Abstract

A physically based integrated rainfall-runoff and erosion model, capable of handling the catchment heterogeneity, distributed information of rainfall, landuse, slope and soil parameters is prepared on grid-based approach. The model can calculate runoff and erosion at any interior point of basin. The model was applied to some isolated storm events of Lesti river basin, Indonesia. Model inputs such as slope, flow direction and overland flow are generated for each cell of the catchment using a digital elevation model and information about landuse, vegetation, soil, etc. were derived through digital analysis of satellite data. Infiltration in cell areas is computed by Richard’s equation. A relationship of normalized differential vegetation index (NDVI), which is an alternative measure of vegetation amount and condition, and roughness coefficient was established which was used for assigning the roughness coefficient to particular grid. The model utilizes a relationship explaining the dependence of flow resistance on surface roughness. Variation of the seasonal vegetation in a basin highly changes the roughness of particular grid, which eventually changes the runoff and the erosion pattern. The seasonal NDVI indexes were used to incorporate seasonal change in vegetation and thus the roughness coefficient. Results from different rainfall events shows that the model can simulate reasonably well the runoff hydrograph at the catchment outlet. The model also realistically predicts the sediment flow measured at the outlet. Use of single roughness coefficient and NDVI based variable roughness coefficient were used for comparison. It is clear from the result that the use of NDVI improves the runoff and turbidity simulation.

Keywords: rainfall runoff, erosion, NDVI, turbidity, simulation