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The Coachella Canal Unit is one of three components authorized under Title I of the Colorado River Basin Salinity Control Act. The other two components are the Desalting Complex Unit and the Protective and Regulatory Pumping Unit.
The original 123-mile Coachella Canal was a feature of the Coachella Division of the All-American Canal System, Boulder Canyon Project. The Coachella Canal delivers Colorado River water from the All-American Canal to irrigate 78,530 acres of agricultural land in the Coachella Valley of California. Originally, the first 86 miles of the waterway were unlined, and the remaining 37 miles were concrete lined. The original canal also had six turnouts to serve about 6,500 acres of non-federal land on Imperial East Mesa, of which about 500 acres were developed. The capacity of the original canal was 2,500 cubic feet per second at the turnout from the All-American Canal where it began, and was decreased through successive reaches to 1,300 cubic feet per second at the beginning of the last 37 miles -- the lined section (terminal end).
After the canal`s completion in 1948, seepage losses developed along the 86-mile unlined section. The initial 49 miles of the original 86-mile unlined section traversed the coarse, sandy soils of Imperial East Mesa where the most severe seepage occurred. At the canal`s starting point, the turnout from the All-American Canal at Drop No. 1, the average annual diversions were 497,800 acre-feet. Of this amount, an estimated average of 168,470 acre-feet per year had been lost because of canal seepage.
The primary purpose of the Coachella Canal Unit was to reduce the water losses in the Coachella Canal by constructing a new concrete-lined canal to replace the initial 49 miles of the unlined section of the canal. This 49-mile replacement extends from the turnout at Drop No. 1 on the All-American Canal to Mile Post 49, where the replacement rejoins the original canal just upstream from siphon No. 7. The water saved by the new lining was used to replace water bypassed to the Santa Clara Slough, which is not counted as part of Mexico`s allotment of Colorado River water.
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The plan called for a principal feature of the unit to be a new 49-mile canal which replaced the initial 49 miles of the original 86-mile unlined section. Other features consisted of four new check drop structures, eight siphons, six irrigation turnouts, and operating roads. The existing Coachella Canal Turnout, siphon No. 7, and flood protective works were retained with only minor modification. All other existing structures on the first 49 miles of the canal were abandoned, including the replaced unlined section of the canal. The new canal is designed to accommodate a flow of 1,550 cubic feet per second.
The estimated average seepage of the originally unlined 49-mile length of canal was 141,000 acre-feet per year. This loss was reduced to 9,000 acre-feet per year after lining was completed, representing an annual savings of 132,000 acre-feet of water.
When the Coachella Canal was first placed into service in 1948, it was estimated the irrigation potential on Imperial East Mesa would be about 6,500 acres. However, only 500 acres of this land have been developed. Congress made a provision in the law, and authorized the Colorado River Basin Salinity Control Project to approve purchase of private lands on Imperial East Mesa adjacent to the Coachella Canal. The acquisition of these lands by the Federal Government was at Federal expense, with the lands returning to public domain. By purchase of these private lands, the Imperial Irrigation District was relieved of responsibility to provide these lands with irrigation services.
A reduction in greenbelt areas and seepage ponds occurred as a result of construction of the newly lined section, causing loss of wildlife habitat. Five measures were recommended for mitigation:
1. Construct wells with windmills and watering devices for wildlife use. Each windmill is capable of producing 300 gallons of water per hour when operating under optimum conditions. The California Department of Fish and Game is responsible for the operation and maintenance of the windmills with funds provided by the Bureau of Reclamation.
2. Contract with the California Department of Fish and Game to restore fish and wildlife habitat at the Finney-Ramer Wildlife Management Unit.
3. Acquire and develop about 363 acres of additional land adjacent to the Salton Sea National Wildlife Refuge through the construction of dikes, ponds, and marshes.
4. Purchase the Oasis Tract of land which contains high wildlife value, is dedicated to public ownership, and will be maintained in its present condition.
5. Develop and 160-acre Wister Habitat Area by constructing perimeter roads, levees, ponds, and supply ditches to provide marsh habitat suitable for wildlife.
