CHALLENGES OF MODELING POST-FIRE RUNOFF AND SEDIMENT TRANSPORT IN EPHEMERAL FORESTED WATERSHEDS IN THE ARID SOUTHWEST
Schultz Creek is a 17 km2 drainage network within the Dry Lake Hills area that flows into densely populated residential areas and the cultural center of Flagstaff. Previous studies and local catastrophic wildfires provide evidence to suggest that runoff from post-fire monsoonal precipitation could result in flooding 2.2 to 6 times greater than the pre-fire 100 year flood, with costly damages caused by hyperconcentrated flows and erosion.
Hydrologic and hydraulic models are being constructed using Hydrologic Engineering Center (HEC) software to predict how peak discharges will be affected by FWPP treatments in the Schultz Creek watershed. The sediment record is being analyzed to determine the individual watershed’s sediment transport dynamics, using radiocarbon dating of macroscopic charcoal for age constraints on deposition. Peak discharges have been successfully modeled using HEC software, but modeling transported sediment and erosion, particularly in ephemeral channels, poses unique challenges. Existing sediment mobilization models have limited applications. Without an appropriate sediment model, predictions of the full impact of post-fire runoff and sediment yield are limited.