o Marsh and mangrove edges should 

 not be bulkheaded because this 

 eliminates productive fish and wild- 

 life habitat (Carstea et al. 1976, 

 Silberhorn et al. 1974). 



o Bulkheads should be set landward 

 of the mean high waterline because 

 this allows a buffer strip of shore- 

 line vegetation to remain (Carroll 

 undated, Clark 1974). 



o Amounts of suspended sediments 

 should be restricted during con- 

 struction (Carstea et al. 1975a). 



o Bulkheads which would adversely 

 affect littoral drift and sand depo- 

 sition on barrier and sand islands 

 and sand beaches are not accept- 

 able (U.S. Department of the Inte- 

 rior, Fish and Wildlife Service 

 1975b). 



Vertical wooden, steel, and con- 

 crete bulkheads provide poor habitats 

 for marine organisms (Gantt 1975). The 

 other biological considerations may be 

 found in the Summary of Physical and 

 Biological Impacts section. 



Construction Materials 



There are two structural classes of 

 bulkheads. Massive freestanding gravity 

 structures, sometimes called seawalls, 

 make up the first class (Figure 23). 

 Seawalls have two functional compo- 

 nents, the stem and the base. The stem 

 of the structure may be curved, verti- 

 cal, or inclined and is designed to with- 

 stand the full force of oncoming waves. 

 The stem generally is constructed of 

 rubble or concrete. The base often in- 

 cludes foundation piles which support 

 the structure and prevent settling, and 

 sheet pile cut-off walls which help to 

 prevent loss of foundation material (Col- 

 lier 1975, U.S. Army Corps of Engineers 

 1973b). 



The second class of bulkheads is 

 constructed either of concrete slabs or 

 sheet piles that are driven into the 

 ground and anchored by tie rods. Con- 

 struction materials include steel, con- 

 crete, timber, or combinations of these 

 materials. Pipes, cables, tires, wire 

 netting, and baled hay have also been 



used as construction materials in tem- 

 porary bulkhead structures to promote 

 the establishment of shoreline vegeta- 

 tion (Webb and Dodd 1976). Other mate- 

 rials such as plywood, sheet metal, and 

 fiberglass panels have limited useful- 

 ness (Bellis et al. 1975). 



Steel sheet piling is a commonly 

 used bulkhead construction material in 

 the Great Lakes. About 70% of all bulk- 

 head projects in the Chicago Corps of 

 Engineers District use steel sheet pil- 

 ing (Boberschmidt et al. 1976). Steel 

 sheet piling, when used to construct 

 bulkheads, should be interlocked, driven 

 into the ground, and tied back for sta- 

 bility. Steel corrodes in warm moist 

 marine climates and should be protected 

 with plastic, bitumin, concrete, or 

 other suitable materials or should be 

 made of a chemical composition resistant 

 to marine environments (Collier 1975). 

 Cellular steel sheet pile bulkheads are 

 often used in place of sheet pile bulk- 

 heads when the ground substrate cannot 

 be penetrated due to rocks near the sur- 

 face (U.S. Army Corps of Enqineers 

 1973b). 



Concrete bulkheads are commonly 

 used in Florida and other more tropical 

 climates due to their durability in com- 

 parison to steel or timber structures 

 (Gantt 1975). Concrete bulkheads may be 

 vertical, sloped, concave, convex, or 

 stair-stepped. They are, generally, 

 either cast in place or constructed of 

 concrete slabs with a cast-in-place con- 

 crete cap (Figure 24). 



Wood is the most popular type of 

 construction material (Figures 25 and 

 26). The timber should be treated with 

 a wood preservative in warmer areas 

 where decay and rot, insects, or marine 

 borers pose a problem (Collier 1975). 

 The components of timber sheet pile 

 bulkheads usually include piles, walers, 

 sheet piles, tie rods, and deadmen or 

 anchor piles (Figure 27). Piles are 

 driven or jetted into the beach, and 

 walers are bolted horizontally to the 

 landward side of the piles. Tie rods 

 are also secured to the piles and at- 

 tached to anchor piles or deadmen behind 

 the structure. Timber sheet piling is 

 bolted or nailed to the walers. Piles 

 and walers are generally made of heavy 



49 



