PMF Routing MWS Elev . Authorized in 1954, this joint water conservation and flood control project consists of Twitchell Dam and Reservoir, formerly called Vaquero Dam and Reservoir, constructed by the Bureau of Reclamation, and a system of river levees constructed by the Corps of Engineers. The Cuyama River, with its principal tributaries Alamo Creek and Huasna River, is the main source of water for the project. The drainage basin, comprising approximately 1,135 square miles above Twitchell Dam , lies along the southern boundary of San Luis Obispo County and the northern edge of Santa Barbara County. Twitchell Dam is located on the Cuyama River about 6 miles upstream from its junction with the Sisquoc River.
All water used within the area is obtained by pumping from the ground-water reservoir.
The objective of the project is to release regulated water from storage as quickly as it can be percolated into the Santa Maria Valley ground-water basin. Therefore, Twitchell Reservoir is empty much of the time, and recreation and fishing facilities are not included in the project. Twitchell Dam is an earthfill structure, has a structural eight of 241 feet, of which 216 feet are above streambed , a crest length of 1,804 feet, and contains approximately 5,833,000 cubic yards of material. The dam regulates flows along the lower reaches of the Cuyama River and impounds surplus flows for release in the dry months to help recharge the ground-water reservoir underlying the Santa Maria Valley, thus minimizing water waste.