Statistical analysis of long-term deformations and determination of warning thresholds for near-dam reservoir bank slopes

With the construction and operation of a large number of hydropower engineering projects in China, the deformation and failure behaviors of reservoir bank slopes pose increasing threats to the stability of hydraulic structures, as well as upstream and downstream residents and infrastructures. This study aims to offer a novel perspective for exploring the long-term deformation behavior of near-dam reservoir bank slopes through statistical analysis, and to put forward a quantitative method to determine velocity thresholds for early warning procedures. In this paper, the monitoring data of velocities recorded from four reservoir bank slopes are counted at first, and then generalized Pareto distribution and power law distribution are applied to fit the empirical cumulative distribution of statistical data. Further, two risk measures, value-at-risk and conditional value-at-risk, are used to analyze the characteristics of the distribution tails and evaluate the risk levels corresponding to different velocities. Combined with risk measures, a quantitative method for defining threshold levels based on velocities is proposed for early warning procedures. Statistical results show that generalized Pareto distribution and power-law distribution have the potential as unified models to describe the deformation behavior of the reservoir bank slopes. Case analyses verify the effectiveness of the method for defining the early-warning thresholds. The proposed methods could easily be transferred to slope movements with similar deformation behaviors in other hazardous areas.