Measuring Post-fire Rill Network Density

Abstract:

Over the past several decades, the number and severity of annual wildfires has increased in the Western United States, a trend that is expected to continue as a result of global warming. Following wildfire, landscapes often experience elevated erosion rates, partially due to increased bare ground exposure and changes in soil hydrologic properties that result in increased overland flow. This overland flow can concentrate into rills, which can account for a significant amount of sediment erosion and transport. In addition to their contribution to erosion following fire, several studies have linked rills with the initiation of debris flows. Better understanding the controls on rill formation is therefore important, but observations have been limited due to the small size and short duration of rills in post-fire landscapes. Here, we use high-resolution topographic data to examine automated methods for assessing rill network density following the Thomas Fire in Montecito, California. These methods include both direct identification of networks through flow routing, and proxies for bulk network density based on spatial statistics such as surface roughness and lidar return intensity. A proxy for rill network density may act as a useful metric for assessing erosion mechanisms or provide a rough estimation for sediment budget calculations following wildfire, which may help to improve the understanding of the impacts of fire on the landscape.