Boulders placed along Russian River preserve access for 400 Alexander Valley residents

A temporary fix involving tons of large rocks placed along the Russian River near Geyserville has halted erosion that threatened to isolate about 400 Alexander Valley residents, a Sonoma County official said Tuesday.

Standing atop the river bank on River Road about a mile north of Highway 128, Johannes Hoevertsz, the director of transportation and public works, said the $200,000 project, authorized by county supervisors as an emergency repair in February, has preserved the road from nature’s onslaught.

“So far this is working perfectly,” he said. “We’re not losing the embankment.”

The dark gray rocks cover about 180 feet of the sloping river bank.

A year ago, Hoevertsz pointed out, the bank adjoining a vineyard in the 21000 ?block of River Road extended about 30 feet farther out into the river.

River Road is a dead-end road that reaches the Vineyard Club division and about 100 homes, Geyserville Fire Chief Marshall Turbeville said.

“There is no alternative to make access to this area for a fire or emergency,” he said.

Two rainstorms in mid-January and early February alerted county road crews to the dramatic erosion on a sweeping bend in the river, where a 1,200-foot wide gravel bar forces water up against the river’s exposed left bank.

“We’re losing ground every time it rains,” Hoevertsz said at the time.

Supervisor James Gore, whose district includes the Geyserville area, called the erosion “something that happened overnight.”

To halt the incursion, a county contractor placed rocks 3 to 4 feet wide along the bank, and the river, still flowing high, “was just blowing them away,” Hoevertsz said.

So boulders 5 to 6 feet wide and weighing more than a ton were installed. They did the job last weekend when the river flow surged tenfold - exceeding 3,000 cubic feet per second - before quickly resuming its previous level.

But the river remains about 20 feet away from the edge of River Road, which is the only connection to Highway 128 and then to Geyserville and Highway 101 for residents and vineyards north of the spot where River Road veers away from the river.

With several typically rainy months to go, there’s concern, Hoevertsz said, that the river may cut into the bank near the upstream edge of the rocks, renewing its threat to the road. In that case, more rocks would be installed, he said.

The county has designed a proposed permanent fix, with more rocks, willow trees and other features that would slow the river, create fish habitat and protect the bank. “Really a world-class project,” Hoevertsz said, noting that the county is seeking $1.5 ?million in state funding to build it.

Realigning River Road is an alternative, but the various options would cost millions of dollars more because they would involve purchase of private property, he said.

A contributing factor to the erosion was the end of gravel mining on that stretch of the river 15 to 20 years ago, allowing the gravel bar to alter the river’s course. Hoevertsz said.

“I just want to keep giving the residents a way to get home,” he said.

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