Engineering And Design Risk Based Analysis For Flood Damage Reduction Studies

Risk involves exposure to a chance of injury or loss. The fact that risk inherently involves chance leads directly to a need to describe and to deal with uncertainty. Corps policy has long been (1) to acknowledge risk and the uncertainty in predicting floods and flood impacts, and (2) to plan accordingly. Historically, that planning relied on analysis of the expected long-term performance of flood-damage-reduction measures, on application of safety factors and freeboard, on designing for worst-case scenarios, and on other indirect solutions to compensate for uncertainty. These indirect approaches were necessary because of the lack of technical knowledge of the complex interaction of uncertainties in predicting hydrologic, hydraulic, and economic functions and because of the complexities of the mathematics required to do otherwise.

Reducing flood damage is a complex task that requires multidisciplinary understanding of the earth sciences and civil engineering. In addressing this task the U.S. Army Corps of Engineers employs its expertise in hydrology, hydraulics, and geotechnical and structural engineering. Dams, levees, and other river-training works must be sized to local conditions; geotechnical theories and applications help ensure that structures will safely withstand potential hydraulic and seismic forces; and economic considerations must be balanced to ensure that reductions in flood damages are proportionate with project costs and associated impacts on social, economic, and environmental values. A new National Research Council report, Risk Analysis and Uncertainty in Flood Damage Reduction Studies, reviews the Corps of Engineers' risk-based techniques in its flood damage reduction studies and makes recommendations for improving these techniques. Areas in which the Corps has made good progress are noted, and several steps that could improve the Corps' risk-based techniques in engineering and economics applications for flood damage reduction are identified. The report also includes recommendations for improving the federal levee certification program, for broadening the scope of flood damage reduction planning, and for improving communication of risk-based concepts.

Describes & provides procedures for risk & uncertainty for U.S. Army Corps of Engineers (ACE) flood damage reduction studies. The guidance presented & procedures described in this manual apply to all ACE elements, major subordinate commands, labs, & field operating activities having civil works responsibilities. The procedures described herein lead to estimation of expected benefits of proposed flood damage reduction plans using risk & uncertainty analysis. Quantitative & qualitative methods of representing the likelihood & consequences of exceedance of the capacity of selected measures are also included. Illustrated.

This engineer technical letter provides guidance for establishing the final top of levee grade for flood control projects and flood damage reduction studies formulated using risk-based analysis.

The U.S. Army Corps of Engineers (Corps) policy is to apply risk-based analysis in the formulation and evaluation of flood damage reduction projects. These projects include dams and reservoirs, levees and flood walls, diversions, channel modifications, bypass channels, and a variety of nonstructural measures. Most projects include more than one measure, particularly projects that include reservoirs. This policy is viewed as a significant step forward in improving the basis for Corps project development. The risk-based analysis approach explicitly incorporates uncertainty of key parameters and functions into project formulation, benefits, and performance analyses. Particular focus is the impact of the uncertainty in the discharge-probability, elevation-discharge, and elevation-damage functions that represent effects of the proposed protective works. Reservoir projects that reduce flood damage result in a downstream reduction in flood frequency. This paper briefly describes the risk-based analysis approach in contrast to historical project development study methods, and presents results of a recent risk-based analysis for the American River (near Sacramento, California, USA) project studies. Comments are offered on technical issues of methods and data, communication of risk-based analysis results with local officials and the public, and project design implications of the policy.