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Project Data


Project # 409

Project Water Supply
Project Water Quality


Project Water Supply

Current Conditions

National Weather Service Station KSAN -- San Diego, California

Graphs from Natural Resources Conservation Service SNOTEL Data -- Basins in Lower Colorado Region -

Streamflow Forecast Map - Western Climate Center - USDA

Spring and Summer
Snowpack Information - Western Climate Center - USDA

Mountain Snowpack Maps for Great Basin and California
Mountain Snowpack Maps for Colorado and river Basin
Water Quality Information - EPA - Surf Your Watershed

San Diego
Drought Information

Palmer Drought Index Map

- Most recent map from Climate Prediction Center, NOAA

Explanation of Palmer Drought Severity Index (Text)

Third selection in list of Drought Indices from National Drought Mitigation Center

Historic Conditions

Annual Precipitation
Normal9.90 in
Maximum - 197819.41 in
Minimum - 19683.68 in
San Diego, California 1961-1990

Mean Annual63.5 ?F
Daily Maximum - 09/26/1963111 ?F
Daily Minimum - 01/04/194929 ?F
San Diego, California 1927-1996

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Project Water Quality

The MWD obtains water for distribution to its member agencies from two sources. The Colorado River Aqueduct, owned and operated by the MWD, transports water from the Colorado River to its terminus at Lake Mathews. In 1978, the MWD was entitled to 1,212,000 acre-feet per year from this source. With the completion of the Central Arizona Project in the 1980`s, this entitlement would be reduced to 550,000 acre-feet per year. MWD`s second source of water is the State Water Project, which is owned and operated by the California State Department of Water Resources. Water from this source is transported from the delta at the confluence of the Sacramento and San Joaquin Rivers to an MWD delivery point. The district`s ultimate contractual entitlement from the State is 2,011,500 acre-feet per year.

State Water Project water is transported from the State`s system through Reach 4 of the Inland Feeder System which extends from the Parris Control Facility to the Casa Loma area in San Jacinto Valley. Connections at Casa Loma permit delivery of water from the Inland Feeder directly into the San Diego Canal or into the Colorado River Aqueduct. The San Diego Canal transports State Project water as well as Colorado River water to Lake Skinner, from which deliveries are made to MWD`s member agencies in southern Riverside County and San Diego County via the San Diego pipelines.

Supplies for San Diego County Authority are diverted from MWD`s Colorado River Aqueduct near the west portal of San Jacinto Tunnel into the First San Diego Aqueduct (Pipelines 1 and 2). Pipelines 1 and 2 enter and traverse San Diego County without going through any other major MWD facilities. The San Diego Canal, which received California State Water Project water from the Casa Loma Canal, terminates at Lake Skinner. A portion of the water from Lake Skinner flows directly into Pipeline 4, while another part is processed through the Skinner Filtration Plant before entering Pipeline 3. This operational procedure may be reversed in the future.

California State Water Project water is blended with Colorado River water at the Casa Loma Turnout as both supplies flow south in the San Diego Canal to Lake Skinner.

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Facilities in Operation
Storage Facilities
Carriage Facilities


Facilities in Operation
Storage Dams1
Aqueducts225.1 mi
Pumping Plants

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Storage Facilities

Lake Skinner

- Auld Valley Reservoir

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Carriage Facilities
San Diego Aqueduct
Type:Consists principally of two parallel reinforced concrete pipelines. Includes 3.6 mi of steel pipeline (total in both pipelines), and 9.7 mi of single pipeline (full capacity) and tunnels
LocationFrom the end of the San Jacinto Tunnel of the Colorado River Aqueduct (MWD of Southern California near San Jacinto, California, south to San Vicente Reservoir, about 15 mi northeast of San Diego, California.
Construction period
Pipeline 11945-1947
Pipeline 21952-1954
Length71.1 mi
Diameter96-48 in
Design capacity of the Furst Aqueduct - Includes Pipelines 1 and 2196 cfs

