Draft EIS_072312.pdf - Middle Fork American River Project ...

20120723-4002 FERC PDF (Unofficial) 07/23/2012
Minimum flows would be maintained or increased relative to existing conditions
in all project-affected reaches under both the proposed and our recommended regime.
In addition, minimum flows would vary by month and water year type under both action
alternatives, better reflecting natural seasonal and year-to-year variability in the
watershed. Under both alternative flow schedules, summer flows in wet and abovenormal
water years would be higher than under existing conditions in all projectaffected
reaches. In summers of critical, dry, and below-normal water years, minimum
flows would be increased or maintained in all bypassed and peaking reaches compared
with existing conditions.
Minimum flow increases in the peaking and bypassed reaches in the wettest
water year types would increase wetted stream perimeters, which may increase habitat
area and habitat diversity for fish and aquatic invertebrates in some reaches. Increased
edge habitat may improve rearing success of YOY fish in wet water years if shallow
water or cover is available to increase their ability to avoid aquatic and terrestrial
predation. Higher minimum flows should provide more area for aquatic
macroinvertebrate communities that make up a large portion of the diet of trout and
other fish.
The range of proposed minimum flows in the peaking reach would be from 75 to
450 cfs, whereas our recommended minimum flows would range from 90 to 450 cfs.
However, many of our recommended minimum flows would be from 15 to 100 cfs
higher than the comparable proposed measure for comparable water years and time
frames. For the reasons stated in the previous paragraph and in section 3.3.2.2, Aquatic
Resources, this prevailing higher minimum flow would result in our recommended
regime providing habitat enhancements compared with the proposed flow regime.
Typically, the period of snowmelt and high runoff occurs between April through
mid-June in the Middle Fork basin. Restoring flows that mimic the spring snowmelt
pulse may provide benefits to the aquatic community by helping to maintain a variety of
seasonal life-history behaviors. Spring minimum flows would be substantially higher
than under existing conditions in all water-year types under both PCWA’s and our
recommended minimum flow regimes and would provide flow change that simulate
those found under unregulated conditions during the seasonal snowmelt period. Both
the proposed and our recommended minimum flow regimes would enhance flow
conditions for spawning by resident trout during spring (mid-March through June),
based on our review of instream flow study results. Higher spring flows may provide
access to additional spawning or rearing habitat.
Precipitation in the Middle Fork watershed has high inter-annual variation;
water-year types tend to be either wet or dry, with few years receiving “average”
precipitation. Under existing conditions, no provision is made for within-year or
between-year variation in flows to reflect local seasonal changes. Many fish and
aquatic macroinvertebrate species may use changes in flows as cues for behaviors such
as spawning or movements into appropriate winter or summer habitat. Year-to-year
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