In-stream point mitigation projects utilize low-tech wood and rock structures within gullies, rills, and tributary streams to reduce the impacts of post-fire flooding. In the years following a severe wildfire, flooding can occur, especially in smaller tributaries, as excess water runs off hillslopes due to hydrophobic (water repellent) soils and a lack of vegetation. In unburned areas, vegetation and hydrophilic (water absorbing) soils absorb large quantities of water during rain events, reducing the amount of water that runs downhill and into waterways. When the vegetation and topsoil are burned away, rain flows downhill carrying sediment, ash, and debris with it. This leads to the incision of gullies and rills which can funnel water and debris into waterways that often do not have the capacity to handle large flows of water, resulting in flash flood events.
To help reduce the impacts of post-fire flooding, we will install various low-tech wood and rock structures in priority gullies, rills, and streams within the Cameron Peak Fire footprint. These structures help to slow the flow of water while catching sediment and debris. When sediment and debris are retained behind these structures it can raise the streambed helping to reconnect the stream to its surrounding floodplain. This allows for water to spread across the landscape rather than being channeled downstream through narrow waterways which can impact communities, roadways, and water quality. Further, by using native wood and rock on site, these structures become a part of the landscape over time reducing the need for structure removal and maintenance.
Post-fire flooding in the Big Thompson has heavily impacted a number of mountain communities washing away roadways, clogging culverts, and damaging houses.