Spring rains replenish reservoirs in Sonoma and Mendocino counties

Two spring storms that soaked Sonoma County have helped fill huge reservoirs and small farm ponds, and even more precipitation is expected over the next two months, erasing the anxiety from a bone-dry February.

Santa Rosa had received 23.83 inches of rain by Wednesday for the season beginning Oct. 1, reaching 72 percent of average precipitation for the period, with a chance of showers Thursday and again on Sunday and Monday, the National Weather Service said.

Accuweather, a private forecasting service that does long-range predictions, expects an additional 0.6 inches through the end of April and 1.83 inches more in May. It follows a soggy March that delivered nearly 6 inches of rain to Santa Rosa, twice the amount Accuweather had predicted.

“Miracle is one word you could use for it,” said Joe Pozzi, a Valley Ford sheep and cattle rancher.

As arid February closed with 3 percent of normal precipitation in Santa Rosa, Pozzi was lamenting half-empty ponds on west county livestock ranches. Spring rains have since filled the ponds and soaked the soil at a time when livestock ranchers count on the water to grow grass as the days get longer and typically warmer.

“We're in good shape right now,” Pozzi said.

And if rain keeps falling for two more months, “we'll take it for sure,” he said.

Water managers were equally pleased with Mother Nature's timing.

Lake Sonoma northwest of Healdsburg, the region's largest reservoir, gained about 7,000 acre feet of water in the past week, bringing it to 93 percent of targeted capacity with nearly 226,000 acre feet of water.

In both of the past two rain seasons, the reservoir held about 250,000 acre feet at this time of year. In the drought-impacted years of 2014 and 2015 it had less water than it does this spring, said Brad Sherwood, a Sonoma County Water Agency spokesman.

An average California household uses between one-half and one acre-foot of water per year for indoor and outdoor use.

Lake Mendocino near Ukiah added nearly 11,000 acre feet in the past week, raising it to about 80,500 acre feet and 98 percent of targeted capacity.

“That's a tremendous amount of water for this time of year,” Sherwood said.

The water agency delivers Russian River water, impounded in both reservoirs, to 600,000 customers in parts of Sonoma and Marin counties.

Like ranchers, the agency's water managers favor spring rains because they can “top off the reservoirs,” Sherwood said.

Both reservoirs were designed for flood control, requiring managers to release water to ensure there is enough room to contain runoff from winter and spring storms. By late in the rainy season, managers have less reason to worry about the threat of flooding and can retain more water for use in the summer, he said.

Bolstered by rain during the first three days of spring in March, inflow to Lake Sonoma surged from about 750 gallons per second to more than 33,200 gps, the largest spike since January.

Rain last Friday and Saturday, amounting to 4.47 inches in Santa Rosa, triggered a near repeat, pumping up inflow to 25,170 gallons per second. In both instances, the inflow returned to the previous level in a few days.

Rainfall since Oct. 1 in the Santa Rosa basin totals 24.12 inches, nearly 4 inches below average, the water agency reported Wednesday.

The Ukiah basin had 21.84 inches, nearly one foot below average.

You can reach Staff Writer Guy Kovner at 707-521-5457 or guy.kovner@pressdemocrat.com. On Twitter @guykovner.