Assessment of Water Supply and Demand in the Lower Mahi Sub-basin using WEAP Model

This study deals with the future water demand assessment in Lower Mahi Sub-basin, Bihar, India using Water Evaluation and Planning Model (WEAP). The river Mahi is flowing through the Mahi sub-basin, which is a tributary to the Ganga river. Understanding and analyzing the past and present water supply and demand scenarios and prediction of future scenarios are indispensable for this area. In the WEAP model development phase, two scenarios are considered: past scenario (2004-2013), present and future scenarios (2016-2021) together. The water supply nodes used are Mahi river, groundwater and canals from Gandak river. The results from the trend of supply and demand shows that the sub-basin is water deficit for most part of year except during July to September. The water deficit is also observed during Rabi season when there is no rainfall or availability of surface water is nil for the crops, especially wheat. This results in more and more usage of groundwater and hence leads to groundwater depletion. By analyzing the results of the WEAP Model for the present and future scenario, a depletion in groundwater storage at a faster rate is observed with the existing climatic conditions and increased population, livestock and industry.