Submitted to: Proceedings of the American Society of Agricultural and Biological Engineers International (ASABE)
Publication Type: Proceedings
Publication Acceptance Date: July 15, 2011
Publication Date: September 18, 2011
Citation: Flanagan, D.C., Frankenberger, J.R., Cochrane, T.A., Renschler, C.S., Elliot, W.J. 2011. Geospatial application of the Water Erosion Prediction Project (WEPP) model [abstract]. In: D.C. Flanagan, J.C. Ascough II, and J.L. Nieber, editors. Proceedings of the International Symposium on Erosion and Landscape Evolution (ISELE). ISELE Paper No. 11084. American Society of Agricultural and Biological Engineers, September 18-21, 2011, Anchorage, AK. 711P0311cd. Technical Abstract: The Water Erosion Prediction Project (WEPP) model is a process-based technology for prediction of soil erosion by water at hillslope profile, field, and small watershed scales. In particular, WEPP utilizes observed or generated daily climate inputs to drive the surface hydrology processes (infiltration, runoff, ET) component, which subsequently impacts the rest of the model components, including subsurface hydrology (percolation, subsurface lateral flow), hillslope erosion (interrill detachment, rill detachment, sediment transport, sediment deposition), channel hydrology/erosion (channel flow routing, detachment, sediment transport, deposition), plant growth, and residue decomposition. For application of WEPP at the hillslope profile and/or field scale, simple Windows graphical user interfaces (GUIs) have been developed and can be used to easily specify the slope, soil, and management inputs. Likewise, simple watershed configurations of a few hillslopes, channels, and/or impoundments can also be fairly easily created and simulated with the Windows GUI. However, as the size of the area of interest increases, the complexity of developing and organizing all of the erosion model inputs greatly increases, due to the multitude of potential variations in topography, soils, and land management/cropping practices. For these types of situations, numerical approaches and special user interfaces have been developed to allow for easier WEPP model simulation setup, utilizing either publicly-available or user-specific geospatial information (Digital Elevation Models (DEMs), Geographic Information System (GIS) soil layers, GIS land-use layers). The basic approach used to automatically generate the necessary slope input files for hillslope profiles is to analyze and process a DEM of an area in three iterations: 1.) channel network delineation, 2.) watershed boundary and subcatchment delineation, and 3.) flow-path and representative hillslope profile determination. The TOpographic PArameteriZation (TOPAZ) digital landscape analysis tool is used for channel, watershed, and subcatchment delineation. In whichever interface is being used, once the user selects a rectangular region of interest within a DEM, TOPAZ delineates the network of channels within that region. The next step is for the user to use the mouse cursor to select the outlet point on a channel for their watershed of interest, after which TOPAZ is run a second time to delineate the watershed boundary and the subcatchments within it, and which will subsequently be used as WEPP model hillslopes. The final step before progressing on to the actual erosion model simulations is to create the actual slope, soil and management input files for WEPP, using custom software (called WeppPrep) that utilizes data from the extracted land use, soils, DEM, and TOPAZ watershed structures. Specifically, in regards to the hillslope profile slope inputs, there are two options for running WEPP: 1.) creating a single representative hillslope profile slope input for each subcatchment based upon an averaging of all the computed TOPAZ flowpaths within a subcatchment; and/or 2.) running WEPP model simulations for all TOPAZ-identified flowpaths within each subcatchment. The model slope inputs for each of the channels within the delineated watershed also are obtained from the TOPAZ output. A user has the option of specifying a single soil and land management for each subcatchment, or utilizing information in soil and land use GIS layers to automatically assign these. Once WEPP model simulations are completed, the output is scanned (again by the WeppPrep custom software), results are interpreted, and maps of spatial soil loss and/or sediment loss by hillslope are generated and sent to the GIS for display. These procedures have been implemented within a number of GIS platforms. The GeoWEPP interface is an ArcView and 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 information. Since about 2004, a web-based WEPP geospatial interface has been available that utilizes publicly available databases, as well as using the MapServer web GIS software for handling and displaying the spatial data and model results. Most recently, the WEPP model and geospatial handling logic has been integrated with the Google Maps system, which provides some significant enhancements over the MapServer system. This presentation will discuss in detail the logic and procedures for developing the WEPP model inputs, the various GIS interfaces, and future directions.