Excessive groundwater withdrawal and resultant land subsidence in the Su-Xi-Chang area, China

Excessive groundwater withdrawal has caused severe land subsidence in the Su-Xi-Chang (SXC) area, China. The restriction and prohibition on groundwater pumping have been carried out since the late 1990s. Based on the latest updated field data, the changing pattern of groundwater level and the distribution of land subsidence are analyzed. The distribution of land subsidence in SXC is closely related to that of the cone of depression in the second confined aquifer in time and space. But land subsidence is not in synchronization with the changing groundwater level. Both aquitards and aquifers compacted continuously in the early period of groundwater level rising and behaved as creep materials. A series of laboratory tests were conducted on aquifer sands, which indicated that the creep deformation under virgin compression is much greater than that under recompression and unloading, and that the creep of sands decreases rapidly with the cycles of repeating load. The test results reveal the mechanism of sand creep under the condition of long-term groundwater pumpage. As a consequence of the restriction and prohibition on groundwater pumping, groundwater level has obviously recovered in the vast majority of the SXC area, and land subsidence has slowed down and even a little rebound has occurred in some sites in Suzhou and Changzhou. If the pumpage is strictly limited continuously, the groundwater level will not decline below the historical lowest value but fluctuate within a certain range. In such a case, land subsidence in SXC will no longer develop obviously.