A Second Aqueduct
The challenge of water supply continued to press.
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
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
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 if improved construction equipment and the lower
cost of steel pipe. The new
aqueduct added another 50% capacity to the water system.
The two Los Angeles Aqueducts now deliver an average of 430
million gallons a day to the city.
Under normal circumstances, 70% of the city’s water comes from the Eastern Sierra. Wells in the San Fernando Valley and other local groundwater basins supply 15%, and purchases from MWD furnish the last 15%. From a system of ditches and waterwheels in the 1780s, the system has grown to 105 reservoirs, including four major reservoirs along the aqueduct system.