ESTIMATION OF WATER BALANCE OF BARSACHHU WATERSHED IN CHUKHA BHUTAN USING REMOTE SENSING AND GIS

The water balance of a watershed is critical for the estimation of the water budget to meet the present and future domestic and economic demand and supply of water. Water balance parameters like precipitation, temperature, evapotranspiration soil moisture content deficit and surplus determine the water budget of a watershed which is further influenced by factors like land use, soil types, seasonal variation and other environmental factors. This paper intends to estimate the water balance of the Barsachhu watershed using Thornthwaite and Mather (TM) model. The use of Remote Sensing data and GIS as a tool were used in deriving the required data in executing the model. The study indicates that the monthly soil moisture content (deficit or surplus) is substantially influenced by the change in monthly rainfall, temperature and land use land cover pattern. April to October remain water surplus months while November to March remains a period of deficit. The soil moisture content has a different response to different land use in the Barsachhu watershed. The maximum annual moisture deficit and surplus of the basin are 126.27 mm and 2430.79 mm respectively and is observed in built-up areas. The runoff coefficient of the Barsachhu watershed computed from the runoff simulation of the TM model is 0.63.