Land subsidence and uplift related to groundwater extraction in Wuxi, China

Wuxi City is located in the Yangtze River Delta region, China, it is underlain by a multi-layered aquifer system in the Quaternary porous deposits. Groundwater extraction mainly from the second confined aquifer (CA2) has led to severe regional land subsidence. The ground surface started to recover due to the restriction and banning of groundwater pumping. This paper reports the results of long-term surveying, groundwater piezometric head (GPH) measuring, and ground surface deformation monitoring by levelling and borehole extensometer. The subsidence is attributed to the compression of both aquifer and aquitards in the porous strata. The spatial characteristics of subsidence are related not only to GPH distribution, but also to the thickness and compressibility of different strata, as well as distance from the pumped aquifer, and pumping distribution. There was a temporal lag in the subsidence compared with the groundwater drawdown. The land uplift can be related to a period of recovery following the peak pumping period and groundwater recovery subsequent to the restriction and/or banning of groundwater pumping. The uplift was less than 10 mm under these two conditions, although the GPH had recovered more than 40% of the previous maximum at Qianzhou borehole extensometer station (QBES).