When storm waves carry away a beach, they are taking sand out of 

 storage. In the optimum natural state there is enough sand storage 

 capacity in the berm or dune to replace the sand lost from the beach to 

 storms. Consequently, the effects are usually temporary, with the dune or 

 berm gradually building up again. 



The potential processes and activities that disturb the equilibrium 

 of a beach can be classified as either natural or man-made. Natural 

 causes are conveniently grouped according to their time scales [56]. 



1. Short-term (measured in hours or days). Individual storms can 

 often be the predominant natural factor in determining the 

 condition of a beach, especially in the northeastern United 

 States [57]. 



2. Intermediate-term (months). Seasonal variations in wave energy 

 can produce significant alterations to beach equilibrium, 

 especially on the United States Pacific coast. The different 

 beach conditions are often referred to as the "summer" and 

 "winter" beach profiles, the former being the result of the 

 lower, shorter waves typical of summer conditions, while the 

 latter are produced by the higher, longer waves of the winter 

 season [58]. 



3. Long-term (years or decades). Fluctuations in mean sea level 

 over periods of only a few years have been blamed for some long- 

 term alterations of beach equilibrium. Similarly, the slow but 

 definite rearrangement of bottom sediments by storm waves and 

 tidal currents can alter bathymetry to the extent that significant 

 changes occur in the behavior of waves approaching the 

 shoreline [59]. 



Man-made disturbances to beach equilibrium are usually the result 



of construction activity within the coastal zone; however, the equilibrium 



of some beaches is so delicate that it can be upset just by heavy usage 



for recreational purposes (e.g., by dune buggies and other vehicles [56]. 



In all these examples, whether natural or man-made, a disruption to 

 beach equilibrium will occur if one or more of the three elements essential 

 to the preservation of that equilibrium is altered. The disruption will 

 generally occur in the following way(s) [56]: 



1. The supply of beach material (sand) is altered. If the supply is 

 reduced, the beach can respond only by eroding until a new 

 equilibrium level is established--in the extreme case the beach 

 can virtually disappear; if the supply is somehow enhanced, the 

 beach will widen (i.e., "accrete") until equilibrium is 

 established once again. 



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