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17 <br />2.0 EXISTING METHODS FOR INSTREAM FLOW ASSESSMENT <br />5 <br />Resolution of the conflict between the instream use of water for <br />4 hydroelectric generation and other instream uses, such as the <br />maintenance of aquatic habitats, will require information on the flow <br />regimes needed to preserve these habitats. Because numerous methods <br />have been proposed to assess the instream flow needs for fishery <br />resources, it is the purpose of this document to review and evaluate <br />these methods and to recommend a strategy that can be used to assess <br />instream flow needs at small-scale hydroelectric sites. In this way, <br />small-scale hydroelectric developers will have greater access to the <br />existing methods, and assessment studies can be conducted in a more <br />cost-effective manner. <br />A variety of assessment methods were developed in response to the <br />relatively recent emphasis that was placed on evaluating the <br />biological effects of flow regulation. Our review is not meant to be <br />totally comprehensive but rather is intended to provide a <br />representative summary of approaches which are currently available for <br />quantifying instream flow requirements. This information provides the <br />background for later comparisons and recommendations. For more <br />detailed information on individual techniques, the reader is referred <br />to the list of references (Sect. 5.0). Other reviews of assessment <br />methods for instream flow needs can be found in Stalnaker and Arnette <br />(1976) and in Wesche and Rechard (1980). <br />Listed below are several general characteristics which are <br />important in distinguishing among the various instream flow assessment <br />methods: <br />• Use of existing stream flow records, <br />• Application of hydraulic simulation techniques, <br />• Use of habitat rating procedures to measure the <br />physical condition of the lotic environment,