Acceptable Risk Considerations for Dam Safety. D. S. Bowles, Utah Water Research Laboratory, Utah State University, Logan, UT 84322-8200
Dams are subject to various natural hazards, notably floods and earthquakes. The cost of meeting new dam safety standards, and a desire for a more objective basis for selecting dam safety modifications, has lead to the evaluation and use of risk-based approaches in several countries. Risk-based approaches can produce useful insights into the relative risks associated with flood and earthquake loading, various types of internal problems which can threaten the integrity of a dam, and options for mitigation of the hazard posed by an unsafe dam. They can also lead to quantitative measures of risk for existing dams and risk reductions for proposed remedial actions. In this paper alternative approaches to defining acceptable risk for dam safety modifications will be presented, together with examples of their applications to several dams. A comparison of socially acceptable risk criteria with currently used hazard criteria for defining inflow design floods and design earthquakes will also be presented for hazard criteria from several countries.