Effects of South-to-North Water Diversion Project on groundwater and land subsidence in Beijing, China

The South-to-North Water Diversion Project Central Route (SNWDP-CR) is the largest water control project which has ever been built, and the aim of which is to optimize the reallocation of water resources from South China to North China. Since it was put into operation in December 2014, it has delivered more than 6 × 109 m3 of water to Beijing, which has changed the water supply pattern in Beijing and provided conditions for reducing groundwater extraction and controlling land subsidence. In this study, a variety of monitoring data are used to analyze the changes of the groundwater flow field, groundwater level, land subsidence, soil deformation, and hydrogeology parameters before and after the SNWDP-CR. The study showed that the groundwater level of the first to fourth aquifer groups rose on average by 2.72 m, 3.68 m, 3.31 m, and 1.91 m from 2015 to 2020. The average subsidence rate decreased from 18.8 mm/year in 2015 to 10.85 mm/year in 2020. The deformation characteristics of different lithological soil layers under different water level change modes can be summarized into 4 categories. The sand layer is mainly characteristic of elastic deformation. The cohesive soil layers of different depths have elastic, plastic, and creep deformation, and the viscoelastic-plastic characteristics are obvious. For different stages of soil deformation, the changes of elastic and inelastic skeletal specific storage rates are not constant. As the groundwater level decreases, the soil skeletal specific storage rate shows a decreasing trend.