Patterns of subsidence in the lower Yangtze Delta of China: the case of the Suzhou-Wuxi-Changzhou region.

Investigation indicates that the subsidence pattern in the lower Yangtze Delta area is related to groundwater extraction. Suzhou-Wuxi-Changzhou region ("Su-Xi-Chang") belongs to the hinterland of the lower Yangtze Delta that has a total area of 12,000 km2. From 1979 to 2000, long-term pumping of groundwater at Su-Xi-Chang has caused a rapid decline in groundwater table, resulting in large-scale land subsidence. In this paper, establishment of a GPS-based monitoring system for land subsidence using 30 years of data, is presented. The data were obtained through monitoring of 184 wells. Also analyzed herein is the relationship between the observed lowering of the groundwater table and subsidence. Monitoring data indicate that the depression cone of groundwater table and the occurrence of subsidence are basically identical in time and space. The generation of both features is attributed to excessive extraction of ground water in the region. Finally, countermeasures against subsidence are proposed.