Wildfires and debris flows: Santa Barbara County researchers unravel factors in the one-two punch
Experts say while the focus in the Tri-Counties is on two Montecito creeks which caused the 2018 debris flow, there are many other waterways posing threats.
It was a terrifying experience, as rocks and debris surged down a Montecito street. Marco Ferrell fled back into his family’s home with his mother, followed by a waist-high torrent of mud and rock.
Ferrell and his family survived, but 23 others died in the January 9, 2018 debris. The December, 2017 Thomas Fire set the stage for the debris flow, stripping the mountainsides bare above the community just before a major storm arrived.
Researchers are looking at this connection between fires, and floods, and how much recovery time is needed between the two.
"In the Montecito debris flow case, we had no time," said Dar Roberts, who is is a professor in UC Santa Barbara’s Department of Geography. "The fire was still actively burning when the storm hit."
He said the fire was so fresh, and heat so intense, that it created almost a polished surface on the stripped mountainsides, adding to the runoff problem during the intense storm.
Roberts talks about the key role vegetation plays in preventing flash flooding, and debris flows.
"We're worried that we're going to see more intense, more frequent fires," said Roberts.
He said factor in other things like the drought, and a longer fire season and there's room for concern.
A UCSB hydrology and slope stability researcher says the unique geological makeup of the Santa Ynez mountains also played a role in the deadly 2018 Montecito debris flow.
Paul Alessio said on the top of the Santa Ynez Mountains, you have shale, that produces fine rain sediment, which makes mud and slurry. He said there is a layering of shale and sandstone which sets the stage for debris flows during intense rain.
Alessio thinks so much debris came down from the mountains during the 2018 disaster that it’s helped lessen the current threat to Montecito. But, he said there are lots of other spots which haven’t received much attention, but pose bigger threats.
The UCSB researcher says they are currently studying another area above Santa Barbara which could pose one of the biggest threats in the region if it’s hit by a rapid fire-flood one-two punch.
"Mission and Rattlesnake Creeks...they're not burned right now. But, if and when those burn, that's going to pose the biggest hazard in Santa Barbara County," said Alessio.
The researchers said it can sometimes be hard to pin down the threat from a fire-flood combination. What’s the terrain and soil like? How much vegetation was burned, and how much has grown back. What’s the intensity of the storm? What role does climate change play? They are looking at the variables, with public safety officials also hoping to learn more about the potential threats we face.