Modeling of Rainfall-Runoff Response of the Manimuktha Catchment Using TOPMODEL

The semi-distributed topographic based rainfall-runoff model (TOPMODEL) has been applied to the Manimuktha watershed sub-catchment of Vellar River;one of the important catchment which contributes lot of flow in the rainy seasons. Remote Sensing was applied to estimate spatially distributed catchment parameters such as landuse, soil DEM and catchment parameters. SRTM 90m DEM was used to compute the topographic index, the basement and basic input for the TOPMODEL to simulate the stream flow of the sub-catchment. TOPMODEL calculates the actual evapotranspiration from the potential evapotranspiration, the ischolar_main zone storage deficit and maximum ischolar_main zone storage deficit for its water balance calculation. The first step in applying TOPMODEL to a watershed involves GIS analysis which results in a raster grid of elevations used for the calculation of the topographic index. Analyses were also performed to determine the sensitivity of TOPMODEL hydrographs to several model parameters. A sensitivity analysis of the model indicated significant changes in the simulation result for the three parameters that are the exponential transmissivity function (m), the soil transmissivity at saturation (To) and the ischolar_main zone available water capacity (SR_max). The hydrographs generated for six storm events and the results are satisfactory with Nash efficiency as much as 78.8% in and Correlation Coefficient 0.69.