Why Giant Rubber Dam Is Inflating On Russian River

SONOMA COUNTY, CA — A giant rubber dam rose from the floor of the Russian River this week as Sonoma Water launched the annual securing of summer drinking water for Sonoma and Marin counties.

The 100-foot seasonal dam near the Wohler Bridge slowly filled with air Tuesday, like a giant water balloon, beginning an inflation operation that can last from four days to two weeks, depending on river flows.

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Once fully inflated, the dam creates a pool of water that feeds Sonoma Water’s off-stream infiltration ponds, where water filters naturally through layers of sand and gravel before flowing to taps across the North Bay.

The summer supply operation has become a yearly ritual on the Russian River since the 1970s, timed to the arrival of hotter weather and heavier water use.

More than 600,000 Sonoma and Marin county dwellers rely on water from the system. During most of the year, they use about 40 million gallons of water a day, according to agency numbers.

During the summer, when temperatures climb and river levels shrink, demand on any given day can surge to 60 million gallons, according to the Sonoma Water agency.

Unlike permanent concrete dams, the inflatable structure sits flat along the riverbed for much of the year. The design is intended to reduce impacts on the river ecosystem, according to Sonoma Water.

When the dam rises, fish still move through the area using a "fish ladder" that helps Coho salmon, Chinook salmon, and steelhead continue their migration.

Sonoma Water biologists also monitor fish movement through an underwater video system installed in the ladder. Visitors can watch migrating fish at the agency in Forestville.

As the dam inflates, Sonoma Water officials warned boaters to avoid the rubber dam and look for notices posted nearby. Boaters should carry their boat and gear around the rubber dam. State regulations also ban fishing within 250 feet upstream and downstream of the dam.

Water officials also urged residents to conserve as summer approaches by repairing leaking faucets and toilets and reducing unnecessary water use.

An aerial view of the Russian River from the Sonoma Water website.