Russian River water sustains more than 600,000 North Bay residents

Water drawn from the Russian River by six wells near Forestville serves more than 600,000 residents from Windsor to San Rafael. And it will not run out this year or next, officials say — though stored supplies are lower now at this time of year than they’ve ever been.

Sonoma Water, the county agency the operates the regional water system, maintains 88 miles of pipelines transporting water to Santa Rosa, Windsor, Rohnert Park, Cotati, Petaluma and Sonoma, two water districts in Marin County and one in Sonoma Valley.

Counting a host of smaller customers as well, the system delivered more than 45,600 acre feet of water in the fiscal year ending in June, 2020, enough to cover that many football fields in a foot of water.

The system relies on water impounded by two reservoirs — Lake Sonoma northwest of Healdsburg with a 381,000 acre-foot capacity and 118,000 acre-foot Lake Mendocino at Ukiah — both at the lowest levels ever for this early in the year with the warmest, driest months ahead.

But they won’t run dry, even with a third straight water-poor winter, because Lake Sonoma holds several years worth of water and “we know our community will save water this year to ensure supplies for future years,” Sonoma Water spokesman Brad Sherwood said.

The system also has safeguards, such as “mandatory conservation measures that kick in once Lake Sonoma gets below a certain point,” he said.

The water agency has already obtained state permission to sharply reduce minimum river flows, cut supplies to cities by 20% and restrict landowner water rights along on the upper river.

Lake Sonoma, located behind Warm Springs Dam at the confluence of Warm Springs Creek and Dry Creek, captures runoff from a 130-square-mile drainage area, while Lake Mendocino, behind a dam on the East Fork of the Russian River, drains a 105-square-mile watershed.

In addition to the riverside well complex, Sonoma Water owns three wells in the Santa Rosa Plain built in response to the 1976-77 drought. Tapping groundwater several hundred feet below the surface, the wells can produce up to 7 million gallons of water per day.

At least one well will be operating in August or September, Sherwood said.

In contrast, each of the six wells on the river downstream from Wohler Bridge — with a dozen vertical turbine pumps (two per well) totaling nearly 15,000 horsepower — can produce 15 to 20 million gallons of water per day.

The first two wells were built in the late 1950s close to the bridge, followed by three more between 1975 and 1985. The sixth well, completed in 2006, is the largest collector well of its type in the world, capable of pumping up to 30 million gallons per day.

The wells plunge about 80 feet below the surface of the natural riverbed, with six to 12 perforated pipes extending horizontally into the water-bearing sand and gravel aquifer.

This natural filtration yields water fit for drinking, and the system adds chlorine to prevent possible contamination in the distribution system and reduces acidity to curb corrosion of lead and copper in indoor plumbing fixtures.

Three cities in Sonoma County operate their own water systems. Cloverdale maintains wells next to the river, Healdsburg has wells along the river and Dry Creek, and Sebastopol, which operates wells around the city, is unique in using no river water.

Farther north in Mendocino County, Ukiah and other smaller suppliers draw water from Lake Mendocino and the upper river. Those dwindling lake levels and river flows are under strain like few times in our recorded past.

Mired in a “historic drought,” Sonoma Water is waiting to see how much water Lake Sonoma holds by the end of the calendar year, Sherwood said.

If the drought continues, the region would experience declining groundwater levels and “additional pressures on our water resource systems,” he said.

“We would still supply water to our customers but not without more drastic conservation measures,” Sherwood said.

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