An Investigation on the Effects of DEM Resolution and Stream Delineation Thresholds on the Performance of the Kinematic-wave-based GIUH Model

Digital elevation models (DEMs), due to their capacity for extracting many of geomorphologic parameters such as: streams network, sub-watersheds area, slope of streams and sub basins have obtained a very important role in rainfall - runoff modeling. One of the most important issues that affect the results of these models is the DEM resolution and the assigned threshold for artificial river network delineation. In this study, the effect of DEM resolution on the geomorphologic parameters of watersheds and the performance of a kinematic wave based model, called as GIUH, is investigated. The results show that by decreasing the DEM resolution, parameters such as sub-basin's mean slope and the number of streams (specially of order 1 and 2) decrease and the area of the i-th order sub basins and the mean length of the overland flow increase. Moreover, the results indicate that the reduction of the DEM resolution at a fixed threshold causes the peak flow and hydrograph time base to decrease up to cell size of 100 meters and then after experiencing a jump, again decrease with increasing cell size. According to the results obtained, above the threshold of 2%, the difference between the peak flows of different hydrographs at different resolution is meaningful. In a fixed threshold, the time to peak flow is independent of DEM cell sizes.