Study on controlling measures of ground water resources and the effects on alleviating land subsidence in Shanghai, China

Land subsidence in Shanghai caused by overly exploitation of ground water has been 93 years since 1921, with the largest cumulative land subsidence of 2.6m. Studies on controlling and alleviating land subsidence have been 53 years since 1961. Control on ground water exploitation, change in pumping aquifers, increase in artificial recharge have been used as the three measures to mitigate land subsidence. The amount of ground water exploitation decreased from 0.2 billion m3 in 1963 to 13 million m3, which meant the amount decreased by 93.5%. The amount of artificial recharge increased from 1.9 million m3 in 1963 to 18 million m3 in 2011, which meant it increased by 9.5 times. The amount of recharge was even 6 million m3 larger than the discharge. The main pumping aquifers were shift from the second and third confined aquifers to the fourth and fifth confined aquifers. With the application of the three measures, ground water levels in second and third confined aquifers increased from -20m in 1965 to -1m in 2011 and that in the fourth confined aquifer increased from -36m in 1998 to -9m in 2011. Some regional ground water drawdown cones disappeared. Land subsidence rate reduces from 38mm/year before 1965 to 7mm/year by now and some areas even rebound. The details of measures taken to control land subsidence between 1961 and 2011, and the responses in ground water flows and land subsidence characteristics are introduced. It concludes that decrease in ground water pumping is the most effective way to control land subsidence, increase in artificial recharge is a good assistant measure, and changing in pumping aquifers is not always show good results. Shanghai got increased land subsidence rate from 1990 to 2000 when changing pumping aquifers from the second and third to the fourth and fifth ones without properly evaluating the amount of exploitation in advance. It must be very careful when take the measure of changing pumping aquifers, and the proper amount of pumpage in the new aquifers should be evaluated by land subsidence models. Analysis of measures taken to control land subsidence in Shanghai and the final results could be valuable experience to refer for other areas with land subsidence problems. Acknowledgement: Funding supported by NSF of China No. 41272259 and NSF of Jiangsu Province No. BK2012730 is appreciated.