Spillway Analysis in Dam Safety Evaluation

Abstract

This work develops, tests, and applies a non-dimensional flood damage model which includes both overtopping and non-overtopping dam failures. The model represents a catchment, reservoir, dam, channel, and damage site. Peak reservoir flood inflow, initial reservoir stage, and overtopping failure stage are represented as stochastic variables. The model computes the expected value of total flood damage and of the damages attributable to natural floods, overtopping failures, and non-overtopping failures. The model also computes overtopping failure probability. Four dams are used as case studies. Parameters of the catchment, reservoir, and dam are estimated from real data. Channel and damages site parameters are hypothetical. Sensitivity of model results to variations of uncertain model parameters is examined. Channel and damage site parameters are also varied. Estimates of expected damage and failure probability are shown to vary substantially as parameters which are difficult to estimate are varied within reasonable ranges. It is also shown that expected damage can decrease, increase, pass through a minimum, or remain fairly constant as spillway size is increased. The influence of spillway size varies with the initial reservoir stage.