The final flow recommendations for each reach (Table 16) 

 were derived to meet the needs of adult trout. For the rivers 

 of southwest Montana, the amount of water or living space re- 

 quired by adults is believed to be greater than the amount 

 needed by any other life stage, including spawning and incuba- 

 tion. The minimum recommendations in Table 16 should, there- 

 fore, meet the needs of all life stages. 



The instream flow recommendations are assumed to apply to 

 all of the low water or non- runoff months even though recom- 

 mendations may have been derived for only a portion of this 

 period, such as the summer irrigation season. In the head- 

 waters of the Missouri River drainage of southwest Montana, 

 the low water period generally includes the months of August 

 through April. During the high water or snow runoff period, 

 which generally occurs during May, June and July, the Montana 

 Department of Fish, Wildlife and Parks bases its flow recom- 

 mendations on the high flows judged necessary to maintain the 

 channel morphology and to flush bottom sediments. This method- 

 ology is discussed and the flow recommendations for each of 

 the five reaches during the high water period are given in 

 Montana Department of Fish and Game (19 79) . 



Single Transect Method 



The minimum instream flow recommendation was selected at 

 the inflection point on the graph of wetted perimeter versus 

 discharge for a single riffle cross-section within the Madison 

 #3, Beaverhead, Gallatin and Big Hole reaches. For the Madison 

 #1 reach, a cross-section through a shallow area containing 

 weed beds was used since well defined riffles were absent. 

 These curves are shown in Figures 20 through 24. 



The recommendations generated by the single transect 

 method compare favorably to those derived from the trout-flow 

 data (Table 16). In three of the five reaches, the inflection 



Table 16. Comparison of the minimum instream flow recommenda- 

 tions derived from the single transect method and the 

 trout standing crop and flow data for five reaches 

 of the Madison, Beaverhead, Gallatin and Big Hole 

 rivers. 



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