Landslides keep Caltrans geologists busy following atmospheric rivers

GUERNEVILLE, Calif. - Jerry Knight knew it was only a matter of time. A rain soaked and muddy hillside slipped in early January directly in front of the historic River Theater he runs in downtown Guerneville. He had a front row seat when it spilled into the street.

"I was sitting on that fire hydrant over there when I saw it moving," Knight said. "Literally!"

It prompted Caltrans to send geologists to assess the saturated, unenforced, steep slope and design a solution.

The state has a team devoted to designing retaining systems and bridges and to respond to storm damage.

"At this time of the year we rely on them a great deal," Caltrans spokesperson Jeff Weiss said. "They have to tell us what’s happening on the hillsides with all the rain and saturation."

First, state workers installed debris flow barriers and k-rail to prevent dirt, rock and vegetation from spilling farther into the roadway.

"Caltrans jumped right on it because that whole hill as you can see could end up here in the middle of Main Street," Knight said.

Engineering geologist, Nick Bel, was tasked with making sure another mudslide doesn’t happen. It’s just one of nearly a dozen similar projects in the Bay Area.

"If we did nothing, it would definitely happen again," Bel said. "Homes could be in danger."

His plan involves installing a 15-foot retaining wall keep the loose materials and vegetation in place. It’s not the only fix considered to mitigate landslides, however, he said in this case with homes above and businesses below, it’s the ideal option.

Knight and nearby business owners said the previous landslide did put a damper on business and limited the foot traffic. But they've taken it in stride.

"We live in California," Knight said. "Look at down south of San Francisco. It happens."

The hillside has been covered in recent days to keep the soil from getting more saturated.

"With shallow landslides like this when they become saturated like this, they’ll lose their cohesive strength and cause future failures," Bel said.

More than 600 landslides were recorded in the first few weeks of January alone, according to the California Geological Survey.

But anticipating failures is tough.

For that, Caltrans uses drones to catch a bird’s eye view and gather data quickly in order to spot any trouble spots.

"Over the steeper slopes -- cracking above the road, cracking in the road," Bel said. "Typically it’s also assessing site history. Areas that have failed, continue to fail."

Advanced mapping software and data assists in pinpointing likely landslide locations.

Caltrans also said it has instrumentation inside some hills and mountains across the state to measure and monitor movement.

All of these tools are aimed at safety. But the most valuable way of preventing future disasters is relying on its daily work crews.

"We can stay ahead of the game by using our maintenance crews to observe and our geologists to design and start the work on a repair process," Weiss said. "Or at least some preventative maintenance."

That comes as peace of mind for people like Knight who has been patiently waiting to get the show on the road.

"I think this is a good step," he said.

Brooks Jarosz is an investigative reporter for KTVU. Email him at  brooks.jarosz@fox.com and follow him on Facebook and Twitter @BrooksKTVU