of existing programs for ecosystem mitigation, Master Manual revisions, and Biological Opinion compliance, has led to confusion regarding relationships and boundaries among these new initiatives and the older, existing governance system. Although the new initiatives may ultimately improve Missouri River decision making, they have added to institutional complexity.

The Missouri River basin has seen its share of disputes over shared water and sediment resources. Not only have there been differences of opinion regarding the Corps of Engineers mitigation projects along the lower river, basin states often have held different views on appropriate reservoir release schedules and other decisions. One impetus for the many new initiatives is to address continuing environmental and socioeconomic changes along the river, and to mediate and reconcile the often sharp differences of opinion over operations and other decisions affecting flows of water and the transport and deposition of sediment.

As a consequence of studying the role of sediment in Missouri River management decisions, this committee made several observations regarding river resources and the role of science. These observations fall into two broad categories: (1) trade-off choices and resource limits, and (2) science and decision making. The following two sections are presented in the spirit of contributing to river management decision making and expectations regarding the role of the science community in such decisions.

TRADE-OFF CHOICES AND RESOURCE LIMITS

In many ways the Missouri River is no different from other large U.S. river systems, as difficult choices are inevitable and priorities among competing uses ultimately must be established—especially during periods of high and low river flows. Furthermore, preferences for the goods and services provided by the Missouri dam and reservoir system have changed and shifted over time. Some differences of opinion regarding water releases and mitigation activities along the Missouri River have been highly controversial. This may not always be the case, however, and future conditions on the Missouri River may provide better opportunities for compromise and common understanding.

The Missouri River was fundamentally altered and changed during the twentieth century. The changes represented a conscious, national policy decision to transform the free-flowing, preregulation Missouri River into a system with dams, reservoirs, and a commercial navigation channel. The installation and operation of this extensive water control infrastructure produced many social benefits. This also resulted in unforeseen costs, such as the loss of habitat for native species that may have been underappreciated while most of the dams and river training works were being built. For example, nearly 3 million acres of riverine and floodplain habitat were



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