Wildfires and Cascading Post-Wildfire Impacts

Wildfire in mountain communities can be devastating. Unfortunately, in many cases the fire is the beginning of cascading events that can include flooding, severe erosion, and debris flows. These post-wildfire impacts can pose risks to life safety, homes, infrastructure, and ecosystems. There are ways that we can be prepared for, and in some cases lessen the severity of these events. This can be accomplished with robust emergency preparedness actions and a holistic approach to watershed restoration.
Due to the topography, number of homes, tree density and weather conditions in the Coal Creek area, high wildfire intensity and severity would not be unlikely. High intensity describes the, “energy released from the fire or characteristics of the fire behavior such as flame length and rate of spread and fire severity refers to the ecosystem impacts of a fire such as mortality of trees or loss in biodiversity” (J.E. Keeley, in Encyclopedia of Ecology, 2008).
Both high intensity and high severity wildfire have the potential to alter physical and chemical composition of soil and increase the rate and volume of water that runs down a hillslope for at least two to three years after a wildfire event. Fire removes vegetation, litter and duff on the ground and soil can become hydrophobic after a wildfire, temporarily becoming unable to absorb precipitation and runoff. When this occurs, there is a greater likelihood of sheet flow of water from hillslopes increasing flood risk downstream. With altered soil composition and watershed hydrology, hillslopes are more prone to severe erosion and debris flows.

Images from USGS: How Wildfire Threatens US Water Supplies

Debris flows, mud flows and landslides all have slightly different definitions, but all involve mass movement of sediment and debris (trees, homes, cars, etc.). Since 2020 large debris flows have occurred in numerous burn areas. The Black Hollow debris flow in 2021, located in the Cameron Peak burn area in Larimer County, killed four people. The debris flow in the Grizzly Peak burn area impacted I-70 outside of Glenwood Springs and closed the highway multiple times. It is difficult to prepare for or mitigate debris flow hazards. However, improving awareness of what areas are at risk (especially post wildfire) and having robust alert and warning systems in place can save lives.
There are many other mitigation actions landowners, communities and agencies can take to reduce the risk of high severity wildfire and post wildfire impacts. These actions include tree thinning and prescribed fire, reconnecting streams to their floodplains and enhancing meadows. Using tree thinning to reduce forest density and create openings in the forest can alter the intensity and severity of wildfire behavior, protecting soil and reducing the amount of larger vegetation that is completely burned. Prescribed fire will reduce accumulated understory litter and duff (needles, brush) similarly protecting soils and larger vegetation.
Connected floodplains and healthy meadow and riparian areas have the ability to capture large pulses of sediment after a wildfire and redistribute it throughout the floodplain or meadow. Straightened stream channels with disconnected floodplains transport water and sediment at high velocities and have greater potential to negatively impact roads, bridges and other infrastructure. In narrow canyons like Coal Creek Canyon even small pockets of floodplain can capture sediment to protect downstream culverts and bridges.
Last, but certainly not least, it is incumbent upon all of us to make sure we are prepared for natural disasters and evacuations. You can sign up for emergency notifications through the Coal Creek Canyon Fire District’s website (https://coalcreekcanyonfd.org/community-resources/). Pack a Go Bag. If there is an evacuation notice, leave early, as traffic congestion in the canyon could drastically impact the amount of time it takes to evacuate. Talk with your neighbors. Make sure evacuation plans include children that may be home alone, people without vehicles and pets. Assume that emergency personnel will not be available to assist you with evacuation and plan accordingly. Preparing for wildfire and post-wildfire impacts takes the entire community. You can find more information on how you can participate at CoalCreekCWPP.org.

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