Empirical Tool for the Assessment of Annual Overtopping Probabilities of Dams

Abstract

This paper presents a simple tool for the assessment of maximum overtopping probabilities of dams. The tool is based on empirical relations between the overtopping probability and the basic hydrological and hydraulic characteristics of the dam-reservoir system: the unit storage capacity, VF*, and the unit spillway capacity, QCap*, both weighted with the relative importance of the 1,000-year flood. The surface issued from the tool represents the limit above which no VF*−QCap* combination is statistically expected to offer a higher probability. The tool was calibrated using the detailed overtopping models of 342,233 synthetic cases generated from 30 existing dams and then validated against a set of 21 independent cases. The tool is useful when analyzing a portfolio of dams in previous screening phases of dam risk analysis. It aims at identifying overtopping as a relevant failure mode and easily classifying each dam in terms of its overtopping probability. The tool is also a support for the definition and prioritization of corrective measures since it assesses their impact in the overtopping probability reduction.