Effectiveness of post-fire channel treatments in reducing sediment transport

Wildfires can dramatically increase overland flow and thereby increase hillslope and channel erosion and sediment transport rates. Land managers often attempt to mitigate these effects by applying channel treatments, but questions about the effectiveness of post-fire channel treatments in reducing erosion and sediment transport rates in headwater streams remain largely unanswered. Further, the effects of these treatments on channel processes are not well-documented. We modeled a post-fire channel using a laboratory flume to determine if straw bale check dams reduce the sediment delivery rate or affect channel incision rates. The model was based on field measurements of post-wildfire peak flow rates and sediment concentrations from an instrumented watershed in Colorado. Sediment for the experiment was collected from a post-wildfire debris flood in central Idaho. The flume had a slope of 8.5%, a width of 0.4 m, and a length of 11.4 m. Five runoff events with flow rates between 0.0108 and 0.0120 m3 s-1, sediment addition rates between 0.5 and 2.4 kg s-1, and flow durations between 15 and 20 min were conducted in the untreated flume model. The channel was rebuilt with the addition of straw bale check dams before the same five events were repeated. Bed load sediment delivery rates were measured continuously during each runoff event. Channel topography was measured before and after each event using a laser elevation profiler. Initial results indicate that sediment production rates for the 5 untreated events produced 1030 kg of sediment while the treated channel produced 930 kg of sediment. Channel incision also was less in the treated channel. These results will help land managers assess the potential benefits of using straw bale check dams as a post-fire channel treatment.