65 



success is probably limited by the heavy deposition of sediments in spawning 

 gravels. Too few estimates are available in the Barretts Upstream (15) 

 Section to evaluate the impact of flows. 



Spring estimates of age II and older brown trout in the Hildreth 

 (2) and Pipeorgan (8) Sections are compared in Table 30. Except for 1972, 

 total numbers exhibited similar trends in both sections. Fall estimates 

 of age I brown trout also displayed similar trends (Table 31), although 

 numbers of yearlings in 1967 and 1971 were considerably greater in the 

 Pipeorgan (8) Section. The similarity of population trends in sections 

 having similar flow regimes suggests flow was the dominant factor in- 

 fluencing numbers of trout in both the Hildreth (2) and Pipeorgan (8) 

 Sections. 



Physical and Hydraulic Characteristics 

 Physical and hydraulic values at various flows were predicted for 

 20 cross sections in the Hildreth Section of the Beaverhead River using the 

 WSP (Water Surface Profile) computer program of the Bureau of Reclamation. 

 Each cross section was classified as a pool, run, or riffle. Mean 

 physical and hydraulic values were calculated for each water type. The 

 mean values at various flows in percent of the mean values at 1000 cfs, 

 the approximate bank full flow, are given in Appendix Table 32. 



Flow reductions affected riffle areas in the Hildreth Section more 

 severely than pools and runs. Five of the six measured characteristics 

 showed the greatest rates of loss in riffles (Appendix Table 32). 

 Riffles are important to trout because they are the primary food pro- 

 ducing and spawning areas in a stream. The importance of desirable 

 flow patterns in riffle areas during the rainbow and brown trout 

 spawning periods was demonstrated during this study. 



