Spatially Distributed Watershed Mapping and Modeling: GIS-based Storm Runoff and Hydrograph Analysis: (part 2)

Advances in scientific knowledge and new techniques of remote sensing permit a better understanding of the physical land features governing hydrologic processes, and make possible efficient, large-scale hydrologic modeling. The need for land-cover and hydrologic response change detection at a larger scale and at times of the year when hydrologic studies are critical makes satellite imagery the most cost effective, efficient and reliable source of data. In this work, remotely-sensed data and geographic information system (GIS) tools were used to estimate the changes in runoff response for three watersheds (Etonia, Econlockhatchee, and S-65A subbasins) in Florida. Land-use information from Digital Orthophoto Quarter Quadrangles (DOQQ), Landsat Thematic Mapper, and Enhanced Thematic Mapper Plus were analyzed for the years 1984, 1990, 1995, and 2000. Spatial distribution of land-cover was assessed over time. The corresponding infiltration excess runoff response of the study areas due to these changes was estimated using the United States Department of Agriculture, Natural Resources Conservation Service Curve Number (USDA-NRCS-CN) method. A Digital Elevation Model-GIS technique was used to predict stream response to runoff events based on the travel time from each grid cell to the watershed outlet. The method was applied to a representative watershed (Simms Creek) in the Etonia sub-basin to study the effect of land-cover on storm runoff response. Simulated and observed runoff volume and hydrographs were compared. Isolated storms, with volumes of not less than 12.75 mm (0.5 inch) were selected (the minimum amount of rainfall volume recommended for the NRCS-CN method). Results show that the model predicts the total runoff volume with an average efficiency of 98%. The model is applicable to ungaged watersheds and useful for predicting runoff hydrographs resulting from changes in the land-cover.