other mechanism is that bars are formed by the convergences and divergences 

 of mean flows associated with partially standing waves with long periods 

 (Bowen and Inman 1971, Short 1975, and Holman and Bowen 1982). What is 

 understood is that bars provide a natural protection to the beach by causing 

 incoming waves to break farther offshore, reducing the energy reaching the 

 beach. Offshore bars also provide a mechanism for the temporary storage of 

 eroded sediments as part of the cycle toward beach recovery. 

 Beach recovery 



21. As a storm subsides, the wave height decreases, and the wave 

 period usually increases, eventually resulting in a wave steepness below the 

 critical value for erosion. Then the beach recovery process begins. In the 

 inner part of the surf zone, sand is transported onshore, and a new berm is 

 created by the runup. Because sand is removed from the surf zone and carried 

 onshore, the slope of the surf zone becomes steeper. The process of berm 

 creation has been little studied and is, therefore, not well understood. The 

 rate of beach recovery can be quite rapid; for example, Birkemeier (1979) 

 reported that within one day of the peak of a storm, over 51 percent of the 

 eroded material had returned to the beach at Long Beach Island, New Jersey. 



22. In the offshore, the storm-induced bar will move landward and 

 ultimately onto the beach. The rate of recovery can vary considerably 

 depending on wave conditions and the depth over the bar. Figure 5 



PROFILE LINE 188 

 — — 24 FEB 82 



- 17 tiny 82 



24 RUG 82 



200 t00 600 BOO 



DISTANCE FROM BASELINE, m 



Figure 5. Slow recovery of an offshore bar at Duck, 

 North Carolina (Birkemeier 1985a) 



12 



