Report of the Secretary of the Army
on Civil Works Activities for Fiscal Year 1996
Department of the Army Corps of Engineers
Extract Report of the Walla Walla District

Mill Creek-Bennington Lake, Washington

Existing project. The project includes an off-stream earthfill storage dam, about 125 feet above the streambed and 3,200 feet long at the crest, two concrete-lined outlet channels, an earthfill diversion dam, and diversion structures. Project provides for flood control and recreation. Authorizing legislation to provide a channel through the city of Walla Walla was added to the project in 1941. Recreation was added to the project purposes through the Federal Water Project Recreation Act of 1965.

Construction of the dam and appurtenant works was completed in 1942. Paving of the channel through the city of Walla Walla was completed in 1966 (for details, see page 2,005 of the 1962 Annual Report). Since 1942, $45,633,000 (adjusted to October 1996 price index) in potential flood damage has been prevented by the combined storage and channel operation.

Rehabilitation of the existing project was initiated in Fiscal Year 1978 and completed in Fiscal Year 1979. The plan of rehabilitation included action to correct the seepage and internal erosion which has occurred during each subsequent filling of the reservoir. A cutoff wall was constructed, but did not alleviate the seepage problem, thus requiring limited flood control use of the project. The seepage and internal erosion create a high vulnerability for dam failure.

Local cooperation. Fully complied with (for details, see page 2,006 of the 1962 Annual Report).

Operations during fiscal year. Operation and Maintenance: Normal operation and maintenance continued, which included regulation of water control structures and care of recreation areas. Initiated diversion forebay silt removal due to 1996 flooding. Fiscal year costs were $805,150.