Remote Sensing and Geographic Information System in Runoff Coefficient Estimation in China Taipei

Emerging technologies of remote sensing and GIS were integrated to estimate runoff for watershed basins in China Taipei and Florida. Two basins were selected in each region, with each pair representing a static and a developing case. Remotely sensed images from the Landsat 4, 5, and 7 satellites were used to develop land cover maps of the study areas for the years 1990, 1995, and 2000. GIS analysis, based on land-cover and soil map data, was used to estimate NRCS-CN curve numbers on a 30-meter grid and to compute runoff depths for a 10 -year maximum rainfall event. Runoff coefficients were computed by the Rational method for each year of the study. Temporal changes in spatial distribution of land cover, runoff coefficients, and runoff volume were estimated. A runoff hydrograph, based on the above information and digital elevation model, was developed for a representative watershed in Etonia basin, Florida. The land cover for both the study regions in China Taipei and Florida showed an increase in urban area and a corresponding decrease in agricultural area. A significant increase in modeled runoff volume and peak flow is attributed to this change in land cover. The results of this study indicate a need for planning and designing new control structures to reduce the effect of floods in the developing basins.