JWSS - Journal of Water and Soil Science

The last two decades have seen increasing applications of digital terrain modeling in hydrological, geomorphological, pedagogical, and biological research, aided by rapid advancement of geographic information system (GIS). Hydrologic models are sensitive to change in the input values to the model, so the change of pixel size input data affects the output values of the model and produces different significant results. In this study, using topographic maps 1:25000 and 1:50000 and choosing ten pixel sizes (10, 15, 20, 25, 30, 50, 75, 80, 100, and 200) and software Arc GIS and HEC-HMS, output values of HEC-HMS model have been studied. Results of this study indicate that accuracy of peak discharge calculated by HEC-HMS model in the spatial scale map 1:50000 is more than the peak discharge calculated by HEC-HMS model in the spatial scale map 1:25000. Also accuracy of the calculated peak flows in a smaller pixel sizes (20 to 50) is more than the larger pixel sizes.