HAZ-2021-01 Post-wildfire Hazards: Mud Slides :: Debris Flows


With the incidence of catastrophic wildfires increasing in many areas of Colorado, the US, and the world, we decided to update an older brochure that provides a concise outline of the dangers and ways to reduce the risk of post-wildfire debris flows and mud slides. Digital PDF download. HAZ-2021-01D


People living directly downslope of mountainous wildfire areas should be aware that, in addition to debris flows, landslides, and rockfall; there is another, potential deadly hazard—mud flooding at and near the mouths of channels that drain burned-over, ash-laden slopes. Studies have shown that, in the first year following a wildfire, the volume of sediment and water runoff in streams greatly increases. People living, working, or traveling near such streams could be killed or injured by flooding that contains enormous amounts of debris and mud washed off burned hillsides.

Prior to a “1,000-year rain event” in September 2013—more than 18 inches in 24 hours—the area around Jamestown in Boulder County, Colorado had already experienced a number of wildfires. The momentous flash-flooding and debris flows following that rain caused extensive infrastructure damage to much of the town, along with a number of fatalities and more than 1,500 homes destroyed in the wider Boulder and Larimer County region.