A team of engineers and geo-scientists in the United States say a historic, long-buried seawall in the state of New Jersey played a key role in saving local homes from the wrath of last year’s Hurricane Sandy.
The 1,260-metre seawall, buried beneath the sands of Bay Head on the New Jersey shore, dates back to 1882 and had long been forgotten by local residents.
Despite its venerable age and state of neglect, however, the stone structure was instrumental in enabling local houses to weather the onslaught of Hurricane Sandy - the largest Atlantic hurricane on record and the second costliest in US history.
A comparison with the adjacent borough of Mantoloking highlights the extent to which Bay Head's hidden seawall reduced the damage inflicted by the hurricane.
In Mantoloking the entire dune almost disappeared completely, and the inrush of water was able to create breaches of 165 metres, 59 metres and 35 metres.
In Bay Head, however, only part of the dune situated on the seaward side of the seawall had been eroded, while the dune on the other side of the seawall managed to survive largely intact.
Research conducted by scientists from the College of Engineering at Virginia Tech found that this resulted in dramatic differences in the survival rates for homes in the two areas.
While all the oceanfront homes in the two boroughs suffered some damage, from ground-floor flooding to total leveling, the Virginia Tech team found that only one oceanfront home in Bay Head had been completely destroyed. In Mantoloking, however, over half of the oceanfront homes were classified as damaged or destroyed.
Jennifer L. Irish, associate professor in civil and environmental engineering at Virginia Tech's College of Engineering, says the aged, forgotten seawall was what made all the difference.
"The beach and dunes did their job to a certain point, then, the seawall took over, providing significant dampening of the waves," she says. "It was the difference between houses that were flooded in Bay Head and houses that were reduced to piles of rubble in Mantoloking."
"It's amazing that a seawall built nearly 150 years ago, naturally hidden under beach sands, and forgotten, should have a major positive effect under the conditions in which it was originally designed to perform," said H. Richard Lane, program director with the Division of Earth Sciences of the National Science Foundation (NSF), which was responsible for funding the research.
The research performed by Irish and her team on the impact of the Bay Head stone wall has been published online in the journal Coastal Engineering and is scheduled for publication in the October print edition.