undermining of the jetties. The side slopes of the channel cut must be stable for the type of 

 material required, and for the characteristics of wave action and currents that are 

 anticipated within the jetty confines. When a cutterhead dredge is used, it is customary to 

 cut the channel to full project depth slightly outside the design bottom-of-slope limits. This 

 leaves the steeper slope that the material will initially stand on and allows wave action to 

 flatten it to an approximation of the design slope later. The width of the berm will vary 

 with construction methods and characteristics of the bottom material. A good general rule is 

 to make the berm width either 25 feet, or the cut-depth multipUed by the 

 horizontal-to-vertical ratio of the design side slope of the channel, whichever is greater; 

 however, considerable judgment should be used in actual design. The width may be allowed 

 to vary from a quite narrow width at the outer end, where the depth of excavation is 

 minimal, to a generously wide width at the shoreline where the cut is deep. 



Where a jetty nears the shoreline, a transition must be made in the entrance section from 

 that of a jetty -flanked channel to a protected-bank channel (Fig. 26). This protection bank 

 usually consists of a revetted slope, but it may be a sheet-pile wall or poured-in-place 

 concrete wall as shown in Figure 28. 



Concrete L Wa 



Place Rip-rap As Soon As 

 Excavation is Completed 



Figure 28. Narrow channel construction by land-based equipment. 



The channel may be trimmed to design side slopes where narrow entrances are flanked 

 by retaining walls or riprapped slopes and behind which land equipment can be maneuvered 

 to excavate the channel (Fig. 28). Whatever type of bank protection is used, it should 

 extend at least 5 feet below the extreme low water level to avoid wave erosion. A berm may 

 be left between the toe of the wall of revetment and the top of the design side slope of the 

 navigation channel, using the above general rule if desired. Land or water area may be saved, 



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