Debris Flows/Mudflows

Debris flows pose a risk in hilly or sloped areas following large fires. Residents within and below the CZU Lightning Complex burn area should be aware that the dangers to life and property from these hazards are significant and have a higher likelihood of occurring for several rainy seasons following a fire. County geologists are working with state and federal partners to assess debris flow risks in neighborhoods throughout the burn area. Residents should be prepared to evacuate and may not locate temporary housing on their properties until approved by the County.

What is a Debris Flow?

A debris flow is a fast-moving, deadly mass of mud, rocks, boulders, entire trees - and sometimes, homes or vehicles. They are similar to landslides but often carry, or “flow,” over a large area. Debris flows range from a few square yards to hundreds of acres in area, and from a few inches to 50 feet deep. Even smaller ones can be locally dangerous: Imagine trying to walk through a 3-inch deep mass of wet concrete moving at 30 mph.

What makes Debris Flows so dangerous?

Debris flows are fast and unpredictable. They travel faster than you can move. While the County is mapping areas of risk, debris flows can be unpredictable in where they will start or stop. It could begin in a stream channel, then jump out and spread through a neighborhood. A debris flow may happen where others have occurred, or in a place that has never seen one before. You cannot “ride out” a debris flow. Once you see or hear one, it is too late. The only effective protection is early evacuation. You can see the impact of the 2018 Montecito debris flows in this short video.

In many natural disasters, debris flows can cause more fatalities and injuries than wildfires. Learn your evacuation zone and use your mobile device to download the Code Red app today and sign up for emergency notifications. It is important to understand the Debris Flow Map and where you are located on the map.

The map above shows evacuation zones and debris flow risk throughout the CZU Lightning Complex fire zone. Areas shaded light blue are at elevated risk, while areas in darker blue include neighborhoods determined to be at highest risk for debris flow or blockade, and will likely see evacuations during periods of intense rainfall.

Debris Flow Resources