timed to avoid fish spawning and migra- 

 tion seasons, and times when birds are 

 nesting in the vicinity of the construc- 

 tion site. Turbidity control devices 

 should be employed whenever possible, 

 and associated dredging should be mini- 

 mized to avoid damage to the biota( Flor- 

 ida Department of Natural Resources 

 1973). Shellfish habitat and other areas 

 rich in plant and animal life should be 

 avoided. Hopper dredges seem to cause 

 the least damage to the biota (Thompson 

 1973) and should be favored over hy- 

 draulic dredges. However, the use of 

 hopper dredges is usually limited to the 

 construction and the maintenance of en- 

 trance channels. 



Construction Materials 



Breakwaters can be constructed 

 from a wide variety of materials. Gen- 

 erally, these can be classified as rock, 

 wood, concrete, metal, rubber tires, 

 filled bags, and rubber-type synthetic 

 materials (Table 1). Almost any material 

 possessing structural integrity could be 

 used in breakwater construction. 



The lifespan of breakwaters de- 

 pends greatly en the construction mate- 

 rials. For this reason, preliminary mate- 

 rial testing is necessary, both of physi- 

 cal characteristics and ability to with- 

 stand wave action. Tests of stone, for 

 example, should include specific gravity, 

 abrasion, slaking, freeze-thaw, and 

 other relevant examinations (Allison and 

 Savage 1976). Granites or basalts are 

 preferable to limestone, due to the Tat- 

 ter's tendency to abrade readily and to 

 lose weight by dissolution of solids. If 

 concrete is used, it should be alkali-re- 

 sistant. Metals should be galvanized or 

 coated to resist corrosion and wood 

 should be treated with chemical preser- 

 vatives. Whatever materials are used, 

 they should be chosen on the basis of 

 breakwater components being adaptable 

 to substitution, ability to resist corro- 

 sion and abrasion, durability, and cost- 

 effectiveness (U.S. Army Corps of Eng- 

 ineers 1973b). 



The most common facing material 

 seen on breakwaters along the United 

 States coastlines is rubble, rough stone, 

 or precast concrete in a variety shapes 

 (Figures 5 and 11). The size, weight, 



and random or patterned placement of 

 rubble components must be determined by 

 individual site studies. Other facing 

 materials include steel or concrete 

 sheet piles, timber, and gabions, which 

 are rock-filled wire baskets (U.S. Army 

 Corps of Engineers 1973b). Core material 

 is usually chosen on the basis of its 

 permeability and whether an individual 

 structure is designed to be permeable or 

 impermeable. The cap, if included, is 

 generally of rubble or precast concrete 

 (U.S. Army Corps of Engineers 1973b). 



Ex pected Life Sp an 



Data are not available concerning 

 overall life spans of breakwaters. How- 

 ever, periodic maintenance can be ex- 

 pected to prolong a structure's effec- 

 tiveness. Floating breakwaters are gen- 

 erally not as long-lived as fixed ones. 

 Breakwaters are constructed of materials 

 similar to jetties; thus, some compari- 

 sons can be made concerning lifespan. 

 Rubble mound structures, if repaired 

 when unit displacement is severe, can 

 last up to 50 yr (U.S. Army Enqineer 

 District, Portland 1975b). Steel," con- 

 crete, and timber structures should last 

 up to 35 yr, depending on site-specific 

 environmental factors (U.S. Army Corps 

 of Engineers 1973b). Lifespan also de- 

 pends on the severity of the design wave 

 for a particular structure relative to 

 the wave environment it will actually 

 encounter (Saville et al. 1965). 



Sum mary of Physical and Biological 

 Impacts 



Construction effects . Physical ef- 

 fects from placement of breakwaters are 

 similar to those for jetties, groins, 

 piers, and other structures in the near- 

 shore areas. Rock dumping, jetting or 

 driving piles, dredging to a solid bed 

 or required depth, or any other con- 

 struction-associated activity which dis- 

 turbs the bottom sediment increases tur- 

 bidity (U.S. Army Engineer District, 

 Seattle 1971) and can impact bottom 

 dwelling aquatic organisms, remove sub- 

 merged vegetation beds, drive away fish 

 and other mobile organisms, and alter 

 the existing habitat at the structure 

 site (Morton 1976, Cronin et al. 1971). 



Some degree of noise, air, and 



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