Modeling Postfire Soil Erosion and Sediment Deposition on the Tonto National Monument with the Unit Stream Power Erosion and Deposition Model

Abstract

A major consequence of wildfire events is the acceleration of soil erosion by surface runoff. During a rainfall event, soil may become detached, transported, and eventually deposited elsewhere on the landscape. One approach to predict whether and where this erosion process could occur requires determining six empirically established factors, namely, rainfall erosivity, soil erodibility, slope length, slope steepness, vegetation cover, and erosion management methods. This project analyzed these landscape factors on the Tonto National Monument, an archaeologically rich site containing 14th century cliff dwellings in central Arizona’s Tonto Basin. In the summer of 2019, over 80% of the monument burned, threatening its natural and cultural resources both from the fire itself and from the postfire erosion that followed. Chosen for its ability to predict both soil erosion and sediment deposition, the Unit-Stream-Power-Erosion-and-Deposition Model identified areas of the monument where the erosion process may have occurred and to what extent. This project used high resolution data to obtain each factor in raster format followed by further calculations based on changes in sediment transport capacity using a Geographic Information System (GIS) called ArcGIS Pro. The model predicted that 13.5% of the monument had high erosion, 27% moderate erosion, 15.5% low erosion, 8.7% stable, 3.2% low deposition, 6.2% moderate deposition, and 25.7% high deposition. Although this project’s methodology focused on the 2019 fire event, it offers resource managers on the monument an approach to monitor and mitigate potential future fire events, reducing costs and focusing efforts to areas of highest risk.