Initiative for Risk‐Based Flood Design

A recent report of the Interagency Advisory Committee on Water Data found that there is “no current procedure for assigning an exceedance probability to the probable maximum flood (PMF)… in a reliable, consistent, or credible manner.” This conclusion was used as justification for continuation of the current, quasi‐deterministic, PMF‐based spillway design methods used by all federal agencies. This is despite criticism by both researchers and practitioners that PMF‐based methods tend to lead to a false sense of security and to misallocation of resources for dam safety improvements. As an alternative to perpetuation of the status quo, the writers outline four general areas in which research should be promoted for improved estimation of extreme floods, as well as research aimed at development of a method for incorporation of risk information into spillway design. The writers believe that if the federal action agencies were to promote research in the areas suggested, the current stagnation that has set in would be broken, and the self‐fulfilling prophecy that there are no alternatives to current practice could no longer be justified.