Reclamation will be performing maintenance and repair work on two 8-foot diameter powerplant control valves. These valves, known as butterfly valves, are used to shut off the upstream flow to the generator turbines for inspection and maintenance.

"Over their 50-year history, both valves have developed leaks which require repair of the sealing surfaces," said Steve Jarsky, Operations and Maintenance Manager. "In order to repair these valves, the main gate to the powerplant, called the fixed wheel gate, will be closed."

Closing the fixed wheel gate shuts off the water through the powerplant, and the only way to pass river flow is by opening the spillway radial gates. The discharge through the turbines is presently at 600 cubic feet per second and starting on June 7 there will be a gradual three day transition from powerplant discharge to spillway flows.

During flow transition, and throughout the maintenance and repair project, a constant flow of 600 cfs will be maintained in the South Fork of the Boise River below the dam.

At the end of the project a gradual transition will be made from spillway flows back to powerplant discharge over a period of four days. Transition back to powerplant discharge should be completed by July 9.

The timing of water releases has been coordinated with the U.S. Fish and Wildlife Service and the Idaho Department of Fish and Game to minimize the effect on upstream and downstream fish habitat, Jarsky said.

Anderson Ranch Dam, constructed in 1950, is owned and operated by the Bureau of Reclamation. The 456 feet high dam and powerplant make up a multiple-purpose structure providing benefits for irrigation, power, and flood and silt control.

The powerplant supplies power to irrigation loads in the Boise, Owyhee, and Minidoka Projects as part of Reclamation's Southern Idaho Power System. Surplus power is delivered to the BPA for marketing and distribution to regional industries and municipalities.