Figure 20, 

 Reference 



The effects 

 64). 



of groins on littoral drift (Source: 



Beach 



Shoreline • 



Ocean 



•Groin 



Effect of Single Groin 



Beach 



Shoreline- 



Ocean 



Groin 



Effect of a Series of Groins 



Jetties generally stabilize the location of the inlet channel and 

 protect vessels from the direct force of waves. Sand is impounded at 

 the updrift jetty and much is lost into deep water at the seaward end as 

 the littoral drift process attempts to maintain sand movement. The 

 supply of sand to the shore downdrift from the inlet jetty complex is 



thus reduced, causing erosion of 

 erosion on the downdrift side of 

 a bypass system for dredging the 

 are designed to ensure a flow of 

 prevent shoaling of the entrance 

 accomplished in conjunction with 



4.4.6 Breakwaters 



that shore 

 the jetty, 

 impounded sand, 

 sand to nourish 

 channel (Figure 



[64]. To eliminate undesirable 

 some inlets are provided with 

 These bypass systems 

 the downdrift beach and 

 21) . This may also be 



an offshore breakwater. 



Breakwate 

 safer passage 

 of them. When 

 breakwater may 

 channel . They 

 across the nav 

 the shore [51] 

 stream, deposi 

 buildup actual 

 the downdrift 



rs are constructed to break incoming waves and to provide 

 for vessels through inlets as well as prevent sand blockage 

 placed on the updrift side of a navigation opening, a 

 impound sand, preventing it from entering the navigation 

 also afford shelter for a dredge to routinely pump sand 

 igation opening back into the stream of sand moving along 

 . However, in the absence of wave action to move the sand 

 ted material builds seaward toward the breakwater. The 

 ly serves as a barrier to littoral sand drift, depriving 

 beaches of sand [66]. 



109 



