Debris Flow Poses Possible Danger in The Santa Cruz Mountains

Written by Lucas Murawsky (News Writer)

After a wildfire has passed the danger is not over, as 2020 has proven, it is just the beginning.  After a fire like the CZU Complex happened, it left behind a trail of loose debris and loose soil, which can turn into a mudflow, also known as a debris flow, which is when a significant amount of rain falls in a short period of time causing all of the loose soil debris to rush down a mountain, river, canyon, or road as fast as 30 mph or avalanche speed, taking out anything in its path. 

According to county communications manager Jason Hoppin if we see greater than 0.3 inches of rainfall in a 15 minute time period, or 0.5 inches of rainfall occurring over a 30 minute time period, or  0.7 inches of rainfall occurring over an hour time period, it could possibly trigger a debris flow. “There’s actually quite a bit of risk for people that never saw the fire in their backyard,” Hoppin said. “But because they live below the burn scar, they are at increased risk for the debris flows.”

People on the HWY 9 corridor including Boulder Creek, Ben Lomond, and Felton, and along HWY 1, including the Davenport area are most at risk of a debris flow and being evacuated. According to the Watershed Emergency Response Team (WERT) landslide map, areas around Scott Creek, Big Basin State Park, and Cascade State Ranch have a 60% to 100% risk of debris flow. “Unlike fires and floods, there is no way to fight or ride out a debris flow in place,” county Senior Civil Engineer Carolyn Burke said during a presentation Tuesday to the Board of Supervisors. “Early evacuation is the only sure way to survive a debris flow event. If you see or hear the debris flow, it is too late.” 

 Burke said the county is taking lessons from the Santa Barbara mudslides which killed 23 people after the 2018 Thomas Fire. “What Santa Cruz County staff learned from their counterparts in Santa Barbara is that early and consistent public messaging regarding the unique risks related to debris flows, as well as clear evacuations are key to saving lives,” Burke said. “Debris flows activate so quickly, the public can not wait until after the rain starts falling for people to start evacuating. People need to evacuate early/” 

The County held two town halls last week talking about the most life-risk areas for debris flow which is the Highway 9 corridor, they talked about getting an evacuation warning up 48 hours before the rain starts. “Twenty four preceding that amount of rain, our deputies are going to go out in the areas that are affected, and we’re going to go door-to-door and let people know an evacuation order has been enacted and it’s time to go,” Chief Deputy Chris Clark said during the town hall.

The county is urging people to know their evacuation zones and specific risk percentage for a debris flow. Sign up for Community Emergency Response Team (CERT) notifications and know how you’ll be receiving information to pre-pack and get ready for an evacuation warning or order and go through evacuation preparedness with the family. Be sure to know your evacuation route and know where you are planning on staying when you evacuate.  If the county issues evacuations, they are asking residents to take the risk very seriously and leave the area. If there is a debris flow, emergency personnel may not have access to impacted areas.


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