them, and none to adjacent areas upcoast or downcoast. When built on a reced- 

 ing shoreline, the recession on adjacent shores will continue and may be 

 accelerated. Any tendency toward the loss of beach material in front of such 

 a structure may well be intensified. Where it is desired to maintain a 

 beach in the immediate vicinity of such structures , companion works may be 

 necessary. 



3. Functional Planning of the Structure . 



The siting of seawalls, bulkheads, and revetments is often not a difficult 

 process, since their primary function is usually to maintain existing fixed 

 boundaries. Considerations for design of such a structure include: use and 

 overall shape of the structure, location with respect to the shoreline, 

 length, height, stability of the soil, water levels seaward and landward of 

 the wall, availability of building materials, economic feasibility limits, 

 environmental concerns, and institutional constraints. 



4. Use and Shape of the Structu re. 



The use of the structure typically dictates the selection of the shape. 

 Face profile shapes may be classed roughly as vertical or nearly vertical, 

 sloping, convex-curved, concave-curved, reentrant, or stepped. Each cross 

 section has certain functional applications, as illustrated and discussed in 

 detail in Chapter 6. If unusual functional criteria are required, a 

 combination of cross sections may be used. 



A vertical- or nearly vertical-face structure lends itself to use as a 

 quay wall, or docking or mooring place. Where a light structure is required, 

 the construction of a vertical face (of sheet piling, for example) may often 

 be quicker and less expensive than other types. This ease or speed of 

 construction is important where emergency protection is needed. A vertical 

 face is less effective against wave attack, and specifically against over- 

 topping, than the concave-curved and reentrant face. The use of vertical- or 

 nearly vertical-face walls can result in severe scouring when the toe or base 

 of the wall is in shallow water. Waves breaking against a wall deflect energy 

 both upward and downward. The downward component causes scouring of the 

 material at the base of the wall. To prevent scouring, protection should be 

 provided at the base of the wall in the form of armor stone of adequate size 

 to prevent displacement, and of such gradation as to prevent the loss of the 

 foundation material through the voids of the stone with consequent settlement 

 of the armor. Vertical walls also reflect energy back offshore where resonant 

 effects may cause beach profile changes. 



Coarse rubble slopes effectively dissipate and absorb wave energy, 

 reducing wave runup, overtopping, and scour. Convex-curved face and smooth 

 slopes are least effective in reducing wave runup and overtopping. 



Concave-curved or reentrant face structures are the most effective for 

 reducing wave overtopping when onshore winds are light. Where the structure 

 crest is to be used for a road, promenade, or other purpose, this design may 

 be the best shape for protecting the crest and reducing spray. This is 

 especially true if the fronting beach is narrow or nonexistent, or if the 

 water level is above the structure base. If onshore winds occur at the same 



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