Power transmission lines were constructed from existing powerlines. They provide energy to electric motors to operate gates and sensory devices located at control points for regulating and measuring flows.
The check gates in the canal have motorized controls which also match the sensory gate opening equipment. This equipment was furnished and installed by the Coachella Valley Water District. Monitoring equipment was installed at all check structures, and remote control sensory equipment measures the rate of flow through each of two parshall flumes located at the inlet and outlet transition of the 49-mile lined portion of the canal.
The entire length of the relocated canal is flanked by two operating roads. A 20-foot-wide gravel surface road, used for operations and maintenance, was constructed along the southwest bank of the new canal; and a 16-foot unsurfaced service road was graded along the northeast bank. Abutments were provided on each side of the canal, about 2,000 feet downstream from the turnout, for a vehicle bridge to provide access to a Bureau of Land Management recreation area.
Prior to the new lining, the Imperial Irrigation District operated the first 49 miles of the original canal, and the Coachella Valley Water District operated and maintained the remaining 74 miles. Upon completion of the lining project, the operation and maintenance of the entire 123-mile length of the canal was assumed by the Coachella Valley Water District.
Fish and wildlife mitigation measures are operated by local agencies at their expense.
Title I of the Colorado River Basin Salinity Control Act provided the means to comply with the obligations made by the United States to Mexico in Minute No. 242 of the International Boundary and Water Commission, United States and Mexico. This minute, formally approved by the United States and Mexico on August 30, 1973, is an agreement by the two governments. It provides that the United States shall adopt measures to ensure that 1.36 million acre-feet of water delivered annually to Mexico upstream of Morelos Dam shall have an average salinity of no more than 115 +/-30 parts per million over the annual average salinity of Colorado River water arriving at Imperial Dam. The agreement further provides for the United States to deliver to Mexico, across the land boundary at San Luis, Arizona, and in the Limitrophe Section of the Colorado River downstream from Morelos Dam, approximately 140,000 acre-feet of water annually, with salinity substantially the same as that of water customarily delivered there. The minute also provided that the concrete-lined Main Outlet Drain Extension (MODE) be extended from Morelos Dam to the Cienaga de Santa Clara in Mexico at United States expense. The Coachella Canal Unit is one of the features authorized under Title I of the 1974 Salinity Control Act.
Since the Coachella Canal was first placed into service in 1949, numerous tests, studies, and surveys have been conducted to determine the effectiveness of the waterway and the approximate amount of water lost by seepage along the entire 123-mile length. Several official studies and reports have been published.
The Coachella Canal Unit was authorized by the Colorado River Basin Salinity Control Act, Title I, of Public Law 93-320, 93rd Congress, H.R. 12165, dated June 24, 1974 (88 Stat. 266). An amendment to the act provided funds for mitigating fish and wildlife losses associated with replacing the initial 49 miles of the Coachella Canal.
Construction of the relocated portion of the Coachella Canal, including advance planning and reconstruction activities, required about 3 years. The lining work was completed in 1980, and operation and maintenance was transferred to the Coachella Valley Water District on November 1, 1981.
In October 2003, the San Diego County Water Authority, Coachella Valley Water District, Imperial Irrigation District, Metropolitan Water District of Southern California, the state of California, and the U.S. Department of the Interior completed a complex set of agreements to conserve and transfer Colorado River water. One of the key agreements, known as the Colorado River Quantification Settlement Agreement, settled decades of dispute over Colorado River water use and provided a means for California to live within its 4.4-million-acre-foot basic annual apportionment of water from the Colorado River.
Projects to line the All-American and Coachella canals were critical components of the Quantification Settlement Agreement. As part of this agreement, the San Diego Water Authority obtained the rights to the canal lining water. This amounts to 77,700 acre-feet per year for 110 years from the lining of these canals. The lining conserves water lost due to seepage and help California reduce its overdependence on Colorado River water. Under this agreement, 35 miles of parallel, concrete-lined canal were constructed next to the existing Coachella Canal; all work was completed in Dec 2006.
The lining of the first 49 miles of the Coachella Canal resulted in direct benefits by saving 132,000 acre-feet of water per year, and a reduction in operation and maintenance costs.