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1. INTRODUCTION <br />The value of instream uses of water (e. g., fish and wildlife <br />y habitat, recreation, and aesthetics) is increasing as greater demands <br />are placed on our water resources to meet various industrial, <br />agricultural, and domestic needs (offstream uses). Although the <br />problem of inadequate surface water supply is or will be severe by the <br />year 2000 in many regions of the Midwest and Southwest, some regions <br />of the East may also have water supply problems during low-flow <br />months. The competition between offstream and instream uses will also <br />intensify as a result of the estimated 27% increase in consumptive <br />water use by the year 2000 (U.S. Water Resources Council 1978). <br />Resolution of the conflict between the various uses of water raises <br />important questions regarding the quantity of water that should remain <br />in a stream or river to protect existing instream (nonconsumptive) <br />r uses. Because the value of these instream uses has only recently been <br />recognized within a legal/institutional framework, many of the <br />Y methods* that have been developed to assess instream flow requirements <br />are relatively new. <br />Instream flow requirements (or needs) refer to the amount of <br />flowing water within a natural stream channel that is needed to <br />sustain the instream values (or uses made of water in the stream <br />channel) at an acceptable level. Such a requirement identifies the <br />flow regime that will maintain all uses of water within the channel, <br />including fish and wildlife populations, recreation, aesthetics, water <br />quality, hydropower generation, navigation, and ecosystem maintenance <br />which includes freshwater inflow to estuaries, riparian vegetation, <br />and floodplain wetlands (Bayha 1978, Wassenberg et al. 1979). Methods <br />have been developed to assess the instream flow requirements <br />*The term 'methodology,' defined as a group of related methods, is <br />often found in the literature on instream flow needs. Because the <br />connotation is frequently ambiguous, we have intentionally avoided <br />use of the term in this report.