File:Coast watch (1979) (20659769805).jpg

Title: Coast watch
Identifier: coastwatch00uncs_1 (find matches)
Year: 1979 (1970s)
Authors: UNC Sea Grant College Program
Subjects: Marine resources; Oceanography; Coastal zone management; Coastal ecology
Publisher: (Raleigh, N. C. : UNC Sea Grant College Program)
Contributing Library: State Library of North Carolina
Digitizing Sponsor: North Carolina Digital Heritage Center

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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- Continued on next page

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