Abstract

Wuxi City is located in the Yangtze River Delta region, China and is underlain by a multi-layered aquifer system in porous Quaternary deposits. Groundwater extraction, mainly from the second confined aquifer, has led to severe regional land subsidence. The ground surface started to recover after the restriction and, ultimately, the banning of groundwater pumping. This paper reports the results of long-term surveys, groundwater piezometric head (GPH) measurements and the monitoring of ground surface deformation by levelling and borehole extensometers. The subsidence is attributed to the compression of both the aquifer and aquitards in the porous strata. The spatial characteristics of subsidence are related not only to the distribution of the GPH, but also to the thickness and compressibility of different strata, the distance from the pumped aquifer and the distribution of pumping. There was a temporal lag in subsidence relative to groundwater drawdown. The uplift is 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 <10 mm under these two conditions, although the GPH recovered to >40% of the previous maximum at the Qianzhou borehole extensometer station.

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