Beaches are extremely dynamic systems. We 

 have already seen how they respond to 

 rises in sea level and how their size and 

 form is determined by the relative 

 importance of wave and tidal energy. They 

 also respond predictably to the increase 

 in wave energy produced by storms (Figure 

 29). During a storm, waves take sand from 

 the upper beach or the first dune and 

 transport it to the lower beach. The 

 beach becomes more flattened and storm 

 waves expend their energy over a broader 

 and more level surface. The upper beach 

 can lose a great deal of sand during a 

 storm. Much of it is replenished, 

 however, during fair weather. Sand is 

 pushed shoreward by fair-weather waves or 

 carried in by long-shore transport. The 

 source of sand after storms is the same 

 sand that was on the upper beach prior to 

 the storm. 



5.2 SHORELINE ENGINEERING 



We have seen that barrier islands in 

 the South Atlantic Bight are extremely 

 dynamic systems. They migrate landward as 

 sea level rises, are moulded by waves and 

 tides, and respond in predictable ways to 

 storms. All of these responses involve 

 the transport of enormous quantities of 

 sand. The engineer's response to this 

 movement, labelled erosion, is to try to 

 stop it and "stabilize" the shore. The 

 most common method is with rubble 

 structures: jetties, groins and seawalls. 



Both groins and jetties are 

 successful sand traps. If longshore 

 transport of sand is significant, sand 

 will pile up on the updrift side of the 

 structure. However, this accumulation of 

 sand on the updrift side limits the supply 



First dune 

 Beach 



Normal high tide 

 Steep slope 



New first dune forming 



\ 



" . Fallen house 



New beach position 



o 



Figure 29. Beach flattening in response to a storm. Shaded area in A 1 is about equal to shaded area in A. House 

 is not drawn to scale. (From Pilkey et al. 1984). 



49 



