FEMA - Shoreline Protection
FEMALINCROFT, N.J. — FEMA — With the most developed and densely populated coastline in the country, New Jersey has communities along the Shore that are discovering the numerous ways to protect lives and property when storm clouds gather off the coast.
Yet, not all beach protection methods are the same. Not all of them will stop an ocean hell-bent on raging into the community.
Rock walls, geotubes, sand dunes and gabions are options for reducing the risk of damage during storms. But which one is best?
“You can’t say one is better than the other. Different site or community circumstances play into which protection measure a community may want or need to provide the protection they expect,” said Michael Foley, group supervisor with the mitigation branch of the Federal Emergency Management Agency.
In New Jersey, the U.S. Army Corps of Engineers’ Philadelphia and New York districts are managing several projects that will deposit about 15 million cubic yards of sand on beaches along the Atlantic coast. Another 875,000 cubic yards will be deposited along the south shore of Raritan Bay near Keansburg. That’s almost 800,000 dump trucks of sand – a single dump truck holds about 20 cubic yards. The projects are 100 percent funded under the Hurricane Sandy Relief Bill.
Sand dunes, mounds of dry sand built up naturally by wind and vegetation, are important first lines of defense against coastal storms, acting as a buffer to reduce losses to inland coastal development. Dune grasses anchor the dunes with their roots, helping to trap the sand, and also have the ability to grow new stalks up through layers of sand.
“For most areas along the oceanfront, beach fill represents the most cost-effective and least environmentally intrusive method to reduce risk from storm damage,” said Stephen Rochette, spokesman for the Corps’ Philadelphia District, which is constructing a dune and berm beach fill to restore four miles of Long Beach Island.
In 2010, the Corps built 22-foot dunes on parts of Long Beach Island, specifically Harvey Cedars, Surf City and Brant Beach. After Superstorm Sandy hit last October, the Hurricane Sandy Relief Bill provided the funding to restore the dunes in the three communities to full design level. The project illustrated the value of sand dunes.
Harvey Cedars “sustained very minimal damage mostly because the dunes were in place to protect it against the storm,” said Keith Watson, the Corps’ project manager on the Long Beach Island dune project. “The dunes really did their job.”
Geologists study the ocean bottom sediment to locate potential sources of suitable beach sand. Not all sand is the same. Grain size variation within the sediment is a critical factor in designing a stable beach, according to the New Jersey Geological Survey.
The Corps further conducts an analysis to determine the method and scope of a beach nourishment project.
“We look at a 50-year economic period and we run all the potential storms and combinations of storms that can occur over that time frame and look at the damages reduced from each design – big dunes, small dunes, flat berms, structures,” Watson said. “We choose the plan that maximizes the net benefits – that is, the damages prevented versus the costs.”
Wave action, tidal action and storms move sediment from one place to another. According to the Coastal Research Center’s website at The Richard Stockton College of New Jersey, “the total absence of bedrock along the shoreline means that all the oceanfront is vulnerable to be removed and redeposited elsewhere over relatively short periods of time.”
Long Beach Island communities on either end of the Corps’ beach restoration project saw significant damage from Sandy. Tidal surges washed the beaches right across the island, depositing sand up and down streets and yards. Some beachfront homes were washed off their foundations, some were left teetering after sand beneath the structures washed away.
But damage was less severe in areas of the island that were protected behind the sand dunes. “Superstorm Sandy came along and really vindicated what we’re doing and (illustrates) that our design is the right one for this island,” Watson said.
Along New Jersey’s 127 miles of coastline, communities have constructed timber bulkheads, large rock walls and concrete seawalls. To stabilize their dunes, some Shore communities have placed geotubes and gabions underneath the dunes. Geotubes are filled with sand and water, and wrapped in an ultra-strong geotextile fabric. Gabions are wire baskets filled with large rocks.
Geotubes have been used on the north end of Ocean City and along Cape May beaches; gabions in the West Atlantic City portion of Little Egg Harbor. Those measures were credited with protecting the communities from significant damage during Sandy.
Stockton College will host the 2013 conference of the Northeast Shore and Beach Preservation Association 9-11 September 2013.
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