Advances in watersheds modeling using remote sensing and geographical information systems technologies

Remote sensing and geographic information systems (GIS) technologies have become indispensable tools for watershed-scale hydrologic analyses and modeling. These integrative capabilities can emulate real-world complexities, facilitating interdisciplinary research and communication. Landsat 5 Thermal Mapper raster images represent topography, land use, land cover, and soil types. These data are all integrated in GIS themes using views, tables, charts, and layouts. GIS is being used for data visualization, processing, and management. This paper presents a case study on the integration between the Geographical Resources and Assessment Support System (GRASS) and the distributed parameter and physical process watershed model, Soil and Water Assessment Tool (SWAT) for simulating large watershed processes. A cross checking was conducted on the spatial data extracted from the GIS map layers. Some major errors in the input data, due to the inadequate resolution of the GIS raster map layers, were detected. The spatial data were adjusted then the model calibration showed a significant success. The spatial variations of the SWAT model output results were successfully visualized using Geomedia-Intergraph software. By using the SWAT-Geomedia integration, sub-areas under severe pollution problems could be identified. The interdependence of sediment and nutrient loads under different watershed land uses was studied to determine a better land management in large rural watershed.