Figure 19. Wave and surge barrier, Monterey Harbor, California. An outer breakwater inter- 

 cepts most of the wave action, but timber diaphragm with braced king-pile 

 supports keeps large diffracted waves from reaching berthing area. 



Other breakwater types include: (a) sand-filled sheet-pile or prefabricated concrete cells 

 set side by side and securely fastened together, (b) concrete superstructure built on a 

 submerged rubble base where large pieces of stone are not available for an all rubble 

 structure, and (c) the perforated swiss-cheese breakwater, which partially dissipated wave 

 energy in a chamber behind a perforated wall (Fig. 20). Design details for these structures 

 may be found in the Shore Protection Manual (U.S. Army, Corps of Engineers, Coastal 

 Engineering Research Center, 1973), and Chancy (1961). 



Regardless of the type of construction used, special attention must be given to the 

 foundation and bottom materials. Any wave resisting, vertical-faced structure built on a 

 bottom of unconsolidated materials can cause the waves to generate toe-scouring currents 

 and undermine the structure or make it unstable. Caissons or other large structural units 

 that rest on the bottom rather than imbedded, are particularly vulnerable; they have been 

 known to topple seaward into their own scoured-toe trench. Sheet-pile walls have sometimes 

 lost so much embedment from toe scour as to threaten their integrity. Such scour can be 

 prevented by dumping stone of appropriate size (large enough not to be carried away by the 

 toe currents) along the toe of the newly placed structure (Fig. 21). The individual stone size 

 and overall fillet size will vary with the height of the design wave. 



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