CS(AR)-22/96-97 : GIS based rainfall runoff modelling for Hemavathi catchment

Abstract

The TOPMODEL is a variable contribution area conceptual model in which the predominant factors determining the formation of runoff are represented by the topography of the basin and a negative exponential law linking the transmissivity of the soil with the vertical distance from the ground level. In this model the total flow is calculated as the sum of two terms: surface runoff and flow in the saturated zone. The TOPMODEL is attractive because of its structural simplicity and parsimonious parameterisation. It is one of the few conceptual models that accounts explicitly for the saturation excess overland flow mechanism and integrates the variable contributing area concept, both of which are essential to model the catchment accurately.

Calibration and validation of the TOPMODEL is carried out on Hemavati catchment situated in Western Ghats. Raster DEM input for the model is generated through ILWIS after digitization contour map from Survey of India toposheets. In all 5 years of data was available for simulation study. Available data series was broken in two parts and first part i.e. June 1975-December 1977 was used for model parameter calibration and remaining data series i.e. January 1978 to December 1980 was used for model validation. Simulation results are encouraging. Model efficiency (Nash-Sutcliffe) was more than 0.84 both for model calibration and validation on independent data series.