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Lake Mendocino water storage retained for future needs

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Lake Mendocino water storage retained for future needs

U.S. Army Corps of Engineers Agrees to Hold Back Water in Lake Mendocino

Minor deviation will save 5,825 acre-feet behind Coyote Valley Dam

Every year when winter rains fill Lake Mendocino, the US Army Corps of Engineers releases water just in case heavy rains put stress onthe dam. But not too long ag, after early winter rains had filled the lake, they released water that was needed later in the year when rains did not follow the normal pattern. With Climate Change making rainfall unpredictable, early winter rains have been followed by drought set in and the water was never regained. Water supplies became critically low over the following summer and everyone involved regretted the release. This year, the Sonoma County Water Agency requested that water not be released as flood protection, just in case rains stop like they did before.

The U.S. Army Corps of Engineers (Corps) today approved a request by the Sonoma County Water Agency (Water Agency) to keep an additional 5,825 acre-feet of water behind Coyote Valley Dam at Lake Mendocino in an effort to preserve water supply while meeting flood control and dam safety requirements.  The minor deviation will allow an increase of water in the water supply pool from 68,400 acre-feet to 74,225 acre-feet. 

“Our community greatly appreciates the Corps’ flexibility in how they operate Lake Mendocino for the betterment of our water resources and environment,” said Water Agency Chairwoman Shirlee Zane.  “Lake Mendocino’s water supply relies on annual rainfall to fill.  While recent atmospheric river events have helped bolster our water supplies, there is never enough water to waste.  This deviation allows us to save extra water when we have it, so we can use it when we absolutely need it.”

The Corps will continue to release water from Lake Mendocino due to the considerable amount of water within the current flood control pool.  As of January 25, there was 86,440 acre-feet of water in Lake Mendocino, or 140% of water supply capacity, which means the Corps will release approximately 12,000 acre-feet from the flood control pool. 

The Water Agency manages reservoir releases when water levels remain in the water supply pool.  When water rises enough to enter the flood control pool of the reservoir, the Corps takes charge of releasing water for flood protection and dam safety purposes.  

In order to maximize that additional water storage, on December 16, 2016, the Water Agency requested that the Corps allow an additional 5,825 acre feet of water to be stored in the flood control pool – the Corps calls this action a “temporary deviation” from its flood control manual.  This manual that was written in the 1950s and mandates when and how much water must be released from the reservoir for flood control and dam safety purposes. 

To read the minor deviation and learn more about Lake Mendocino, please visit

www.sonomacountywater.org/reservoir-operations/