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

20120723-4002 FERC PDF (Unofficial) 07/23/2012
• result in higher minimum summer water surface elevations in Hell Hole
reservoir during wet, above normal, below normal, and critical water year
types;
• result in higher winter minimum water surface elevations in Hell Hole
reservoir during critical water year types; and
• implement the summer to winter minimum pool elevation transition
immediately after Labor Day instead of at the end of September as occurs
under existing operations.
Alternative 1 would generally provide these same circumstances. However, the
transition from summer to winter minimum pool management occurs at different times
based on water year type. Alternative 1 also specifies higher minimum water surface
elevations for French Meadows reservoir during the peak recreation season than what
PCWA proposes.
Our Analysis
Based on operation model runs for the period of record, both PCWA’s proposed
action and Alternative 1 would result in relatively little change in the actual operational
reservoir elevations and volumes as compared with existing operations, and these
measures would not substantially affect surface area or water depth in French Meadows
or Hell Hole reservoirs. Objectives for mid-summer reservoir levels specified in
Alternative 1 are similar to the water surface elevations that typically occur under
existing project operations. Reservoir levels based on projected future demand are also
similar to or greater than what is specified in Alternative 1. We expect the effects of the
proposed action and Alternative 1 on French Meadows and Hell Hole reservoir fish
habitat to be negligible.
Middle Fork Interbay and Ralston Afterbay Sediment Management and
Maintenance
Periodic removal of sediment in Middle Fork interbay and Ralston afterbay would
continue under both action alternatives, as would annual drawdown for gate inspection
and maintenance at the powerhouses. These activities require partial or complete
dewatering of the impoundments for about 6 to 8weeks. Fish are present in both
impoundments, with Ralston afterbay in particular providing habitat for hardhead, a
Forest Service Sensitive Species. The proposed Sediment Management Plan included in
both action alternatives specifies that water surface elevations in Ralston afterbay would
be maintained at no lower than 1,149 feet, the elevation of the bottom of the spill gates, to
provide a refuge pool for fish during these activities. During drawdown of both
reservoirs, surveys would be conducted and any stranded fish observed would be
removed and placed downstream of each reservoir. A hardhead tagging study is
proposed under both action alternatives to investigate hardhead movements during the
first sediment removal at Ralston afterbay.
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