that maximized overall benefits to society. As part of the 1936 Flood Control Act, the Corps was mandated to ensure that benefits from proposed flood control projects exceeded the costs; this criterion was extended to all water resources projects by 1950. But as Congress, the administration, and the Corps have learned, the notion of optimal river management is viewed differently by different groups, and thus not easy to realize to the satisfaction of all. Attempts to tame the river for the benefit of one class of user have usually changed the river in ways that have negative consequences for other users. With changes in economies, affluence, and social preferences over time, the public has sought a changing mix in services, resulting in changing priorities for managing the river. The need to address shifting social and economic preferences, while also servicing traditional users, has posed great challenges to the Corps during this 175-year period and will continue to do so in the future.

The Corps’ Restructured UMR-IWW Feasibility Study represents the most recent rendition of these efforts to manage UMR-IWW resources. The Corps encountered several analytical challenges in the course of a study process that took more than 15 years. Despite these problems and a number of serious criticisms—including some from this committee—the Corps took a major step forward by considering ecological restoration and commercial navigation in the same study. Nevertheless, as pointed out in this committee’s second report, the ecosystem restoration plan’s objectives are limited, stopping far short of correcting cumulative ecological changes that have resulted from construction and operation of the UMR-IWW navigation project. In its first two reports this committee noted the complexities of integrated river management and the challenges of encompassing all relevant water-related sectors within a single unifying framework. A lesson for future planning studies is that it is not sufficient to simply accumulate more information and consider additional water-related sectors in the analysis; improved planning will require careful understanding of the opportunities for trade-offs among major classes of river users and values.

The Corps’ feasibility study had to address high levels of uncertainty in many of its subject areas, including waterway traffic forecasts, river responses to operational changes, and future navigation and shipping technologies and practices. These uncertainties are characteristic of all studies of this kind and were particularly prominent in the UMR-IWW Feasibility Study. The existence and nature of trade-offs among river management purposes and goals are similarly uncertain. In the interest of reducing uncertainties the committee has stressed the need for the best professional planning and analysis. But improved planning and analysis can only reduce uncertainties, not eliminate them. The possibility of making costly, inappropriate decisions based on uncertain data still exists. In a project and system like the UMR-IWW that must be operated over a long period of time, however, learning from experience—that is, applying adaptive management principles—can lead to better choices over the life of the project. To its credit the Corps has proposed a comprehensive application of



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