In essence, the dynamic response of a beach under storm attack is a 

 sacrifice of some beach, and often dune, to provide material for an offshore 

 bar. This bar protects the shoreline from further erosion. After a storm or 

 storm season, natural defenses may again be re-formed by normal wave and wind 

 action. 



Besides causing erosion of the shoreline, storm surges can damage shore 

 structures that are inadequately protected and located close to the water by 

 either direct wave attack or undermining of the structure. 



At locations where there is a low section of protective dunes, or when the 

 storm conditions are particularly severe, the storm surge and wave action may 

 succeed in completely overtopping the dunes causing extensive coastal flood- 

 ing. When this occurs, beach and dune sediments are swept landward by the 

 water, and in the case of barrier islands, are deposited as ovenjash fans on 

 the backshore or in the lagoon. This process results in a loss of sand from 

 the dynamic beach system. Often, storm overwash and storm flooding return 

 flow will erode enough sand to cut a new tidal inlet through the barrier 

 island. Depending on various factors, the new inlet may become a permanent 

 feature of the coastline. 



3. Beach and Dune Recovery from Storm Attack . 



Following a storm there is a return to more normal conditions which are 

 dominated by low, long swells. These waves transport sand from the offshore 

 bar, built during the storm, and place the material on the beach. Winds then 

 transport the sand onto the dunes where it is trapped by the vegetation. In 

 this manner the beach begins to recover from the storm attack. The rebuilding 

 process takes much longer than the short span of erosion which took place. 

 Therefore, a series of violent local storms over a short period of time can 

 result in severe erosion of the shore because the natural protection does not 

 have time to rebuild between storms. Sometimes full recovery of the beach 

 never occurs because sand is deposited too far offshore during the storm to be 

 returned to the beach by the less steep, normal waves which move material 

 shoreward. This is particularly true in the Great Lakes and in bays and 

 estuaries where waves are fetch-limited and do not develop into long swell 

 waves . 



Alternate erosion and accretion may be seasonal on some beaches; the winter 

 storm waves erode the beach, and the summer swell (waves) rebuilds it. 

 Beaches also appear to follow long-term cyclic patterns, where they may erode 

 for several years and then accrete for several years. 



4. Littoral Transport . 



Another dynamic feature of the beach and nearshore physical system is lit- 

 toval transport, defined as the movement of sediments in the nearshore zone by 

 waves and currents. Littoral transport is divided into two general classes: 

 transport parallel to the shore (longshore transport) and transport perpen- 

 dicular to the shore (onshore-offshore transport). The material that is 

 transported is called littoral drift. 



Onshore-offshore transport is determined primarily by wave steepness, 



1-13 



