Travel Time Distribution-based River Basin Management Plan for Sustained Dry Season Flow

Abstract:

The key questions regarding the availability of water resources to be answered for effective management are: ‘where’, ‘how much’, and ‘how long’. Hydrograph, although is extensively studied for solving the above questions, it does not provide the holistic picture at the catchment or river basin scale, especially in the lean season. The travel time distribution (TTD) seems to be the suitable alternative. The travel or residence time of water on hillslopes dictates the in-stream water availability and its duration. Further, it has been observed worldwide that the lean season streamflow is decreasing in many non-glacial rivers. These rivers are primarily groundwater-fed during the non-rainy period. Hence, to sustain the low flow, it is essential to maintain the aquifer storage that is affected by recharge. However, managing recharge at all places in a basin is neither feasible nor useful for maintaining the lean season streamflow. Then, the question arises that which are the locations in a river basin to be prioritized as recharge zones so that the recharge would be available as streamflow during the lean season. To answer this question, in this study, a suitable river basin management plan based on the TTD is suggested for the Baitarani river basin in eastern India. First, flow distance map was generated for the entire river basin. From the flow distance map, the groundwater TTD map was generated using the geographic information system. Further, the onset time of the streamflow with exceedance probability (POE) of 80% was estimated to be February. Accordingly, areas in the TTD map with the travel time of five to eight months are identified to be dedicated for managed recharge. To verify the outcome of the implementation of the suggested land use land cover (LULC) management plan, the hillslope storage Boussinesq model was forced with the recharge from the hypothetical suggested land use. It is observed that the suggested LULC, when followed, could sustain the streamflow with 80% POE. However, it costs 18% and 24% of barren land to be converted to forest and cropland, respectively.