Landslide and mudslide dangers increasing throughout Bay Area

With the ground thoroughly soaked, the consequences of each additional atmospheric river is more mudslides and landslides. Slides are bad, but additional rain can make them much worse.

Old Redwood Highway, just north of Novato, above southbound Highway 101, suffered a substantial landslide that destroyed several hundred feet of the marginal road. If it continues moving, it could threaten the freeway. The road leads to and now blocks access to popular Olompali State Park.

At the gaping maw at the top of the slide, a Pacific Gas & Electric's high pressure 16 inch gas pipeline, one of two up there, has been exposed forcing the utility to cut the gas pressure way down for safety. 

"Our geo-science engineers and our gas pipeline engineers are up there right now assessing the situation, but they say there is no immediate risk to the public," said PG&E spokesperson Megan McFarland. 

And, while it's exposed, that may not be dangerous, but with more rain coming and the possibility of a bigger slide, that is very dangerous. "When the mudslides occurred, it also took out two of PG&E's electric poles in the area, so we're working to repair those as well," said McFarland.

At the foot of the slide, the long string of tiny blue flags indicates the presence of a critical 30-inch water main that brings water from the Russian River in Sonoma County into Marin. The damaged roadway has already pushed a bit over the blue flag line and could be putting pressure on that pipeline and the ground continues to move.

The US Geological Survey says slides can cause tree falls, structure displacement or destruction, traffic blockages, street surface and road bed destruction as well as damage to above and underground utilities.

Caltrans says slides are among the hardest challenges they face. "Here in the Bay Area, we're dealing…Caltrans is dealing with four major slides in different areas. And, then there are 20 other locations currently that we have got crews responding to that are just downed trees and smaller slides due to earth movement from these storms," said Caltrans Bay Area public information officer, Bart Ney.

System-wide, PG&E says since the first of the year, though mid-March, it has dealt with 538 slide events mostly taking out power lines and poles.