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District Description
Westlands Water District consists of nearly 1,000 square miles of prime farmland between the Diablo Range of the California Coast Range mountains and the trough, or lowest point, of the San Joaquin Valley in western Fresno and Kings Counties(map). Westlands (borders) averages 15 miles in width and stretches 70 miles from Mendota on the north to Kettleman City on the south.
District Formation
Westlands was formed under California Water District Law in 1952 upon petition of landowners located within the District's proposed boundaries. Nearly all land within the current Westlands' boundaries was at one time farmed using groundwater.
Negotiations between Westlands and the U.S. Bureau of Reclamation began on a contract to provide a dependable, supplemental supply of surface water through the Bureau's Central Valley Project (CVP) shortly after the District's formation. At that time, the federal government was considering the development and construction of the CVP's San Luis Unit (SLU). This involved cooperation between the federal and state governments with regard to shared water storage facilities and conveyance systems.
When the original Westlands was organized, it included approximately 376,000 acres. In 1965 it merged with its western neighbor, Westplains Water Storage District, adding 210,000 acres. Additionally, lands comprising about 18,000 acres were annexed to the District after the merger to form the current 604,000-acre District with an irrigable acreage of 567,800 acres. The original Westlands is referred to as Priority Area I and Westplains is referred to as Priority Area II, each under a separate water service contract with the Bureau. Priority Area III currently does not have a firm water service contract and receives only surplus CVP water or hardship water when available from the Bureau during drought periods to preserve trees and vines.
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Total Acres |
Irrigable Acres |
|
Original size |
376,000 |
337,000 |
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Current size |
604,000 |
570,000 |
Westlands Water District does not have a M&I contract for Project water, but the District does convey water to other entities that do have contracts for Project water. Westlands does deliver water for incidental agricultural uses and it’s contract allows for non-agricultural uses that has been termed M&I.
The purpose of a district is to administer the water contract and to maintain the distribution system.
Soils and Hydrology
The San Joaquin Valley is a wide bedrock basin filled with thousands of feet of alluvial sediment deposited by streams and rivers flowing out of
the adjacent mountains on both the east and the west. Westlands is located near the centerline of this basin, bordered on the east by the Fresno Slough and on the west by the Diablo Range of the California Coast Ranges.
The Sierra Nevada on the east side of the Valley is predominately comprised of uplifted granitic rock overlaid in areas by sedimentary and metamorphic rock. Sierran alluvial deposits in the District consist primarily of well-sorted sands, with minor amounts of clay. The Sierran alluvium decreases in thickness and increases in depth below the surface toward the west. These coarse-textured sediments are characterized by high permeability and a low concentration of water soluble solids.
One of the principal subsurface geological features of the San Joaquin Valley is the Corcoran Clay formation. Formed as a lake bed about 600,000 years ago, this clay layer ranges in thickness from 20 to 200 feet and underlies most of the District. Varying in depths from 200 to 500 feet in the Valley trough to 850 feet along the Diablo Range, the Corcoran Clay divides the groundwater system into two major aquifers--a confined aquifer below and a semi-confined system above.
The Diablo Range consists of complex, folded, and uplifted mountains which are composed predominantly of sandstones and shales of marine origin. These sandstones and shales contain salts, as well as trace elements such as selenium. Eroded by creeks flowing from the Diablo Range, sediments form gentle sloping alluvial fans. The texture of the Diablo Range deposits depends on the relative position on the alluvial fan and ranges from coarse sand and gravel to fine silt and clay. Generally, those portions of Westlands lying high on the alluvial fans have permeable, medium-textured soils. With decreasing elevation from the west to east, soil textures become finer. These fine textured soils are characterized by low permeability and increased concentrations of water soluble solids, primarily salts and trace elements.