of construction projects in the coastal 

 environment. The farfield effects, such 

 as the potential contribution to hypersa- 

 linity and associated ecological modifica- 

 tions, are not as well known. It is 

 probable that potential effects of cause- 

 ways on the marine environment will be 

 debated for many years. At present 

 the key issue controlling the replace- 

 ment project is the potential loss of life 

 or serious injury that could result due 

 to structural failure. 



dynamics in this coastal region. A 

 hypothetical island is nearly "breached 

 at one point, so a groin is built down- 

 drift to cause accretion at the weak 

 area. The construction of the groin 

 approximately 50 ft (15 m) long by" 5 ft 

 (1.5 m) wide causes little environmental 

 damage because it is small. Turbidity, 

 destruction of bottom habitat, and 

 beach disturbance are minor when view- 

 ed in light of the extent of nearby 

 shoreline. 



CASE HISTORY - GROINS IN COASTAL 

 REGION 5 - SOUTH ATLANTIC 



Coastal region from Cape Canaveral 

 to Cape Hatteras is characterized by 

 barrier islands, marshes, and estuaries 

 (Virginia Institute of Marine Science 

 1976). The barrier beaches are long, 

 narrow sand beaches separated from the 

 shore by embayments of varying widths 

 up to 30 mi (48 km). Most of the shore- 

 line lacking barrier beaches is also 

 sandy and flat and is broken by estuar- 

 ies and tidal marshes. The sand is fine 

 and is easily transported by the sea. 

 The natural beach erosion resulting 

 from the storms and tides has been ac- 

 celerated by the often carelessly plan- 

 ned placement of shoreline structures, 

 such as groins, bulkheads, jetties, and 

 breakwaters (Bruun and Manohar 1963). 



Some assumptions can be made 

 about an undisturbed barrier island a 

 mile or more in length and separated 

 from adjacent islands by wide inlets. 

 Natural processes will cause erosion 

 and accretion of sand at various points; 

 the storm winds and tides will break 

 through islands, opening a channel into 

 the lagoon while the other channels will 

 close. The barrier islands will, over 

 time, change in shape, size, and topo- 

 graphy. The plants and animals found 

 there will, as they always have, adapt 

 to these changes. Unfortunately, man is 

 often not tolerant of normal shoreline 

 dynamics. Beaches must be stabilized 

 to provide recreation, real estate, in- 

 dustrial sites, or harbors. 



Insufficient data were available to 

 provide a case history, so a hypotheti- 

 cal situation was developed to demon- 

 strate the effects of groins on shoreline 



There are effects which do not ap- 

 pear immediately. The groin interrupts 

 the littoral transport of sand, causing 

 it to accumulate updrift. The beach 

 updrift of the groin grows higher and 

 extends out nearly the length of the 

 structure. The updrift area is protected 

 from erosion forces by a broad expanse 

 of sand. This does little harm to the 

 resident organisms because it is a slow 

 accumulation process and not different 

 from that to which they have adapted. 

 The beach recedes downdrift since its 

 normal supply of sand now lies updrift 

 of the groin. If unchecked, it will re- 

 cede until a breach occurs and the sea 

 flows into the lagoon. The natural pro- 

 cess has, therefore, been displaced in 

 time and space. To protect the human 

 investment, another groin is built and 

 another until the barrier beach is en- 

 tirely protected by a vast groin field. 

 Each time a minor amount of damage is 

 done to the environment, a few square 

 feet of habitat is lost. However, in the 

 mile of barrier beach, there could even- 

 tually be as many as 50 groins. The 

 amount of habitat lost becomes more 

 significant. 



One little discussed effect of beach 

 stabilization on barrier island systems is 

 that of changing the physical and chem- 

 ical characteristics of the estuaries and 

 embayments lying behind the barrier 

 islands. Periodic wave overwash or 

 dune breaching allows seawater to reach 

 behind the islands, causing salinity var- 

 iations. Plants adapted to such an alter- 

 ed environment survive, while others do 

 not. When the beach is stabilized, suc- 

 cession is toward plants not well adapt- 

 ed to oceanic conditions (Bolan et al. 

 1973). The advantages or disadvantages 

 of this situation depend on what is 



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