Theme 6-10-Assessment of cumulative watershed effects using WASTED model.

Abstract

In the present study an attempt has been made to understand the applicability of WATSED model, a computer based model to estimate the Cumulative Watershed Effects. The study has been carried out in two parts, (i) sensitivity analysis and, (ii) model application to Malaprabha representative basin, Belgaum district, Karnataka, India. . The sensitivity analysis of the model indicated that, though the parameters such as rainfall, monthly runoff and peakflow, mass erosion coefficients etc are taken into consideration, these factors do not show any direct impact on model output. However, it is observed that the model is very sensitive to alternative forest cutting and soil disturbing activities including silvicultural practices, alternative road construction practices and wild fire. In the second part, runoff and soil loss were estimated. The runoff coefficient obtained through WATSED model is 0.5 and the soil loss predicted by the model is 189 tonnes/sq km/year which is almost double the observed soil loss for the year 1987-88. The projected soil loss for the year 1996, without any management activities (after 8 years of recovery period) is 83 tonnes/sq km/year which is reduced by more than 50%. Based on the study, it is understood that the model can be used for the estimation of cumulative watershed effects due to various management activities. However, for broader application, it is suggested that the model must be oriented to take cognizance of climatic, soil and hydrological data availability and data constraints in order to make it a generally applicable user tool for realistic water resources decision making, rather than merely a multi-parameter site specific user tool.