Combined Lake Sonoma, Lake Mendocino storage at highest level ever for this time of year

Remember this time last year, when water stores depleted by several years of drought left water managers and consumers alike hoping desperately for a wet winter ahead?

Well, Sonoma Water says the region’s main reservoirs — Lakes Sonoma and Mendocino — ended this August with the highest combined storage level since 1985, the first full year the newly constructed Lake Sonoma was filled.

This, less than nine months after the reservoir on Dry Creek reached its lowest level in history on Dec. 9 — 96,310 acre feet, just more than a third full.

Lake Sonoma now has nearly 240,000 acre feet in it, while Lake Mendocino, which is smaller, has nearly 84,000 acre feet, for a combined total of more than 322,000 acre feet. (An acre foot of water equals 325,851 gallons, or about the amount of water needed to flood most of a football field one foot deep.)

“The combined storage of Lake Mendocino and Lake Sonoma has never been higher” at this time of year, said Brad Sherwood, assistant general manager of Sonoma Water, the Sonoma County Water Agency.

For comparison, the record low storage for Aug. 30 was just two years ago, in 2021, when combined stores in the two lakes totaled 134,598 acre feet — less than half what’s available now.

The average late-August storage combined is about 264,500 acre feet, Sherwood said.

Sherwood credits “one heck of a rain year,” with abundant rainfall last winter, as well as community conservation efforts and revised reservoir operations that allow retention of additional water in Lake Mendocino during flood season if no major storms are on the horizon.

The new Forecast Informed Reservoir Operations account for at least 11,000 acre feet in Lake Mendocino, outside Ukiah on the Russian River’s East Fork.

Sonoma Water and the U.S. Army Corps of Engineers, which owns and operates the reservoirs during flood season, are working on a plan to apply FIRO to Lake Sonoma, as well.

You can reach Staff Writer Mary Callahan (she/her) at 707-521-5249 or mary.callahan@pressdemocrat.com. On Twitter @MaryCallahanB.