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Debris Flow Prevention Ring Nets, Effective or Overkill: Comparison of Wildfire Impacts and Debris Flows in Colorado Springs, Colorado, and Montecito, California

Authors: Kiki Patsch*, California State University Channel Islands, Anne Chin, University of Colorado Denver, Linda O'Hirok, California State University Channel Islands, Mauricio Gomez, The Partnership for Resilient Communities
Topics: Geomorphology, Land Use and Land Cover Change
Keywords: Wildfire, Debris Flows, Mitigation Measures
Session Type: Poster
Presentation File: No File Uploaded

This study seeks to assess the effectiveness of the installation of ring debris flow prevention nets to retard erosion and the movement of water and sediment through river corridors following wildfire. Wildfires devastate steep slopes which cause the loss of vegetation and thus destabilize soil. This increases sediment supply at the landscape scale which greatly facilitates subsequent mud and debris flows. Post-fire changes and mitigation treatments were evaluated in Colorado Springs, Colorado, and Montecito, California. Aside from significant environmental effects as the fluvial systems adjust and recover, there were considerable social impacts because of the proximity of both fires to populated areas including costs of the fire fighting and costs of post-fire flooding and mitigation efforts. In anticipation of post-fire summer thunderstorms, citizens living downstream of the Waldo Fire constructed fences composed of rings with diameters of 30cm and 11.3cm with the purpose to trap only larger particles. Installation of debris flow fences minimizes threats to property and lives but also affects the movement of sediment through the fluvial system which may trigger feedbacks having their own risks. In the case of the Waldo Fire, the capture of larger sediment caused widespread downstream channel erosion and a change in form and function. A similar mitigation technique was applied in Montecito where four steel ring nets have been installed to capture debris flows resulting from the Thomas Fire. The devastating January 2018 debris flows occurred while the fire was still burning. The effectiveness of these nets is being monitored and evaluated.

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