Second San Diego Aqueduct - Pipeline 3 - MWD Section
LocationExtends from the Colorado River Aqueduct, near San Jacinto, to about 6 miles inside San Diego County, the MWD point of delivery to the Authority
Construction period1957-1960
Description:Consists of 16 miles of open canal that discharges blended Colorado River and Colorado State Water Project water into Lake Skinner and 19.3 miles of 72-in-diameter pipe from the Robert A. Skinner Filtration Plant to the Authority`s delivery point
Open Channel16 mi
Pipeline19.3 mi
Diameter72 in
Open canal500 cfs
Pipeline250 cfs

Second San Diego Aqueduct - Pipeline 3 - Authority`s Section
LocationExtends from the MWD delivery point to the terminal structure at Lower Otay Reservoir.
Construction period1957-1960
Description:The first 10.6 mi of the pipeline, extending from MWD`s delivery point to the Twin Oaks Vent about 5 mi north of San Marcos, consists of 72- and 75-in-diameter steel pipe. In reaches of the pipeline where heads exceed 600 ft, the pipe was cement-mortar lined and coated. The reach of the pipe from Twin Oaks Vent to Black Mountain Vent, 18.2 mi, is 75-, 72-, 69-, and 66-in prestressed concrete pipe and cement-mortar coated and lined steel pipe
Total Length59 mi
MWD delivery to Twin Oaks
Length10.6 mi
Diameter72-75 in
Twin Oaks to Black Mountain
Length18.2 mi
Diameter66, 69, 72, 75 in
MWD delivery to Miramar Reservoir
Distance34 mi
Capacity250-175 cfs
Miramar Reservoir to Otay Reservoir
Distance25 mi
Capacity:157-144 cfs

Second San Diego Aqueduct - Pipeline 4 - MWD`s Section
LocationThe first reach of MWD`s section of Pipeline 4 starts at Lake Skinner, where it receives water either from the lake or from the end of the San Diego Canal near Auld Valley and extends 9.5 mi south to the town of Temecula. The second reach starts at a point south of U.S. Highway 395, near Temecula, and extends to the Authority`s delivery point about 9.8 mi south of the Riverside-San Diego County line.
Construction period
Reach 11968-1969
Reach 21969-1971
DescriptionThe pipeline in the first reach of MWD`s section consists of 9.5 mi of 99-in-inside-diameter, prestressed concrete cylinder pipeline. The second reach consists of 9.8 mi of 89-in-inside-diameter, mortar-lined and coated, welded-steel pipe.
Total Length19.3 mi
Auld Valley to Temecula99 in
Temecula to delivery point88 in
Capacity380 cfs

Second San Diego Aqueduct - Pipeline 4 - Authority`s Section
LocationPhase I extends from Rainbow to the Crossover Aqueduct diversion structure near San Marcos. Phase II, from the Crossover Aqueduct to Escondido Mountain. Phase III, from Escondido Mountain to Miramar Reservoir. The Pomerade Pipeline (Phase IV) includes an extension of Pipeline 4 from Miramar Reservoir to Shepherd Canyon and a section of pipeline in Shepherd Canyon to the intersection of Clairemont Mesa Boulevard and Santo Road in San Diego.
Construction periodFirst 3 phases, 1969-1973. Phase IV extension, 1979.
DescriptionPipeline 4 was constructed in four phases. Phase I consists of 10.6 mi of 88-in-prestressed concrete pipe. Phase II is composed of 11.23 mi of 96-in-mortar-lined and coated, welded-steel pipe. Phase III consists of 12 mi of 96-, 72, and 69-in prestressed concrete pipe. Phase IV consists of 6.59 mi of 84-, 72-, and 54-in prestressed concrete cylinder pipe.
Total Length40.4 mi
Phase I88 in
Phase II96 in
Phase III92, 72, 69 in
Phase IV84, 72, 54 in

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Last updated: May 17, 2011