constructed. Comrr unities which occur 

 on breakwaters are those characteristic 

 of intertidal and subtidal rocky shores. 

 The exposed side is often characterized 

 by communities adapted to high-energy 

 environments while the back side is 

 generally inhabited by organisms typical 

 of less hostile environments. 



Placement Constraints 



Enqineering. 



Breakwater design 

 must consider the physical environment 

 in which the structure is to be placed, 

 the availability and cost of construction 

 materials, and the function of the struc- 

 ture. In addition to these factors, the 

 effects of the breakwater upon its envi- 

 ronment must be considered. 



Design criteria for fixed breakwa- 

 ters must consider several factors of 

 the physical environment, including 

 wave climate, sediment transport, bot- 

 tom topography, characteristics of the 

 protected areas, tides, and currents at 

 the site. The design wave and the max- 

 imum wave must be determined. At this 

 point a trade-off is often necessary be- 

 tween economic feasibility and failure- 

 proof design (Saville et al. 1965). A 

 generalized diagram of a typical rubble- 

 mound breakwater is contained in Fig- 

 ure 8. 



After the design wave is determin- 

 ed for the construction site, other fac- 

 tors must be considered. Studies must 

 be made of the subtrate upon which the 

 breakwater will rest to determine what 

 precautions must be taken to prevent 

 settling and erosion of foundation mate- 

 rial (Saville et al. 1965). Prevention of 

 erosion and settling is often accomplish- 

 ed by using filter blankets cr mats sim- 

 ilar to those used under revetments. 

 This filter cloth material prolongs the 

 settling of the breakwater stones into 

 the substrate, which occurs due to the 

 weight of the materials and slight move- 

 ment due to wave attack. The core, 

 cap, facing, and foundation material of 

 the breakwater must be chosen to pre- 

 vent damage or component displacement 

 by the design wave. 



Wave deflection and absorption is a 

 primary function of breakwaters. This 

 function is affected by the type of 



facing material, face slope, structure 

 height, water depth, and wave climate at 

 the site. A breakwater must be designed 

 and constructed to allow breaking waves 

 to expend their energy over a large area 

 rather than a single point (Coen-Cagli 

 1932). The outer slope of a breakwater 

 should be a low angle. The crest should 

 reach a height which either prevents 

 overtopping by the design wave or allows 

 only a preplanned amount of overtopping. 

 The design should also include provi- 

 sions to prevent piling up of water be- 

 hind the structure and to prevent trans- 

 mitted waves from damaging facilities 

 behind the breakwater. The required 

 width and height of a breakwater rela- 

 tive to the height and wave length of 

 the design wave are discussed by Saville 

 et al. (1965). The conventional rubble 

 mound or rock construction is most typ- 

 ical, although numerous other designs 

 have been employed with varying degrees 

 of success (Figure 9). 



Floating breakwaters are sometimes 

 a functional alternative to fixed struc- 

 tures, but they have some unique design 

 criteria. Unless they are designed to be 

 constantly in motion, some sort of an- 

 chor is necessary. Piles or other anchor 

 devices are generally placed on the bot- 

 tom with lines, cables, or chains at- 

 tached to the floating structures (Fig- 

 ure 10). These anchor lines should have 

 a tested strength at least twice that of 

 the design load and should be as nearly 

 horizontal as possible (Killer 1974b). 



Most breakwaters protect waterways, 

 consequently, their siting is dictated 

 by the configuration of the shore and by 

 the desired harbor design. Many existing 

 breakwaters are in the worst possible 

 locations as far as obstruction of lit- 

 toral drift is concerned (Snodgrass 

 1964). In the future, design modifica- 

 tions and breakwater locations should 

 cause minimal disruption of longshore 

 transport. Cn relatively shallow, 30 ft 

 (9 m) or less, open shorelines, fixed 

 breakwaters are considered the better 

 choice (Seymour and Isaacs 1974). Float- 

 ing breakwaters interfere less with sand 

 movement, water circulation, and fish 

 habitat and are preferred for temporary 

 installations in deep water, or where 

 bottom conditions are unsuitable for 

 placement of a fixed structure (Miller 



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