How America Built a $14B Wall to Stop the Next Katrina?

[00:00:00]A wall rises out of the water east of New Orleans, nearly 2 miles long, 26 ft tall, concrete and steel standing in open marsh where there used to be nothing at all. It's the largest thing the US Army Corps of Engineers has ever built, part of a system that cost 14 and 1/2 billion dollars.

[00:00:21]And it exists because of one day, August 29th, 2005.

[00:00:27]The water came over the old walls right here. 80% [music] of the city went under. Nearly 1,400 people died.

[00:00:35]This is what America built so it never happens again.

[00:00:39]Now, watch how they built it because before they could stop the next storm, they had to beat something that fought them the whole way down, the ground itself. Start with the storm.

[00:00:50]Hurricane Katrina drives an 18-ft surge in from the Gulf. 7-ft waves ride on top of it. The surge finds a shortcut, a shipping channel called the Mississippi River-Gulf Outlet. Locals call it Mr. Go. It funnels the water straight at the heart of the city.

[00:01:10]The old flood walls are thin, steel sheet driven into soft soil.

[00:01:14]The surge climbs them. Then, it pushes past them.

[00:01:19]Then, they fail in more than 50 places.

[00:01:23]The 17th Street Canal, the London Avenue Canal, >> [music] >> the Industrial Canal. Water pours into a bowl that sits 6 ft below the sea, and it doesn't drain for weeks.

[00:01:35]So, the order comes down from Congress.

[00:01:38]Build a system that can take the 100-year storm, a surge with a 1% chance of striking in any single year. And build it in years, not decades.

[00:01:48]That's the engineering problem, and here's why it's brutal. New Orleans sits on delta mud, soft, wet, [music] and deep. There's no bedrock underneath.

[00:01:59]Nothing solid to anchor a wall against a wall of water.

[00:02:03]Watch what they do. They choose the worst spot on purpose.

[00:02:08]The confluence of the Intracoastal Waterway and Mr. Go, the exact path the surge took in 2005.

[00:02:16]Wall off the funnel and you close the door the storm walked through.

[00:02:21]But, it's open water and the mud below it can swallow a building.

[00:02:27]So, the wall doesn't sit on the ground.

[00:02:29]It hangs from it.

[00:02:31]The backbone is a row of concrete cylinder piles, 66 in across, 144 ft long, 96 tons each.

[00:02:41]1,271 of them driven in a line for nearly 2 mi.

[00:02:48]There's no rock to stop them.

[00:02:50]Each pile holds by friction alone, the grip of the mud along its whole length.

[00:02:56]So, they drive it to precisely 130 ft below sea level. Come up short and the friction isn't there. The pile can't hold the surge and the wall bleeds water.

[00:03:08]80% of this wall lives below the mudline. It stands 150 ft tall. Only 26 of those feet ever see daylight.

[00:03:18]Now, the ground fights back. The custom pile driver can only hammer straight down.

[00:03:24]The first stretch is easy. Soft mud takes 13 tons of steel like a knife into butter.

[00:03:30]Then, the pile hits packed older ground.

[00:03:33]Progress stops.

[00:03:36]It takes 40 hard blows, sometimes more, to move it the rest of the way.

[00:03:41]And there's a gap, 6 in between every cylinder pile.

[00:03:46]Leave it and the surge threads straight through.

[00:03:49]So, the crews drive a slim five-sided closer pile into each gap, set in a 3-ft column of grout.

[00:03:56]Miss the seal and 2 mi of wall means nothing.

[00:04:00]This is the critical part.

[00:04:03]A wall this tall doesn't just hold water. Water shoves it sideways with enormous force.

[00:04:09]So, behind the concrete, they drive steel piles on a slant, 2 ft out for every 3 ft down. 288 ft long. Too long to drive in one piece, so each goes in as two sections. The lower half driven deep, the upper half welded on top and hammered home.

[00:04:27]More than 600 of them angled into the earth like the legs of a runner braced against a shove.

[00:04:34]One weak pile here and the wall bends when the storm leans on it.

[00:04:39]On October 21st, 2009, they drive the last of the 1,271 main piles.

[00:04:46]The backbone is done.

[00:04:48]Now, the wall goes up. They cap the piles with precast concrete blocks, 18 ft long, 6 ft high, 90 tons a piece, and pour 6-ft closures between them.

[00:05:00]Block by block, the barrier climbs to 26 ft.

[00:05:05]And then, they do something that looks like a mistake.

[00:05:09]They build it lower than the walls on either side.

[00:05:12]The levees it ties into stand 30 to 32 ft. The barrier stops at 26. On purpose.

[00:05:20]In the worst storm, they want a little water to spill over the top into empty wetlands behind it, where it can sit and do no harm.

[00:05:30]Fight the sea head-on and the wall can break. Let it win a few feet and the wall survives.

[00:05:37]They let the water win a little.

[00:05:39]It buys them the city. But, a wall across a shipping lane has to open.

[00:05:44]So, three gates break the line.

[00:05:47]A barge gate and a sector gate on the Intracoastal, each 150 ft wide.

[00:05:53]A vertical lift gate at Bayou Bienvenue, 56 ft across.

[00:05:57]Building a gate in open water means first making the water disappear.

[00:06:03]Crews sink a steel cofferdam, a box of sheet piling roughly 160 ft by 380 in water 30 ft deep, and pump it dry.

[00:06:13]Then comes the seal at the bottom.

[00:06:16]10,000 cubic yards of concrete poured underwater in one continuous operation.

[00:06:23]Stop the pour and the seal is compromised and the whole box can flood.

[00:06:28]So, it doesn't stop.

