Photo by Steve Murray 



Sandbag groins are used to reclaim lost beachfront 



worth of erosion overnight. And, 

 although much of the sand lost during 

 storms returns, gradually, with calmer 

 weather, that is no consolation to 

 someone whose house collapsed after a 

 storm tide swept the land right out 

 from under it. 



"One of the troubles with predicting 

 erosion rates is that we really do have 

 no idea how to predict what the short- 

 term erosion is going to be like during a 

 major storm," Riggs says. "In a major 

 hurricane, the barrier island itself be- 

 comes the surf zone, with twenty-foot 

 waves crashing against the buildings. 

 You can't design anything to with- 

 stand that." 



There are never very many people or 

 machines around logging data and tak- 

 ing notes during a major hurricane. 

 And, the exact interaction of waves, 

 wind, sand and buildings is still un- 

 known. Also, the mathematical models 

 available for predicting short-term ero- 

 sion do not take into account all of the 

 variables. 



John Fisher and Margery Overton, 

 two North Carolina State University 

 (NCSU) civil engineers, are doing Sea 

 Grant research into one of those 



variables — the role of dunes in short- 

 term storm erosion. They say that 

 predictive models have been based on 

 the assumption that a storm would 

 take as much sand from the dunes as it 

 needed to offset the increased wave 

 energy and reassert what has been 

 called a "dynamic equilibrium." 



"The old model depends on looking 

 at the beach profile if an extreme 

 storm took the beach to an equilibri- 

 um, on the assumption that beaches 

 tend to erode to a stable profile, a 

 geometric shape," Fisher says. 



And Overton continues: "In the case 

 that you have a shorter-term storm, a 

 model like that is not going to be ap- 

 propriate, because the beach won't 

 have had time to reach that state." 



Fisher and Overton are using a wave 

 tank to simulate dune erosion and 

 suggest ways to shape their model. 

 They are trying to find how much sand 

 is eroded from a dune with each 

 "uprush" of water, so that, given the 

 strength and number of uprushes, and 

 the storm's duration, they may be able 

 to predict the rate of dune loss. 



"I think the motivation for this, in 

 terms of the state's interest, is that the 



FEMA guidelines (federal flood in- 

 surance) assume that if there are dunes 

 present, then the waves will not breach 

 them, and that therefore dunes are 

 barriers to storm penetration," Fisher 

 says. "But we all know that dunes are 

 lost. Areas that look relatively safe on 

 FEMA maps turn out to be not very 

 safe." 



Fisher and Overton say they plan to 

 collaborate with scientists in Holland, 

 where battling the sea is a way of life. 

 Fisher says the Dutch are doing the 

 most advanced work in beach 

 processes. 



"They're afraid that when that big 

 storm comes along, most of the low- 

 lying parts of Holland will go with it," 

 Fisher says. "They want to be sure 

 that they know just how stable their 

 dunes are." 



While scientists and public officials 

 grapple with the immediate problem of 

 how to improve the guidelines for 

 coastal construction, most of them 

 agree with the geologists that no com- 

 puter model, building code or setback 

 rule can guarantee a beach house 

 safety. The forces behind beach ero- 



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