Land surface response to groundwater drawdown and recovery in Taiyuan city, Northern China, analyzed with a long-term elevation change measurements from leveling and multi-sensor InSAR

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In recent years, a comprehensive program of groundwater management was adopted in Taiyuan city, Northern China, with the aim to prevent the lowering of groundwater level and manage land subsidence due to excessive groundwater pumping in the past decades. Groundwater recovery has been observed in this city following the termination of groundwater pumping. While the link between land subsidence and groundwater pumping is well documented, how the land surface responds to the recovery of groundwater has not been studied in detail. In this study, we analyzed the leveling data from 1956 to 2000 to investigate changes in ground elevation in response to groundwater drawdown prior to the termination of groundwater pumping and combined them with InSAR (Interferometric Synthetic Aperture Radar) displacement data during 2003–2020 to evaluate the effect of groundwater recharge after the termination of groundwater pumping. A method was proposed to merge InSAR time series of displacement derived from multiple satellites (ENVISAT, COSMO-SkyMed, TerraSAR-X, and Sentinel-1) to achieve a consistent, long-term continuous deformation. We found that previous groundwater depression cones in Taiyuan (Xizhang, Wanbailin, Wujiabao, and Xiayuan) have turned into groundwater recovery and the corresponding subsidence centers have switched to land uplift. The subsidence center of Xizhang, north of Taiyuan city, experienced a total subsidence of 749 mm by Aug 2003; it then turned into uplift with an amount of rebound of 9.2 % of previous subsidence by the end of 2020. In central area of Taiyuan, the cumulated subsidence is 1127 mm in Wanbailin, 1817 mm in Xiayuan, and 3343 mm in Wujiabao. Beginning in Aug 2010, they all turned into land uplift, with a rebound of 7.9 %, 4.8 % and 3.6 % of the previous subsidence in each center, respectively. An analysis of the correlation between groundwater level and ground displacement suggests that the ground uplift is related to the poro-elastic rebound mechanism in the porous aquifer system, which is caused by the rise in pore pressure with groundwater recovery, and the amount of subsidence/uplift is controlled by the stratigraphic properties. The adverse impacts on the built environment due to the rising groundwater level were discussed. The findings improve our understanding of anthropogenic ground deformation in complex urban aquifers influenced by groundwater pumping and recharge and provides essential information that can contribute to future groundwater management and groundwater-related hazard mitigation over the Taiyuan city.

近年来，太原市（中国北方）采取了全面的地下水管理计划，旨在防止由于过去几十年过度地下水抽取造成的地下水位下降，并有效管理因地下水过度开采而引起的土地沉降。在停止地下水抽取后，太原市已观察到地下水恢复的现象。尽管土地沉降与地下水抽取之间的关系已有充分文献记载，但土地表面对地下水回补的响应尚未得到详细研究。在本研究中，我们分析了1956年至2000年的水准测量数据，探讨了地下水位下降前的地面高程变化，并将其与2003至2020年期间的InSAR（干涉合成孔径雷达）位移数据结合，以评估地下水抽取停止后地下水回补的影响。我们提出了一种方法，将来自多个卫星（ENVISAT、COSMO-SkyMed、TerraSAR-X 和 Sentinel-1）获得的InSAR位移时间序列合并，旨在实现一致的长期连续变形。

研究发现，太原市先前的地下水下降漏斗区（如西张、万柏林、吴家堡和下元）已转变为地下水回补区，相应的沉降中心已转变为地面抬升。太原市北部的西张沉降中心，到2003年8月经历了749毫米的总沉降；到2020年底，地面开始抬升，回弹量达到了之前沉降量的9.2%。在太原市的中心区域，万柏林、下元和吴家堡的累计沉降分别为1127毫米、1817毫米和3343毫米。从2010年8月开始，所有这些地区都转变为地面抬升，其中万柏林、下元和吴家堡的回弹量分别为之前沉降量的7.9%、4.8%和3.6%。

通过分析地下水位与地面位移之间的相关性，结果表明地面抬升与多孔含水层系统中的孔弹性回弹机制相关，这一机制是由于地下水回补导致孔隙压力上升所引起的。沉降/抬升量受地层特性的控制。研究还讨论了由于地下水位上升对建成环境可能带来的不利影响。研究结果有助于加深我们对受地下水抽取和回补影响的复杂城市含水层中人类活动引起的地面变形的理解，并为未来太原市的地下水管理和地下水相关灾害减缓提供了重要信息。