HomeMy WebLinkAboutFERC 1985 Amend Natural Res Sumwould be up to 3°C higher than natural. As project energy production
increases in Stage III, the differences between with -project and natural
spring and summer temperatures would decrease, and the differences in
winter temperatures would increase.
In the lower river, temperature differences will be greater in Stage II than
in Stage I. Spring temperatures may be up to 2°C cooler than natural and
fall temperatures may be up to 2.5°C warmer than natural near Talkeetna.
Further downstream the differences would be less. During the summer and
winter, temperatures would be the same as natural. Stage III lower river
temperatures will at first be similar to Stage II but as energy production
increases, differences between natural and with -project summer temperatures
will decrease toward Stage I values.
Sediment. The simulations of reservoir suspended sediment behavior indicate
that between 80 and 90 percent of the sediment influent to the reservoir
would be trapped. This would include most of the larger sized particles,
which settle out more rapidly. Thus, after project development, material
with a size range of 0-3 microns would comprise the majority of sediment in
the middle river below the dams. The concentration of suspended sediment
would be reduced from summer natural levels which average 700 mg/l to
approximately 100 mg/1 in Stage I, 80 mg/l in Stage II and 60 mg/1 in Stage
III. Average winter concentrations would increase from near 0 mg/1
naturally to approximately 70 mg/l in Stage I, 60 mg/l in Stage II and 50
mg/1 in Stage III. Lower river suspended sediment concentrations would be
generally unaffected in the summer because of the large sediment inflow from
the Chulitna River. In the winter, lower river sediment concentrations
would also increase over natural values and the increase would be about
10 - 20 mg/1 less than in the middle river in all three stages, due to
dilution by the Chulitna and Talkeetna Rivers.
Ice. Under natural conditions the Susitna River first becomes ice -covered
near its mouth at Cook Inlet in late October or early November. The ice
cover then generally progresses upstream and reaches Talkeetna between
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mid -November and early December. The middle river becomes ice covered at
the confluence with the Chulitna River generally about the same time, and
the ice cover progresses upstream to Gold Creek by mid -December. The river
remains ice covered until late April to mid -May.
Under with -project conditions the lower river is expected to become ice
covered in generally the same manner as in natural conditions. However,
progression of the ice cover to Talkeetna is expected to be delayed by 2-4
weeks in Stage I, and 4-7 weeks in Stages II and III because of reduced
frazil ice production in the middle river. Progression of the ice front in
the middle river is expected to be delayed by comparable amounts.
Additionally, because of the warmer (3'C) reservoir releases, a section of
the middle river below the dams is not expected to become ice covered. In
Stage I, the ice cover is expected to reach near RM 140 and the area
upstream to Watana Dam would be open water. In Stage II, the ice cover is
expected reach near RM 135. In early Stage III the ice cover would extend
to near RM 125 and, as energy production increases, the ice cover would
extend only up to near RM 115.
The higher than natural winter releases would cause winter water levels to
be higher than natural within ice covered areas. In areas where an ice
cover existed under natural conditions but would not exist with -project, the
water level may be less than natural. The increase in water level in the
middle river is expected to be 2 to 6 feet in Stage I 1 to 4 feet in Stage
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II and approximately 2 feet in Stage ill.
These water level increases are of concern since they may cause overtopping
of natural berms at the upstream ends of peripheral habitat areas. This
could introduce cold mainstem water (near 0°C) into the slough or side
channel habitats (see discussion below) and could affect overwintering and
incubating salmonids. Therefore, the Applicant has proposed to protect the
important habitat areas by raising the berms above the expected maximum
winter water levels. The increase in winter water level in ice affected
areas may be beneficial by providing additional winter groundwater upwelling
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to the adjacent habitat areas. Upstream of the ice —affected area water
levels are expected to be lower than natural but similar to average summer
water levels. In all areas, upwelling, a major component of suitable
spawning and incubation habitat in these peripheral habitats, is expected to
be generally more stable all year than for natural conditions.
Fish and Fish Habitat
Twenty species of fish are known to inhabit the Susitna Basin. The most
important are five species of Pacific Salmon, rainbow trout, Dolly Varden
char, arctic grayling and burbot.
The majority of fish production in the system occurs in tributaries outside
the area of anticipated project affects. Devil Canyon acts as an effective
passage barrier to upstream mitigation so no salmon have been observed above
the Watana Dam site and only a few (less than 100) move past the Devil
Canyon damsite. Salmon production from the middle river, the reach expected
to experience the greatest project induced changes, is quite small compared
to total production from the Susitna system. Only approximately six percent
of the total Susitna salmon runs spawn in the middle river and less than one
percent spawn in the mainstem influenced, non —tributary habitats. Resident
fish populations in the middle river are relatively small and low density.
