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<br />19 <br /> <br />e <br /> <br />Montana (Tennant) Method <br /> <br />In most instances the Montana Method gave a recommendation <br />(Table 7) approximating the recommendations of the other three <br />methods. The one notable disparity was on the Lake Fork of the <br />Gunnison River where no plausible explanation existed for the <br />difference between the Montana Method flow recommendation and the <br />other three recommendations. <br /> <br />Flushing flows are defined by Stalnaker and Arnette (l976, <br />p. l2) as "That discharge (natural or man-caused) of sufficient <br />magnitude and duration to remove fines from the stream bottom <br />gravel to maintain intragravel permeability." In trout streams <br />this is necessary to maintain the viability of spawning beds. A <br />survey of the gaging histories indicates that all of the streams <br />included in this study have discharges that meet or exceed flushing <br />flows during peak run-off in an average water year. <br /> <br />Minimum flow recommendations of 30% of the average flow are <br />recommended by Tennant (l975) as flows that will maintain adequate <br />habitat for most forms of aquatic life over a long (months) period <br />of time. To establish how close the 30% value used in the Montana <br />Method is to the other methods' recommendations, all minimum flows <br />have been converted to percentage of average discharge (Table 8). <br /> <br />e <br /> <br />The most remarkable part of the data is how similar the single <br />and multiple R-2 Cross and IFG4 recommendations for an individual <br />stream are as compared to the Montana Method. Wesche (1974) found <br />that available cover is reduced at its greatest rate in the range of <br />25% to 27% of the average discharge. Using this as one parameter, <br />he recommended that for summer rearing flows the average discharge <br />not be allowed to fall below 25%. The average percentage of average <br />discharge for the l8 study reaches were 28.4, 26.4, and 27.9 for <br />the Single Transect R-2 Cross, Multiple Transect R-2 Cross, and <br />IFG4 Methods, respectively. <br /> <br />Based on the findings in this evaluation and the almost identical <br />findings of Wesche (l974), when synthetic methods of analysis are <br />used, 25% of the average flow should be the minimum acceptable level <br />for summer rearing flows for trout. This level is regarded as a <br />common denominator between methodologies. It was used to determine <br />a synthetic minimum flow recommendation for all Class I (U.S. Fish <br />and Wildlife Service classification) streams with adequate U.S.G.S. <br />...", gaging histories in the State of Colorado. These recommendations <br />'are presented in Appendix B. <br /> <br />e <br />