Event Title

Describing Post-wildfire Geomorphic Response Using the River Styles Framework

Presenter Information

Keelin R. Schaffrath

Location

Ellen Eccles Conference Center

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Abstract

Wildfires have profound, highly variable impacts on erosion, sediment transport, and stream channel morphology. Climate change and fuel management actions have altered the current fire regime relative to the historic fire regime. The Twitchell Canyon fire burned 45,000 acres in Fishlake National Forest, near the town of Beaver, UT in July 2010. Over 30% of the area burned at high severity and monsoonal thunderstorms in the summer of 2011 resulted in massive debris flows and sheetflow erosion that have potentially altered the main stream channels in the burned area. We present the results of a reach-scale geomorphic analysis for pre- and post-fire conditions, based on the River Styles classification framework. Pre-fire classifications indicate that most channels are variable sinuosity with continuous floodplain. Post-fire classifications indicate a massive influx of sediment with a shift in River Styles classifications to accommodate that sediment. We have also calculated the probability and volume of post-fire debris flows that may be acting either as sources of sediment or barriers to sediment flux. Both models consider slope, percent of basin burned at high severity, average intensity of a defined thunderstorm, and generalized soil properties (% clay content and organic matter). Evidence of debris flow activity was observed in the two main creeks that we present (Shingle and Fish Creeks) and the model predicted high probability of debris flows for all of the sub-basins in each watershed. We have not verified models results for volume estimations but we use those volumes as relative measures of the size of barrier that a debris flow may have created in the main channels of Fish and Shingle Creeks, where a barrier refers to a barrier to sediment and movement or streamflow. We use the barriers to explain the observed changes to the River Styles classifications.

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Oct 21st, 10:00 AM Oct 21st, 10:10 AM

Describing Post-wildfire Geomorphic Response Using the River Styles Framework

Ellen Eccles Conference Center

Wildfires have profound, highly variable impacts on erosion, sediment transport, and stream channel morphology. Climate change and fuel management actions have altered the current fire regime relative to the historic fire regime. The Twitchell Canyon fire burned 45,000 acres in Fishlake National Forest, near the town of Beaver, UT in July 2010. Over 30% of the area burned at high severity and monsoonal thunderstorms in the summer of 2011 resulted in massive debris flows and sheetflow erosion that have potentially altered the main stream channels in the burned area. We present the results of a reach-scale geomorphic analysis for pre- and post-fire conditions, based on the River Styles classification framework. Pre-fire classifications indicate that most channels are variable sinuosity with continuous floodplain. Post-fire classifications indicate a massive influx of sediment with a shift in River Styles classifications to accommodate that sediment. We have also calculated the probability and volume of post-fire debris flows that may be acting either as sources of sediment or barriers to sediment flux. Both models consider slope, percent of basin burned at high severity, average intensity of a defined thunderstorm, and generalized soil properties (% clay content and organic matter). Evidence of debris flow activity was observed in the two main creeks that we present (Shingle and Fish Creeks) and the model predicted high probability of debris flows for all of the sub-basins in each watershed. We have not verified models results for volume estimations but we use those volumes as relative measures of the size of barrier that a debris flow may have created in the main channels of Fish and Shingle Creeks, where a barrier refers to a barrier to sediment and movement or streamflow. We use the barriers to explain the observed changes to the River Styles classifications.