A digital elevation model (DEM) is an important spatial input for automatic extraction of topographic parameters for the soil and\nwater assessment tool (SWAT). The objective of this study was to investigate the impact of DEM resolution (from 5 to 90m) on the\ndelineation process of a SWAT model with two types of watershed characteristics (flat area and mountain area) and three sizes of\nwatershed area (about 20,000, 200,000, and 1,500,000 hectares). The results showed that the total lengths of the streamline, main\nchannel slope, watershed area, and area slope were significantly different when using the DEM datasets to delineate. Delineation\nusing the SRTMDEM(90 m), ASTERDEM(30 m), and LDDDEM(5m) for all watershed characteristics showed that the watershed\nsizes and shapes obtained were only slightly different, whereas the area slopes obtained were significantly different.The total lengths\nof the generated streams increased when the resolution of the DEM used was higher.The stream slopes obtained using the small\narea sizes were insignificant, whereas the slopes obtained using the large area sizes were significantly different. This suggests that\nwater resource model users should use the ASTER DEMas opposed to a finer resolution DEMfor model input to save time for the\nmodel calibration and validation.
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