The San Diego Aqueduct 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 mi First Aqueduct consists of pipelines 1 and 2, which run from the Colorado River Aqueduct near San Jacinto, California, to San Vicente Reservoir, approximately 15 mi northeast of the city. Pipelines 3 and 4 make up the 94 mi Second Aqueduct. Together, these four pipelines have a capacity of 826 ft3/s. The smaller, 12.5 mi Fallbrook-Ocean Branch branches from the First Aqueduct into Murray Reservoir. The La Mesa-Sweetwater Branch originates from the First Aqueduct, flowing into Sweetwater Reservoir.

Construction

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 mi, 8.5 ft San Vicente Pipeline, connecting San Vicente Reservoir to the Second Aqueduct. Construction on the project was completed in 2010.

First Aqueduct

The First Aqueduct, built of two parallel precast concrete pipes, ranging in diameter from 96 to 48 in, branches from the Colorado River Aqueduct in San Jacinto, California, just north of the San Jacinto River, continuing 70 mi south to its terminus at San Vicente Reservoir. There are seven tunnels on the First Aqueduct, which range in length from 500 to 5700 ft. The total capacity of the First Aqueduct is 196 ft3/s.

Second Aqueduct

The Second Aqueduct is 94 mi 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 from the Colorado River Aqueduct to Lake Skinner, Pipeline 3 consists of an open canal handling approximately 500 ft3/s. The remaining 78 mi consist of pre-stressed 72 in diameter concrete pipe and steel pipe. Pipeline 4 consists of pre-stressed concrete pipe with a capacity of 380 ft3/s.