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Conceptual Perspective <br />Assessing flows for any resource requires <br />a conceptual framework; one option is <br />shown in Figure 1. Flow is the variable <br />driving the system, and it can come from <br />natural or human - regulated sources. <br />Flow, in turn, affects resource conditions. <br />Immediate effects are related to hydraulics <br />(depth, velocity, width, wetted perimeter, <br />and turbulence), but longer -term effects <br />occur though interactions with channel <br />geomorphology and riparian vegetation. <br />Taken together, hydraulics, channel <br />morphology, and riparian vegetation form <br />a dynamic system of resource conditions <br />that define biophysical and recreation <br />Flow <br />N; <br />"habitats.' Combinations of resource <br />conditions associated with a given flow <br />regime, in turn, provide resource outputs, <br />Broad categories of outputs include <br />recreation opportunities (e.g., whitewater <br />boating, wading -based fly fishing, family <br />swimming and wading) and biophysical <br />resources (e.g., quality of a sport fishery, <br />amphibian populations, beach size <br />or abundance). <br />To the extent that flow regimes can <br />be managed to produce different <br />combinations of outputs, the final element <br />in the framework assesses resource <br />trade -offs. Here the framework moves <br />from the "descriptive" arena (where <br />scientists determine how flows affect <br />resource conditions and outputs), to <br />the "evaluative" arena (where decision - <br />makers, resource managers, and interest <br />groups consider the desirability of <br />different combinations of outputs; Shelby <br />and Heberlein, 1986). These evaluations <br />are generally made in decision - making <br />processes (such as FERC license <br />proceedings) where social values are often <br />central (Kennedy and Thomas 1995). <br />Resource Conditions <br />H ydraulics <br />Vegetation <br />Channel Form <br />Resource Outputs <br />Recreation opportunities <br />Biophysical resources <br />Trade -offs and Negotiation <br />Figure 1. A framework for assessing flows for recreation or other resources. <br />Flows and Recreation: 1 5 <br />A Guide for River Professionals <br />