Submitted to: Laboratory Publication
Publication Type: Government Publication
Publication Acceptance Date: 6/1/2007
Publication Date: 6/1/2007
Citation: Parker, C., Thorne, C., Bingner, R.L., Wells, R.R., Wilcox, D.L. 2007. Automated Mapping of Potential for Ephemeral Gully Formation in Agricultural Watersheds. USDA-ARS National Sedimentation Laboratory Research Report. No. 56. US Department of Agriculture, Agricultural Research Service, National Sedimentation Laboratory, Oxford, MS. Interpretive Summary: Ephemeral gullies serve as effective links transferring sediment and associated agrichemicals from upland areas to stream channels. Current erosion prediction technologies often require the exact topographic location of an ephemeral gully to be known, which greatly limits the application of such models. Within a watershed system, there may be hundreds of ephemeral gullies that are present or may be present if management conditions were performed that promotes the formation of ephemeral gullies on the landscape and would require a considerable amount of time to manually identify their locations. An automated approach is needed to help identify watershed ephemeral gully locations and their downstream beginning points that can be used to simulate ephemeral gully erosion by watershed models. The approach adopted builds on previously developed technology to estimate locations of ephemeral gullies at the field level through the utilization of topographic information analyzed within a geographic information system (GIS) interface. A number of field sites were used to compare the predicted and observed locations and extents of ephemeral gullies. The results of the study show that this automated technique works reliably well provided that sufficient resolution and accuracy of the topographic data is available. This technology provides an automated, physically based standard of identifying ephemeral gully locations, including their downstream beginning points in agricultural watersheds that can be used to simulate and track ephemeral gully sediment sources. These tools are necessary to effectively manage the Nation’s soil resources.
Technical Abstract: Erosion associated with ephemeral gullies in cultivated areas is known to contribute significantly to soil loss and sediment yield from arable watersheds. Despite this, no automated method currently exists for mapping the potential for ephemeral gully formation. This study identifies that the capability to perform these tasks within a GIS environment would be useful, and explores how such a methodology might be developed. The approach adopted builds on the results of research previously performed at the USDA-ARS National Sedimentation Laboratory, which developed a Compound Topographic Index (CTI) to predict soil loss due to ephemeral gullying at the field level. In this study, the potential for a GIS-based version of the CTI to reliably predict the locations and extents of ephemeral gullies has been investigated using data from a number of field sites. At this field level it was possible to compare the predicted and the observed actual locations and extents of ephemeral gullies. The requirements for scaling up the automated technique to the watershed level were also explored. The results of the study show that the automated CTI technique works reliably provided that topographic data of sufficient resolution and accuracy are available. While the limited availability of high resolution topographic data currently limits application of the CTI method to research sites, given the increasing level of data availability the CTI method should become practically applicable to erosion assessments at the field scale in the near future. However, investigation of the impacts of digital elevation model resolution, data source and data errors on the technique’s results, and a consideration of the resolution and accuracy of readily available elevation data in the United States suggest that the widespread application of this method to predict ephemeral gullying at the watershed scale is currently unfeasible.