Comparing the Effects of Fuel Treatments and Wildfire on Small Catchment Runoff and Sediment Yield at Two Spatial Scales

Abstract:

The role of wildfire in the Rockies continues to be a major concern—especially fire’s effect on water quantity and quality, thus protection of water resources is of great management importance as wildfire occurrence and water needs increase. Since high burn severity wildfires often affect soils, vegetation, and hydrologic processes, fuel treatments are often implemented to reduce the risk of high severity fires. The effects of fuel treatments and wildfire on runoff and sediment yields are often examined separately at the hillslope scale but few studies compare the effects of fuel treatments directly to those of wildfire or allow upscaling effects to the small catchment scale. We studied hillslope scale (0.01 ha) sediment yields and catchment scale (2 to 9 ha) runoff and sediment yields at seven fuel treatment sites and one high severity wildfire site in the northern Rockies. The fuel treatments consisted of thinning or timber harvest followed by low to moderate severity prescribed fire. Mean runoff rates from snowmelt and summer rainfall were often similar between the fuel treatments and wildfire catchments, sediment yields were two to three orders of magnitude higher in the wildfire site than in the fuel treatment sites, and much of the sediment was produced during summer rainfall. Comparing results across scales, sediment yields from the fuel treatments and wildfire sites decreased exponentially with increasing area. These results suggest that fuel treatments that reduce the risk of wildfire do not cause significant erosion.