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  • I'm about to step onto brand new land.

  • And admittedly, yes, it is a little bit underwater right now

  • because, well, that river there is in flood.

  • But 50 years ago, this would've been open water

  • and I would've been jumping off this boat up to my neck.

  • And yes, I was extremely nervous

  • about that little jump [laughs]

  • 'cause that's the first time I came off here.

  • But yeah, this is the Wax Lake Delta.

  • 50 years ago: no trees, no plants, nowhere to put your feet,

  • I would've been swimming, on a coastline that's famous

  • not for building up but for eroding.

  • And to explain why, we have to go just a little bit inland.

  • The Mississippi River is so murky and brown

  • because it's filled with silt and sediment.

  • Throughout history, roughly every thousand years or so,

  • deposits of that sediment build up enough

  • that the river basically blocks itself

  • and then takes a different and steeper route to the ocean,

  • at least until silt builds up on that new route

  • and the river moves again.

  • That massive and relatively sudden change

  • is called an avulsion.

  • And avulsions were fine until modern times,

  • when the industry that you can hear

  • and the livelihoods of untold numbers of people

  • rely on the river being exactly where it is.

  • But in the past, every time that humans

  • have tried to fix the rivers around here,

  • there have been unintended consequences.

  • We built levees like this one

  • to protect towns like Baton Rouge here,

  • but they make the river flow faster and higher

  • because all the water is now concentrated into one channel.

  • And because they restrict water flow, they move the flooding upstream,

  • which means the next neighbourhood over

  • has to build their levee higher to deal with it.

  • There are regulations to prevent 'levee wars',

  • when communities have to keep building their levees higher

  • because their neighbours are doing the same.

  • Those regulations aren't always followed.

  • And downstream, levees mean that instead of a wider river during floods,

  • you get a faster river, eroding away those silt and sediment deposits,

  • literally washing away the land that it once created.

  • And now, the river doesn't flood as much,

  • so the ground next to it dries out and settles and sinks.

  • Louisiana's coastline is disappearing.

  • In 2011, government cartographers retired 35 placenames,

  • taking them off the maps

  • because those islands and bays just don't exist anymore.

  • They're just open water.

  • But there is one place on the coastline, a couple of hours south of Baton Rouge,

  • where land is appearing again,

  • and that is also an unintended consequence,

  • which brings us back to where I was standing

  • at the Wax Lake Delta.

  • - The Wax Lake Outlet is a channel off the Atchafalaya River.

  • The Atchafalaya River is a channel off the Mississippi.

  • So, a channel off a channel off the Mississippi River. [thunder booms]

  • Excuse me, I heard a little thunder.

  • - Okay, no, we-- - Let's get out of here.

  • - The Wax Lake Outlet was built in the early 1940s

  • and it was designed to pull water off the Atchafalaya River

  • and reduce flood stress on Morgan City.

  • One of the unintended consequences

  • was the development of a delta at the mouth of the Wax Lake Outlet.

  • And so, the Wax Lake Outlet and the Atchafalaya River

  • carries a lot of sediment,

  • and then when it gets to the coast, the river flow slows down

  • and all of the sediment in the river settles out.

  • We're talking tens of millions of metric tonnes of sediment every year.

  • This is solid enough land that you can walk on it

  • and you can stand on it.

  • Louisiana has lost nearly 2,000 square miles' worth of land over the last century,

  • and there's a large effort to rebuild the coast.

  • A big part of that effort is to try to partially divert

  • the flow of the Mississippi River

  • to create new deltas that are like the Wax Lake Delta.

  • And so, people like myself want to study the Wax Lake Delta

  • so we understand how deltas build

  • so we can better design coastal restoration projects.

  • It's important to restore the coast,

  • one, to push back the sea to enhance flood protection in Louisiana,

  • and it's also a place where you could potentially bury carbon.

  • We have too much CO2 in the atmosphere,

  • and highly productive deltas like the Wax Lake

  • may be one of those places where we can do that.

  • I often feel like the numerical models

  • that we have to understand the coast are pretty darn good.

  • The much more difficult thing to model is to understand people

  • and how people are going to behave with this changing coast.

  • And I feel like, that, we barely even know the equations.

  • We don't necessarily know even what the rules are

  • to govern how do people deal with a stressful changing environment.

  • - So, yes, it's still wet underfoot here right now

  • because this whole area's still in flood.

  • But that just means there's more mud, more sediment being deposited.

  • This land is going to be a couple of centimetres higher

  • and this coastline is going to be just a little bit safer.

  • I've sunk about an inch into the mud

  • and it's gone in my shoes. It's in my shoes.

  • Right, I should totally have gone with the sandals.

  • [laughing]

  • [grunts] All right.

I'm about to step onto brand new land.

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B1 river wax sediment lake coastline flood

The Only Bit Of Louisiana's Coast That Isn't Sinking

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    林宜悉 posted on 2020/04/01
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