In the eye of a storm, not all beaches are created equal. As my colleague Mireya Navarro and I just reported in The Times, some seaside communities fared better than others when Hurricane Sandy surged into New Jersey and New York in late October. Specifically, towns that preserved or restored their sand dunes suffered far less damage ? millions of dollars less ? than those that did not maintain them.
But as some experts point out, storm-buffering sand dunes alone will not save the day. An array of efforts are needed to effectively reduce storm damage to coastal communities.
?If I was king, we would restore dunes, but we wouldn?t rebuild destroyed homes close to the beach, and we?d move some buildings back anyhow,? said Orrin H. Pilkey, the James B. Duke Professor Emeritus of Earth and Ocean Sciences at Duke University. ?We would also put in regulations prohibiting intensification and development.?
Much of the dune debate leaves out those factors, Dr. Pilkey said. It?s a problem, he said, given that a severe storm will breach or remove even a large dune system. Whether a system holds up during the storm depends upon its size, the amount of vegetation anchoring the dunes and the storm?s ferocity.
A smaller storm of a long duration can wreak just as much damage as a larger storm like Hurricane Sandy that delivers its surge in a single blow. ?You need to assume that the dunes will be breached,? Dr. Pilkey said.
As our article mentioned, beachfront communities in New York State and New Jersey served as testing grounds for the effectiveness of dune barriers during Hurricane Sandy. In Bradley Beach, N.J., several miles of restored dunes were breached, although smart development decisions prevented excessive damage for residents.
The storm pushed the community?s 15-foot-high dunes flat, leveling them, along with a boardwalk set about 200 feet back from the beach, and funneling water onto the adjacent road. The dunes absorbed much of the storm surge?s force, but the community would not have fared as well had businesses and homes, rather than a boardwalk, directly lined the beachfront.
Dune preservation often goes hand in hand with careful development decisions, which means researchers must labor to discern the relative mitigating effects of each strategy. They know that a dune system will be preserved if houses are not built on top of it, and that houses are less likely to succumb to flooding if they are not built directly atop a former dune system.
When development encroaches on dunes, it intensifies erosion and compromises nature?s ability to absorb wave impact. Homes built on top of former dune systems, like those in Galveston Island, Tex., eventually begin eroding into the ocean.
?I think we should consider natural sand dunes as protective treasures,? said Samuel Brody, a professor in marine sciences and urban planning at Texas A&M University. ?Once you take those away, you can?t get them back, and inland communities become much more vulnerable.?
For homes and businesses directly on the beach, dunes often create a false sense of security. Developers up and down the East Coast and along the Gulf Coasts may see dunes as a free pass for increasing seaside density. Homeowners assume that dunes will protect their properties, so they do not take protective measures like raising their house on stilts while preparing for the worst. ?One approach is to make sure all first floors can be sacrificed to floods,? Dr. Pilkey said.
Of course, some dunes are better than no dunes, even if other mitigation efforts are lacking. Vegetated dunes prove most capable of blocking storms because plant roots hold sand in place to fortify the natural barrier. And if woody plants like mangroves also grow nearby, all the better for breaking waves and surge.
?If you leave dunes alone and they are healthy and vegetated, it?s pretty convincing that they will protect inland communities from storm surge,? Dr. Brody said.
Beyond other protections like its famous dike system and moving homeowners out of flood zones, the Netherlands is particularly deft at preserving and restoring dunes. It recently invested around $170 million in adding 32 foot-high dunes along a 13-mile stretch of beach in The Hague, for example.
When they are completed, the dunes will add about 65 feet to a 590-foot-wide beach, and they will be covered in long-rooted grass to keep the sand in place. The restoration efforts are intended to address the rise in sea levels predicted over the next 50 years.
The Netherlands may be an exception to the rule, however. As our article pointed out, community preferences often clash with mitigation strategies, whether they involve restoring dunes, raising houses on stilts or removing or limiting development entirely.
?In the U.S., there?s a real struggle between protecting public good and private property rights,? Dr. Brody said. ?But in terms of the greater good, there probably should be a stronger emphasis on protecting our existing dunes and making sure they?re naturally vegetated, and also building and restoring degraded dunes.?
For the time being, such efforts generally rely on strong local ordinances like those in Bradley Beach.
?This is not purely an engineering or ecological issue but a human development issue,? Dr. Brody said. ?If we?re going to make progress protecting our coast, we have to think about the way we develop our local communities and impact the physical environment.?
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