Inflatable dam going up on the Russian River signals advance of warm weather months

A sure sign of summer, unnoticed by most people, appeared on the Russian River last week, as the Sonoma County Water Agency began inflating its rubber dam near Wohler Bridge in Forestville.

The seasonal dam — a kind of long, skinny water balloon, according to one agency official — is part of the region’s water supply system. It is used to increase production on nearby wells to meet consumer demand during warm weather months.

The deflated dam lies flat on the river bottom in winter but once the river settles into summer flows — usually in May or June — it is filled with water over several days.

Despite abundant winter rain, that time has come, though cool weather and remaining ground moisture have kept irrigation needs low so far, according to Don Seymour, Deputy Chief Engineer for Sonoma Water.

The dam creates a deep pool of water that allows for diversion into nearby ponds that aid aquifer recharge and increase capacity at three nearby collector wells, Assistant General Manager Pam Jeane said.

It also backs water up for several miles behind the dam, increasing recharge of the deep, underlying aquifer for three additional collector wells upstream of the bridge, she said.

Those wells contribute to the wholesale water supplied to more than 600,000 people in Sonoma and North Marin counties through municipal water providers and other agencies. Demand from those customers in a normal summer is about twice what it is in winter, except in years of severe drought like the last three, Jeane said.

Weeks of winter storms swelled the river in January, raising the flow rate to 30,000 cubic feet per second at the Hacienda Bridge, according to data from the California Department of Water Resources. Continued wet weather kept the current moving at a fairly high rate through early spring.

Though there remains natural flow in the watershed, in addition to what is discharged into the river from Lakes Mendocino and Sonoma, the flow downstream of Healdsburg is now below 300 cubic feet per second and declining by the day.

In the meantime, anticipated warm, dry weather ahead means consumers are likely to use more water for outdoor irrigation and yard maintenance, Seymour said, though officials urge residents to continue using water efficiently. The rubber dam allows Sonoma Water to raise the water around its collection wells so the water agency can more easily provide it.

The dam inflation started Monday and usually takes four to 14 days to be complete. It was fully inflated by June Thursday night, a water agency spokeswoman said.

A fish ladder at the site allows for fish passage and is equipped with underwater video to allow for monitoring and counting of migrating salmon and steelhead when in season.

Canoeists, paddle boarders, kayakers and other recreators must portage around the dam when traveling the river. The California Department of Fish and Wildlife also prohibits fishing within 250 feet upstream or downstream of the dam.

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