USGS suspended sediment data jfor the upper river and WQB 

 data for the entire drainage are summarized below. 



Silver Bow Creek . Water Quality Bureau data indicate 

 that Silver Bow Creek has a severe inorganic suspended 

 sediment problem. Concentrations were highly variable in FY 

 85-87 (Figure 3-23) , and for its size, sediment production 

 was high, presumably as a result of the preponderance of 

 unvegetated mine tailings in the floodplain. The suspended 

 sediment criterion to maintain a high level of protection for 

 freshwater fisheries was exceeded in 11 to 64 percent of the 

 samples, depending on the year and the monitoring location. 

 Various stations fell in the low level of protection category 

 in up to 11 percent of the samples. Suspended sediment 

 concentrations, loads, and problem severity generally 

 increased from Butte downstream to above the Warm Springs 

 Ponds. The Butte WWTP discharge was responsible for an 

 increase in organic suspended sediment in Silver Bow Creek 

 for several miles below the outfall. However, organic 

 concentrations were only a fraction of the total suspended 

 sediment concentrations. 



Warm Springs Ponds . The Warm Springs Ponds caused major 

 reductions in Silver Bow Creek's suspended sediment con- 

 centrations through their function as large settling basins. 

 Estimated annual total suspended sediment loads in Silver Bow 

 Creek in FY 86 and 87 were decreased fourfold to sixfold from 

 above and below the ponds, and up to 2,000 tons of material 

 were trapped in one year. From the standpoint of fisheries 

 protection. Silver Bow Creek suspended sediment concentra- 

 tions below the ponds were consistently good. 



Upper Clark Fork . Median suspended sediment concentra- 

 tions for March 1985 to September 1987 at the six USGS 

 sampling stations were low, ranging from 8 mg/1 in the 

 Blackfoot River to 36 mg/1 in Flint Creek. These values 

 indicate that the quantities of sediment transported during 

 most flows of 1985-87 were minor. Considerably higher 

 concentrations can occur during high-flow conditions, with 

 the highest values measured in the Clark Fork mainstem during 

 the February 1986 snowmelt runoff (1,390 mg/1 at Deer Lodge 

 and 1,370 mg/1 at Turah Bridge). The large differences in 

 concentration between median and runoff conditions indicate 

 that the amount of suspended materials transported is highly 

 variable, with short-duration events possibly representing a 

 significant portion of the annual load. 



3-76 



