enough landward to allow predictable recession of the beach in a 

 reasonable period of time, usually as long as the "useful length of 

 life" of the structure. Because of current general rising sea level, 

 setback lines may require frequent review as increased sea height 

 forces the beach inland and the shore profile adjusts to equilibrium 

 (Figure 22). 



Figure 22. Recession of beachfront in response to a relative rise 



in sea level over a shore slope of one percent (Source: Reference 55), 



Movement of dune (erosion) - approximately 100 times "d" 



Profile before rise In sea Iflvel 



V 



^""mmmmm, 



''''''''-''''«''««''^m„.„,„,^„^^^^^ 



Artificial beach nourishment is a desirable method of beach protec- 

 tion in many situations and is nearly always preferable to structural 

 methods. If the beach reduction is due to natural causes, any effort to 

 maintain the beach is probably futile. If it is due to man-made disrup- 

 tion of the equilibrium, man must become involved in the system to the 

 extent that he has disrupted it. He must provide sand and often the 

 energy to keep it moving [56]. However, nourishment projects should not 

 become substitutes for balanced long-term beachfront management. 



With the recent knowledge of the ecological values of estuarine 

 ecosystems (and of the fact that estuarine sands are often too fine to 

 withstand ocean currents) estuarine and bay sources are usually not 

 considered available for beach nourishment. 



Also removal of sand is known to threaten the beach profile because 

 of reduction of storage, whether taken from dunes, the beach itself, or 

 from the longshore bar or nearshore submerged bottoms. Shore erosion 

 problems would not necessarily be solved by bringing sand from some other 

 part of the same beach system. 



The two major sources of beach nourishment are the open ocean 

 and inlets or other areas of accretion where the supply is constantly 

 repleneished by natural forces, particularly when navigation dredging 

 is continuously required. 



Ill 



