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Santa Maria Project History (43 KB) (pdf)
General Description| Plan| Development| Benefits

General Description

The Santa Maria Project is about 150 miles northwest of Los Angeles, California. Authorized in 1954, this water conservation and flood control project also provides full and supplemental irrigation water to approximately 35,000 acres of cropland. Reclamation constructed Twitchell Dam and Reservoir, formerly called Vaquero Dam and Reservoir, and the U.S. Army Corps of Engineers constructed a system of river levees.

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. All water used within the area is obtained by pumping from the ground-water reservoir.

The Santa Maria Project is one of three `seacoast projects`capture the seasonal floodwaters that would otherwise `waste to the sea.` The others are the Cachuma (http://www.usbr.gov/dataweb/html/cachuma.html) and Ventura River (http://www.usbr.gov/dataweb/html/ventura.html) Projects.

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Twitchell Dam is on the Cuyama River about 6 miles upstream from its junction with the Sisquoc River. The multiple-purpose Twitchell Reservoir has a total capacity of 224,300 acre-feet. It stores floodwaters of the Cuyama River, which are released as needed to recharge the ground-water basins to prevent salt water intrusion.

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.

Facility Descriptions

Twitchell Dam

Twitchell Dam is an earthfill structure, has a structural height 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.

Operating Agencies

After construction, Reclamation transferred operations to the Santa Barbara County Water Agency. The Santa Maria Valley Water Conservation District physically operates the reservoir.

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The area was devoted to cattle ranching until the great droughts of 1862-1864 caused a decline in the industry. In about 1867, settlers arrived and introduced new types of agriculture. Grain production soon developed into an important industry, and fruit and bean crops were started. By 1900, fruit production began to decline, mostly from the unfavorable climate. Cattle raising continued to be prominent since a major part of the watershed was suitable for grazing.

Irrigation was introduced in 1897 when the Union Sugar Company of San Francisco began growing sugar beets near Betteravia. Development of artesian wells to irrigate the beets offered new opportunities, which led gradually to the establishment of intensive vegetable growing. In 1898, a company was organized to take water from the Sisquoc River and transport it east by gravity canal to the city of Santa Maria and adjacent lands. Several years later a flood destroyed the dam and headgates, discouraging further efforts in this method of irrigation. During the 1920`s, the crop pattern shifted from beans and grain to vegetables and flower seeds. Irrigated agriculture is now attained by pumping from wells.


The first hydrologic report on the area was submitted to the county of Santa Barbara in 1931. This report discussed the feasibility of storage reservoirs on the Cuyama and Sisquoc Rivers. Results of other flood control investigations are contained in reports of the U.S. Army Corps of Engineers and the U.S. Department of Agriculture.

Reclamation activities in the Santa Maria area were initiated under a cooperative contract dated July 1, 1941, between the Santa Barbara County Supervisors and Reclamation.

In 1942, a land classification survey was made, followed by a report on the Santa Maria Basin as part of the county water resources investigations. This report, issued in 1946, was made in cooperation with the County Board of Supervisors.

The investigation, which resulted in construction of the project, was given impetus at a conference with the Corps of Engineers in November 1949, where an agreement was made to investigate a joint conservation and flood control project for the basin.

During this investigation, a reconnaissance geologic survey was made of 14 damsites, and a more detailed study was made of 7 of the most promising sites. A total of 68 miles of river profile was surveyed and detailed topographic maps made of 5 sites. Three foundation explorations were made before the Vaquero site was selected.

The resulting report was sent to the Reclamation in November 1951. After approval by the Commissioner, the Secretary of the Interior, and the Bureau of the Budget, it was printed as House Document 217, 83d Congress, 1st session, dated July 29, 1953.


The project was authorized on September 3, 1954, by act of Congress (Public Law 774, 83d Congress, ch. 1258, 2d session, 68 Stat. 1190).


Construction of Twitchell Dam was started in July 1956 and completed in October 1958. During the construction period, the name of Vaquero Dam and Reservoir was changed to Twitchell Dam and Reservoir through the efforts of the Santa Maria Valley Water Conservation District and Board of Supervisors of Santa Barbara County, with the concurrence of the Board of Geographic Names and Reclamation.

As part of the project, the Corps constructed a series of levees and channel improvements along the Santa Maria River to protect the city of Santa Maria and the Santa Maria Valley.

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Twitchell Reservoir impounds winter floodwaters for later release down the river channel at a predetermined rate for maximum percolation into the ground-water reservoir. Individual landholders pump water from this reservoir.

The principal irrigated products of the project area are field crops, including lettuce, beans, broccoli, carrots, and potatoes; vegetable and flower seeds; and irrigated pasture.

Flood Control

Flood control benefits are achieved through storage of winter floodwaters in Twitchell Dam.

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Last updated: May 17, 2011