time as high waves, a rubble slope should also be considered to reduce runup 

 on the structure face and overtopping due to wind forces. 



A stepped-face wall provides the easiest access to beach areas from 

 protected areas, and reduces the scouring of wave backwash. 



5 . Locatio n of Structure with Respect to Sh o reline . 



A seawall, bulkhead, or revetment is usually constructed along that line 

 landward of which further recession of the shoreline must be stopped. Where 

 an area is to be reclaimed, a wall may be constructed along the seaward edge 

 of the reclaimed area. 



6 . Length of Structure . 



A seawall, bulkhead, or revetment protects only the land and improvements 

 immediately behind it. These structures provide no protection to either 

 upcoast or downcoast areas as do beach fills. Usually, where erosion is 

 expected at both ends 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 at the ends. Short-term beach changes due to storms, as well 

 as seasonal and annual changes, are design considerations. Erosion updrift 

 from such a structure will continue unabated after the structure is built, and 

 downdrift erosion will probably be intensified. 



7. Height of Structure . 



Seawalls, bulkheads, and revetments can be built so high that no water 

 could overtop the crest of the structure, regardless of the severity of wave 

 attack and storm surge levels; however, it is usually not economically feasi- 

 ble to do so. Wave runup and overtopping criteria on which the height of a 

 structure should be based can be estimated from data presented in Chapter 7, 

 Section II (WAVE RUNUP, OVERTOPPING, AND TRANSMISSION). Physical model tests 

 can be carried out if greater accuracy is warranted. 



8 . Determination of Ground Elevation in Front of a Structure . 



Seawalls and revetments are usually built to protect a shore from the 

 effects of continuing erosion and to protect shore property from damage by 

 wave attack. The exact effect of such a structure on erosion processes is 

 usually not determinable, but can be estimated using the method described in 

 this section. For safety, even though erosion processes seem to have been 

 halted or reversed, the designer should consider the possibility that they 

 will continue. Changes in the beach profile subsequent to construction of a 

 seawall or revetment should be carefully monitored, as they may produce 

 adverse long-term effects. 



As an initial short-term effect, scour may be anticipated at the toe of 

 the structure, forming a trough with dimensions governed by the type of 

 structure face, the nature of wave attack, and the resistance of the bed 

 material. At a rubble slope seawall, scour may undermine the toe stone, 

 causing stones to sink to a lower, more stable position. The resultant 

 settlement of stone on the seaward face may be dealt with by overbuilding the 

 cross section to allow for settlement. Another method is to provide excess 



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