ally contain large quantities of gravel and, therefore, are often utilized 

 as gravel sources (Figure 93). The bed load carrying capacity of these 

 rivers is large, thus facilitating the replenishment of extracted gravels 

 after site closure. 



Braided river systems are dynamic and lateral shifting of channels from 

 year-to-year is common, therefore, any channel shifting resulting from lower- 

 ing bars through gravel removal would be similar to the natural processes. 

 For example, any diversion of a channel through an area that was lowered by 

 the removal of gravel possibly would have occurred naturally sometime in the 

 future. Material sites in these areas typically are scraped because required 

 quantities of gravel usually can be obtained over large areal extents and it 

 Is more efficient to work a site above the existing water level. Due to the 

 bed load carrying capacity of these systems, the typical shal low scraped 

 sites are subject to sedimentation rates similar to natural depressions 

 occurring in these floodplains. Therefore, the minded sites can return 

 relatively quickly to near natural conditions. This recovery is particularly 

 true if the site is located near the active channel. An example of rapid 

 recovery is the Ivishak River site, which was shallow scraped over a large 

 area of unvegetated gravel bars. After several years the only evidence of 

 gravel mining is the presence of access roads and fill ramps that connected 

 the material site with an airstrip and drill pad. 



Long-term effects of gravel removal on water quality were not evident 

 at the four sites located in braided systems. Due to the relative insta- 

 bility of channels in a braided river system, any channels routed through an 

 abandoned material site probably would be affected in a manner similar to a 

 channel being rerouted due to natural hydraulic processes. An exception 

 would be where an aliquot of a material site was used as a settling pond 

 during a gravel removal operation. The accumulated fines could be suspended 

 during subsequent high flows if this material was not armored and was left 

 in the depression during site closure. None of these situations was en- 

 countered at the study sites, however, the possibility would exist in simi- 

 lar site conditions. 



334 



