34 Scientific American, April 2019
O
n August 27 , 2011 , HurricAne irene crAsHed into nortH cArolinA,
eviscerating the Outer Banks. The storm dumped rain shin-high
and hurled three-meter storm surges against the barrier island
shores that faced the mainland, destroying roads and 1,100 homes.
After the storm, a young ecologist then at the University of
North Carolina at Chapel Hill named Rachel K. Gittman decided
to survey the affected areas. Gittman had worked as an environ-
mental consultant for the U.S. Navy on a shoreline-stabilization
project and had been shocked to discover how little information
existed on coastal resilience. “The more I researched, the more I
realized that we just don’t know very much,” she explains. “So
much policy and management is being made without the under-
lying science.” She decided to make shorelines her specialty.
What Gittman found was eye-opening. Along the hard-hit
shorelines, three quarters of the bulkheads were damaged. The
walls, typically concrete and about two meters high, are the
standard homeowner defense against the sea in many parts of
the country. Yet none of the natural marsh shorelines were
impaired. The marshes, which extended 10 to 40 meters from
the shore, had lost no sediment or elevation from Irene. A l-
though the storm initially reduced the density of their vegeta-
tion by more than a third, a year later the greenery had bounced
back and was as thick as ever in many cases.
Gittman’s study confirmed what many experts had begun to
suspect. “Armored” shorelines such as bulkheads offer less pro-
tection against big storms than people think. By reflecting wave
energy instead of dispersing it, they tend to wear away at the
base, which causes them to gradually tilt seaward. Although
they still function well in typical storms, they often backfire
when high storm surges overtop them, causing them to breach
or collapse, releasing an entire backyard into the sea.
In a later study, Gittman and other researchers surveyed 689
waterfront owners and found that the 37 percent of properties
protected by bulkheads had suffered 93 percent of the damage.
And bulkhead owners routinely had four times the annual
maintenance costs of residents who relied on nature instead.
Salt marshes bent but did not break.
In recent years more scientists and policy makers have come
to believe that “living shorelines”—natural communities of salt
marsh, mangrove, oyster reef, beach and coral reef—can be sur-
prisingly effective in a battle coastal residents have been losing for
years. U.S. shores are disintegrating as higher seas, stronger
storms and runaway development trigger an epidemic of erosion
and flood damage. Every day waves bite off another 89 hectares of
the country. Every year another $500 million of property disap-
pears. Overall, some 40 percent of the U.S. coastline is suffering
ongoing erosion. In some places, the rate of loss is breathtaking.
Go to Google Earth Engine’s Timelapse feature and watch Shack-
leford Banks melt away like ice cream on a summer sidewalk.
Historically, almost all money spent on coastal defense has
gone toward “gray” infrastructure: seawalls, bulkheads, levees
and rock revetments. That is beginning to c-hange as research-
ers become more sophisticated in measuring the long-term im -
pact of “green” coastal defenses. Insurance companies and gov-
ernments are finally taking notice and might actually turn the
tide toward living defenses.
WETLANDS OUTPERFORM WALLS
Around tHe time that Hurricane Irene was barreling up the East
Coast, Michael W. Beck, a research professor at the University of
California, Santa Cruz, and then lead marine scientist for the
Nature Conservancy, was initiating a collaboration with the
insurance industry that today may begin to change coastal con-
servation. “A lot of people were saying that ecosystems worked
for flood protection, but the evidence was thin,” Beck tells me at
his Santa Cruz office. The physical mechanisms were clear: oys-
ter and coral reefs limited erosion and flood damage by acting
as natural breakwaters (offshore seawalls), dispersing wave
energy with their corrugated surfaces. Salt marshes and man-
groves, with their earthen berms and friction-generating for-
ests of stalks, could rake more than 50 percent of the energy out
of storm surges in less than 15 meters of territory.
IN BRIEF
Surprising data show that in many places marshes
protect shorelines better than walls and are cheaper
to construct.
Scientists are perfecting techniques for rebuilding
tattered wetlands, creating custom configurations
for individual shorelines.
Governments and disaster planners are starting
to give more consideration to living shorelines, and
money to restore them is rising.
Rowan Jacobsen is author of A Geography of Oysters,
The Living Shore and other books. He wrote about
the genes of extinct flowers in our February issue.
