Indian River Inlet, Delaware (Oct. 1972) 

 Figure 5-24. Effects of entrance jetties on shoreline. 



2. Type s. 



Breakwaters may be rubble mound, composite, concrete caisson, sheet-piling 

 cell, crib, or mobile. In the coastal United States, breakwaters that have 

 been built on the open coast are generally of rubble-mound construction. 

 Occasionally, they are modified into a composite structure by using a concrete 

 cap for stability. Precast concrete shapes, such as tetrapods or tribars, are 

 also used for armor stone when sufficient size rock is not obtainable. In 

 the Great Lakes area, timber, steel, or concrete caissons or cribs have been 

 used. In relatively sheltered areas, single rows of braced and tied Wakefield 

 (triple lap) timber piling or steel sheet piling have occasionally been used 

 in breakwater construction. Several types of floating breakwaters have been 

 designed and tested. Between 1970 and 1980, a total of 27 floating break- 

 waters of various types have been installed in the United States with varying 

 degrees of success; 17 were tire breakwaters and 8 were concrete caissons or 

 pontoons (Western Canada Hydraulic Laboratories Ltd., 1981). 



3 . S iting . 



Shore-connected breakwaters provide a protected harbor for vessels. The 

 most important factor in siting a breakwater is determining the best location 

 that will produce a harbor area with minimum wave and surge action over the 

 greatest period of time in the year. This determination is made through the 



5-59 



