A GIS based distributed rainfall–runoff model

Abstract

A grid or cell based process oriented distributed rainfall–runoff model capable of handling the catchment heterogeneity in terms of distributed information on landuse, slope, soil and rainfall is developed and applied to isolated storm events in several catchments. Model inputs such as slope, flow direction and overland flow sequencing (drainage path) are generated for each cell of the catchment using a digital elevation model and information about landuse, soil, etc. were derived through digital analysis of satellite data and published information. The input variables for each cell area are provided to the model through geographic information system. Infiltration in cell areas is computed by Philip two-term infiltration model, the parameters of which were determined mainly through the information on soil type in the cell. The mechanics of overland flow is described by the diffusion wave approximation of St Venant equations which are numerically solved for depth of flow and runoff by the method of finite volume. The model utilizes a relationship explaining the dependence of flow resistance on depth of flow and surface roughness. Results from several catchments indicate that the model can simulate reasonably well the runoff hydrograph at the catchment outlet. The model also realistically predicts temporal variation of the spatial distribution of flow depth and runoff over the catchment. Also the grid or cell based structure of the model allows studying the effect of catchment modifications in terms of soil and landuse changes on spatial and temporal distribution of the runoff. However, the proposed model has the limitation that the values of some parameters of the model need to be obtained through calibration.