more cheaply than any other type. This may be an important consideration 

 where emergency protection is needed. Against wave attack^ and specifically 

 in regard to reduction of overtopping, a vertical face wall is more effective 

 than anjjr but the concave curved and re-entrant face walls. 



1160 A backward sloping or convex curved face wallo or revetment is 

 the least effectivdof all "types against wave attack for a given height of wall. 

 It is, however, more adaptable to use as emergency protection, (sand bag, 

 or dumped stone mounds, for example) than the other types. Actually the 

 use of such a wall type should be restricted to those areas in which wave 

 overtopping is not a problem, or where esthetic, emergency, or strxictural 

 considerations prohibit the use of other wall shapes. 



117. The concave curved or re-entrant faced walls are the most effective 

 in reducing wave overtopping to a minimum. Where the wall crest is to be 

 used (for a roadway or promenade for example), a wall so designed will be 



of the most desirable shape for protecting the crest. This is especially 

 true if the beach is narrow or entirely absent, and the water level is over 

 the base of the wall during high or storm tides. 



118. Stepped face walls provide the most ready access to beach areas 

 from protected areas and in addition act to disrupt the scouring action cf 

 the wave backwash. 



119. Location of Structure With Respect to Shore Line . - Ordinarily 

 the locatidn of a seawall or bulkhead is determined more by the needs of 

 the locale than by any consideration of possible wave attack. In general 

 a seawall would be constructed along that line landward of which further 

 recession of the shore ]ine cannot be permitted. VJhere an area is to be 

 reclaimed^ the seawall wou].d be constructed along the seaward edge of the 

 reclaimed area. A seawall constructed in the water, isolated from shore, 

 becomes an offshore breakwater, 



120. Length .' - A seawall, revetment or bulkhead protects no more 

 than the land and improvements iraraediately behind it. No protection is 

 afforded either to upcoast or downcoast areas as is the case with beach 

 fills. However, it must be emphasized that where erosion may be expected 

 to occur at either end of a structure, wing walls or tie-ins to adjacent 

 land features must be provided to prevent flanking and possible progressive 

 failure of the structure from the ends. Short term beach changes due to 

 storms, as well as seasonal and annual changes must be accounted for. It 

 must be remembered that changes updrift from a seawall will continue un- 

 abated after the wall is built, and that downdrift, these changes will 



be, if anything, intensified. 



121. Height of Structure . - Seawalls can be designed to be of such 

 height that no water would overtop the wall regardless of wave attack. 

 However, it is not ordinarily economically '^feasible to do so^ and certain 

 lesser criteria must be adopted. For examplLe,, if it is desired to prevent 

 overtopping water which has damaging horizontal momentum, the wall crest 



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