Presented at Irrigation district sustainability - strategies to meet the challenges: USCID irrigation district specialty conference held on June 3-6, 2009 in Reno, Nevada.The Yolo County Flood Control & Water Conservation District (District) releases about 250,000 acre-feet per year from two water supply reservoirs in the Cache Creek watershed for the irrigation of about 60,000 acres of farmland in Yolo County, California. That water is diverted into the Winters Canal and the West Adams Canal at Capay Diversion Dam on Cache Creek. The continued operation of Capay Dam is vital to the sustained future of irrigated agriculture of the District. Urbanization and infrastructure construction in California resulted in extensive sand and gravel extraction from Cache Creek downstream of Capay Dam. Although that mineral extraction ceased many years ago, the streambed of Cache Creek has degraded. Presently the streambed elevation at the toe of Capay Dam is as much as 15 feet below the elevation of the apron of the dam and the dam is at risk due to downstream channel bed degradation and local scour during floods. Capay Dam is a concrete diversion that was constructed in 1915. The main portion of the dam is an overflow section about 475 feet long with low-level sluice gates and service spillways at both abutments. The abutments also contain the headworks for the irrigation canals. Due to streambed degradation, local scour at the toe of the apron and the more than 90-year service life of the structure, the District embarked on a program of dam inspection, including the use of non destructive testing of the concrete, and rehabilitating the dam and headworks so as to continue to provide a sustainable irrigation supply of surface water from Cache Creek. The dam inspection and rehabilitation and betterment program for Capay Diversion Dam is presented. This includes the issues of environmental permitting, stream morphology, sediment transport and historic data collection
