Santa Barbara, California- 1948 

 Figure 5-16. Effects of Shore-Connected Breakwater on Shoreline 



5.93 SITING 



Offshore breakwaters are sited to provide shelter to a harbor 

 entrance, or to create a littoral reservoir. They may also provide a 

 calm area where small craft may seek refuge or where a pipeline dredge 

 can operate to pump sand to downdrift shores (see Section 5.5, SAND BY- 

 PASSING). An example of this type of siting or use is illustrated in 

 Figure 5-17, which shows Channel Island Harbor entrance at Ventura, 

 California. Offshore breakwaters have also been sited seaward of massive 

 seawalls to provide a first line of defense as illustrated in Figure 5-18. 



5.94 EFFECTS ON THE SHORELINE 



The effects of an offshore breakwater on a shoreline are illustrated 

 by Figure 5-19. Offshore breakwaters are probably the most effective means 

 of completely intercepting movement of littoral material. They are usually 

 positioned in water significantly deeper than the seaward ends of jetties or 

 groins. This makes it possible for them to control a wider part of the 

 littoral zone than structures tied to the shore. Because longshore trans- 

 port is the direct result of wave action, the extent to which the breakwater 

 intercepts the movement of littoral drift is directly proportional to the 

 extent of wave attenuation by the breakwater. 



5.95 OPERATION OF AN OFFSHORE BREAKWATER 



An offshore breakwater initially causes littoral drift to deposit 

 on the shore in its lee by dissipating the wave forces that cause littoral 



5-51 



