24 



Beaverhead River before impoundment. The primary effect of the reservoir 

 has been to reduce fluctuations in water temperature near the dam's 

 outfall. Diel fluctuations in the summer of 1971 and 1972 at the Grant 

 station had a range of approximately 2F while those at the Red Rock River 

 station had a range of approximately 9F (Smith, 1973). From July through 

 September, 1972, mean water temperatures at the Grant station exceeded 

 those at the Red Rock River station by approximately 5F. This is a 

 result of the solar heating of the reservoir. 



Water temperature fluctuations at the Blaine and Red Rock River 

 stations were similar, even though these two stations are separated by 

 a distance of over 50 miles. Water temperature fluctuations at these 

 two stations were similar because they both reflect variations in air 

 temperatures. 



Additional water temperature data was collected on the Beaverhead 

 River between 1963 and 1968 at three stations, located approximately 

 0.25, 15, and 52 miles below the dam. The maximum water temperature 

 recorded at the three stations during this period was 76.5 F. It 

 would appear that water temperatures in the Beaverhead River are 

 not high enough to adversely affect the survival of trout. The 

 temperature data is presently being analyzed using a computer program 

 developed by the Civil Engineering Department, Montana State University. 

 The results will be presented in a separate report. 



Nine study sections were selected along the Beaverhead River 

 primarily on the basis of differences in annual flow patterns. Due to 

 irrigation withdrawals, annual flow patterns, as indicated by Figures 

 1 and 2, vary greatly between the upper and lower river. Selected 

 physical and cover characteristics of these sections are given in Table 1. 



