Bishop Intake #2 Spillway Modifications: A Case History

by J. E. Throckmorton, Southern California Edison Co, Rosemead, United States,
C. M. Knarr, Southern California Edison Co, Rosemead, United States,

Document Type: Proceeding Paper

Part of: Waterpower '91: A New View of Hydro Resources


This paper covers the history of the events leading to the modification of Southern California Edison's (SCE) Bishop Intake 2 to pass a site specific design flood. From the initial request by SCE's Consulting Board to increase the dam's spill capacity to final construction, the project met with numerous regulatory difficulties. SCE's Bishop Intake 2 is a small 115 acre feet reservoir impounded by an earthfill dam. The dam is 41 ft. high and 443 ft. long. It has a center concrete corewall for about one-half of its length. The reservoir and downstream power plants were originally constructed to supply water and electricity to mining operations in the Bishop area around the turn of the century. SCE acquired the entire Bishop system of five power houses and reservoirs from Calectric when a merger took place with SCE in the 1960's. The dam was designed and constructed with a cyclopean concrete overflow spillway through the central portion of the dam. This spillway is capable of safely passing the 100 year flood. To provide additional protection downstream, including the town of Bishop, California, it was necessary to increase the spill capacity to protect the dam from overtopping. A risk analysis was performed to size the design flood. A roller compacted concrete (RCC) overflow spillway was selected as the most viable solution for the design. Acceptance of the RCC spillway by regulatory entities and environmental impact were the major causes of delay for this small project. The paper covers the design, construction and regulatory hurdles encountered during the life of the project.

Subject Headings: Case studies | Hydraulic design | Reservoirs | Concrete dams | Spillways | Earthfill dams | Risk management | Water intakes | California | United States

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