CALISTOGA — In the wake of October’s fires, attention has turned to recovery efforts with an emphasis on protecting the region’s water supply.
“Right now, our focus is on debris removal and watershed issues,” Jeff Sharp of Watershed Information Center and Conservation Council of Napa County said at a Calistoga meeting last week.
“Municipal water supply is one of the top priorities. We have been working with the City of Calistoga on Kimball Reservoir and the City of Napa on Milliken Reservoir ...” said Sharp. The goal is to “prevent as much burn material coming off the burn sites and entering the reservoirs as much as we can.”
Most of the burned areas are showing a low- to moderate soil burn severity though there are some patches where the soil burn is considered “high,” said Drew Coe, a hydrologist for Cal Fire.
The most important thing to gauge is the soil burn severity, which is determined using satellite images of pre- and post-fire and then those areas are validated to make sure it matches the satellite imagery, Coe said.
“If you’ve ever walked around (after a fire) and you start kicking dirt and it looks like moon dust, that’s severely burned soil,” Coe said. “That stuff is very easily eroded and can produce a lot of runoff on sites.”
Coe recommends tackling those areas that show “high” soil burn severity first then assessing the areas marked “moderate”. Some moderate areas may not need treatment, or treatment can be delayed, while others could be treated at the same time as the more at-risk areas.
Areas marked “low” don’t need to be addressed now, officials said. Many of the areas that have been assessed in the Atlas Peak Fire area have good soil cover – material such as wood chip or rock – and don’t have the risk of debris flow or sediment flow.
“We have rocky soils out here; rock is very good cover. That’s why during the Atlas Fire assessment, we actually downgraded the soil burn severity based off of rock cover,” Coe said.
The Tubbs Fire burned the upper headwaters of the Napa River causing some concern of debris flow into Kimball Reservoir.
“Some of the waters to Kimball Reservoir have a higher probability of debris flow, and it makes sense. It’s steep and it was burned at moderate severity,” he said.
There was mostly low soil burn severity in the Nuns Fire area with some “higher proportions of moderate burn severity in the Redwood Creek drainage,” Coe said.
Waddles have been strung along the sides of both of Kimball and Milliken reservoirs to prevent sediment from flowing into the water, officials said.
“It’s kind of like a Band-Aid on a hatchet wound,” said Joy Eldredge, the city of Napa’s water manager.
Two layers of waddles were placed on the east side of Milliken, she said. While doing the work, crews discovered “about 26 different culverts” they didn’t know existed because they were overgrown.
The fire burned up within 12 feet of Calistoga’s water treatment plant near Kimball.
“We are extremely fortunate that we did not lose our plant there,” said Derek Rayner, deputy city works director.