Optimal Allocation of Groundwater Resources: Managing Water Quantity and Quality

Despite the importance of groundwater in the economy of the Hai River Basin (HRB), falling water tables and salinization of aquifers are both occurring in the region. Hydrological and hydrogeological studies have shown that increases in the salinization of parts of the freshwater aquifers are closely related to the extraction of groundwater. This study uses a framework that considers the interaction between water quantity and quality to examine how the presence of the prehistoric saline water layer affects groundwater management. Simulation results show that in a region where there is a salinization problem like in the HRB, it is optimal to pump at high rates in the early stage of extraction when the quality of groundwater is high. It is then optimal to reduce the pumping rate rapidly as the quality of groundwater deteriorates. Given this characteristic of the optimal pumping path, the heavy extraction currently observed in the HRB does not necessarily indicate that groundwater resources are being overused. However, unregulated extraction by non-cooperative users would eventually cause both the depletion of the water resource and the deterioration of water quality. Hence, joint quantity–quality management is required in the HRB. The study also shows that benefits to groundwater management are higher and costs are lower in regions with salinization problems.