deposit (Figure 18) [61]. If the deflected wave forces erode away sand at 

 the footing of the structure, the beach will disappear and the seawall can 

 become undermined and collapse. 



Figure 18. Erosion of beach area caused by wave energy deflected 

 in front of a seawall (Source: Reference 55). 



'■Future fill 



t 



(AFTER) 



Profile after time lapse 

 Note that profile Is steeper am 

 narrower, that recreational area 

 has diminished or disappeared. 



' mmwM^m^^/M'>'^^'i'^^^''^^^'>'^'>^mmM/ 



4.4.3 Revetments 



Revetments are built to absorb and reflect wave energy at the beach 

 front and are constructed from one or more layers of rock (riprap) or 

 concrete placed on the slope face of a dune or bluff (Figure 19). 



Revetments constructed of crushed stone and large riprap are 

 generally more desirable environmentally than solid-faced seawalls. If 

 properly designed and constructed, they will permit the natural flow of 

 groundwater and runoff to pass through the structure. Other ecological 

 advantages of revetments include a design that can easily be built to 

 conform to the natural configuration of the shoreline, and a submerged 

 area of the structure that permits the attachment of aquatic organisms. 



107 



