The emergency that unfolded recently at Oroville Dam in Northern California poses no immediate or projected impact to water supplies in San Diego County. Voice of San Diego’s story on the crisis, though, states that “we could lose a significant chunk of our water supply, perhaps even 20-25 percent.”


Low winter water demand, significant water reserves in Southern California and local investments in water supply reliability will allow the San Diego County Water Authority to provide uninterrupted water service here even if deliveries from Oroville are impacted.

The Water Authority’s preparations mean that the county does not depend on Lake Oroville and the State Water Project for “nearly a third” of its water supplies, as has been widely reported for Southern California as a whole. That may be true for all of Southern California, but it’s not true for San Diego water customers.

Over the past five years, an average of 17 percent of the region’s water supplies were from the State Water Project via the Metropolitan Water District of Southern California (the county’s only source of water from the State Water Project). In 2016, just 4 percent of San Diego County’s water supplies were from the State Water Project, and yet there was enough water to meet normal demands.

Deliveries to San Diego County from the State Water Project are driven by operational decisions at the Metropolitan Water District. While we don’t expect deliveries to always be as low as they were in 2016, that scenario illustrates what could happen again in a very dry year with minimal water coming from the State Water Project. Even in that scenario, we had sufficient supplies.

San Diego County’s reliance on the State Water Project continues to decline due to conservation-and-transfer agreements for Colorado River water and the Claude “Bud” Lewis Carlsbad Desalination Plant, which produces roughly 10 percent of the region’s annual water supply and directly reduces our demands for imported water.

The Water Authority also has taken other strategic steps to minimize the local impact of emergencies at Oroville Dam or elsewhere in the long and complex system of reservoirs, canals, pipes and pumps that deliver water to us from hundreds of miles away. The Water Authority’s $1.5 billion Emergency & Carryover Storage Project is a system of reservoirs, interconnected pipelines and pumping stations designed to make water available to the San Diego region should imported water deliveries be interrupted.

As repairs at Oroville Dam come into focus, the Water Authority will work with the state Department of Water Resources and other agencies to stay updated on conditions at the reservoir.

Our confidence in the San Diego region’s water supply reliability is based on several factors:

Even if State Water Project deliveries were reduced to accommodate Oroville repairs, there’s sufficient water in storage to meet local needs, in combination with supplies from the Colorado River and local resources such as the desalination plant.

San Luis Reservoir, a major reservoir south of the Bay-Delta, is at 95 percent of capacity, providing significant reserves for Southern California.

Southern California’s largest reservoir, Diamond Valley Lake, has risen dramatically this winter and currently holds more than 626,000 acre-feet of water.

San Vicente Reservoir currently holds about 100,000 acre-feet of carryover storage for dry years and just under 40,000 acre-feet of emergency storage that could be tapped if needed.

A continued regional focus on water-use efficiency means water use in the San Diego region this winter remains well below 2013, stretching supplies.

The Water Authority modeled three years of low water deliveries from the State Water Project as part of the state’s stringent “stress test” in 2016. We actually modeled much lower state deliveries than any likely scenario linked to Oroville repairs, and we had sufficient supplies to meet demands.

We will continue to strategically reduce our vulnerability to the kind of threats highlighted by the situation at Oroville Dam. While it’s important to be ready to respond to crises, it is even more important to minimize our vulnerability to disasters before they happen. Thanks to the unwavering support of the region’s water ratepayers, that’s what the Water Authority and its 24 member agencies have done for decades.

Mark Muir is the chair of the board of directors of the San Diego County Water Authority. Muir’s commentary has been edited for style and clarity. See anything in there we should fact check? Tell us what to check out here.

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