those for a meandering system but, because floodplains generally are more 

 narrow and contain smaller point bars, the potential for permanent altera- 

 tion is generally greater (Table 40). Proper placement of the material site 

 and operational procedures can minimize permanent change and these should be 

 selected to prevent or minimize changes to the hydraulic characteristics of 

 the channel . 



Stra i ght 



Straight channel patterns are less common than other types. The thalweg 

 of a straight river typically winds back and forth within the channel. 

 Gravel bars form opposite where the thalweg approaches the side of the 

 channel (Figure 93). These gravel bars may not be exposed during high flow. 

 Banks of straight systems typically are stable and floodplains are usually 

 narrow. These river systems are considered to be an unusual configuration in 

 transition to some other configuration. Only the material site studied at 

 Oregon Creek was situated on a straight channel system. 



As with other types of single channel systems the major potential 

 effect from scraping floodplain gravels is decreased stability of the chan- 

 nel and a tendency to develop a braided configuration. These are probable 

 occurrences because of the typically narrow floodplains and the limited 

 number of exposed bars available. Often the adjacent floodplain will have to 

 be disturbed, or even the channel itself, because of the limited area avail- 

 able. The Oregon Creek site typified the extensive long-term changes that 

 can occur when gravel is removed from within the channel and the adjacent 

 floodplain (Table 40). The channel stability was greatly reduced and the 

 channel had become braided within the confines of the abandoned site. These 

 conditions exist 13 years after the site was closed and probably will remain 

 in that condition for many more years. 



The change from a single to a braided channel alters water quality 

 parameters and aquatic biota as discussed in previous sections on sinuous 

 and meandering systems. These alterations include the potential for changing 

 water temperature and increasing sedimentation in the disturbed site where 



34-6 



