An integrated GIS-AnnAGNPS modeling interface

AnnAGNPS (Annualized AGricultural Non-point Source), a continuous simulation and distributed pollution model, is widely applied in evaluating non-point source pollution and watershed management practices. However, the complexity of required input data and modeling procedure keep it from being an efficient modeling tool. An integrated GIS interface was developed to facilitate organizing and preparing the input data, running the model, and visualizing modeling and management results. The interface is operated in ArcGIS 8.x environment as a new command bar that was developed with Microsoft Visual BASIC 6. It consists of three major components: topographic data processing, soil and land use related data manipulation, model output visualizing. Introduction Nonpoint source pollution (NPS) is a widely concerned water quality issue. Due to the NPS nature and the limitation of experiments and field measurements, NPS management is highly dependent on the spatial simulation. Spatial simulation is an important technique of using models to deal with the NPS pollution problems associated with spatial uncertainty. Numerous models such as USLE (Wischmeier and Smith 1978), AGNPS (Young et al. 1987 and 1989), HSPF (Johnson et al 1980), ANSWERS (Beasley et al 1980), SWAT (Arnold et al. 1995) have been developed to aid in understanding parts of the NPS system and evaluating/identifying watershed management, land use, pollution control and conservation practices. The application of NPS models to assess water quality requires efficient acquisition, storage, manipulation, visualization, analysis, and interpretation of model input and output data. Because GIS is powerful to store, manipulate, retrieve, and display spatial and nonspatial data, integration of GIS with NPS models can facilitate and reduce burden of the task of compiling necessary data for watershed modeling, interpreting and visualizing of model results. Moreover, the integration can enable decision-makers to determine critical area and to perform various “what-if?” scenarios of alternative management strategies. Currently many NPS models have been integrated with GIS (Engel and et al 1993; Arnold et al. 1995; Liao and Tim 1997; He et al 2001). Objectives Annualized Agricultural Nonpoint Source (AnnAGNPS) designed by U.S. Department of Agriculture (USDA ARS and NRCS), is a continuous and distributed simulation model widely used for watershed assessment. It expands the capabilities of its predecessor AGNPS which is a single event model. The newest version is 3.2 and can be downloaded for free from web site (http://www.sedlab.olemiss.edu/agnps.html). This model has an extensive input data requirement (up to 400 input parameters of 34 data categories). Preparing input data is very time-consuming and difficult without visualization support. Therefore, a user-friendly GIS integrated system was desired to reduce the complexity, time, and labor involved. There’re some GIS interface existed for AnnAGNPS model. The original AnnAGNPS package provided an ArcView 3.x interface (USDA ARS and NRCS). Some other researchers have also developed ArcView 3.x interface for it (Tsou, Misgna and et al