c. Scraping in high-water and abandoned channels should follow 

 the alignment of the channel. Gravel removal design depends 

 on several factors listed below: 



• Side slopes should be stable for expected flow conditions 

 during a 2-year recurrence interval flood. This will reduce 

 the potential for rapid channel shifting. 



• Channel-full top width should not be increased if it can 

 be avoided. If additional material is needed that cannot 

 be obtained from other dry channels or unvegetated bars, 



the channel being worked can be widened to a width no greater 

 than that of the active channel and preferably half that of 

 the active channel (especially on meandering, sinuous, and 

 strai ght r i vers) . 



• Longitudinal channel slope into the material site should not 

 exceed 10 times the average slope of the channel (Figure 14). 

 This will minimize the potential for extensive upstream bed 

 degradation. The upstream end of the section of increased 

 slope should be a sufficient distance from the nearest active 

 channel to minimize the potential for channel diversion. 



Top of Adjacent Bar or Bank 



Original Channel Bed 



^//// MatenaTRemoved^ 



•^'-UUl-i LJU.U ij-ijjuju UjIl/Uj 



-Slope < 10 X Overall 

 Channel Slope 



Maintain Positive Slope- 

 Low- Flow Buffer 



Figure 14. Sketch of high-water or abandoned channel longitudinal 

 profile showing recommended channel bed slopes resulting from scrap- 

 ing the channel bed. 



68 



VI . SITE OPERATION 



