Heavy Rains force lowering of Russian River Rubber Dam in Forestville

Less than a week after it had fully inflated its rubber dam on the Russian River in preparation for summertime water demands, heavy rains forced the Sonoma County Water Agency (Sonoma Water) to reverse field Thursday and begin lowering the rubber dam back down. The unusual rainstorms that swept into Sonoma County this week are forecast to raise river flows to 6,000 cubic feet per second (cfs) by Sunday night, flows that could potentially damage the inflatable dam.

Sonoma Water began inflating its rubber dam on the Russian River near Forestville on Monday, May 6 and it was fully inflated by Saturday, May 11. By Thursday, May 16, however, the decision was made to begin lowering the dam to protect it from damage that could be caused by the high flows. It is Sonoma Water’s protocol to lower the rubber dam when river flows exceed 2,000 cfs.It is expected to take 1-2 days for the dam to be lowered.

Boaters are encouraged to exercise caution in the area of the dam during the lowering process as conditions can change quickly.

The rubber dam is a critical component of the Russian River water supply system that provides naturally filtered drinking water to more than 600,000 residents in portions of Sonoma and Marin counties. Once inflated, the rubber dam normally would remain inflated through summer and into the fall.

The rubber dam is typically inflated in spring when demand for potable water increases. When fully inflated, the rubber dam creates a small pool of water from which Sonoma Water draws water for use in four off-stream infiltration ponds. The infiltration ponds help recharge groundwater which is then naturally filtered through sand and gravel and delivered to Sonoma Water’s customers.

When it is fully inflated, boaters must portage around the rubber dam, located downstream of Wohler Bridge. Public notices have been posted around the rubber dam warning the public not to recreate on or near the dam.California Department of Fish and Wildlife regulations prohibit fishing within 250 feet of the upstream and downstream sides of the rubber dam.

Mirabel Inflatable Dam

Sonoma Water operates an inflatable dam on the Russian River in the Mirabel area to increase production capacity during peak demand months. Operation of the inflatable dam increases production capacity in two important ways. First, surface water immediately behind the dam can be diverted to a series of infiltration ponds that are constructed adjacent to the three Mirabel collector wells. Fish screening facilities ensure the safety of the fish in the river. Second, infiltration to the underlying aquifer behind the dam is significantly improved by increasing the recharge area from the river. Permanent fish ladders provide fish passage when the dam is raised.

The Russian River Biological Opinion, issued in 2008 by National Marine Fisheries Service, found that fish screens at Sonoma Water’s River Diversion Structure could harm small fish, including young endangered Coho salmon, and threatened Chinook salmon and steelhead. In order to comply with the Biological Opinion and continue operating its system, Sonoma Water in 2016 installed a new, improved fish screen. In conjunction with the installation of the fish screen, Sonoma Water also constructed an improved fish ladder and viewing gallery. The new fish ladder creates better conditions for adult and juvenile salmon moving up or downstream, and allows more native species to use the ladder for migration. Sonoma Water also operates traps downstream of the dam, and throughout the Russian River watershed, to county fish annually.

For more information about the rubber dam and how the Sonoma Water delivers naturally filtered Russian River water to its customers, please visit www.sonomacountywater.org/water-supply .