Submitted to: Federal Interagency Sedimentation Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: January 15, 1996
Publication Date: N/A
Interpretive Summary: Evaluating practices for water quality control on large watersheds can be difficult without the aid of water quality modeling technology. Techniques were developed and validated in this study to reduce the manual data entry requirements of runoff and erosion prediction computer models while maintaining the prediction accuracy needed to make best management practice decisions. This technology utilizes geographical information systems, combined with graphical interface programs, to extract the necessary model data. A validation of the capabilities of this scheme was performed using ten years of measurements from a highly instrumented watershed in Mississippi. Runoff was shown to be adequately predicted, except for periods with above normal rainfall, when runoff was underpredicted. Using the modeling scheme, sediment yield of small size particles determined at fourteen locations in the watershed was 35% of the measured values. Thus, 65% of the sediment yield can be estimated from channel and gully sources past the outlets of individual subbasins, since the predicted sediment yield did not include erosion processes within the channel. Predictions from areas of the watershed with different cropping practices, soil types, and topography demonstrated the modeling schemes ability to include the variability of the landscape within the simulations. These tools are valuable when erosion control decisions are required concerning how one area or management practice may affect the water quality of an entire watershed system.
Technical Abstract: A validation of the integration of GIS, topographic analysis tools and watershed models is presented. This scheme involves the use of GRASS geographic information system (GIS) layers, the digital elevation analysis model, TOPAZ, and the watershed model, SWAT. The GRASS-TOPAZ- SWAT scheme is validated using data collected by the USDA-ARS, National Sedimentation Laboratory at the Goodwin Creek Watershed (GCW) in northern Mississippi. A combination of GRASS GIS layers digitized for GCW, such as landuse, soils, and topography, and measured input parameters were used to develop the database needed for validating the modeling scheme. The SWAT model's results were compared to the measured runoff and sediment yield collected over ten years from fourteen instream measuring stations. Results show that the SWAT model runoff and sediment yield predictions followed the relative trends described by the measured data from various locations within the watershed. The GRASS- TOPAZ-SWAT scheme provides a relatively accurate, integrated and simplified approach to develop information needed for evaluations of erosion control measures on watersheds with minimal model user involvement