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Approximately six miles south of the Riverside-San Diego County line, the San Diego County Water Authority (Authority) takes delivery of imported water from the Colorado River and northern California that The Metropolitan Water District of Southern California (Metropolitan) has conveyed from Lake Skinner in Riverside County. Through five large-diameter pipelines that traverse the county north to south, the Authority delivers this water to its member agencies. The pipelines are 48 to 108 inches in diameter, and carry either filtered or unfiltered water. They have a combined capacity to carry 900 million gallons a day.
Most of the pipelines in the aqueduct system have been constructed to deliver water by gravity. However, pipeline sections constructed after 1993 are strong enough to withstand pumping pressure that could send water in the opposite direction in case of an emergency.
The pipelines are divided into two alignments, or routes, known as the First Aqueduct and the Second Aqueduct. The First Aqueduct includes Pipelines 1 and 2. The Second Aqueduct includes Pipelines 3, 4 and 5. The newer sections of these pipelines also have names reflecting the communities where they are located.
Four additional, shorter pipelines run east and west connecting the two aqueducts.
In addition to the major pipelines, many other aqueduct system components keep the water flowing. Flow control facilities, pump stations and other facilities along the pipelines ensure that the right amount of water is flowing to customers.
The San Diego Project consists of the First and Second San Diego Aqueducts. These two aqueducts, with two branch lines, make up the backbone of the San Diego County Water Authority system. The First Aqueduct consists of Pipelines 1 and 2, which extend from Metropolitan's Colorado River Aqueduct near San Jacinto, California, to the city of San Diego`s San Vicente Reservoir, approximately 15 miles northeast of the city. Pipeline 1, designed by the Bureau of Reclamation, was constructed by the Department of the Navy to relieve a water supply emergency in San Diego County. Pipeline 2, roughly paralleling the first, was designed and constructed by the Bureau of Reclamation. The two pipelines share common tunnels and inverted siphons. They are operated as single units.
The Second Aqueduct consists of Pipelines 3, 4 and 5. Although these pipelines are in common right-of-way for most of their length, they do not share any facilities south of Skinner Lake and are operated separately. Pipeline 3 extends from the Colorado River Aqueduct near Hemet, in Riverside County, to San Diego`s Lower Otay Reservoir. Pipeline 4 terminates at San Diego`s Alvarado Treatment Plant near Lake Murray. Pipeline 5, 96-inches in diameter and 20 miles long, delivers 400 cfs to users between the Authority's Diversion Structure and the Miramar Reservoir.
Metropolitan, of which the San Diego County Water Authority is a constituent member, constructed the northern 35 miles of the Second Aqueduct to a major delivery point of the Authority, located about 6 miles south of the Riverside-San Diego County line. Metropolitan owns and operates this section of the aqueduct. The Authority constructed the remaining 59 miles of the aqueduct, and owns and operates it.
The 12.5-mile Fallbrook-Ocean Branch originates from the First Aqueduct at Rainbow and extends to Morrow Reservoir. The La Mesa-Sweetwater Branch also originates from the First Aqueduct at Slaughterhouse Canyon, and extends through Lakeside and El Cajon to Sweetwater Reservoir.
A number of connecting pipelines have been constructed to provide flexibility in operating the system. One pipeline runs from the Second Aqueduct at Twin Oaks Valley to refill the First Aqueduct north of Escondido with untreated water after the agencies to the north have utilized the original capacity of the aqueduct. An interconnection upstream from Twin Oaks Valley permits transfer of flows between Pipeline 3 and Pipeline 4.
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Metropolitan diverts water from the Colorado River at Lake Havasu and conveys it through the Colorado River Aqueduct to its terminus at Lake Mathews. Reach Five of the Metropolitan Inland Feeder System comprises the First and Second San Diego Aqueducts. The four San Diego pipelines of the two aqueducts have a combined capacity of 826 cubic feet per second. Included in this reach of the inland feeder system is Lake Skinner, a regulating and storage reservoir, and the Robert A. Skinner Filtration Plant.
