Risk analysis and risk assessment, like many modern dam safety practices, began with the failure of Teton Dam in June of 1976. The resulting dam safety legislation mentions the need to develop risk assessment procedures. Although initial development work in this area began shortly thereafter, it was not until the mid-1990’s that the Bureau of Reclamation began using risk analysis as the primary support for dam safety decision-making. The U.S. Army Corps of Engineers recognized the need to implement risk assessment procedures following levee failures that occurred in New Orleans during Hurricane Katrina in August of 2005, and soon thereafter began implementing risk analysis and risk assessment procedures.
Manuals, guidelines, and practical reference material detailing risk analysis methodology for dam and levee safety applications are generally lacking. This training manual attempts to help fill that need. It contains what are considered the “Best Practices” currently in use for estimating dam and levee safety risks at the Bureau of Reclamation and the U.S. Army Corps of Engineers. These risk analysis practices have evolved over the years and will continue to evolve.
From the outset of implementing risk analysis, it was recognized that procedures and data available for dam and levee safety risk analysis, while quantitative (or semi-quantitative), do not provide precise numerical results. Therefore, this manual strives to present useful information, tools, and techniques, while stopping short of a “cookbook” approach. This allows the risk analyst(s) to use the proper balance of engineering judgment and calculations in estimating risks, and to understand and “build the case” for what most influences the risk. The numbers, while important, are less important than understanding and documenting what the major risk contributors are and why.
By definition, “risk” is the product of the likelihood of an adverse outcome and the consequences of that outcome. The likelihood of an adverse outcome is the product of the likelihood of the loading that could produce that outcome and the likelihood that the adverse outcome would result from that loading. This manual covers primarily “risk analysis”, or the development of risk estimates. “Risk assessment”, or the process of evaluating the risks and determining the best course of action, is not discussed in detail although the section on Public Risk Tolerance and Risk Guidelines provides an introduction to this topic.
Best Practices have been documented in the "Best Practices in Dam and Levee Safety Risk Analysis", dated 3 December 2012.