CHAPTER 1. INTRODUCTION 



The South Atlantic Bight borders the 

 United States coastline from Cape 

 Hatteras, NC, to Cape Canaveral, Fl_. The 

 shoreline along the Bight is sandy and 

 characterized by numerous barrier islands 

 separated by tidal inlets. Interspersed 

 along this coastline, especially at 

 inlets, are various artificial structures 

 composed of hard rubble materials. These 

 rubble structures are the focus of this 

 profile. 



1.1 DEFINITION OF RUBBLE STRUCTURES 



Rubble structures are mounds of 

 random-shaped and random-placed stones 

 protected with a cover layer of selected 

 stones or specially shaped concrete armor 

 units (Whalin et al . 1984). Most commonly 

 they are constructed of large boulders, 

 but they can be built from a wide variety 

 of materials, including steel, concrete, 

 pilings, wood timbers, and plastic bags 

 filled with sand (Whalin et al . 1984). 

 Rubble structures can be divided into two 

 general categories based upon their 

 position relative to the shoreline and 

 their purpose. The first category 

 includes those structures built 

 perpendicular to the shoreline and 

 designed to interrupt the littoral 

 transport of sediment. This category 

 includes jetties, weir jetties, and 

 groins. The second category of rubble 

 structures includes those built parallel 

 to the shoreline and designed to prevent 

 waves from reaching the higher elevations 

 of the beach. This category includes 

 breakwaters, seawalls, bulkheads, and 

 revetments. 



Structures Perpendicular to the Shoreline 



Jetties are structures used at inlets 

 to stabilize the position of the 



navigation channel, to shield vessels from 

 wave forces, and to control the movement 

 of sand along the adjacent beaches so as 

 to minimize the movement of sand into the 

 channel . 



Weir jetties are updrift jetties with 

 a low section or weir. Littoral drift 

 moves over the weir section into a 

 predredged deposition basin which is 

 dredged periodically. 



Groins 



are shore protection 



structures built to trap littoral drift or 

 retard erosion of the shore. They are 

 usually shorter than jetties and are used 

 along the beach away from inlets. 



Structures Parallel to the Shoreline 



Breakwaters are wave energy barriers 

 designed to protect any landform or water 

 area behind them from the direct assault 

 of waves. 



Seawal 1 s are structures separating 

 land and water areas, primarily designed 

 to prevent erosion and other damage due to 

 wave action. Seawalls are designed to 

 receive the impact of the sea at least 

 once during each tidal cycle. 



Bulkheads are structures built higher 

 on the shore than a seawall or a revetment 

 to retain or prevent sliding of the land. 

 A secondary purpose is to protect the 

 upland against damage from wave action 

 during storms. 



Revetments are facings of stone, 

 concrete or wood built to protect a scarp, 

 embankment, or shore structure against 

 erosion by wave action or currents. 

 Revetments are a protective armor, rather 

 than a retaining structure. 