Metropolitan's San Diego Canal receives California State Water Project water from the Casa Loma Canal. Flow in the San Diego Canal is normally diverted into Lake Skinner and then routed to San Diego Pipelines 3 and 4 or into the Robert A. Skinner Filtration Plant through the outlet works. Water from Lake Skinner is routed directly into the filtration plant; treated water from the plant is diverted into San Diego Pipeline 3. Untreated water from the lake is diverted directly into Pipeline 4 after passing through the Auld Valley Control Structure. This structure controls the flow of water either from Lake Skinner, or directly from the San Diego Canal through the reservoir bypass pipeline. Lake Skinner has a total capacity of 44,000 acre-feet, and a maximum elevation of 1,479.0 feet.
In 1977, the Skinner Filtration Plant, located near Lake Skinner, had a capacity of 150 million gallons per day. An extension of the plant in 1979 increased the capacity to 240 million gallons per day. A further expansion, completed in 1980, raised the capacity to 340 million gallons per day.
The San Jacinto Regulating Reservoir of the First San Diego Aqueduct was removed from service on October 24, 1974, because of a requirement of the State of California Safety of Dams Division. Water for Pipeline 2 was subsequently taken from Pipeline 1 at Rainbow Pass, and Pipeline 1 receives water directly from the San Diego Canal near San Jacinto.
No storage facilities are owned or operated by the Authority. However, it has contractual rights to store up to 40,000 acre-feet in San Diego's San Vicente Reservoir, terminus of the First Aqueduct. The Authority also has an agreement with the city of San Diego which permits storage of up to 2,500 acre-feet in Lower Otay Reservoir, terminus of Pipeline 3. Lake Jennings is used to store as much as 2,000 acre-feet, under terms of an agreement with Helix Water District. The Authority has agreements to store up to 1,800 acre-feet in the city of Escondido`s Dixon Reservoir and 3,855 acre-feet in the Sweetwater Reservoir of the California American Water Company.
The First San Diego Aqueduct is about 70 miles long and water flows by gravity from an intake at an elevation of 1500 feet to the San Vicente Reservoir at an elevation of 760 feet. The first two miles, the tunnels, and certain other sections not readily accessible were built to full capacity during construction of the first pipeline. The remaining sections, approximately 60 miles, compose a double pipeline. The separate pipelines are precast concrete pipe. The design capacity of the First San Diego Aqueduct is 196 cubic feet per second.
There are seven tunnels ranging in length from 500 to 5,700 feet. These tunnels, together with the diversion line to the regulating reservoir and the short reaches of full capacity pipeline, total about 14 percent of the length of the aqueduct.
The 94-mile-long Second San Diego Aqueduct flows by gravity from Metropolitan's takeoff point to the Otay Reservoir through Pipelines 3 and 4. Pipeline 3 consists of a 500-cubic-foot-per-second, 16-mile-long canal. The remaining section, from Lake Skinner to its terminus, is composed of a combination of prestressed concrete pipe and steel pipe, and has an initial capacity of 250 cubic feet per second. At the Otay Reservoir, the pipeline's capacity is 144 cubic feet per second. Pipeline 4 is composed of 99-inch-diameter prestressed concrete pipe with an initial capacity of 380 cubic feet per second.
The San Diego County Water Authority is responsible for the operation and maintenance of the First and Second Aqueducts south from Metropolitan's point of delivery. The Metropolitan Water District of Southern California is responsible for the operation and maintenance of the aqueducts north of the delivery point. On December 3, 1997, title for the First Aqueduct (Pipelines 1 and 2) was transferred from the United States to the San Diego County Water Authority. The Authority subsequently transferred title to that portion of the aqueduct north of The Metropolitan Water District delivery point to Metropolitan.
