Glass Fire, Other Napa Fires Mean Winter Rains May Trigger Mudslides

Glass Fire, Other Napa Fires Mean Winter Rains May Trigger Mudslides

Heavy winter rains may finally put an end to California’s fire season, but experts say they could lead to mudslides in Napa County.

Toby O’Geen of the University of California, Davis told the Napa Valley Register that fires like the Glass Fire and Hennessey Fire can be devastating to soil by destroying plant root systems, destabilizing the land and making it prone to erosion or flooding.

“The most important way to battle erosion is to have surface cover – living vegetation anchoring your soil,” he said. “We have none of that. If you have soil with existing susceptibility (to erosion) and now nothing to hold it in place, it’s a disaster.”

O’Geen said severe fires can make soil water repellent, causing rain to “pond up” on the surface, creating higher concentrations of run-off rainwater.

“That creates more massive erosive events – it gives rise to accelerated erosion, and in some extreme instances, mudslides,” he said.

Patrick Ryan with Napa County planning, building, and environmental services said most parts of Napa County appear to have avoided becoming water repellent. However, he said there are small parts of water-repellant land in areas where chaparral trees or madrone gave flames plenty of fuel.

Ryan said the county identified debris flows, rock fall and flooding as the primary hazards associated with fire-induced erosion and has started reaching out to property owners. He said degree of risk depends on burn severity, soil type and how steep the nearby land is.

A report was released this week by the Watershed Emergency Response Team, identifying seven properties with the potential for erosion that might pose “a high threat to life-safety.” The report identified two properties north of Pope Valley, three in the Lower Putah Creek area and two in Napa Valley.

A similar report regarding the Glass Fire is expected soon, Ryan said. Ryan said the Glass Fire burned in areas with a history of landslides and erosions, specifically noting the Franciscan Formation, which encompasses the Conn Creek Tributary, Spring Mountain and Sulfur Springs.

The Glass Fire damaged wineries and vineyards at Spring Mountain, an area with steep, sloping hillsides.

“Some places are so much steeper than I’d even thought, because with all of the trees, leaves and vegetation, you couldn’t really see it for what it was until now, when that’s all gone,” said Ashley Anderson-Bennett, associate vineyard manager at the Spring Mountain winery Cain Vineyard and Winery.

Anderson-Bennett hopes the area will see enough rain this year to regrow vegetation on hillsides but not so much as to trigger mudslides. “People want rain – we do want rain… I’m just hoping it will come gently,” she said.


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