Bulkheads and seawalls, generally 

 built to separate land from water areas, 

 can serve a number of diverse functions 

 (see Structure Functions section). They 

 are found in many types of coastal hab- 

 itats including areas with eroding shore- 

 lines, narrow fringe marshes, salt and 

 freshwater marshes, and other areas 

 with eroding mud, silt, sand, or shin- 

 gle beaches. Because bulkheads and 

 seawalls are expensive to build, they 

 typically are found in the developed 

 areas where shorefront real estate is 

 valuable. 



Placement C on straints 



Engineering. A number of factors 

 must be considered in bulkhead design 

 and construction. Important considera- 

 tions include height and location on 

 beach, toe protection, shape of the 

 structure, pile penetration, structural 

 anchorage, alignment with adjacent 

 bulkheads, and erosion of supporting 

 beach materials from behind the struc- 

 ture. 



Many authors recommend that bulk- 

 heads be constructed above the mean 

 high waterline for both engineering and 

 biological reasons (see Biological Con- 

 straints section). Bulkhead height and 

 placement on the shoreline should be 

 such that waves do not overtop the 

 structure and erode away supporting 

 beach material, or saturate the soil and 

 cause structural failure due to the 

 buildup of hydrostatic pressures. When 

 bulkheads are located on the shoreline 

 so that they are regularly exposed to 

 wave action, the equilibrium of the shore 

 profile is disrupted. The foreshore typ- 

 ically steepens and higher waves reach 

 the structure causing increased toe 

 scour and structural damage from un- 

 dermining (Earattupuzha and Raman 

 1972). 



Toe protection can help prevent 

 scour at the toe of a bulkhead and also 

 protect the structure against changing 

 beach profiles. Wave energy is deflect- 

 ed as waves break against bulkheads 

 (Figure 21). Wave energy which is not 

 dissipated by the structure can cause 

 scouring of material at the toe of the 

 bulkhead. Important factors in deter- 

 mining toe scour include wave height 



and steepness, beach slope, roughness 

 and slope of the bulkhead, and beach 

 sand size (Chestnutt and Schiller 1971, 

 McCartney 1976). In general, structures 

 which are not vertical and have rougher 

 faces, such as revetments or stepped 

 concrete seawalls, tend to reflect less 

 wave energy seaward and are less affect- 

 ed by toe scour (Coen-Cagli 1932, Pallet 

 and Dobbie 1969, Sanko 1975). 



Adequate pile penetration is anoth- 

 er means of preventing undermining of 

 bulkheads from toe scour. It also pre- 

 vents the toe of the structure from 

 sliding seaward (Collier 1975). Sheet 

 piling must be driven to a depth to 

 withstand the outward pressure from ma- 

 terials behind the structure (Ayers and 

 Stokes 1976). Generally pilings are 

 driven to a depth such that at least 

 two-thirds of the piles are below ground 

 (Michigan Sea Grant Advisory Program un- 

 dated). 



Bulkheads should be securely an- 

 chored at their ends and along their 

 length. Adequate tiebacks along the 

 length of the structure prevent seaward 

 tilting (Collier 1975) (Figure 22). Tie- 

 back rods should be coated or wrapped to 

 prevent corrosion. Both ends of a bulk- 

 head should be secured to prevent struc- 

 tural failure due to erosion of materi- 

 als from behind the bulkhead and from 

 the shore adjoining the structure. Wing 

 or cut-off walls are two methods of pre- 

 venting such erosion and of tying the 

 structure to the shore (Collier 1975, 

 Michioan Sea Grant Advisory Program un- 

 dated). In areas where bulkheads are 

 adjacent to each other additional an- 

 chorage comes from alignment of the 

 structures. Irregular alignment of bulk- 

 heads can cause "side erosion and cavi- 

 tation by reflected corner waves" (Bauer 

 1975). 



Supporting materials behind bulk- 

 heads may be washed away by leaching of 

 sand through cracks, weep holes, and 

 joints in the structure. Addition of a 

 filter cloth to the structure's design 

 will prevent such erosion and allow wa- 

 ter drainage(Barrett 1966, Collier 1975, 

 Dunham and Barrett 1974). In areas where 

 the soil has a high silt or clay con- 

 tent, the addition of a 6-inch (15-cm) 

 sand pad between the filter cloth and 



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