Twitchell Reservoir
Encyclopedia
Twitchell Reservoir is a reservoir in southern San Luis Obispo County
and northern Santa Barbara County
in California
. The reservoir has a capacity of 225000 acre.ft and is formed by Twitchell Dam on the Cuyama River
about 66 miles (106.2 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 (355.6 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 recharge by 20000 acre.ft annually. Sedimentation is a problem for the reservoir, as the reservoir is being filled 70 percent 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.
San Luis Obispo County, California
San Luis Obispo County is a county located along the Pacific Ocean in the Central Coast of the U.S. state of California, between Los Angeles and the San Francisco Bay Area. As of the 2010 census its population was 269,637, up from 246,681 at the 2000 census...
and northern Santa Barbara County
Santa Barbara County, California
Santa Barbara County is a county located in the southern portion of the U.S. state of California, on the Pacific coast. As of 2010 the county had a population of 423,895. The county seat is Santa Barbara and the largest city is Santa Maria.-History:...
in California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
. The reservoir has a capacity of 225000 acre.ft and is formed by Twitchell Dam on the Cuyama River
Cuyama River
The Cuyama River is a river in southern San Luis Obispo County, northern Santa Barbara County, and northern Ventura County, in the U.S. state of California. It joins the Sisquoc River forming the Santa Maria River...
about 66 miles (106.2 km) from its headwaters in the Chumash Wilderness Area and about 6 miles (9.7 km) from its confluence with the Sisquoc River
Sisquoc River
The Sisquoc River is a river in northeastern Santa Barbara County, California. It is a tributary of the Santa Maria River, which is formed when the Sisquoc River meets the Cuyama River. The river is long and originates on the north slopes of Big Pine Mountain, at approximately...
, where they form the Santa Maria River. Twitchell dam was built by the United States Bureau of Reclamation
United States Bureau of Reclamation
The United States Bureau of Reclamation , and formerly the United States Reclamation Service , is an agency under the U.S...
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
Santa Maria, California
Santa Maria is a city in Santa Barbara County, on the Central Coast of California. The 2010 census population was 100,062, putting it ahead of Santa Barbara for the first time and making it the largest city in the county...
, a proponent of the project.
The dam and reservoir provide flood
Flood
A flood is an overflow of an expanse of water that submerges land. The EU Floods directive defines a flood as a temporary covering by water of land not normally covered by water...
control and water conservation
Water resources
Water resources are sources of water that are useful or potentially useful. Uses of water include agricultural, industrial, household, recreational and environmental activities. Virtually all of these human uses require fresh water....
. The Central Coast of California only receives significant amounts of rainfall during the winter, this area averaging 14 inches (355.6 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
Groundwater
Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of rock formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock...
. This means that the reservoir is usually far from full. It is estimated that the project increases recharge by 20000 acre.ft annually. Sedimentation is a problem for the reservoir, as the reservoir is being filled 70 percent faster than expected. This reduces its capacity and blocks the water inlet to the control gates. Some sediment
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
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.