1974b) . If disruption or obstruction of 

 littoral drift is unavoidable, provisions 

 must be made to allow for bypassing 

 sand to avoid starvation of downdrift 

 beaches and shoaling of waterways. 



Breakwaters are used for shore 

 protection either with other structures 

 (e.g., revetments, seawalls, groins) or 

 as an alternative to them. Steep shore- 

 lines and sandy beaches can be protect- 

 ed and sand accretion can be caused or 

 enhanced by breakwaters. Sometimes a 

 breakwater is placed in the intertidal or 

 subtidal zone as an erosion prevention 

 device (Figure 9). 



Maintenance requirements must be 

 considered when choosing a breakwater 

 design. Floating breakwaters are more 

 vulnerable to extensive wave action and 

 often require more frequent maintenance 

 than fixed structures. Vertical face 

 breakwaters must be thick or firmly 

 braced, or high waves will damage them. 

 Rubble mound structures can generally 

 withstand extensive wave action, but 

 are vulnerable to erosion at the toe, 

 particularly at breaches and ends which 

 can lead to a slope failure (Savffle et 

 al. 1965). Overtopping waves can dis- 

 lodge cap rock. Extended storms can 

 disarrange facing stones and cause 

 slumping or structural failure. Sub- 

 merged rubble mound structures with 

 well-chosen facing material probably re- 

 quire the least maintenance of all types 

 (Saville 1960). 



The physical effects of construc- 

 tion and presence of a breakwater must 

 be considered in design and location. 

 These effects are discussed in the Sum- 

 mary of Physical and Biological Impacts 

 section. Design of long-lasting, func- 

 tional breakwaters is not a simple pro- 

 cess. A thorough discussion of design 

 criteria of rubble mound breakwaters is 

 found in Saville et al. (1965). 



Socioeconomic. 



Offshore fixed 



breakwaters tend to be more costly than 

 shore-connected structures, partly due 

 to the problem of transporting the con- 

 struction materials offshore and partly 

 due to the logistics of maintenance(U . S. 

 Army Corps of Engineers 1973b). A 

 less costly breakwater is the scrap tire 

 artificial reef. Usually placed to provide 



an artificial fish habitat, it can also 

 function as a breakwater. They are 

 inexpensive and are considered a good 

 method of disposing of used tires 

 (Alfieri 1975). Floating breakwaters are 

 also generally less expensive to build 

 and maintain than fixed structures, but 

 provide substantially less wave attenua- 

 tion (Seymour and Isaacs 1974). The 

 cost of shore-connected fixed breakwa- 

 ters compares with that of jetties of 

 similar size. 



Low or submerged offshore break- 

 waters are usually unobtrusive and do 

 not interfere with aesthetic enjoyment of 

 the shore. Their visual impact is low, 

 and they are usually far enough from a 

 beach that they do not interfere with 

 recreation (Cole 1974). In some cases, 

 their presence can contribute to the at- 

 tractiveness of a beach since they serve 

 to attenuate incoming waves and provide 

 a sheltered, low wave energy area for 

 recreation. However, construction activ- 

 ities may hamper recreational use of the 

 shoreline to a considerable degree, and 

 the presence of a breakwater may lead 

 to changes in shoreline topography. 

 These changes could be either beneficial 

 or detrimental to recreation. The con- 

 struction of a breakwater can cause 

 secondary impacts, such as changes in 

 use patterns and accumulation of litter. 

 Breakwater-associated restrictions on 

 future public use of an area should be 

 considered before the structure is plac- 

 ed. 



Biolooical. Fixed breakwaters are 



subject to the same biological placement 

 constraints as jetties, groins, revet- 

 ments, and bulkheads. Riprap or durrp- 

 ed stone faces are biologically more de- 

 sirable than flat faces since they pro- 

 vide more habitat for aquatic species. 

 Sloping faces are preferable because 

 vertical faces lack the shallow water 

 zone and create less hard bottom sub- 

 strate. Breakwaters should not be al- 

 lowed to interfere with fish migratory 

 runs or spawning areas (Persaud and 

 Wilkins 1976). The base of the break- 

 waters should be protected so that 

 scouring does not affect structural 

 integrity and, therefore, the aquatic 

 organisms in the area. 



Construction activities should be 



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