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ABSTRACT <br />w <br />Protection of instream uses of water, such as fish and wildlife <br />habitat, recreation, and aesthetics, has been identified as a <br />I <br />significant environmental issue, especially in the West where water <br />supplies are limited and offstream uses (e.g., irrigation) are <br />well-defined by law. The growing recognition nationwide of the <br />importance of protecting these instream uses of water has coincided <br />with the recent emphasis on the development of small-scale hydropower <br />resources. The issue of instream flow maintenance in hydropower <br />development is essentially a problem of evaluating the effects of <br />planned modifications in hydrologic patterns. Because hydroelectric <br />projects can alter natural flow regimes on both spatial and temporal <br />scales, downstream water users and the aquatic ecosystem can be <br />adversely affected. Assessment of the instream flow needs of aquatic <br />biota (primarily fishes) has been the most difficult and controversial <br />aspect of the instream flow issue. <br />Numerous methods have been developed to assess the effects of <br />stream flow regulation on aquatic biota and to provide instream flow <br />recommendations. The methods differ in their use of hydrologic <br />records, hydraulic simulation techniques, and habitat rating criteria <br />and in their capability to provide seasonal or species-specific <br />recommendations. Because of these differences in data requirements, <br />application costs and the level of resolution associated with the <br />instream flow recommendations vary greatly. Consequently, guidance is <br />needed to ensure that the most appropriate methods are selected for <br />instream flow assessments at small-scale hydroelectric sites. To <br />provide this guidance to developers of small hydropower projects, the <br />methods were reviewed and evaluated to determine their applicability <br />in the assessment of instream flow needs for fishery resources at <br />` small hydropower sites. The methods were grouped into three <br />categories based on (1) level of resolution associated with the <br />y instream flow recommendation, (2) data needs, and (3) costs of <br />vii