• Longitudinal channel slope out of the material site at the 

 downstream end should not be adverse (bed elevation in- 

 creasing in the downstream direction). Adverse slopes cause 

 ponding and potential fish entrapment. Maintaining a positive 

 slope (bed elevation decreasing in the downstream direction) 

 is recommended to allow for channel drainage during a flood 

 recession. The downstream end of the disturbance should be 

 separated from the nearest active channel by at least the 

 width of the low-flow buffer for that channel (Figure 14). 



d. Scraping in active side channels that have been diked and de- 

 watered should follow the alignment of the channel and should 

 stay between the low-flow buffers. Gravel removal design depends 

 on other related factors listed below. 



• Side slopes should be stable for expected flow conditions 

 during a 5-year recurrence interval flood. This will minimize 

 the potential for slope failure and subsequent deterioration 

 of the low- flow buffer. 



• The width of excavation is limited by the limits of the 

 low-flow buffers (Figure 15). The bottom width is limited 

 only by the equipment used. 



""^^ 



Low-Flow 

 Buffer - 



Low Summer Flow Stage 



Maximum Excavation Width 



Stable Side Slopes 



-^WA^ 



777} 



Material Removed ' 



Low -Flow 

 ^—Buffer 



Figure 15. Sketch of active side channel cross section defining 

 excavation limitations. 



69 



VI. SITE OPERATION 



