Twitchell Dam


Twitchell Dam

Twitchell Reservoir is a reservoir in southern San Luis Obispo County, California. The reservoir has a capacity of 224,300 acre-feet (277,000,000 m³) and is formed by Twitchell Dam on the Cuyama River about 66 miles (106 km) from its headwaters in the Chumash Wilderness Area and about 6 miles (9.7 km) from its confluence with the Sisquoc River, where they form the Santa Maria River. Twitchell dam was built by the United States Bureau of Reclamation between 1956 and 1958. The original names were Vacquero Dam and Vacquero Reservoir, but they were changed to honor T. A. Twitchell of Santa Maria, a proponent of the project.

The dam and reservoir provide flood control and water conservation. The Central Coast of California only receives significant amounts of rainfall during the winter, this area averaging 14 inches (360 mm) per year.

The water is stored in the reservoir during big winter storms and released as quickly as possible while still allowing it to percolate into the soil and recharge the groundwater. This means that the reservoir is usually far from full. It is estimated that the project increases reacharge by 20,000 acre feet (25,000,000 m3) per year.

Sedimentation is a problem for the reservoir, as the reservoir is being filled 70% faster than expected. This reduces its capacity and blocks the water inlet to the control gates. Some sediment has been removed by flushing it out during releases, but much of it is simply deposited immediately downstream, interfering with flows.

There is no public access to the dam or reservoir.

RegionFacilities in Mid-Pacific | Mid-Pacific Home Page
CountySan Luis Obispo
ProjectSanta Maria
Dam Type
WatercourseCuyama River
Original Construction1956-1958
Modified Construction
National ID NumberCA10197
Hydrologic Unit Code

Structural Height241.0 ft
Hydraulic Height (Normal Operating Depth at Dam)210.5 ft
Top Parapet (Elevation)
Spillway Crest Elevation651.6 ft
Crest Elevation692.0 ft
Crest Length1804.0 ft
Crest Width
Base Width
Volume of Dam Construction Materials
Streambed at Dam Axis476.0 ft
Top of Exclusive Flood Control Pool (Elevation)
Top of Joint Use Pool (Elevation)623.0 ft
Top of Active Conservation Pool (Elevation)623.0 ft
Top of Inactive Conservation Pool (Elevation)511.0 ft
Top of Dead Storage Pool (Elevation)474.0 ft

Hydraulics & Hydrology
Total Water Storage at Elevation
Maximum Water Surface Elevation
Normal Water Surface Elevation623.0 ft
Spillway Type
Auxiliary SpillwayNo
Spillway Capacity at Elevation26350.0 cfs at 686.5 ft
Auxiliary Spillway Capacity at Elevation
Uncontrolled Spillway Capacity at Elevation
Outlet Works Capacity at Elevation12700.0 cfs at 651.5 ft
Diversion Capacity at Elevation
Drainage Area1135.00 sq mi
Hydrometeorological Report (HMR)HMR 36
Probable Maximum Flood (PMF) Report

Contact Information
TitleArea Office Manager
OrganizationSouth-Central California Area Office
Address1243 "N" Street
CityFresno, CA 93721-1813
Phone (Office)559-487-5116
OrganizationSanta Maria Valley River Water Conservation District
AddressPO Box 364
CitySanta Maria, CA 93456
Phone (Fax)805 739-0763
Phone (Office)805 925-5212

Last updated: Jun 04, 2009