Estimated rates of failure for dams in the United States

Annual rate of failure for dams in the United States were estimated by examining the National Inventory of Dams and the Worldwide Historical Dam Failures Database. Based on information from these databases, there has been a total of 5,628,516 dam-years, 2,694 dam failures, and thus 0.00048 dam failures per dam-year. Concrete and earthfill dams both have less than 0.0005 failures per dam-year; masonry and rockfill dams have more than 0.001 failures per dam-year and timber dams have more than 0.0035 failures per dam-year. For all dam types, failures per dam-year are greatest in the first five years after construction. For all types of dams, except for earthfill and rockfill, data shows a steady decline in failure rates as dams age. However, earthfill and rockfill dams reach the lowest rates of failures per dam-year when they are between 20-50 years old with an increase in failure rate, especially for earthfill dams, after 50 years after construction. Results from this study are predicated by the available data, which likely does not include information on all failed dams. In addition, these databases do not include certain types of information, e.g., construction activities and contractor performance.