Using DTMs and GIS to define input variables for hydrological and geomorphological analysis

The ARC/INFO 6.1 Grid system was applied in the 170 km large Henley Dam and the 19.4 km large Cedara basins, KwaZulu Natal, South Africa, to determine hydrological and geomorphological parameters required to simulate water quantity and water. A sensitivity analysis was carried out to evaluate the effects of the grid mesh size on basin slope by producing a number of grids with grid mesh sizes ranging from 400 to 50 m for the Henley and 400 to 5 m for the Cedara catchment. This paper discusses how the grid mesh size used for the generation of digital terrain models (DTMs) effects the representation of slopes, and subsequently a number of slope-related hydrological and geomorphological parameters. There is a decrease of the mean and maximum basin slopes with increase in grid size. Mean annual soil loss potential estimations differ by up to 160 % between the different grid sizes. Subsequently, terrain representation, soil delineation and potential soil loss estimation vary depending on the grid mesh size. Mean slopes differ by up to 213 %, and mean annual potential soil loss estimations differ by up to 160%.