April 2019, ScientificAmerican.com 35But although scientists understood the physics, no one had
put it into a form that could be used easily by policy makers.
Beck set out to rectify that. “If I want to change practices, I can’t
bring my ecosystem model to femA or the U.S. Army Corps of
Engineers,” he explains. “I have to look at their risk model and
put ecosystems into that. ”
Beck and his colleagues began collaborating with Lloyd’s of
London, Swiss Re and others in the insurance industry, which
have some of the best data and models in the world on assets and
risk. When he plugged data on coastal ecosystems into their risk
models, it became clear that living shorelines were excellent de -
fenses. And, he notes, “when I tell the Corps, femA and the devel-
opment banks that these are the numbers from the insurance
industry, I automatically have a different level of credibility.”
The first study focused on damages from Superstorm Sandy,
which clobbered New York and New Jersey in 2012. Working with
Risk Management Solutions, a leading risk-modeling firm, the
scientists showed that wetlands prevented $625 million of flood
damage from the storm, which was surprising given that the
coasts in the region had already lost 60 to 90 percent of their
protective wetlands over time. In areas that flooded, the few re -
maining wetlands lowered flood damage by 11 percent on aver-
age. As important was the ability to buffer garden-variety floods:
in one local study, properties behind marshes suffered 16 per-
cent less annual flood damage than properties that had lost
their marshes. “That’s well within the range for which you could
expect [insurance] premium reductions,” Beck points out.
He and his partners then turned their economic and risk-
management models on the Gulf Coast from Texas to Florida,
which is regularly battered by big storms. They did an exhaustive
analysis of the annual expected benefits and costs of all types of
infrastructure. The team estimated that the coast would suffer
$134 billion of losses over 20 years if no preventive measures
were taken. Elevating homes could prevent $39.4 billion of those
losses, but it is incredibly expensive. At an average of $83,300 per
house, it would cost $54 billion to prevent that $39 billion in
damages. The six-meter-high dikes being built in Louisiana were
a worse option; at $33,000 per meter, they were an absurdly
expensive way to protect a relatively limited amount of property,
returning just $1 in savings for every $4 of expense. Smaller
levees built on land in front of many low-lying coastal communi-
ties prevented much more damage for almost the same cost.
In terms of bang for the buck, sandbags were the best invest-
ment, saving $8.4 billion of damages for a mere $0.84 billion in
expense. Natural defenses ranked high as well. Wetlands restora-
tion, which could prevent $18.2 billion of losses, would cost just
$2 billion. Oyster-reef restoration could prevent $9.7 billion in
losses for $1.3 billion. Barrier island restoration offered $5.9 bil-
lion of prevention for $1.2 billion. And “beach nourishment” (re -
plenishing depleted beaches with sand dredged from the sea-
floor) in the eastern Gulf could save $9.3 billion for $5.5 billion.
That last one surprised many people because replacing
beach sand year after year is often seen as a fool’s errand. “If the
only choices you gave me were beach nourishment versus fully
gray infrastructure,” Beck says, “I’d choose the former as the
lesser of two evils.”
Overall, the research found that $57.4 of the $134 billion
could be prevented cost-effectively, almost all of it through
green infrastructure.
One type of restoration that was not part of the study is large-
scale diversion of the Mississippi River. Diverting sediment-lad-
en water through a gap in the river’s levees and letting that sedi-
ment filter into struggling marshes can restore their health and
elevation, but the region is subsiding so quickly that not even the
famously muddy Mississippi can save it from the encroaching
sea. “It is going to be expensive to re-create an entire ecosystem,”
Beck says, “and it is better and cheaper to start earlier.”
Cost-effective restoration may be tricky on long, sandy coasts,
too. Beaches and barrier islands are by nature transient. Plant-
ing grasses to rebuild dunes can help keep beaches in place but
only temporarily in many cases. At some point, residents will
have to move back from the receding shoreline.
Beck is quick to point out that built infrastructure is still in-
credibly important and that cost-effectiveness is not the only con-
sideration. “Anywhere you’ve got significant people and property,”
he says, natural solutions will “be used together with some form
of built infrastructure.” Metropolitan areas, ports and other plac-
es where the risk tolerance for a major flood would be extremelyDEVELOPERS survey oysters that have settled onto Oyster Catcher,
a jute-and-cement material designed to help babies and adults thrive,
protecting marshes between them and solid land.