Coupling model of groundwater and land subsidence and simulation of emergency water supply in Ningbo urban Area, China

Abstract

Groundwater withdrawal has caused severe land subsidence in Ningbo since 1964. The land subsidence rate slowed down by the prohibition of groundwater exploitation. However, water supply crisis prompted a new task of how to satisfy the emergency demands of water supply. This study tries to provide insights into the prediction of groundwater level and land subsidence and formulate reasonable exploitation plans for emergency water supply in Ningbo urban area. A coupling model of groundwater and land subsidence was developed to quantify the subsidence caused by water withdrawal. The proposed model is recognized for the period 1989–1992 and is verified for the period 1992–1993 using observed groundwater and land subsidence records in Ningbo urban area. Based on the calibrated and evaluated model, six reasonable exploitation plans for emergency water supply in Ningbo urban area are formulated, and the dynamic prediction of groundwater level and land subsidence changes in each plan are made. Numerical results show that the pore confined water in Ningbo urban area has good supply conditions and strong water level recovery ability, which can meet the demand of short-term centralized water supply. A longer time of emergency water supply and a lower controlling depth of water level leads to larger subsidence. After the completion of water supply, areas near exploited well may appear subsidence rebound due to the recovery of groundwater level, but subsidence continues to increase in areas far away from the exploited well due to the delayed settlement of the lagging interbeds.