55 



Sections were selected primarily on the basis of differences in annual 



flow regimes due to irrigation withdrawals and accretion. A comparison 



of the minimum and maximum average daily flows in the nine study sections 



provides a measure of the variations in flow that occur between sections 



and between years (Table 21). The severe dewatering of the Grant (22 cfs 



on October 16, 1974), Barretts Downstream (0 cfs on August 10, 1973), 



and Anderson Lane (21 cfs on July 14, 1973) Sections has undoubtedly 



affected aquatic life. 



TABLE 21. Minimum and maximum average daily flows (cfs) between April 1 

 and March 31 in 9 sections of the Beaverhead River in 1973-74, 

 1974-75, and 1975-76. 



Section 1973-74 1974-75 1975-76 



Grant (0.1) 92-1070 22-1020 56-1320 



Hildreth (2) 127-1115 57-1065 101-1365 



Pipeorgan (8) 122-1110 52-1060 96-1360 



Barretts Up. (15) 172-1150 110-1210 157-1480 



Barretts Down. (18) 0- 746 62- 711 157- 933 



Wheat (27) 148- 701 165- 702 238-1049 



Westside Canal (29) 70- 701 90- 702 201- 974 



Anderson Lane (38) 21- 725 100- 703 163- 997 



Blaine (52) 75- 800 107- 772 153-1600 



Comparison of trout populations in 1975 and 197G 



The flows in the Beaverhead River in 1974-75, which preceeded the 

 Spring, 1975 population estimates, were considerably lower than those 

 which preceeded the Spring, 1976 estimates (Table 21). Between 1974-75 

 and 1975-76 minimum average daily flows in the nine study sections in- 

 creased by 43-155% and maximum average daily flows increased by 22-107%. 

 Trout populations in all nine sections would be expected to increase 

 following these dramatic flow increases if flow was the major limiting 

 factor throughout the system. 



