FLOODING AND EROSION AFTER THE BUFFALO CREEK FIRE: A MODELING APPROACH USING LANDLAB

In May 1996, the Buffalo Creek fire destroyed several thousand hectares of federal and private land throughout central Colorado. Shortly after the fire, a precipitation event with a recurrence interval between 100- and 1000-years ravaged the area. After this event, the United States Geological Survey extensively monitored channel discharge and sediment transport throughout two basins impacted by the Buffalo Creek fire. These storms transported significant amounts of sediment down hillslopes and through the channels. Sediment yields recorded on hillslopes after post-fire storms were orders of magnitude greater than predicted sediment yields in similar unburned watersheds. The abundance of field data and the fact that nearly 80% of the Spring Creek watershed was extensively burned by the Buffalo Creek fire makes this an ideal field site to validate and test new computational models. The new Landlab modeling framework is used in these tests. The Spring Creek digital elevation model is read into Landlab, and is used as the modeling domain. A nonsteady flow routing algorithm is used to calculate water discharge at all points throughout the watershed, which is then used to drive fluvial erosion. This method is novel in that it calculates a hydrograph across a distributed grid, and can be extrapolated to make conclusions about how nonsteady versus steady flow routing methods can impact modeling output. To explore model behavior, modeled discharge is compared against field discharge data. Results from these runs can be used to draw conclusions about changes in infiltration rate post-fire. Additionally, total volumes of sediment can be estimated from the model for smaller precipitation events. The model is then applied to the intense, unmonitored storm from July 1996 to make interpretations about the impact of post-fire erosion during high-intensity flood events. These results will motivate future modeling studies on the processes that drive intense erosion post-fire, and the significance of these post-fire events in driving watershed evolution in steep, semi-arid landscapes.