Modeling Sheet, Rill, and Ephemeral Gully Erosion with Rusler and Ephgee.

A new modeling system is being developed to provide spatially-distributed runoff and soil erosion predictions for conservation planning.  Ephemeral gully erosion is not included in predictions made with the Revised Universal Soil Loss Equation, version 2 (RUSLE2). A new distributed application called RUSLER (RUSLE2-Raster) predicts distributed runoff and soil loss and its output can be linked with the new Ephemeral Gully Erosion Estimator (EphGEE).  Digital representations of the area of interest are created using high-resolution topography and data retrieved from established databases of soil properties, climate, and agricultural operations. The system utilizes a library of terrain processing tools to deduce surface drainage from topography, determine the location of potential ephemeral gullies, and subdivide the study area into catchments for calculations of runoff and sheet-and-rill erosion using RUSLER.  EphGEE computes gully evolution based on local soil erodibility and flow and sediment transport conditions.  These models were applied to a 6.3 ha research watershed near Treynor, IA, where runoff and sediment yield were measured from 1975 –1991. Using a 3-m raster DEM, results indicate that ephemeral gully erosion contributed about one-third of the amount of sheet and rill erosion, and that considerable deposition of sediment originating from both sources occurred within the grassed waterway. For ambient conditions, predicted annual average watershed sediment yield was 17 Mg ha^-1 year^-1, similar to the measured value of 15 Mg ha^-1 year^-1.