integrated approach; this approach reduces the possibility that attempts to solve problems in one realm, or subsystem, will cause problems in another (NRC, 1999a). Incorporating a broader view of natural systems in water resources project analysis will increase the nation’s economic productivity and environmental well-being in a sustainable manner by minimizing the potential that project benefits in one location are offset by adverse impacts (costs) on other components of the system.

A water resource system is defined by this National Research Council (NRC) panel for the purposes of this discussion as “a set of interrelated physical, chemical, and ecologic components of the hydrospheric environment that act upon, or are acted upon, by one another, and by such interaction thereby determine the unity or whole.” Although the division is neither exact nor complete, water resources systems can be usefully divided into two major categories: river basins and coastal systems. “Watershed” and “catchment” are terms similar to river basin and are often used to describe smaller drainages nested within a larger river basin. Coastal systems are geographic units of the coastal zone that can be delineated based on their hydrology, geology, biology, or a combination of the three. The complex nature of coastal systems makes their boundaries harder to define, requiring flexibility and local knowledge in defining a workable unit for environmental management. Most coastal systems—especially estuaries—are strongly influenced by upland watersheds; hence coastal system analysis should generally include both the watershed and the coastal environment.

In addition to linkages between river basins and coastal systems, factors relevant to water project evaluation, particularly its economic, social, and ecologic benefits and impacts, may require consideration across river basin and coastal system boundaries. Water resources project planning that integrates the linkages among the physical, environmental, economic, and societal services of hydrologic systems requires a “systems” approach that is both multi-disciplinary and multi-jurisdictional.


River basins define a well-established and widely accepted framework for designing and evaluating water resources projects (Loucks, 2003; NRC, 1999a,b). River basins are drainage or catchment areas that collect precipitation and transport water, sediment, and dissolved constituents downstream within a system of connected river channels (Figure 2-1). Each basin is separated from surrounding basins by a drainage divide that is a

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