Water and Power Associates Informing the Public about Critical Water and Energy Issues facing Los Angeles and California

First Los Angeles Aqueduct

The construction of the First Aqueduct opened the quest on the part of the City of Los Angeles for further imported water supplies to adequately satisfy the rapidly growing population.  During the 1930’s, the now Department of Water and Power, initiated the acquisition of the water resources of the Mono Basin through an extension of the Owens River supply system.  The construction of the Mono Basin Extension brought the total waterway length of the Los Angeles Owens River Aqueduct system to 338 miles.

Conception of the Second Los Angeles Aqueduct

The original aqueduct system was operated at capacity when the Owens Valley runoff diversion was sufficient, and there were periods when more water was available than the system could transfer to the City.  There were also several periods of drought when the aqueduct was not full.  The Mono Basin Extension Project, initiated in 1930, was a new source of supply that assured full capacity operation of the aqueduct during drought periods. More importantly, water rights filings in the Mono Basin and the capacity of the Extension Project were greater than required for the existing aqueduct, making possible the consideration of a second Los Angeles Aqueduct.

While the City had taken virtually its full Mono Basin entitlement for several years between 1941 and 1970, it found it could not divert the full amount authorized by the 1940s water rights permits on a long-term basis without constructing additional conveyance facilities downstream from Mono Basin. The Water Rights Board and the Department of Water Resources urged the City to take steps to develop its full entitlement or risk the potential that other appropriations might be granted by the Water Rights Board.

At the same time, a U.S. Supreme Court decision in 1963 (Arizona vs. California) had allocated Arizona more water from the Colorado River, reducing MWD’s entitlement to Colorado River water by more than 50%. In addition, water from the MWD was expensive because of the high energy costs involved in delivering it. This consideration, plus the availability of higher quality water, led to a decision to bring more Eastern Sierra water to Los Angeles.

Construction of the Second Aqueduct

The Second Los Angeles Aqueduct, an $89 million dollar facility, was completed in 1970. Beginning at Haiwee Reservoir, just south of the Owens dry lake bed, this project was shorter, half as wide as Mulholland’s “ditch,” and was easier to build as a result of improved construction equipment and the lower cost of steel pipe. The new aqueduct added another 50% capacity to the water system (in 1970.^

Historical Notes

From a system of ditches and waterwheels in the 1780s, the water system of the City of Los Angeles has grown to 105 reservoirs, including four major reservoirs along the aqueduct system. *

Click HERE to see more in Early Los Angeles Reservoirs

Historical Notes

The increased flows provided by the second aqueduct lasted only from 1971 through 1988.  In 1974 the environmental consequences of the higher exports were first being recognized in the Mono Basin and Owens Valley. This was followed by a series of court ordered restrictions imposed on water exports, which resulted in Los Angeles losing water.  In 2005, the Los Angeles Urban Water Management Report reported that forty to fifty percent of the aqueduct's historical supply is now devoted to ecological resources in Mono and Inyo counties