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Imagine you're on a beach.
It's flat, it's wide. With pristine sand.
Looks nice, right?
Unfortunately, many beaches don't look this
way.

They're narrow, with steep cliffs, and waves
breaking close to the property line.

This is a beach that's experiencing erosion.
In America, about 80 to 90 percent of sandy coastlines
have this problem.
So the government spends billions to expand
some of the most rapidly eroding beaches in an

effort to defend the coast.
But this effort, while effective in the short
term, can actually hurt beaches in the long run.

It's because every shoreline on the planet is subject to erosion.
Beach erosion occurs when waves and
currents remove sand from the shoreline.

The loss of sand makes the beach narrower and
lowers its elevation.

This erosion becomes a problem when it reaches
structures built by humans along the coast.

Especially for beaches that generate tourism.
The visitors enjoy the sandy coasts while
the cities and towns nearby enjoy the revenue gained.

But the driving factor there is the beach
— a place like Miami Beach wouldn't have

the same draw if there weren't lots of sand.
In fact there was a time when it didn't
look this way at all.

In the 1970s, a seawall turned
the beach in Miami into a narrow strip.
But by the '80s, the beach in Miami re-emerged
nice and wide.
How?
Well, coastal engineers
rebuilt it through a process called "beach nourishment."

Beach nourishment is a shore protection strategy
to try to counter the loss, the natural loss of sand.

The typical way to do this is with dredging.
Boats will dig up sand from a borrow site and move it onto the beach.
You'll have a big pipe pump and you'll suck
up the sand.

Then it's transferred to the coastline.
Where it's dumped or pumped out onto the beach
and then bulldozers move it around to try
to mimic what the natural beach was like before
the project took place.

The result is a nice wide beach.
The new profile will better defend the property
line from damage during more intense weather

like storm surge flooding.
In the United States, beach nourishment is the main strategy
used to protect coastal properties from risky
erosion.
But there's a problem.
The protection doesn't last.
As the constant
beating of waves and wind takes the sand away

from the shore.
And it soon it looks like it did before the nourishment
occurred.

Every 2 to 8 years, on average, the nourishments
need to be repeated.

Like this beach in Florida.
Well this morning, Lido Beach is under a local state
of emergency —

Just look at how powerful the wind was earlier
today —

— problem getting worse by the hour.
Lido Beach, on the Gulf Coast of Florida, got an emergency nourishment
in 2018 after damage from storms reduced the
beach to a narrow strip.
But the beach had already gotten new sand
15 times since 1964.

And Lido Key isn't an outlier.
More than 200 of the 400 miles of critically
eroding coastlines in Florida have received

one or more nourishments.
And across the United States, there have been nearly
3000 known-nourishment events since 1923.

The funding for these projects gets a little
wonky, but here's what's important: The federal

government pays for a lot of these nourishments.
Up to 65% of the cost.
State and local funds will make up the rest.
But not all beaches that want or need nourishment
will get it.

The Army Corps of Engineers — the group that
approves and designs nourishments —prioritizes

defending some beaches over others, based on
the potential loss of value.

According to ProPublica, the Corps only funds
nourishments where the expected benefit is

2 and a half times as high as the cost.
Poorer communities won't often meet that
criteria.

So places like Miami Beach, Florida, and Ocean City, Maryland,
are more likely to get a lot of nourishment.
They have the expensive shorefront developments
that make the investment worthwhile.

And for beaches that don't make the cut
for nourishment, continued erosion can lead

to damaged or destroyed property.
Nourishments aren't just about protecting
buildings, but also protecting the economies

tied to them and the beach.
Consider the 200 million dollars spent on
nourishments in Florida from 1995-2001.

That might seem like a lot of money, until you see the
revenue from coastal tourism — it was $21.6 billion

in just one year — 2001.
On average, the State of Florida generates
more than 5 dollars of revenue for every dollar

invested in beach nourishment.
Which is why nourishment is so appealing.
It make economic sense.
But they do present one major problem.
According to research published by the American
Geophysical Union, there is a feedback loop.

Nourishment tends to happen along beaches
that generally have expansive properties and

they also seem to drive development along
the same shores, despite the risk of future

erosion.
If you were in a place that had nourished
its beach, the houses behind that nourishment

project were significantly larger, in every
case, than in a place that had never nourished

its shoreline at all.
Research found that areas with nourished beaches
had homes that were about three times bigger

than non-nourished ones.
And this excessive development is a real problem,
because it's based on false security.

According to the researchers, "beach nourishment
may actually mask or reduce the apparent impact

of coastal hazards without changing the natural
processes that drive them."

In fact, building more property in these areas
only increases the potential damage from future erosion.
So, while beach nourishments protect property
and local economies in the short run, they

also trick us into thinking it's safe to
build in places that aren't.

Which sets up coastal communities for an ugly
reckoning at the shore... sooner or later.

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持續消失的海岸線,沙灘重建會帶來什麼樣的問題? (The problems with rebuilding beaches)

120 分類 收藏
Winnie Liao 發佈於 2019 年 7 月 4 日
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