Location: Watershed Physical Processes ResearchTitle: AnnAGNPS GIS-based tool for watershed-scale identification and mapping of cropland potential ephemeral gullies) Author
Submitted to: Applied Engineering in Agriculture
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/27/2011
Publication Date: 5/1/2012
Publication URL: http://handle.nal.usda.gov/10113/54162
Citation: Momm, H.G., Bingner, R.L., Wells, R.R., Wilcox, D.L. 2012. AnnAGNPS GIS-based tool for watershed-scale identification and mapping of cropland potential ephemeral gullies. Applied Engineering in Agriculture. 28(1):17-29. Interpretive Summary: Contributions from ephemeral gullies in agricultural fields have been recognized as an important source of sediment within watersheds resulting in reduced water quality and crop productivity. Technology has recently been developed to quantify and assess the impacts of agricultural practices on ephemeral gully evolution and sediment load within the U.S. Department of Agriculture’s Annualized Agricultural Non-Point Source (AnnAGNPS) watershed conservation management planning tool. Identifying where ephemeral gullies occur can be difficult because often they are hidden by crops or removed with tillage. The identification of ephemeral gully locations and their characteristics used to define model input parameters can require a significant amount of resources, where users may not be able to accurately locate and describe all ephemeral gully locations throughout a watershed system. This study describes a methodology developed within a graphical user interface for use with AnnAGNPS to help locate and characterize areas that have a high probability of where ephemeral gullies will begin based on topographic indices. An iterative process is described that utilizes various topographic thresholds to produce alternatives that represent locations where ephemeral gullies will likely begin in order to assess their impact on sediment loads. Utilizing this technology can provide action agencies with a management tool to assess ephemeral gully erosion control practices, as well as when integrated with other conservation practices, and to develop the most effective management plans that reduces sediment loads within watershed systems.
Technical Abstract: The formation of ephemeral gullies in agricultural fields has been recognized as an important source of sediment contributing to environmental degradation and compromising crop productivity. Methodologies are being developed for assessing gully formation and gully sediment yield. The Annualized Agricultural Non-Point Source (AnnAGNPS) pollution model is an important tool for multi-temporal watershed-scale simulations because it contains the necessary components for ephemeral gully investigation, making AnnAGNPS a commonly used tool for evaluations of agricultural conservation and operation practices. AnnAGNPS requires the user to define the location of ephemeral gullies throughout the watershed, what often constitutes a time consuming task where users may not accurately locate and describe all ephemeral gully locations. Alternatively, herein a GIS-based graphical user interface is described for the automated identification of areas with high probability of forming ephemeral gullies, referred to as potential ephemeral gullies (PEGs), based on the modified Compound Topographic Index (CTI). Through the aid of a study case, PEG mouth locations along with their attributes are generated through an iterative procedure by varying different CTI threshold values (99.9%, 99.5%, 99.0%, 98.5%, and 98%). Three sets of yielded PEG mouth locations and corresponding attributes were then integrated with AnnAGNPS for assessment of the impact of potential ephemeral gullies in the watershed sediment erosion. Analysis of the spatial distribution of estimates of annual average of gully erosion identifies the sub-watersheds prone to ephemeral gully erosion, thus enhancing the applicability of AnnAGNPS to evaluate conservation practices and/or targeted interventions designed to address ephemeral gully erosion at the watershed-scale.