Based on the baseline fisheries studies over the past five years and
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' consultations with VarlOL1S fisheries- agencies, It has been determined that
the most critical 'habitat and 'habitat use in the middle river vis a vis
project —induced flow, temperature and water quality impacts is largely
limited to chum (and sockeye) salmon spawning and incubation in side sloughs
and Chinook (king) salmon rearing in side channels. Mitigation measures,
including flow constraints and design features have been proposed to
maximize the availability of these habitats.
Flow Related Impacts. Mainstem habitat is of little value to the salmonid
populations in the middle river. Upland sloughs and tributaries would be
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essentially unaffected by the project. Thus, the species/habitat
combinations of chinook salmon rearing and chum salmon spawning and
incubation in side sloughs and side channels were chosen after consultation
for primary consideration in developing environmental flow requirements.
Secondary consideration was given to the other evaluation species for flow
allocations and all the species are treated in impact analyses and
mitigation planning.
A plan for regulating river flow (Flow Case E-VI) has been selected as the
preferred set of environmental flow constraints to mitigate flow related
fishery impacts. Briefly, this flow regime establishes seasonal minimum and
maximum flows for the project as depicted on Exhibit 40, as well as limits
on the rate of change in flow. As noted above, the primary focus of this
case is maintenance of rearing habitat for chinook salmon juveniles by
maintenance of high summer minimum flows. Project operation under Case E-VI
requirements would result in maintenance of or an increase in chinook
rearing habitat. The mean total available area for chinook rearing under
natural flows is approximately 6.1 million square feet. This is the
estimated area in all habitat categories that meet the derived suitability
criteria derived in consultation with interested agencies. Estimated
available habitat under Case E-VI flows, using the same suitability criteria
and all habitat categories, is approximately 6.0 million square feet. This
estimated slight decrease in rearing habitat would have no affect on chinook
juvenile survival and production. The area estimates include habitat
categories that rearing Chinook do not use under natural conditions and may
not use under with -project conditions.
Chinook rearing habitat estimates in habitat types used extensively by
juvenile chinook under natural conditions show an increase in area available
under with -project flows. The mean total area available under natural
conditions is approximately 4.2 million square feet as compared to
approximately 4.3 - 4.6 million square feet under with -project conditions.
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Chum salmon spawning habitat and egg incubation success would be reduced by
Case E-VI flows without further mitigation. Since chum spawning in the
middle river is largely limited to a few side sloughs, however, this
potential loss can be easily rectified by structural habitat modifications
in appropriate side sloughs.
Evaluation of the distribution and timing of habitat utilization by the
other evaluation species produced no other expected negative impacts due to
altered flows. Most of the habitat use by other species is outside the area
that would be affected by changes in mainstem flow and use within the
affected area is similar to that of the primary evaluation species. Hence,
the mitigation measures to protect the habitat for the primary species would
also provide the secondary species sufficient protection.
Water Quality Impacts. Factors affecting habitat quality are less
predictable than habitat quantity. The major anticipated changes in
quality -related factors are increased flow stability and altered temperature
and suspended sediment regimes. Increased flow stability would have a
beneficial affect on habitat use by all the evaluation species.
With -project water temperatures are expected to be slightly cooler in the
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early summer and warmer in the fall. Although the expected temperature
changes would alter timing of some annual cycles and behaviors, they are
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well within documented ranges of tolerance for each species and are within
the range of temperatures that Susitna populations experience under natural
conditions. Thus, no significant impact is anticipated.
As dicussed above, project operation would reduce the total suspended
sediments in downstream habitats. Concentrations would be much less during
the summer and slightly greater during the winter. Most of the sediments
that would be transported downstream would be in the category of glacial
flour i.e. particles less than 3 microns in diameter. These small fines are
the major contributor to with -project turbidity. The annual pattern of
turbidity would follow the same trend as for suspended sediments. That is,
turbidity would be less in the summer and greater in the winter than natural
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conditions. The summer reduction in suspended sediment and turbidity would
improve habitat quality for juvenile chinook salmon and other species that
presently use turbid water habitats for rearing. The winter increase would
reduce mainstem habitat quality; however, winter sampling indicates limited
use of mainstem areas during the winter and most of the documented use is by
species known to be tolerant to turbidity, e.g., rainbow trout and burbot.
