it would be
approximately 0.4 ft lower.
The 27 years of simulated monthly streamflows
during the midwinter incubation period were
reviewed and the lowest monthly flow and corre-
sponding water surface elevation for each winter
identified. A comparison was then made between
these water surface elevations and the water
surface elevation associated with a controlled
winter release of 60 cfs (Figure 6).
The low-flow statistics obtained in the flow
variability analysis indicate that the simulated
monthly midwinter streamflows are substantially
greater than the lowest daily flows. Therefore,
it must be remembered that incubating eggs and
alevins are being stressed to a greater extent
than the simulated monthly streamflows would
9.8,.--------------------------,
9.6
5
j Postproject
m 9.4
!l
J! ~ 9.2
.. .. ..
iii
~
3:: 9.0
Pre project
8.8 L..~~_J_~~'--''-'-~~_J_..._~'--'--'-~~...~.-~,__,__.l.__._~--'---'
1950 1954 1958 1962 1966 1970 1974 1978
Year
Figure 6.--Comparison of average monthly pre-and
postproject water surface elevations for 27
years of simulated streamflows during the
incubation season.
imply. Hence, postproject flow regulation near 60
cfs throughout the winter months should do more to
protect incubating redds from dewatering than this
comparison of average monthly pre-and postproject
water surface elevations indicates.
Natural mortality would continue to occur in
the lower Terror River as a result of redd
dewatering but losses would not be as severe or as
frequent as under preproject conditions.
Reduction of water surface elevations during the
spawning period should encourage adults to spawn
closer to midchannel where their redds are not as
vulnerable to dewatering. With reference to
scour, the proposed project would reduce the
magnitude and frequency of flood peaks, thereby
improving the potential survival of incubating
salmonid eggs in the lower Terror River.
ACKNOHLEDGEMENTS
Kodiak Electric Association, Inc. funded the
particular application of the incremental method
upon which this paper is based. The University of
Alaska's Arctic Environmental Information and Data
Center provided financial and staff support for
the presentation of this paper.
Debbie Amos, U.S. Fish and Wildlife Service,
Jean E. Baldrige, Arctic Environmental Information
and Data Center, Willis A. Evans, U.S. Forest
Service (retired), Dr. Dana Schmidt, Terrestrial
Environmental Specialists, Inc., and Dr. Clair B.
Stalnaker, U.S. Fish and Wildlife Service provided
technical review and comment. The author would
especially like to thank Peggy Skeers, Beverly
Valdez and Pamela Barr for their invaluable
assistance in preparing the final manuscript.
240
LITERATURE CITED
Bovee, K.D., and R. Milhous. 1978. Hydraulic
simulation in instream flow studies theory
and techniques. Cooperative Instream Flow
Service Group, U.S. Fish and Wildlife
Service, Fort Collins, CO. Instream Flow
Information Paper No. 5. 130 pp.
Robert W. Retherford Associates and International
Engineering Company, Inc. 1978. Terror Lake
hydroelectric project, Kodiak Island, Alaska.
Definite project report. Report for Kodiak
Electric Association, Inc. International
Engineering Company, Inc. San Francisco,
California. 1 vol.
1979. Terror Lake hydroelectric project,
---K-odiak Island, Alaska. Application for
license. Supplemental Information Report No.
1. Report for Kodiak Electric Association,
Inc. International Engineering Company, Inc.
San Francisco, California. 1 vol.
Simons, D. B., et al. 1980. Analysis of hydrau-
lic, sedimentation and morphological changes
in the Kizhuyak and Terror rivers associated
with the Terror Lake hydroelectric project.
Report for Kodiak Electric Association.
Simons, Li and Associates, Fort Collins,
Colorado. 1 vol.
Stalnaker, G.B. 1978. Methodologies for Pre-
serving Instream Flows, The Incremental
Method. Pages 1-9 in Instream Flow Manage-
ment -State of the Art Proceedings. Upper
Mississippi River Basin Commission. Fort
Snelling, Minnesota.
Trihey, E.W. 1979. The IFG incremental method-
ology. Pages 24-44 in G.L. Smith, ed.
Workshop in instream flow habitat criteria
and modeling. Colorado Water Resources
Research Institute, Colorado State Univer-
sity, Fort Collins, CO. Information Series
No. 40.
u.s. Geological Survey. 1965.
Data for Alaska U.S. Govt.
Hashington, D.C.
Water Resources
Printing Off.,
1966. Water Resources Data for Alaska
---U-.S. Govt. Printing Off., Washington, D.C.
Wilson, W.J., E.W. Trihey, J.E. Baldrige, C.D.
Evans, J.G. Thiele, and D.E. Trudgen. 1981.
An assessment of environmental effects of
construction and operation of the proposed
Terror Lake Hydroelectric facility, Kodiak,
Alaska. Instream flow studies. Final
Report. Arctic Environmental Information and
Data Center, University of Alaska, Anchorage,
Alaska 419 pp.
Acquisition and Utilization
of Aquatic Habitat
Inventory Information
Proceedings of a Symposium held 28-30 October 1981,
Portland, Oregon
Organized by Western Division American Fisheries Society
Acquisition and Utilization of
Aquatic Habitat Inventory
Information
Proceedings of a Symposium
Held 28-30 October, 1981
Hilton Hotel, Portland, Oregon
Neil B. Armantrout, Editor
Organized by The Western Division, American Fisheries Society
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