Flood Risk Management and the American River Basin An Evaluation (1995) / Chapter Skim
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SUMMARY
SUMMARY
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Army Corps of Engineers completed a study, the American River Watershed Investigation (ARWI) , that reviewed the American River's contribution to the area's flood hazard, considered a range of flood control measures, and recommended a preferred flood control strategy (USAGE, Sacramento District, 1991~.
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Congress directed the Secretary of the Army to ask the National Academy of Engineering to form a special committee, the Committee on Flood Control Alternatives in the American River Basin, to review the 1991 ARWI, with attention to the contingency assumptions, hydrologic methods, and other engineering analyses used to support the seven flood control options presented. Significantly, the committee was not asked to recommend a preferred alternative; instead, it was asked to evaluate the scientific and engineering knowledge base on which the selection of a final strategy will ultimately be based.
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For a true reevaluation of the Sacramento District's technical analysis, Congress might wish to request a review of the upcoming Draft Supplemental Information Report and Environmental Documentation, expected to be available in the summer of 1995, because that document will update the 1991 ARWI in detail. THREE PREMISES As the committee conducted this review of the Sacramento District's planning for flood control in the American River basin, it became clear that the members shared certain premises (i.e., assumptions believed to be true on the basis of experience and expertise)
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Paradoxically, efforts to enhance protection for the largely undeveloped floodplain of the Natomas Basin have progressed further in Congress and locally than proposals affecting developed areas, including downtown Sacramento and the State Capitol complex. Ultimately, California and the nation need to reexamine their approaches to public decisionmaking.
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For decades, the predominant response to flood risk was to build large flood control projects dams, reservoirs, levees, diversion channels to store and restrain floodwaters. The adoption of the National Flood Insurance Act of 1968 marked a watershed in national policy on flood hazards because it established nonstructural measures flood insurance, floodplain management, and selective acquisition as mainstays of national flood policy.
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IDENTIFICATION AND EVALUATION OF ALTERNATIVES As the committee conducted its review of the American River planning process, it noted that perhaps the most critical step in the development of a flood control strategy is the selection of alternatives for detailed analysis. The 1991 ARWI presented various alternative approaches to providing flood control for the American River basin, addressing level of protection provided, costs, expected benefits, and environmental impacts.
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If such a dam is to be seriously considered, the committee recommends the formation of a multidisciplinary research team to design and carry out a program to reduce this scientific uncertainty and recommend a gate design and operating strategy that could be followed to minimize environmental impacts. RISK METHODOLOGY USACE has adopted new risk and uncertainty analysis procedures that are an extension of the traditional paradigm for flood control project planning and community flood protection evaluation.
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USACE needs to develop a consistent scientific methodology and an effective vocabulary for communication of residual flood risks and uncertainties to technical and public audiences. FLOOD RISK MANAGEMENT BEHIND LEVEES History shows a close relationship between flood protection and development in flood-prone areas.
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Clearly, the Natomas Basin is well situated in terms of proximity to Sacramento, but it is poorly situated in terms of chronic flood risk. Improvements in the existing flood protection system, including the reoperation of Folsom Dam, levee expansion, and other improvements that are in progress or are foreseeable, can help reduce the risk, but significant residual risk will remain.
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In line with that dual charge, the committee offers findings and recommendations specific to the USACE planning process as applied to the American River basin, as well as some broader comments on the nature of flood risk assessment and its application nationwide. The findings and recommendations presented in detail in Chapter 7 relate to (1)
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The fundamental question in the American River planning process is how to reduce flood risk in the lower American River basin given a decisionmaking arena that includes significant scientific uncertainty and organized opposition to some of the possible risk reduction alternatives. This report discusses the uncertainties that confront floodplain managers and offers recommendations in many
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The recommendations offered in this report are intended to improve the process, not delay it further. THE ROLE OF SCIENCE IN THE DECISIONMAKING PROCESS The issue decisionmakers face is how best to determine and then implement an acceptable flood risk management program for the American River basin.
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