[00:06:30]On top of that, a foundation slab, 14,000 cubic yards of concrete, temperature controlled as it cures so it can't crack from its own heat, [music] poured to tolerances tight enough to receive a steel gate the size of a building.

[00:06:46]And at the far north end of the Industrial Canal, >> [music] >> where it meets Lake Pontchartrain, a second gate, the Seabrook complex, slams the other door.

[00:06:55]Now the canal that flooded the city is walled at both ends.

[00:07:00]Watch what comes next because the wall is only half the defense. The barrier is the famous piece.

[00:07:07]But most of the 133 mi ring is earth.

[00:07:11]Levees raised higher and made stronger all the way around the city.

[00:07:16]And the same enemy waits under all of it.

[00:07:19]The mud won't hold the weight.

[00:07:22]Pile on enough soil for a taller levee and the ground beneath simply sinks and keeps sinking for years.

[00:07:30]East of the city, along a 7 and 1/2 mi stretch, they beat it by wringing the ground out first.

[00:07:36]They stab more than 250,000 plastic wick drains down into the soil.

[00:07:42]Thin channels that let the trapped water escape so the mud can pack down and firm up before the levee ever goes on top.

[00:07:50]It's the largest wick drain project in American history.

[00:07:54]Then they armor the levees, the back slopes especially, so that if a surge does pour over the top, the rushing water can't tear the earth out from behind.

[00:08:04]Because a levee doesn't usually fail where the water hits it. It fails where the water lands.

[00:08:11]Now the real machinery begins.

[00:08:13]Across the river, on the west bank, a different threat.

[00:08:17]Two canals, the Harvey and the Algiers, run straight into the neighborhoods.

[00:08:23]A surge up either one floods 70 square miles. So they gate them off with a single sector gate, 225 [music] ft wide.

[00:08:32]But close that gate and you create a new problem. The rain still has to fall. And with the canals sealed, the water has nowhere to go.

[00:08:42]It backs up behind the gate and floods the city from the inside.

[00:08:47]The answer is the largest pump station on earth.

[00:08:51]11 pumps. Each one moves 1,740 cubic feet of water every second.

[00:08:58]Together, 19,000 cubic feet per second.

[00:09:02]Enough to fill an Olympic swimming pool in 4 seconds flat.

[00:09:07]Each pump is a machine the size of a truck.

[00:09:11]11-ft blades, 70 tons.

[00:09:14]Driven by a diesel engine pushing more than 5,000 horsepower.

[00:09:19]18 million pounds of steel rebar hold the complex together. Enough to build 30 jumbo jets.

[00:09:27]They build it on a deadline that borders on impossible.

[00:09:31]Where there was nothing but pine trees, a 50-acre fortress rises.

[00:09:36]Substantial completion, June 1st, 2011, the first day of hurricane season.

[00:09:43]They make it.

[00:09:44]One weakness is left, the one that drowned the city the first time.

[00:09:49]Three drainage canals cut through the heart of New Orleans, 17th Street, Orleans Avenue, London Avenue.

[00:09:57]They were built open to Lake Pontchartrain, so the city could drain into it by gravity.

[00:10:02]In Katrina, that ran in reverse.

[00:10:05]The lake surge back flowed up the open canals and blew the walls out from the inside.

[00:10:11]The 17th Street canal failed before the storm even made landfall.

[00:10:15]So, they closed the canals at the lake.

[00:10:18]Permanent gates, 18 ft tall, drop across each mouth before a storm arrives, sealing the lake out.

[00:10:26]But, sealed canals can't drain rain.

[00:10:29]So, beside each gate, another pump station.

[00:10:32]Together, they move 24,000 cubic feet of water a second, an Olympic pool in under 4 seconds.

[00:10:40]And the control rooms are built to survive 200 mph gusts, so the operators inside can keep pumping while the storm tears at the walls.

[00:10:50]This is the last piece.

[00:10:52]When it's finished, the ring is closed.

[00:10:56]133 miles of walls, levees, gates, and pumps wrapped around [music] an entire city.

[00:11:04]Then, the test comes, August 29th, 2012, 7 years to the day after Katrina.

[00:11:11]Hurricane Isaac, only a category one, but slow, and it shoves a 10-ft surge at the city, the kind of water a much stronger storm would bring.

[00:11:22]For the first time, the great barrier closes. It holds.

[00:11:26]First proof.

[00:11:28]Then, August 29th, 2021, 16 years to the day, and this time it's a monster.

[00:11:36]Hurricane Ida, category 4, 150 mile an hour winds, some of the strongest ever to strike the American coast.

[00:11:45]The same city, the same date, the whole ring closes. Every gate, every pump, and not a single levee in the system breaches or fails anywhere.

[00:11:58]The great pump station on the West Bank runs for 18 hours straight and turns away 9 ft of surge.

[00:12:06]Along the West Bank walls, the water tops out at 3, maybe 4 ft against tops [music] that stand near 15.

[00:12:14]The storm that would have drowned New Orleans in 2005 hits it again, harder, and the city stays dry. 133 miles of levees and walls, 1,271 piles in the Great Barrier alone, each driven 130 ft into bottomless mud.

[00:12:34]The largest pump station [music] on the planet, the largest civil works project in the history of the Army Corps of Engineers, 14 and a half billion dollars.

[00:12:46]Pile by pile, pour by pour, gate by gate, they built a wall by hanging it from mud that didn't want to hold it. They beat the sea by letting it win a few feet.

[00:12:59]And on the anniversary of the day the water took the city, the same storm came back, and this time the walls held.

[00:13:06]The people who came home got to stay home.