A minimum instream flow recommendation, .based on a single 

 inflection point could be derived for only two (Madison #3 

 and Beaverhead) of the five reaches. The minimum for the 

 Beaverhead reach (100 cfs) was slightly less than the absolute 

 minimum recommendation of 150 cfs derived from the trout-flow 

 data and the minimum for the Madison #3 reach (500 cfs) was 

 less than the absolute minimum of 650 cfs. 



Two inflection points occurred on each of the wetted 

 perimeter curves for the Madison #1 and Big Hole reaches. The 

 lowermost inflection point for each of these two reaches oc- 

 curs at the flow approximately equal to the absolute minimum 

 recommendation. The uppermost inflection point for the 

 Madison #1 reach occurs at the flow approximately equal to the 

 most desirable minimum recommendation. 



The recommendations generated by the multiple transect 

 method for the four reaches having discernible inflection 

 points were judged acceptable although minimum recommendations 

 for two of the reaches were somewhat less than the absolute 

 minimums derived from the trout-flow data. In the two reaches 

 having more than one inflection point, the lowermost occurred 

 at the flow closely approximating the absolute minimum recom- 

 mendation derived from the trout- flow data. 



Non-field Method 



The flow recommendations generated by the Tennant method 

 are listed by river reach in Table 18. The Tennant method 

 greatly underestimates the flows needed to sustain desirable 

 trout populations in all five reaches. Tennant 's minimum flov; 

 recommendations, which are equal to 10% of the mean flow of 

 record, were no more than 32% of the absolute minimum recom- 

 mendations derived from the trout-flow data for the five 

 reaches. Tennant 's minimums are in fact less than the mini- 

 mum average daily flows of record for four of the five reaches 

 (Table 19). The absolute minimums derived from the trout-flow 

 data generally fall within the range of flows Tennant describes 

 as excellent to optimum for the October-March period and fair 

 to outstanding for the April-September period. 



The percentage of the mean flow (10%) chosen by Tennant 

 to derive a minimum flow recommendation is inadequate when 

 compared to the percentages derived from the trout-flow data. 

 The absolute minimxam flow recommendations for the two reaches 

 of the Madison River were at least 45 and 51% of the mean 

 flows. The absolute minimums for the Beaverhead, Gallatin 

 and Big Hole reaches were from 31 to 35% of the mean flows. 

 The Madison River, which generally lacks pool development and 

 is considerably wider and shallower than the other rivers of 

 the study area, required a greater percentage of the available 

 flow. This is expected if one considers the differences in 

 channel morphology between the rivers. 



62 



