constructed of rubble mound. Physical 

 impacts from breakwater construction 

 and presence are similar to those pre- 

 viously described. Deterioration of 

 water quality is frequently a problem in 

 breakwater protected harbors (Slawson 

 1977, Carlisle 1577). Red tides (dino- 

 flagellate blooms) are severe in most 

 harbors in the Los Angeles-Long Beach 

 area (Slawson 1977) and probably occur 

 frequently wherever circulation is im- 

 paired. 



Breakwaters in the Gulf of Mexico 

 (Coastal Region 3) are used both for 

 shore protection and in harbor areas. 

 They are placed either parallel or per- 

 pendicular to the shoreline. Most act 

 as littoral drift barriers and require 

 modifications to bypass sand. Construc- 

 tion materials are rock, concrete, sheet 

 piling, timber, and scrap tires. Scrap 

 tire breakwaters are being developed 

 for protection of the Florida coastline 

 (McAllister 1977). 



Breakwaters are less common than 

 groins in south Florida (Coastal Region 

 4). Most of the existing ones are part 

 of small boat harbors. A large portion 

 of south Florida is characterized by nat- 

 ural offshore reefs and is also somewhat 

 protected by the Bahamas (McAllister 

 1977). Floating breakwaters often at- 

 tract marine animals and is one case a 

 community of marine invertebrates and 

 fish was well established on a floating 

 breakwater within a month of its place- 

 ment (G if ford 1977). 



No unique information concerning 

 breakwaters in the south Atlantic 

 (Coastal Region 5) was found. Physical 

 and biological impacts were similar to 

 those desribed for other regions. 



Sandbag sills (sand-filled nylon 

 tubes or lines of sandbags) were the 

 only type of breakwater for which in- 

 formation unique to the middle Atlantic 

 (Coastal Region 6) was found. These 

 are utilized to prevent erosion of indi- 

 vidual waterfront lots or to improve the 

 effectiveness of a groin system. They 

 are placed much farther inshore than 

 most breakwaters and are considerably 

 smaller than the usual breakwater. 

 Placement is in the subtidal zone, just 

 below mean low water, on sand beaches 



with complex patterns of littoral trans- 

 port. Physical and biological impacts 

 are expected to be insignificant though 

 no quantitative studies have been made. 

 Unless well marked, they may be a navi- 

 aation hazard to small craft at low 

 tide. 



Little information was found con- 

 cerning breakwaters in the north Atlan- 

 tic (Coastal Region 7). 



Breakwaters are frequently used in 

 the Great Lakes (Coastal Region 8) for 

 shore and harbor protection. Most are 

 shore-parallel and detached. Construc- 

 tion materials include many of those 

 listed in Table 1. One rather unusual 

 design is that of a steel or concrete 

 zig-zag wall parallel to shore with its 

 crest just above mean water level (Fig- 

 ure 9). One physical impact of break- 

 waters which is unique to the Great 

 Lakes is the enhancement and prolonging 

 of harbor icing. Protected water behind 

 breakwaters ices over earlier in the 

 fall (U.S. Army Engineer District, Buf- 

 falo 1975a) and remains frozen longer in 

 the spring. 



JETTIES 



Definition 



"A jetty is a structure extending 

 into the water to direct and confine 

 river or tidal flow into a channel and 

 to prevent or reduce shoaling of the 

 channel by littoral material. Jetties, 

 located at the entrance to a bay or riv- 

 er, also serve to protect the entrance 

 channel from wave action and cross cur- 

 rents. When located at inlets through 

 barrier beaches, they also stabilize the 

 inlet locations." (U.S. Army Corps of 

 Engineers 1973b). 



The most common type of jetty is 

 one extending into the ocean at the en- 

 trance to a bay or river (Figure 13). 

 However, training works (including train- 

 ing walls) located in estuaries and 

 along rivers to guide currents and as- 

 sist in channel deepening are also com- 

 monly called jetties. Sometimes a struc- 

 ture placed in a river or on an estua- 

 rine beach to direct currents and stabi- 

 lize the beach is called a jetty or a 

 groin (see Glossary) . 



26 



