The quality of surface runoff modeling is limited by horizontal and vertical accuracy of digital elevation model. Several critical problems and respective solutions are presented. Method of filling pits based on size can distinguish sink cells due to inland catchment from those due to DEM errors. Method combining DEM with stream network leads to a more accurate drainage network from surface runoff modeling

especially for flat area.Method of modifying existing DEM by adding a small value can produce more realistic drainage pattern rather than parallel flow over flat surface.