Are We Preventing Dam Failures? Rethinking Surveillance and Monitoring

摘要

Surveillance and monitoring plans (SMPs) have focused on developing procedures for inspection of dams and installation and review of instruments and instrumental data. Many dams have exhibited warning signs (abnormal behavior) that went unrecognized prior to failure, for example, Malpasset Dam, Swift 2 Dam, and Wanapum Dam. The current SMP programs have yet to show that they can consistently provide early warning of potential failures for many dams, mostly because we usually assume that anomalous behavior can be ignored. It is usually subtle changes in behavior that will indicate unrecognized potential problems, for instance, changes in observed seepage patterns below an embankment. The primary purpose of SMPs is to prevent dam failures, as such; it should focus on determining whether changes in dam behavior and/or anomalous data are tied to an unrecognized Potential Failure Mode (PFM). To understand anomalous behavior, we first need to know what is normal for each dam. Secondarily, SMPs should focus on whether a change in behavior could be indicative of the activation of or an increase in the likelihood of a PFM. In addition, early warning signs in dams might be missed because action levels for instrumental data often only generally provide a sense of the critical state, i.e., when a dam is nearing failure. Action levels should first alert us to unusual behavior and then be set based on how much a change in behavior would increase the likelihood of failure, i.e., how close to the tipping point the dam is. This paper briefly discusses case histories and proposes changes in SMPs to better catch and prevent potential failures.