Characterization of regional land subsidence in Yangtze Delta, China: the example of Su-Xi-Chang area and the city of Shanghai

Su-Xi-Chang area and the city of Shanghai, located in the south of Yangtze Delta, China, has subsided due to groundwater overpumping. Because of the regional scale of the groundwater exploitation, cone of depression and land subsidence at present, Su-Xi-Chang area and Shanghai are treated as a single area for a land subsidence study, which could more clearly elaborate the relationships between the deformation features of hydrostratigraphic units and the different sites of the cone of depression. All hydrostratigraphic units in the study area were discussed throughout. Based on the field data, including data on compression of individual strata from groups of extensometers and groundwater levels from observation wells, the relationship between the deformation and the groundwater level was analyzed. The results indicate that the deformation features of the hydrogeologic units are greatly related to hydrogeologic properties and groundwater-level variations. An identical hydrogeologic unit may exhibit different deformation features in different locations such as along the periphery and in the center of the cone of depression. In addition, in the same location, a hydrogeologic unit also exhibits different features in different periods because of different groundwater level variations. The delay phenomenon of the sandy aquifer is not specific but occurs widely.