San Diego Aqueduct
San Diego Aqueduct
Colorado River Aqueduct
Casa Loma Canal Aqueduct
San Vicente Reservoir
Lower Otay Reservoir
|Official name||San Diego Project|
|Maintained by||San Diego County Water Authority|
|Total length||225.1 mi (362.3 km)|
196 cu ft/s (5.6 m3/s)
canal: 500 cu ft (14 m3)
pipeline 3: 250 cu ft (7.1 m3)
pipeline 4: 380 cu ft (11 m3)
|Construction start||First Aqueduct|
pipeline 1: 1945
pipeline 2: 1952
pipeline 3: 1957
pipeline 4: 1968
pipeline 1: 1947
pipeline 2: 1954
pipeline 3: 1960
pipeline 4: 1971
The San Diego Aqueduct, or San Diego Project, is a system of four aqueducts in the U.S. state of California, supplying about 70 percent of the water supply for the city of San Diego.  The system comprises the First and Second San Diego Aqueducts, carrying water from the Colorado River west to reservoirs on the outskirts of San Diego. The 70-mile (110 km) First Aqueduct consists of the pipelines 1 and 2, which run from the Colorado River Aqueduct near San Jacinto, California, to the San Vicente Reservoir, approximately 15 miles (24 km) northeast of the city. Pipelines 3 and 4 make up the 94-mile (151 km) Second Aqueduct. Together, these four pipelines have a capacity of 826 cubic feet per second (23.4 m3/s). The smaller, 12.5-mile (20.1 km) Fallbrook-Ocean Branch branches from the First Aqueduct into Morrow Reservoir. The La Mesa-Sweetwater Branch originates from the First Aqueduct, flowing into the Sweetwater Reservoir. 
The First Aqueduct was designed by the Bureau of Reclamation and constructed from 1945 to 1947 by the Navy Department. Pipeline 2, of the First Aqueduct, was built by the Bureau of Reclamation from 1952 and 1957, roughly paralleling Pipeline 1. In 1957, the construction of Pipeline 3 of the Second Aqueduct was begun by the Metropolitan Water District (MWD), completing it in May 1960. In 1968, the construction of Pipeline 4, of the Second Aqueduct, began. Pipeline 4 was completed in 1971. In 2005, the San Diego County Water Authority began construction on the 11-mile-long (18 km), 8.5-foot-wide (2.6 m) San Vicente Pipeline, connecting the San Vicente Reservoir to the Second Aqueduct. Construction on the project was complete completed in 2010. 
The First Aqueduct, built of two parallel precast concrete pipes, ranging in diameter from 96 to 48 in (240 to 120 cm), branches from the Colorado River Aqueduct in San Jacinto, California just north of the San Jacinto River, continuing 70 mi (110 km) south to its terminus at San Vicente Reservoir.  There are seven tunnels on the First Aqueduct, which range in length from 500 to 5,700 ft (150 to 1,740 m). The total capacity of the First Aqueduct is 196 cu ft/s (5.6 m3/s). 
The Second Aqueduct is 94 mi (151 km) long, beginning at the Colorado River Aqueduct, flowing into Lake Skinner and then into Lower Otay Reservoir near San Diego. In the first 16 mi (26 km) from the Colorado River Aqueduct to Lake Skinner, Pipeline 3 consists of an open canal handling approximately 500 cu ft/s (14 m3/s). The remaining 78 mi (126 km) consist of pre-stressed 72-inch (180 cm) diameter  concrete pipe and steel pipe. Pipeline 4 consists of pre-stressed concrete pipe with a capacity of 380 cu ft/s (11 m3/s). 
- Smith, Joshua Emerson (2021-02-05).
"A $5-billion water project could drill through Anza-Borrego park. Is it a pipe dream?". Los Angeles Times. Retrieved 2021-02-07.
For decades, 95% or more of the region’s water flowed through the water authority’s connection with MWD. Today that share is down around 70%, with desalination and water recycling coming on line.
- Bureau of Reclamation. "San Diego Project". Dataweb Database. U.S. Department of the Interior. Archived from the original on March 6, 2009. Retrieved 2009-03-24.
- "San Vicente Pipeline". San Diego County Water Authority. Retrieved 29 October 2016.
- Bureau of Reclamation. "San Diego Project Engineering Data". Dataweb Database. U.S. Department of the Interior. Archived from the original on January 18, 2009. Retrieved 2009-03-24.