points occurred at or near the absolute mininrum flow recommen- 

 dations while in the remaining two reaches (Beaverhead and 

 Gallatin) the inflection points occurred midway between the 

 absolute and most desirable minimums. It should be noted that 

 the minimxam flow of 400 cfs derived for the Gallatin reach com- 

 pares favorably to the absolute minimum of 39 3 cfs derived from 

 the trout-flow data for adult rainbow trout. This biological 

 data suggested that a minimum of about 400 cfs is needed if 

 the Gallatin reach were managed primarily for rainbow rather 

 than brown trout. On this basis, the single transect recom- 

 mendation for the Gallatin reach is judged acceptable as an 

 absolute minimum recommendation. 



Multiple Transect Method 



The minimum instream flow recommendation was selected at 

 the inflection point on the graph of wetted perimeter versus 

 discharge for a composite of four to seven cross-sections 

 within each reach. Cross-sections 5, 6 and 7 in the Beaver- 

 head reach were eliminated from the analysis due to problems 

 with the calibration of the WSP model and the placement of the 

 transects. The curves are shown in Figures 25 through 29. 



The flows at which the inflection points occurred are 

 listed by reach and compared to the minimum recommendations 

 derived from the trout standing crop and flow data in Table 

 17. Inflection points were generally not as well defined as 

 those on the wetted perimeter curves used in the single tran- 

 sect method. On the curve for the Gallatin reach, a discernible 

 inflection point was not present and no minimum recommendation 

 could be derived. In the Madison #1 and Big Hole reaches, in- 

 flection points occurred at more than one flow. 



Table 17. Comparison of the minimum instream flow recommenda- 

 tions derived from the multiple transect method and 

 the trout standing crop and flow data for five 

 reaches of the Madison, Beaverhead, Gallatin and 

 Big Hole rivers. 



Reach 



Madison(#l) 

 Madison(#3) 

 Beaverhead (#2) 

 Gallatin(#2) 

 Big Hole(#l) 



56 



