Risk Analysis in Flood Damage Reduction Studies—The Corps Experience

The U.S. Army Corps of Engineers (USACE) studies flood problems and propose solutions. Flood damage reduction studies are highly technical investigations that involve the need to characterize existing and future flood potential, assess the vulnerability of floodplain occupants to flood damage impacts, and formulate and evaluate the costs and benefits of a range of potential solutions. The outcome of these analyses, including consultation with local sponsors and others, is the selection of a recommended plan for consideration by Congress. USACE policy is to perform flood damage reduction studies employing modern concepts of risk analysis. The essence of this policy is to emphasize quantifying flood risk to flood plain property and occupants; quantify how proposed project alternatives reduce flood risk and damages; and to explicitly include uncertainty in key factors in project formulation, evaluation, and reporting. Risk is used herein in the engineering context as a quantitative measure of the chance of flooding or chance of project capacity exceedance, and also risk that the overall project investment and return will be as planned. Uncertainty as used herein reflects being unsure, that we have imperfect or short record data and incomplete knowledge and analysis methods upon which to base estimates of risk and other key factors associated with project studies. This paper provides an overview of flood damage reduction analysis; its extension to include uncertainty needed in risk analysis, provides a chronicle of its evolution in USACE, and identifies needs for future improvements.