point bars and thin overbank deposits along this reach 

 (Hydrometrics 1983b) . 



Sediment Transport Mechanisms 



To effectively deal with the problems caused by 

 floodplain tailings in the Clark Fork system, it is important 

 to have at least a fundamental understanding of the processes 

 of metal transport and accumulation in the sediments. 

 Research that addresses these issues is summarized below. 



Andrews (1987) collected fine-grained bed sediment 

 samples at 21 sites along the Clark Fork from the downstream 

 edge of the Warm Springs Ponds to just below the mouth of the 

 Flathead River in 1984. He also collected a sediment sample 

 from each of the five largest tributaries, including the 

 Little Blackfoot River, Flint Creek, Rock Creek, the 

 Blackfoot River, and the Bitterroot River. Concentrations of 

 arsenic, cadmium, copper, lead, zinc, aluminum, iron, and 

 manganese are summarized in Table 3-12. Andrews concluded 

 that the arsenic, cadmium, copper, lead, and zinc were 

 primarily associated with ferromanganese material on the 

 particle surface, and that with the exception of lead, very 

 little of these elements was bound in silicate minerals. 



In bed sediment samples, copper, zinc, and manganese 

 increased significantly with decreased particle size. 

 Concentrations of arsenic, cadmium, copper, lead, and zinc in 

 fine-grained bed sediments decreased downstream but at 

 different rates. Copper concentrations decreased downstream 

 much more rapidly than lead concentrations, while arsenic, 

 cadmium, and zinc decreased less rapidly than copper but more 

 rapidly than lead (Andrews 1987) . 



The author also found that the addition of relatively 

 clean water and sediment from tributaries had little effect 

 on the distribution of trace metals in the Clark Fork. For 

 example, mixing the sediments with background metal con- 

 centrations from the Bitterroot River did not appreciably 

 dilute the trace metal concentrations in mainstem bed 

 sediments. The exchange of sediment between the river and 

 floodplain in the mainstem is large relative to the quantity 

 of sediment contributed by tributaries; therefore, the 

 tributaries have no appreciable effect (Andrews 1987) . 



In 1986, Brook and Moore conducted a study to evaluate 

 the distribution of metals and the control exerted by 

 sediment particle size on metals concentrations in upper 

 Clark Fork bed sediments. Bed sediments were collected from 

 26 locations in the mainstem Clark Fork and from several 

 locations in the Little Blackfoot River, Flint Creek, and the 



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