bury most existing commercial oyster 

 beds (Jefferson 1974). Jefferson (1974) 

 also blames jetties for contributing to 

 modification of estuarine salt marsh 

 habitats. 



Jetties are commonly found at 

 coastal inlets throughout southern Cali- 

 fornia (Coastal Region 2). In several 

 cases, they are associated with man- 

 made harbors (Reish 1962). Rubble 

 mound construction utilizing rock is 

 most common. No placement constraints 

 are unique to this coastal region. Sea 

 mussels, barnacles, limpets, snails, and 

 other sessile and cryptic organisms pop- 

 ulate most of southern California's jet- 

 ties (Reish 1964). A green algae, Ulva 

 dactylifera , is a pioneer species on new- 

 ly constructed jetties (Reish 1969) and 

 is soon joined by a variety of marine 

 animals. No unique construction related 

 physical or biological impacts were iden- 

 tified for Coastal Region 2. Long-term 

 impacts were similar to those previously 

 described. 



Jetties in the Gulf of Mexico( Coast- 

 al Region 3) are placed in inlets in bar- 

 rier islands, as well as at river mouths. 

 Placement constraints are those previ- 

 ously described. Most are rubble mound 

 structures constructed of stone, includ- 

 ing granite. Varying salinity and cur- 

 rent regimes often exist on opposite 

 sides of jetties, and if the structure is 

 hooked to protect a harbor, there may 

 often be varying wave climates inside 

 and outside (Gifford 1977). Jetties pro- 

 vide a habitat for sessile and cryptic 

 organisms that attract fish and birds. 

 The physical and biological impacts of 

 jetties have been described previously. 

 In addition to those described, Hastings 

 (1972)reported that fish from more trop- 

 ical areas were found in the vicinity of 

 jetties. On the channel side of jetties, 

 the organisms tend to be those with a 

 greater tolerance for the rapid salinity 

 changes, periods of low water clarity, 

 and strong tidal currents while those on 

 the outside were tolerant of surf condi- 

 tions (Hastings 1972). Hastings (1972) 

 further reported that most fish found 

 near jetties were secondary consumers. 



Jetties are common in south Florida 

 (Coastal Region 4) and are found at in- 

 lets and harbor mouths both on the 



mainland and on barrier islands. They 

 are used to stabilize inlets, train cur- 

 rents, and protect beaches. Lying per- 

 pendicular to the shoreline, they extend 

 beyond the surf zone. Placement con- 

 straints are those generally applicable 

 to jetties everywhere. However, the 

 Florida Department of Natural Resources 

 (1973) has pointed out that jetties are 

 not permanently successful in fulfilling 

 their function unless they are integrat- 

 ed with other shore protection measures 

 as part of a comprehensive program cov- 

 ering large stretches of shoreline. No 

 physical or biological impacts unique to 

 this coastal region were found. 



No data were found that were unique 

 to jetties in the south, middle, or 

 north Atlantic (Coastal Regions 5, 6, or 

 7.) 



Jetties in the Great Lakes (Coastal 

 Region 8) are often constructed of mate- 

 rials other than rubble mounds. Steel 

 sheet pile cells, cassions, and timber, 

 steel, or concrete cribs are also uti- 

 lized. Timber and steel sheet piling in 

 single rows are sometimes used in shel- 

 tered areas (U.S. Army Corps of Engi- 

 neers 1973a). 



GROINS 



Definition 



A groin is a rigid structure built 

 out at an angle (usually perpendicular) 

 from the shore to protect it from ero- 

 sion or to trap sand. A groin may be 

 further defined as permeable or imper- 

 meable, depending on whether or not it 

 is designed to pass sand through it. 



Groynes (British), spur dikes, and 

 wing dams are included in this defini- 

 tion. Sometimes the word jetty is used 

 interchangeably with groins; however, 

 jetties generally have a different func- 

 tion. Under certain conditions a struc- 

 ture may be carrying out functions nor- 

 mally associated with both jetties and 

 groins. An example would be directing 

 stream flow in a river, while concurrent- 

 ly stabilizing a beach. 



Structure Functions 



The most common function of a groin 



33 



