Risk Based Analysis For Corps Flood Project Studies

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.

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.

The U.S. Army Corps of Engineers has long been one of the federal government's key agencies in planning the uses of the nation's waterways and water resources. Though responsible for a range of water-related programs, the Corps's two traditional programs have been flood damage reduction and navigation enhancement. The water resource needs of the nation, however, have for decades been shifting away from engineered control of watersheds toward restoration of ecosystem services and natural hydrologic variability. In response to these shifting needs, legislation was enacted in 1990 which initiated the Corps's involvement in ecological restoration, which is now on par with the Corps's traditional flood damage reduction and navigation roles. This book provides an analysis of the Corps's efforts in ecological restoration, and provides broader recommendations on how the corps might streamline their planning process. It also assesses the impacts of federal legislation on the Corps planning and projects, and provides recommendations on how relevant federal policies might be altered in order to improve Corps planning. Another important shift affecting the Corps has been federal cost-sharing arrangements (enacted in 1986), mandating greater financial participation in Corps water projects by local co-sponsors. The book describes how this has affected the Corps-sponsor relationship, and comments upon how each group must adjust to new planning and political realities.

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.

This book reviews the U.S. Army Corps of Engineers' (USACE) investigations of flood control options for the American River basin and evaluates flood control feasibility studies for the watershed, with attention to the contingency assumptions, hydrologic methods, and other analyses supporting the flood control options. This book provides detailed comments on many technical issues, including a careful review of the 1991 National Research Council report American River Watershed Investigation, and looks beyond the Sacramento case to broader questions about the nation's approach to flood risk management. It discusses how to utilize information available about flood hazard reduction alternatives for the American River basin, the potential benefits provided by various alternatives, the impacts of alternatives on environmental resources and ecosystems, and the trade-offs inherent in any choice among alternatives which does not lie in the realm of scientists and engineers, but in the arena of public decisionmaking.

Floods cause distress and damage wherever and whenever they happen. Flooding from rivers, estuaries and the sea threatens many millions of people worldwide and economic and insurance losses from flooding have increased significantly since 1990. Across the European Union, flood management policy is changing in response to the EU Directive on the ass