19 



Clark Canyon Dam and the Big Hole River, the Beaverhead drops 850 

 feet, an average fall of 11.8 ft/mile. River elevations at the dam 

 outlet and mouth are 5450 and 4600 ft, respectively. 



Chemical analyses of water samples collected at sites 0.25, 6, 

 15, and 27 miles below Clark Canyon Dam in the summer of 1972 yielded 



these mean results (Smith, 1973): 



Site (miles) 



~0T25 6 15 27 



Turbidity (JTU) 4 4 7 5 



Conductivity (umhos @ 25C) 565 572 555 617 

 p H 8.1 8.2 8.2 8.1 



Dissolved Oyxgen (ppm) 9.6 9.7 9.3 10.0 



Total Alkalinity (ppm CaC0 3 ) 198 199 190 218 

 Total Hardness (ppm CaC0 3 ) 220 230 216 252 

 Ammonia (ppm NH 3 ~N) .14 .08 .05 .02 



Nitrate (ppm N0~-N) .057 .110 .089 .285 



Nitrite (ppm N0~-N) .015 .018 .015 .006 



Orthophosphate (ppm P0 4 " 3 ) .11 -10 .08 .05 



Smith (1973) evaluated the effects of Clark Canyon Reservoir on 

 some chemical characteristics of the Beaverhead River. The reservoir 

 had its greatest effect upon the dissolved oxygen levels in the tail- 

 waters. DO levels in the tailwaters were well above saturation levels 

 while the reservoir tributaries had mean saturation levels below or 

 near saturation. He concluded that critically low DO due to bottom 

 releases from the reservoir is not likely to become a problem. Compared 

 to the reservoir tributaries, ammonia, nitrite and pH in the tailwaters 

 increased sufficiently to be considered changed by the reservoir. The 

 increase in ammonia and nitrite was attributed to the reduction of 



