Capturing the essential spatial variability in urban hydrologic miodeling by GIS.

Three different digital elevation models with 10 ft, 25 ft, and 50 ft resolutions, and several algorithms were used to derive parameters for HEC -HMS hydrologic model for the prediction of runoff from an urban watershed. GIS techniques were used to delineate the sub-basins and to extract hydrologic parameters required for the HEC-HMS hydrologic model. D8 (deterministic 8 nodes) and DEMON (digital elevation model networks) were used to calculate the area of each sub-basin, while maximum slope and neighborhood methods were used to obtain the slope. Comparison of the simulated runoff peak flow and runoff depth with the observed data showed that the simulation results fit the observed values well. Because of the relatively flat topography, only the different DEN • resolutions caused significant differences in runoff in the study. In addition, the effects of different overland flow plane defining are also discussed in the study. Simulation results using impervious and pervious area to represent two separate planes were much different from those using main channel separated Planes. Meanwhile, pervious and impervious area weighted average CN showed better results than using total plane weighted average CN in an urban area.hydrology collectio