Location: Watershed Physical Processes ResearchTitle: Spatially distributed sheet, rill, and ephemeral gully erosion
|YODER, DANIEL - University Of Tennessee|
|Wells, Robert - Rob|
|Ursic, Michael - Mick|
Submitted to: Journal Hydrologic Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/7/2014
Publication Date: 11/11/2014
Publication URL: http://handle.nal.usda.gov/10113/5695341
Citation: Dabney, S.M., Vieira, D.A., Yoder, D.C., Langendoen, E.J., Wells, R.R., Ursic, M.E. 2014. Spatially distributed sheet, rill, and ephemeral gully erosion. Journal Hydrologic Engineering. pp. C4014009-1-C4014009-12.
Interpretive Summary: This paper describes a new computer modeling system that combined the influences of sheet and rill erosion, tillage erosion, and ephemeral gully erosion. Most existing erosion prediction models require the user to specify a representative hilllslope flow path and do not account for ephemeral gully erosion. The new system uses high-resolution topographic information that is becoming increasingly available from Light Detection and Ranging (LiDAR) sources and produces distributed estimates of soil erosion that are based on existing soil, climate, and management databases that have been published by the Natural Resources Conservation Service (USDA-NRCS). The way watersheds are analyzed to determine the locations of concentrated flow channels and how Revised Universal Soil Loss Equation, version 2 (RUSLE2) is used to determine distributed estimates of sheet and rill erosion that can be mapped in a GIS is described. The output of this distributed model is then linked with a new ephemeral gully model to calculate the additional contribution of ephemeral gullies to total field soil erosion and sediment delivery to water bodies. Predictions are compared with observations obtained on a research watershed located in Treynor, IA. This new technology will make it easier for conservationists and farmers to realistically calculate and visualize the magnitude of their soil erosion problem and this will lead to better management decisions.
Technical Abstract: Ephemeral gully erosion can be a serious contributor to soil degradation in agricultural fields, but few conservation planning tools account for and predict this form of erosion. To address this deficiency, a new modelling system was developed and applied to a 6.3 ha research watershed near Treynor, IA, where runoff and sediment yield were measured from 1975 – 1991. The Revised Universal Soil Loss Equation, version 2 (RUSLE2) was modified to predict a gully-forming runoff event sequence and the slope length estimation methods were modified to allow erosion computations on a raster basis considering the influence of upslope flow convergence and variation in soil and management attributes. Digital representations of an area of interest (field or farm) are generated using high-resolution topography to create a raster-based digital representation of surface drainage patterns, determine the location of potential ephemeral gullies, and subdivide the study area into catchments. Data retrieved from established databases of soil properties, climate, and agricultural operations are combined with the topographic information by a new program, RUSLER (RUSLE2-Raster) that calls RUSLE2 and assembles results. RUSLER output is linked to an existing tillage erosion model (TELEM) and a new Ephemeral Gully Erosion Estimator (EphGEE). EphGEE computes gully evolution based on local soil erodibility, flow, and sediment transport conditions. The Treynor watershed was managed with conventional tillage, was cropped to continuous corn (1975-1991), and contained a grassed waterway in the footslope thalweg. Using a 3-m raster DEM, concentrated flow channels that ended RUSLE2 hillslope profiles were best delineated where contributing areas exceeded 600 m2 (Dabney et al. 2013). Results indicate that in the steeper parts of the field, 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 in less steep channel reaches and within the grassed waterway. For ambient conditions, predicted annual average watershed sediment yield was 18 Mg ha-1 yr-1, similar to the measured value of 15 Mg ha-1 yr-1.