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

20120723-4002 FERC PDF (Unofficial) 07/23/2012
dependent operational flexibility is used to meet the ramping rate requirement
downstream of the Oxbow powerhouse and to make releases for whitewater boating
without requiring operation of the Middle Fork and Ralston powerhouses. Because the
Ralston afterbay is used primarily as a regulating facility, water surface elevations may
fluctuate on a day-to-day or hour-to-hour basis. The Ralston afterbay does not follow a
seasonal fill-and-release pattern like Hell Hole or French Meadows reservoirs.
Fluctuations of the Ralston afterbay occur daily throughout the year, but the daily
pattern varies depending upon the season. Ralston afterbay water surface fluctuation
patterns vary with water year type, electrical demand, and scheduled and emergency
maintenance activities of project facilities. The largest fluctuations in water surface
elevation at the Ralston afterbay typically occur when the source of inflow is
predominately from Ralston powerhouse generation. Water levels in the Ralston afterbay
also fluctuate during the spring, but fluctuations may not be as regular or as large,
depending on water year type. During the winter, regular daily fluctuations are generally
minimal, but fluctuations may occur over the course of days or weeks to allow for
management of runoff resulting from winter storms. In the winter, the Ralston and
Oxbow powerhouses are typically run more synchronously. In general, water surface
elevations in Ralston afterbay remain relatively stable during the winter, although not at
full pool, to allow the capture of runoff from winter storm events and to minimize
reservoir spilling. If a large storm event is projected, Ralston afterbay may be drawn
down substantially in advance to facilitate capture of high flows.
The total water available and the physical capacity of the project limit the timing
and number of hours of generation in a given year. In drier years, when less water is
available, generation is concentrated during the summer and early fall. In wetter years,
generation occurs throughout the year. If the project powerhouses are operated at full
flow, generation may be limited to an average of approximately 5 to 6 hours per day
during a dry year, while in a wet year, the powerhouses may be operated at full flow for
17 hours or more per day.
PCWA currently coordinates with representatives from the California Department
of Parks and Recreation and a designated commercial whitewater boating representative
to schedule project operations during the summer and early fall (June through Labor Day)
to accommodate whitewater recreation in the Middle Fork American River below the
Oxbow powerhouse. Whitewater boating releases are scheduled on a voluntary basis
such that they minimize effects to power generation and do not compromise consumptive
water deliveries or maintenance activities. When sufficient water is available, whitewater
recreation flows are provided by scheduling generation through the Oxbow powerhouse
approximately two to three hours earlier than would otherwise occur to meet peak energy
demand.
Flows are voluntarily reduced in the Middle Fork American River below the
Oxbow powerhouse for two annual competitive long-distance trail events whose routes
cross the river at Poverty Bar. During the races, project operations are modified to the
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