The mechanism of large-scale river valley deformation induced by impoundment at the Baihetan Hydropower Station

Impoundment-induced valley contraction impacts arch dam safety. Baihetan is the second-largest hydropower plant, and there is an urgent need to study its valley deformation mechanism for arch dam safety assessment. The scope of previous studies on engineering cases was mostly limited to the near-dam area, but the large-scale deformation trend has rarely been reported. In addition, the groundwater level change during cofferdam operation has rarely been emphasized in valley deformation analysis. In this paper, a numerical model describing the complex seepage field at the dam site was developed. Furthermore, numerical simulations were performed for characterizing the large-scale valley deformation trend. In addition, monitoring data were collected to validate the simulation method. The large-scale monitoring results showed that the valley near the dam contracted while the valley away from the dam widened. The spatial variability of valley contraction is related to bypass seepage and substantial artificial slope shaping. The main reasons for valley contraction are effective stress reduction and the steep topography excavated for hydraulic building arrangement. In addition, the significant decrease in the groundwater level during cofferdam operation exacerbated valley contraction after impoundment.