Storm fills North Bay reservoirs, easing region’s drought

With two Russian River reservoirs brimful of runoff from a prolonged storm, the North Bay region is nearing an end to its multi-year drought, a water management official said Friday.

“It looks like a March miracle,” said Brad Sherwood, spokesman for the Sonoma County Water Agency, which supplies water to 600,000 customers in Sonoma and Marin counties. “Our water supply system hasn’t looked this good in more than three years.”

Lake Sonoma west of Healdsburg, the region’s largest reservoir, was at 107 percent of capacity for this time of year, and Lake Mendocino, the far smaller reservoir near Ukiah, was at 117 percent, with both lakes the fullest they have been in early March since 2012.

The atmospheric river that delivered the latest rainfall offered not only significant drought relief, but also relented Friday afternoon, offsetting flood forecasts and giving the ground a chance to absorb water, Sherwood said.

The Russian River water system is independent from the network of major reservoirs and canals that serve most of California, which remains under mandatory water conservation measures.

On Thursday, before the latest storm system hit, the U.S. Drought Monitor downgraded most of Sonoma and Mendocino counties from severe to moderate drought. Lake County remained in severe to extreme drought. Nearly half of the state, including the Central Valley, Central and South Coast remain in exceptional drought, the most acute category.

Lake Shasta, the state’s largest reservoir, was at 70 percent of its 4.5 million-acre-foot capacity.

“There’s never enough water to waste,” Sherwood said, noting that conservation still counts in areas where the reservoirs are full.

Before the rain let up Friday afternoon, the dams at Lake Sonoma and Lake Mendocino were holding back a torrent of up to 145 million gallons of storm runoff an hour, according to the U.S. Army Corps of Engineers.

The dams were “doing exactly what they’re supposed to be doing,” said Mike Dillabough, chief of operations and readiness for the corps’ San Francisco Division.

Both reservoirs were above their set capacity for this time of year, when officials leave substantial room in the lakes to absorb winter and spring storms. Lake Sonoma had more than 118,000 acre feet of available storage and Lake Mendocino had more than 31,000 acre feet. An acre foot is 325,851 gallons, or about the amount of water it would take to cover a football field one foot deep.

The dams were releasing minimal amounts of water and had “plenty of room” to handle more rain and prevent flooding, Dillabough said.

“We’re watching it very closely,” he said.

On the lower Russian River, the river was at 24 feet Friday morning and was set to crest in the afternoon at 26 feet, well below the 32-foot flood stage. It had previously been expected to crest at 35 feet in Guerneville on Saturday, but a lapse in the rainfall led river forecasters to cancel that flood warning.

Meanwhile, runoff into Lake Sonoma from small streams and the headwaters of Dry Creek on Friday morning amounted to about a fifth of the Russian River’s volume downstream, or 4,442 cubic feet per second. River flows are measured in cubic feet per second (cfs), with a cubic foot equal to 7.48 gallons.

At Lake Mendocino, runoff into the reservoir was 1,213 cfs.

Earlier in the week, inflow into each reservoir hit 6,000 to 7,000 cfs, Dillabough said.

Rainfall since Oct. 1 in the Santa Rosa basin totaled 23.74 inches, and 28.55 inches in the Ukiah basin, both within an inch of average for the date, the water agency said.

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