Manalapan was especially hard-hit when days of pounding from Hurricane Sandy undermined sea walls at more than 20 homes.
Many complained that poorly maintained sea walls at one property caused the sea wall of their neighbors to fail.
2012 photos by Jerry Lower/The Coastal Star
A Coastal Star Special Report:
Hurricane shows just how fragile our shores are
Dunes vs. Sea walls: Natural vegetative dunes may be best defense
By Cheryl Blackerby
In the aftermath of Hurricane Sandy, many seaside residents were suddenly interested in armoring the coast to prevent beach erosion and damage to homes.
In emotional meetings across Palm Beach County, residents and experts discussed the pros and cons of breakwaters, groins, revetments and sea walls. Most of the news was bad. Sand, it turns out, is difficult to hold onto.
But there are, indeed, ways to capture sand. A breakwater or groin can corral sand behind a beachside house, but most likely will starve sand to the south. And the neighbors to the south will not be happy about it.
Breakwaters in Florida, such as those around Peanut Island in the Intracoastal Waterway near the Lake Worth Inlet, are offshore structures made of rock limestone or granite that run parallel to the shoreline.
“They are usually an engineered structure built to specifications, not just a pile of rocks,” said Michael Stahl, a senior environmental analyst for the county’s Department of Environmental Resources Management.
Stahl and his department designed breakwaters for a beach on Singer Island, where near-shore fish habitats prevented beach renourishment.
But they were unable to get permits from the Florida Department of Environmental Protection and the U.S. Army Corps of Engineers because of the potential for obstructing sea turtle nesting.
“And anytime you restrict sand movement from north to south, you introduce the potential for down-drift impacts. You essentially relocate sand from one section of the beach to another section,” Stahl said.
Groins run perpendicular to the shoreline and accumulate sand on the up-drift part of the structure. The groins just south of the Boynton Inlet retain sand on the south side of the inlet.
“The drawback is they act as a dam to moving sand. Down-drift beaches are being starved of sand which results in additional groin structures being built to the south and the result is a groin field, a series of groins to trap sand,” he said.
And there’s the same problem with nesting turtles. “In Ocean Ridge, the turtle hatchlings next to the groins have to be caged to prevent the hatchlings from getting trapped in the rocks,” Stahl said.
But breakwaters are a good option when compared to sea walls, he said. When you build a sea wall you are saying goodbye to a beach.
“The big drawback is that the beach erodes in front of the wall, and there is a deflation of sand, which then allows the waves to reflect off the walls carrying the sand with it. You are essentially accelerating the erosion,” he said, adding that the waves will eventually undermine the wall itself.
Shore engineers don’t like to see the intermittent sea walls built by residents along the shoreline in Manalapan, Palm Beach and other places. “We would prefer not to have an armored shoreline like that. There’s a loss of sand and a loss of turtle habitat,” he said.
Residents have the right to build sea walls, but they must get permits from the DEP. Homeowners are responsible for maintaining them. When residents lose sand because of their sea walls, their neighbors may also lose sand.
Revetments, sloping shores covered with rock or concrete, are an old-school beach armor that almost no one is considering. Delray Beach city officials tried expensive “waffle revetments,” interlocking concrete blocks on the beach in the 1960s, which kept people off the beach and eventually collapsed under crashing waves.