Over a period of years, the city of San Diego developed a domestic water supply by acquisition or construction of a number of dams. To obtain a dependable, uniform supply of water, the city contracted for storage in Lake Mead, the reservoir formed by Hoover Dam, for a quantity of water not to exceed 112,000 acre-feet annually. On October 2, 1934, the city entered into a contract with the Bureau of Reclamation. This contract provided for the city`s participation in construction of Imperial Dam and the All-American Canal under the Boulder Canyon Project Act. Under that contract, a capacity of 155 cubic feet per second in the All-American Canal was provided for the city.
On November 29, 1944, under a Presidential directive, Reclamation completed plans and specifications for a one-half capacity aqueduct for the MWD connection; the Navy's Bureau of Yards and Docks was directed to perform the construction. In addition, Reclamation, with the Navy Department cooperating, was asked to construct additional works needed to bring the aqueduct to its ultimate capacity for carrying San Diego's allotted water.
A contract dated October 4, 1946, changed the point of delivery of Colorado River water to which San Diego had contractual rights from Imperial Dam to Parker Dam. Under a contract dated October 4, 1946, San Diego assigned its Colorado River water rights to the MWD.
On December 17, 1947, the San Diego County Water Authority was formally annexed to The Metropolitan Water District of Southern California, thereby becoming entitled to Colorado River water from Metropolitan's system for distribution to the Authority's member agencies in San Diego County.
When construction was completed in 1947 and Pipeline 1 of the First Aqueduct was placed in operation, the San Diego County Water Authority recommended that the aqueduct immediately be enlarged to full capacity to safeguard the area from critical water shortages. Reclamation was requested to make the necessary survey and reports. In January 1951, a report was submitted proposing the enlargement of the aqueduct to full capacity by the addition of Pipeline 2 to the conduit of the same capacity as that previously designed and constructed. The Authority selected the parallel location as recommended for Pipeline 2.
In 1956, the California State Legislature appropriated funds for a study to determine the most practical route by which northern California water might be brought into San Diego County. The report recommended that a canal section, about 30 miles long, with a capacity of 1,000 cubic feet per second, be constructed as the northerly portion of the aqueduct, beginning at the west portal of the San Jacinto Tunnel of Metropolitan's Colorado River Aqueduct and extending to the vicinity of Auld Valley in Riverside County. The remainder of the proposed aqueduct, beginning at the end of the canal, was recommended to have a capacity ranging from 432 cubic feet per second at the upper end to 98 cubic feet per second at the terminus at Otay Reservoir. In January 1957, the Authority adopted the route of the Second San Diego Aqueduct, as recommended by the State.
The State of California commenced construction of the Second San Diego County Feeder Line, which is the northerly portion of the Second San Diego Aqueduct, from the West Portal of the San Jacinto Tunnel to a delivery point and connection to the Authority`s system, located about 6 miles south of the Riverside-San Diego County line. The district adopted a canal capacity of 500 cubic feet per second instead of the 1,000 cubic feet per second recommended by the State and a pipeline capacity of 250 cubic feet per second instead of the 432 cubic feet per second recommended by the State.
It was recognized in the 1950's that additional water supply sources for the Southern California area would be required by the early 1970's. On November 4, 1960, the MWD entered into a contract with the State of California for 1,500,000 acre-feet annually from the State Water Project. As a result of the 1963 United States Supreme Court decision in the case of Arizona v. California, MWD was subject to the loss of about half of its 1,212,000 acre-feet entitlement from the Colorado River. In view of this condition, the Metropolitan-State of California contract was amended to increase Metropolitan's entitlement to State water to 2,011,500 acre-feet per year.
The California Aqueduct, the key feature of the State Water Project, was dedicated on May 18, 1973. The terminal storage reservoir of the California Aqueduct is Lake Perris.
In May 1943, the Bureau of Reclamation was requested to investigate feasibility of a conduit connecting the west end of the San Jacinto Tunnel on Metropolitan's Colorado River Aqueduct to the San Diego area, and a conduit connecting the All-American Canal to the San Diego area. A preliminary report on these investigations was submitted in September 1944. In 1945, an interdepartmental committee was appointed by the President of the United States to study the water supply of the City of San Diego, and to recommend a plan for securing a supplemental supply. The report of the President's Committee was published as Senate Document No. 249, 78th Congress, 2d session. Recommended in the report was the immediate construction by the Government of an aqueduct connecting with the Colorado River Aqueduct near San Jacinto.
