Impact of the Three Gorges Dam on the spatial and temporal variation of groundwater level in Jianghan Plain using STL algorithm

The Three Gorges Dam (TGD), located upstream of the Yangtze River, is the largest hydroelectric project in the world. The operation of TGD has changed the spatial and temporal distribution of streamflow in the middle and lower Yangtze River. The operation of TGD can also have varying degrees of impact on groundwater due to stream–aquifer interactions. Jianghan Plain is a major farming area in southern China, where groundwater is a critical source for domestic and agricultural use. Therefore, it is important to study the impact of the operation of TGD on the groundwater level in Jianghan Plain. Based on the STL algorithm, this study examined the interannual, annual, and random variations of groundwater levels in Jianghan Plain, analyzed and quantified the impacts of various factors including the operation of TGD that cause the spatial and temporal variation of the groundwater level. The results show that the operation of TGD can reduce the amplitude of the groundwater level and the frequency of extreme values. From upstream to downstream, the impact of TGD operation on the groundwater level shows a decreasing trend. The operation of TGD has a strong impact on the interannual variation within 6.71 km and annual variation within 5.77 km from the Yangtze River. The conclusions of this study can provide recommendations for local governments to develop groundwater management policies.