The effect that increased turbidity would have on observed periphyton blooms
during the spring and fall and, in turn, how that affect would influence
fish production from the system is not quantitatively predictable. However,
a decrease in the short spring and fall blooms would be offset, at least
partially, by lower rates of productivity over the entire summer season
given reduced summer turbidity levels.
The proposed monitoring plan includes components to measure these habitat
quality parameters and would detect unanticipated changes during project
operation. Monitoring would also detect any loss of fish production
occuring in the event proposed mitigation measures are not as effective as
expected.
In summary, the proposed mitigation plan would avoid, minimize or rectify
the anticipated impacts on aquatic habitats and species that would be caused
by operation of the project. The result would be maintenance of existing
levels of productivity from naturally reproducing populations. The proposed
monitoring plan would measure this productivity to show if refinement or
alteration of mitigation is needed.
Botanical and Wildlife Resources
Botanical. Stage I would result in the permanent removal, through
construction or inundation, of 15,762 acres of vegetation, 84 percent of
which would consist of forest (mostly spruce and spruce -birch) and almost 16
percent of which would consist mainly of dwarf tree scrub and low shrub
vegetation.
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Stage II (Devil Canyon) would result in 6,020 acres of vegetation
permanently lost through inundation and construction. Almost all of this,
some 94 percent, is forest (spruce, spruce -birch, and spruce -poplar).
Construction of Stage III would result in the permanent loss of 16,370 acres
of vegetation. Some 82 percent of this would consist of spruce and spruce -
birch forests and white spruce woodland. The remainder would consist mostly
of dwarf tree scrub and low shrub.
Much of the area to be affected by the project is classified as wetlands, as
in the case for most of Alaska. The areas of palustrine or lacustrine
wetlands permanently lost due to construction or inundation are 3,430 acres
for Stage I, 950 acres for Stage II, and 4,090 acres for Stage III.
However, only about 18 percent of these areas consist of emergent, pond, or
lake wetland types which are considered to be of relatively high value for
waterfowl and other wildlife. The remainder consists of forested and
scrub -shrub wetlands which are usually of equal or lower value to wildlife
than are adjacent uplands.
Mitigation plans for botanical resources were developed primarily to
minimize vegetation losses and support the wildlife mitigation program.
Specific measures include the minimization and consolidation of project
facilities and the siting of these facilities in areas with low habitat
values and the prompt rehabilitation of disturbed areas when no longer
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Moose, From 2,000 to 3,000 moose inhabit the 1,400 square mile area which
includes and surrounds the project area. This represents about 10 percent
of the Alaska Game Management Unit 13 moose population and approximately 1-2
percent of the population in the State of Alaska. Winter habitat is the
critical habitat for these animals. The 38,152 acres of vegetation lost for
Stages I, II and III, would result in loss of winter habitat for some 300
moose (about 0.1 percent of the moose population of Alaska). This loss
would be mitigated by habitat enhancement on mitigation lands in both the
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lower and middle Susitna Basin. Burning and clearing would increase browse
production and resultant carrying capacity sufficiently to over compensate
for moose habitat losses and would also provide out -of -kind mitigation for
other species.
Caribou. The Susitna Project lies within the northwestern portion of the
range of the Nelchina caribou herd, which currently numbers about 24,000
animals or about five percent of the statewide caribou population. Given
the low historic use of the impoundment zone, the habitat loss associated
with inundation is not expected to detestably reduce carrying capacity for
the Nelchina herd. The access road could locally affect caribou movements
and range use and public use of the road for hunting could result in a
redistribution of hunting pressure resulting in greater pressure on the
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local subherd and less pressure elsewhere. However, significant impacts to
Nelchina herd numbers are not expected from these factors. The Watana
impoundment could alter caribou movements and may result in an increase in
the number of crossing -related mortalities over natural conditions; however,
significant population changes or reductions in carrying capacity due to
crossing mortalities or blockage of movements are not expected. A variety
of mitigation measures, including a worker transportation plan to reduce
traffic on the access road, have been incorporated into project plans to
minimize these impacts.
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Bears. Brown bears will lose spring foraging habitat and black bears will
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lose denning and foraging habitat, due to inundation. Increased human use
of the area will likely result in increased bear mortality, particularly for
brown bears. Mitigation measures have been incorporated into project design
and operation plans to minimize these impacts and both in -kind and
out -of -kind compensation through habitat preservation and through enhanced
moose production would mitigate residual impacts.
Raptors. Twenty-three golden eagles and ten bald eagle nesting locations
have been identified in or near the project area. Seven golden eagle and
three bald eagle nest locations would be inundated or significantly
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