WATER RESOURCES MANAGEMENT IN THE GANGES BASIN: A COMPARISON OF THREE STRATEGIES FOR CONJUNCTIVE USE OF GROUNDWATER AND SURFACE WATER

The most important water resources management issue in the Ganges Basin is to reduce the imbalance between water demands and seasonal availability. More than 80% of total annual flow in the Ganges River occurs during the four-month monsoon, resulting in widespread flooding across the basin. During the rest of the year, irrigation, navigation, and ecosystems suffer because of water scarcity in both upstream and downstream basin areas. Storage of monsoonal flow for utilization during the dry season is one approach to mitigation of these problems. We evaluate three conjunctive use management strategies that involve pumping groundwater during the dry season to create storage space in the aquifer that would be replenished during the following monsoon. Numerical models were used to determine and compare the effectiveness of the three strategies. Pumping was considered near rivers and canals, respectively, for the first two strategies, while the third strategy involved pumping at the point of use and seasonal source switching. Results indicate that the first two strategies can store about 7%-20% and 10% of the average monsoonal flow each year, respectively, for different pumping rates, thus reducing flooding. The storage of the third strategy is less. However the first strategy is effective for ephemeral rivers only. In areas where rivers are perennial, canals can be made dry during the dry season and the second strategy can be used. Although each of these strategies has the potential to reduce flooding, provide irrigation water, and improve waterlogging, the first two involve more spatially-concentrated pumping, which may cause other problems such as land subsidence. They also require a shift in existing water use practices in the basin and significant public investment. In contrast, the third strategy is less costly, involves less-concentrated pumping and can be more easily adopted by modifying the existing water use practices in the basin.