ASSESSING CONSERVATION EFFECTS ON WATER QUANTITY AND QUALITY AT FIELD AND WATERSHED SCALES
Location: National Soil Erosion Research Lab
Title: Geospatial application of the Water Erosion Prediction Project(WEPP) model
Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 2, 2012
Publication Date: N/A
Interpretive Summary: Rainfall and runoff can cause soil erosion and movement of water and sediment from fields and forests into streams and lakes. How landowners, farmers, and foresters manage their land can have a very large impact on how much runoff and erosion will occur, and how much sediment may make it into off-site water bodies. Also, natural events such as wildfires occurring in forests can remove large areas of protective cover, and cause high risk for sediment losses. Unfortunately, it is very expensive and very difficult to measure runoff and soil losses in the field, but ways to assess them are needed so that conservation management practices or remediation efforts can be identified and targeted. Computer simulation programs have been developed to simulate the natural processes of runoff, soil erosion, and sediment loss from fields and watersheds. The USDA Water Erosion Prediction Project (WEPP) model is one such tool, allowing users to predict how much soil erosion may occur, how much sediment may travel off-site, and how alternative management strategies may assist in reducing these. For watersheds that consist of hundreds of acres of fields or forests or rangeland, the WEPP model has been integrated with geographic information systems (GIS) that provide detailed data on topography, soils, and existing land management across landscapes. The combination of WEPP and GIS tools allows for much easier application of the model, prediction of soil erosion, and evaluation of management alternatives or targeting of remediation efforts. This paper describes the logic and procedures used in geospatial applications of the WEPP model, and also includes some real-world examples. This research impacts scientists, university faculty, students, action agency personnel, and others involved in soil conservation efforts and natural resources assessments. The erosion model, interfaces, and databases described allow application of WEPP to any location within the United States for rapid assessment of soil erosion in small cropland, rangeland, or forested watersheds.
At the hillslope profile and/or field scale, a simple Windows graphical user interface (GUI) is available to easily specify the slope, soil, and management inputs for application of the USDA Water Erosion Prediction Project (WEPP) model. Likewise, basic small watershed configurations of a few hillslopes and channels can be created and simulated with this GUI. However, as the catchment size increases, the complexity of developing and organizing all WEPP model inputs greatly increases, due to the multitude of potential variations in topography, soils, and land management practices. For these types of situations, numerical approaches and special user interfaces have been developed to allow for easier WEPP model setup, utilizing either publicly-available or user-specific geospatial information (Digital Elevation Models (DEMs), Geographic Information System (GIS) soil data layers, GIS land use/land cover data layers). We utilize the Topographic Parameterization (TOPAZ) digital landscape analysis tool for channel, watershed, and subcatchment delineation, and also to derive slope inputs for each of the subcatchment hillslope profiles and channels. A user has the option of specifying a single soil and land management for each subcatchment, or utilizing information in soils and land use/land cover GIS data layers to automatically assign these. Once WEPP model runs are completed, the output data is analyzed, results interpreted, and maps of spatial soil loss and sediment yields are generated and visualized in a GIS. These procedures have been used within a number of GIS platforms. GeoWEPP is an ArcView/ArcGIS extension that was the first to be developed, and which allows experienced GIS users the ability to import and utilize their own detailed DEM, soil, and/or land use/land cover information, or to access publicly available spatial datasets. An initial web-based GIS system that used the MapServer web GIS software for handling and displaying the spatial data and model results was released in 2004. Most recently, the Google Maps and OpenLayers technologies have been integrated into the web WEPP GIS software to provide significant enhancements. This paper discusses in detail the logic and procedures for developing the WEPP model inputs, the various WEPP GIS interfaces, and provides example real-world applications.