shoreline to flex enough to maintain a 

 natural beach. 



"If the beach is not there you can't 

 begin to fill the motel rooms," he says. 



Groins 



Groins on the beach are usually low 

 walls placed perpendicular to the 

 shoreline in order to trap sand moving 

 in longshore currents. Groins are made 

 with a variety of materials, including 

 sandbags, riprap, and closely spaced 

 posts of wood or concrete, at a range of 

 costs. 



Groins rebuild the beach im- 

 mediately "upstream" of the wall, but 

 they do so at the expense of the beach 

 downstream, because they intercept 

 some of the sand supply. A series of 

 groins tends to give the shoreline a 

 severely scalloped or serrated shape. 

 To work, groins must cross the public 

 beach and extend well into the surf. 

 There have been reports of strong rip 

 currents forming along the down 

 stream sides of groins. 



Rogers says that although property 

 owners can usually get a permit to 

 build groins, they are not widely used 

 on North Carolina beaches, mainly be- 

 cause they frequently fail during 

 storms. But he says that well designed 

 groins can help moderate fluctuations 

 in the banks of an inlet. 



"The reason groins can be con- 

 sidered for an inlet is that sand is being 

 pushed up into shoals inside, which 

 usually does nobody any good," 

 Rogers explains. "The idea is to catch 

 it before you lose it." 



Fabrics and 

 Artificial Grasses 



Two man-made materials have 

 raised some hopes in North Carolina 

 recently because of reports of their 

 success in building beaches or 



Photo by Jim Page 



preventing erosion. One of these is a 

 fabric that a major oil company has 

 claimed protects shorelines from ero- 

 sion. The other is an artificial sea grass 

 designed to be installed in the surf 

 zone, where it may or may not help 

 trap and collect sand. 



Rogers says that the fabric is best 

 used behind walls or bulkheads, where 

 it can help retain sand while allowing 

 water to move. But, while it may im- 

 prove the durability of a rubble retain- 

 ing wall, the fabric itself does not con- 

 trol beach erosion, Rogers says. 



"A lot of people seem to have the 

 understanding that you can lay this 

 fabric on the ground and it stops ero- 

 sion," Rogers says. "It's a good filter 

 fabric, but the success or failure of this 

 kind of system depends not on the 

 fabric but on the very large rocks that 

 you pile on top of it." 



As for the artificial sea grass, which 

 homeowners have begun to buy and in- 

 stall in some areas, Rogers suggests 

 caution: "It's by no means a new 

 method. It's been around several 

 decades, and has in general proven to 

 be ineffective in an ocean-wave en- 

 vironment." 



Much of the optimism about the ar- 

 tificial seaweed arose from reports that 

 the beach around the Cape Hatteras 

 lighthouse was rebuilding after the 

 material was installed in the surf there. 



In September 1983, a team of scien- 

 tists and engineers gathered to study 

 erosion patterns around the light- 

 house. (The team included Rogers, 

 Steve Benton, John Fisher and 

 Margery Overton of NCSU, Robert 

 Dolan and Lorance Lisle of the Uni- 

 versity of Virginia, Curt Mason of the 

 U. S. Army's Coastal Engineering 

 Research Center at Duck, and Kent 

 Turner of the National Park Service.) 



The team reported that, while the 

 Cape Hatteras shoreline shows "a 

 dominant pattern of long-term ero- 



sion," there have been occasional 

 periods of accretion. The study found 

 that beach nourishment, a newly con- 

 structed groin, and changes in wave 

 and sediment-transport patterns have 

 probably had the most influence on ac- 

 cretion at the lighthouse. 



"While there has been some buildup 

 in that area, it's also built up nearby, 

 where the artificial vegetation could 

 not have had any effect on the beach," 

 Rogers says. "The accretion seems to 

 be part of natural fluctuations in the 

 shoreline." 



Precautions 



Although Rogers advised people to 

 be careful of how they spend their 

 money on devices to control beach ero- 

 sion, he does offer some suggestions 

 about how to protect their property 

 and safety: 



— Before you build on the beach, 

 find out the estimated erosion rates for 

 the lot and build on the site that af- 

 fords the greatest protection. Your 

 local CAMA permit officer can advise 

 you. 



— Build on pilings sunk deeply 

 enough to support the house in case 

 short-term erosion removes the dunes 

 and some of the beach profile. 



— Plan the building so that it can be 

 moved when erosion threatens it. 

 Many beach houses constructed on 

 piles can be moved for a fraction of 

 their construction costs. 



— Practice dune conservation. (Sea 

 Grant researchers Ernest Seneca and 

 Steve Broome of NCSU have 

 developed techniques for planting 

 beach grasses and protecting dunes. 

 For a free copy of their book, 

 "Building & Stabilizing Coastal Dunes 

 with Vegetation," write UNC Sea 

 Grant Publications, 105 1911 Building, 

 NCSU, Box 8605, Raleigh, NC 27695- 

 8605. Ask for UNC-SG-82-05. 



—Neil Caudle 



A seawall is used to harden the shoreline at Atlantic Beach 