Investigations led to the preparation of a feasibility report by the Bureau of Reclamation on the San Diego Project, Metropolitan Connection Enlargement (Pipeline 2 of the First San Diego Aqueduct), in September 1951. Construction of Pipeline 2 began March 23, 1953.
On February 9, 1956, the Authority proceeded with preliminary plans for construction of the Second San Diego Aqueduct. The State of California provided funds for investigations to determine the most practical route by which Feather River water might be brought into San Diego County and delivered to the Authority.
The 1956 California State Legislature appropriated funds and instructed the Department of Water Resources to make detailed studies to determine the most feasible route by which Feather River water could be brought into San Diego County and delivered to the Authority for distribution. On January 15, 1957, the Authority approved the report on these investigations and proceeded with construction plans and specifications for Pipeline 3 of the Second San Diego Aqueduct.
On September 18, 1956, Metropolitan initiated the preparation of plans and specifications for construction of the Second San Diego County Feeder Line, which is the northerly portion of the Second Aqueduct.
In June 1966, the Authority contracted with Metropolitan to provide engineering services on the Perris-to-Costa Loma Aqueduct and Pipeline 4 of the Second Aqueduct. At the end of the year, the first reach of Metropolitan's section of the pipeline was under construction, and the Authority was making preliminary investigations of its section of Pipeline 4. In May 1968, the Authority commenced the final designs of its portion of Pipeline 4.
Construction of the initial portion of the aqueduct was authorized by the President on November 29, 1944, as a wartime expedient, and ratified by Congress on April 15, 1948.
The 82nd Congress authorized construction of the second barrel of the San Diego Aqueduct by the Secretary of the Navy under Public Law 171, on October 11, 1951.
On June 7, 1966, voters throughout The Metropolitan Water District of Southern California service area and San Diego County approved bond issues which provided authorization and funds for construction of the Second San Diego Aqueduct. Under this authorization, construction of the Second San Diego Aqueduct was accomplished by Metropolitan and the Authority.
Construction of Pipeline 1 of the First Aqueduct by the Navy began in 1945 and was completed in 1947. Pipeline 2 was constructed by the Bureau of Reclamation from 1952-54. Construction of the Second Aqueduct began in 1957. The Metropolitan section of Pipeline 3 was completed in May 1960, and the Authority's section in November 1960. Construction of the Metropolitan section of Pipeline 4 of the Second Aqueduct started in 1968 and was completed in 1971. The Authority started construction of its section of Pipeline 4 in 1969. Construction of the first three phases of the pipeline was completed in 1973, and the fourth phase was completed in 1979. In 1982, Pipeline 5 was added to the Second Aqueduct.
The Colorado River Aqueduct supplies 75 to 95 percent of all the water used by the more than 3 million people in San Diego County. The total water supply of the Authority comes through the facilities of the First and Second San Diego Aqueducts, providing water for municipal, domestic and other beneficial uses in a 1,474 square-mile service area.
The water serves six cities, one public utility district, five water districts, eight municipal water districts, three irrigation districts, and one federal agency: Carlsbad, Fallbrook, Helix, Lakeside, Olivenhain, Otay, Padre Dam, Rainbow, Ramona, Rincon del Diablo, San Dieguito, Santa Fe, South Bay, Vallecitos, Valley Center, Vista, and Yuima water districts; Camp Pendleton Marine Corps Base; and the cities of Del Mar, Escondido, National City, Oceanside, Poway, and San Diego.
Eighty-five percent of the water goes to municipal and industrial uses, while the other 15 percent serves agricultural areas.
Lake Skinner, constructed by the MWD as part of the San Diego Project from 1970-1972, is managed by Riverside County Parks Department. The recreation area provides hiking, swimming and fishing opportunities, and more than 300 sites for RV and tent camping.