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- [Instructor] Let's talk about dunes.
They're more important than you might think.
Why?
Well, dunes are the first line of defense
against coastal flooding.
They act as a buffer between vulnerable communities
and a volatile ocean.
During a storm, dunes can absorb the energy
of incoming waves and limit their damage.
Which means, if you like visiting coastal towns
and going to the beach, in many ways,
you owe those carefree weekends
to the presence of dunes.
From the boardwalk shops to the neighborhoods nearby,
dunes defend them all.
Some dunes are more protective than others.
Continuous mounds of sand parallel to the beach
with steep slopes on both sides
are called primary frontal dune systems.
Through decades of observation and research,
coastal scientists found that these dunes,
whether natural or manmade, help reduce flood risk.
That's why FEMA evaluates dunes
when mapping coastal hazards.
Manmade and natural dune systems
must be well established and maintained.
They need dune grasses and other plants
to build deep root systems and trap windblown sand.
This helps build up the dune
and hold it in place during a storm.
Despite this, major storms may erode and destabilize a dune.
FEMA assesses potential erosion using the 540 rule.
It considers how much of the dune
would remain above the waves
during a storm with unusually high waters.
The 540 rule considers the cross section of a dune
above the 1%-annual-chance water level
and seaward of the dune crest.
Coastal engineers determine that if this area
is less than 540 square feet,
the dune will not be an effective barrier.
However, even if a dune is larger than 540 square feet,
it is not guaranteed to eliminate the threat of flooding.
One way to keep a dune healthy
is to create an elevated walkway
for people and vehicles to reach the beach.
This protects both the dune and its plant life.
Dunes serve coastal communities in many ways
and may reduce storm damage,
but they do not eliminate the risk of flooding.
Coastal residents should consider buying flood insurance
to protect their property, just to play it safe.
Nature is unpredictable, but we can do our part
in preparing for it.
For coastal communities, that starts with dunes.
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