wider beach is simply shore protection, 

 and the wider beach serves no other 

 functional purpose, then the upland 

 area can be protected by means of re- 

 vetments, bulkheads, or seawalls as 

 alternatives to groins. 



The negative impact most often 

 associated with groins is their tendency 

 to starve downdrift beaches of littoral 

 sand. An offshore breakwater will have 

 this same effect so it does not repre- 

 sent an attractive alternative if down- 

 drift starvation is to be avoided. Direct 

 armoring of the shoreline by the revet- 

 ments, bulkheads, or seawalls can have 

 some effect on shorelines immediately 

 downdrift; but the impact will normally 

 be less than that of groins. Of course, 

 these structures will have impacts of 

 their own which are described elsewhere 

 in the report. 



Artificial beach nourishment by 

 dredging or truck hauling from areas of 

 sand surplus probably represents the 

 most attractive alternative to groins in 

 terms of preventing starvation of down- 

 drift beaches. In fact, beach nourish- 

 ment may cause some short term impacts 

 which can constitute a problem if done 

 during periods of recreational uses of 

 the beach area. 



Regional Considerations 



No information was found that was 

 unique to groins in the north Pacific 

 (Coastal Region 1). 



Groins are common in those por- 

 tions of southern California (Coastal 

 Region 2) where beaches exist. Though 

 permeable groins with removable panels 

 are sometimes used (Riese 1971), beach 

 nourishment is usually required (Carlisle 

 1977). Southern California had a large 

 volume of littoral drift (Berg and Watts 

 1971), but it has decreased in recent 

 years due to reduced volumes of sand 

 reaching the sea from the uplands and 

 from loss of sand into offshore subma- 

 rine canyons (Carlisle 1977). They also 

 provide a habitat for rocky shore or- 

 ganisms (U.S. Army Engineer District, 

 Los Angeles 1974d). 



Groins are frequently used as al- 

 ternatives to seawalls and bulkheads for 



shore protection in the Gulf of Mexico, 

 south Florida, and the south Atlantic 

 (Coastal Regions 3, 4 and 5). They are 

 rare~\y completely successful unless they 

 are planned as part of an area-wide com- 

 prehensive shore protection program 

 (Florida Department of Natural Resources 

 1973). They should be constructed only 

 where the angle of incidence of waves 

 with the shore is small (Herbich and 

 Schiller 1976). The height should be 

 kept low, no more than 1 ft (0.3 m) 

 above normal high water. They should 

 terminate at the 3 ft (0.9 m) depth and 

 the length should be no more than 100 ft 

 (30.5 m) (Collier 1975). Construction 

 materials on the Florida coastline vary, 

 but preformed concrete is probably more 

 commonly used than stone due to the lat- 

 ter 's scarcity in much of the State. 

 Groins generally have little effect on 

 the biota compared to other larger 

 structures, such as jetties and break- 

 waters (Gifford 1977). 



Sand-filled nylon bags were used in 

 an experimental groin field in North 

 Carolina (Machemehl and Bumgarner 1974). 

 They were easily damaged and shortlived, 

 but inexpensive compared to other con- 

 struction materials. They were also re- 

 latively easy to place. 



Groins are common in the middle 

 Atlantic (Coastal Region 6). One study 

 reported 45 such structures in only 

 8,400 ft (2,560 m) of shoreline in Ches- 

 apeake Bay (Schultz and Ashby 1967). 

 Rock construction worked most satisfac- 

 torily and required the least mainte- 

 nance in this area. Well-ring construc- 

 tion was tried, but proved unsatisfac- 

 tory since some of the rings washed away 

 and maintenance requirements v/ere high 

 (Schultz and Ashby 1967). Circulation 

 patterns in Chesapeake Bay areas were 

 altered by groin placement. This affect- 

 ed erosion patterns, as well as nutrient 

 and sediment accumulation rates in 

 marshes (Carstea et al. 1975a). When 

 benthic invertebrate loss and gain due 

 to construction of groins were compared, 

 it was estimated that the net effect was 

 neither beneficial nor detrimental (U.S. 

 Army Engineer District, New York 1976). 

 The same document reports that fish will 

 be attracted to groin areas. 



Groins are common shore protection 



43 



