Application of Dormant Reliability Analysis to Spillways

Abstract

Dams are essential infrastructures for water supply, flood control, energy production, and irrigation. A critical component for the safety of a dam is the spillway system which, by controlling releases, prevents overtopping of the dam. This in turn reduces impacts associated with excessive downstream flows and upstream water levels on infrastructures, the population, and the environment. This paper addresses reliability issues related to emergency spillways and specifically the estimation of their reliability level after prolonged periods of dormancy. During dormancy, spillway components are exposed to the environment and sustain cumulative damage that may trigger latent failures or failures on demand. Regular inspections and tests are used to detect and remediate latent failures and to assess the level of deterioration of components. The purpose of this study is to develop procedures to account for dormancy in the reliability analysis of spillways. It also demonstrates how these procedures can be used to evaluate the impact of the frequency of inspections and tests on the overall reliability of the spillways. This paper introduces measure of performance, dormant availability analysis, and dormant availability analysis via integrity assessment as methods to illustrate the unavailability or probability of failure on demand of a spillway system as a function of its dormancy period. This information can be used to determine the optimum frequency of inspection and tests taking into account the safety of the structure as well as the costs associated with inspection and testing.