Effects of the Three Gorges Dam Operation on the hydrological interaction between the Yangtze River and downstream aquifers

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Abstract
The construction of the Three Gorges Dam (TGD) has profoundly altered the groundwater cycle downstream. The obscure spatiotemporal patterns of exchange fluxes between the Yangtze River and groundwater hinder the resolution of water resources and environmental issues in the watershed. This study investigated the spatial extent of the Yangtze River's influence on adjacent groundwater in the Four-Lake Basin, the first river-lake wetland plain downstream of the TGD, using multiple clusters of monitoring wells installed along the river. A coupled SWAT-MODFLOW model was applied to quantify period-specific surface water-groundwater exchanges. A counterfactual scenario without TGD operation, holding other conditions constant is also simulated for comparison. The results show: (1) Under the combined influence of hydrogeological conditions and distance from the TGD, the influence range of the Yangtze River on confined groundwater is significantly greater in the upper section than in the lower section of the Four-Lake Basin, with a difference of approximately one order of magnitude. (2) River and groundwater exchanges exhibit pronounced seasonal and spatial characteristics: river-to-aquifer recharge dominates during drawdown and flooding periods, while aquifer-to-river discharge dominates during impounding and dry periods. Additionally, the interaction rates between river and aquifer are consistently higher in the upper section than in the lower one. (3) Relative to natural conditions, TGD operation dramatically dampens Yangtze River-groundwater interactions overall. The effect is most pronounced during the dry period in the upper section, when the interaction rate decreases by 40.6 %. These research outcomes serve as a vital theoretical foundation for assessing the effects of the TGD's regulation on the hydrological interaction in the riparian zone of the Yangtze River.
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Funding Information
  • National Natural Science Foundation of China (U2340206)
  • National Natural Science Foundation of China (U23A2042)
  • National Natural Science Foundation of China (42572313)
  • National Natural Science Foundation of China (42272290)
  • Natural Science Foundation of Hubei Province (2023AFD194)

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