Hydromodif ication 



Sedimentation is the biggest NPS problem associated with 

 hydromodif ication projects due to dredging, dam and bridge 

 construction, flow regulation, and erosion from streambanks 

 that are disturbed. 



NPS Problems in the Clark Fork Basin 



The most pervasive nonpoint source problem in the basin 

 is contamination of surface and ground water by metals 

 derived from runoff and leachate from floodplain mine wastes 

 and waste disposal areas. Another major problem is sedimen- 

 tation. A number of activities contribute to this problem, 

 including intensive grazing and agriculture, silviculture, 

 mineral exploration and development, construction activities 

 and hydromodif ication. 



The severity of NPS problems varies somewhat in 

 different parts of the basin due to diverse geology, soil 

 types, moisture regimes, and land management practices. 



Upper Clark Fork Basin 



Specific nonpoint source pollution problems in the upper 

 Clark Fork Basin are provided in Table 3-21. Prevailing 

 problems in the upper basin are sediments, flow and habitat 

 alterations, salts, pathogens and nutrients from agricultural 

 activities; sediments, metals, acid, and habitat alteration 

 from active and historic mines; and sediments, organic 

 compounds, and habitat alteration from silviculture prac- 

 tices. 



The most serious NPS problem in the headwaters and upper 

 river reach is probably erosion of heavy metals-contaminated 

 sediments into the system. Large waste disposal areas (such 

 as the Colorado Tailings) and floodplain mine wastes are 

 major sources of metals during snowmelt runoff and thunder- 

 storms. The principal problem metals in the upper basin are 

 arsenic, copper, cadmium, lead, and zinc. 



Middle and Lower Clark Fork Basin 



Specific nonpoint source pollution problems in the lower 

 and middle portions of the basin are provided in Table 3-22. 

 This section of the basin has some of the same NPS problems 

 as the upper basin, except that there are fewer inactive mine 

 waste sources. Other problems include elevated stream 

 temperatures due to dewatering; nutrients and other 



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