Environment
 

Local officials losing sleep over weakest link in post-Katrina flood defense

Situated at the confluence of the intracoastal waterway and the Gulf outlet, the barge outlet is meant to trap storm surge within Lake Borgne.

U.S. Army Corps of Engineers

Situated on the intracoastal waterway near its confluence with the Mississippi River Gulf Outlet, the barge gate (abutting cranes) is meant to block storm surge.

What do you call a navigation gate in a hurricane protection wall

  • that was plugged into the system because it could be built faster and cheaper than a more proven design?
  • that was installed after research showed it could not perform as originally planned?
  • that might not be able to close unless another, distant gate is closed first?
  • and that now, after almost a year of trials, still has not been operated successfully?

The U.S. Army Corps of Engineers calls it “the barge gate on the Gulf Intracoastal Waterway” and “a system they have confidence in.”

Bob Turner, regional director of the Southeast Louisiana Flood Protection Authority, has another name for it as yet another hurricane season looms: insomnia.

“It’s the thing that keeps me up at night the most,” said Turner, an engineer whose professional sense of worry is heightened by the knowledge that many lives and livelihoods depend on this gate working properly.

“It’s an incredibly complicated design that will take nine hours to close effectively — and that the corps still can’t operate successfully after repeated tries.

“I keep seeing us trying to close that hole in the wall with a storm coming — and having nothing but problems.”

The “barge gate” gets its name from its main element: a mammoth, concrete barge 190 feet long, 70 feet wide and 44 feet deep. It is not so much a gate as an emergency dam to be used on a temporary basis during storms.

On paper, the design calls for the huge barge to be swung into a 190-foot gap in the Lake Borgne Surge Barrier at its junction with the Gulf Intracoastal Waterway. Once in place, the barge is filled with water and sunk to prevent storm surge from pouring through the city’s eastern defenses.

Even as a temporary fix during Hurricane Isaac helped that barge gate plug the hole, members of the flood authority spent anxious days worrying that it might fail.

Corps officials say there is nothing to worry about; all gates have bugs, and they’re working them out.

Turner and fellow members of the flood protection authority don’t share that confidence. “Barge gate” has become a four-letter word as the corps prepares to hand over the keys and responsibility for operation and maintenance of the system by June 1, the onset of the 2013 hurricane season.


View Malfunctioning barge gate in a larger map

Their complaints are numerous: The corps backed off the operational parameters originally promised for the barge gate; closing it takes too long and is too complicated; and, by the way, it has never been closed without breaking.

“Other than that,” Turner said with a rueful laugh, “we love it.”

The story of the barge gate goes back to the aftermath of Hurricane Katrina. Admitting that its own catastrophic engineering failures caused more than 50 ruptures in its levees and floodwalls, killing more than 1500 people and drowning 80 percent of the city in up to 15 feet of water, the corps promised amends. The answer was the $14 billion Hurricane Storm and Damage Risk Reduction System, which was to have been finished ahead of the hurricane season two years ago.*

A key to providing better protection was preventing the confluence of the Mississippi River Gulf Outlet and the intracoastal waterway from funneling storm surge into the Inner Harbor Navigational Canal — also known as the Industrial Canal — that divides the 9th Ward into its upper and lower districts. During Katrina that confluence of storm surge contributed to the collapse of the Industrial Canal’s eastern flood wall and the the devastation of the Lower 9th Ward.

The answer was the massive Lake Borgne Storm Surge Barrier, a 1.8-mile long, 26-foot high concrete wall that stretches across the intersection of the gulf outlet and the intracoastal waterway.

The barge gate is show in the closed position with the sector gate left open.

U.S. Army Corps of Engineers

The barge gate is shown in the closed position with the adjacent sector gate left open.

Permanently shutting the area was not feasible because the intracoastal waterway is a major shipping corridor. The solution was a main gate that would be kept open unless storms were approaching, and a secondary, or bypass, gate that would remain closed except when the main gate needed to be shut down for maintenance.

The corps let the contract to the Shaw Group of Baton Rouge. For the main opening Shaw choose a “sector gate” – a ubiquitous design found in channels the world over, thanks to its simplicity and efficacy: Two arms, mounted on supports, are swung shut as a storm approaches. It takes about 30 minutes to close, corps officials said.

For the bypass gate Shaw chose the rarely executed barge gate design, which officials said takes about 9.5 hours to close.

Chris Gilmore, the corps’ senior project manager for the post-Katrina upgrades, said he knew of only one other barge gate under construction or in use in the U.S.

Gilmore said the barge gate choice was based on budget and speed. The sector gates cost about $33 million, the barge gate $26 million, according to the corps.

“It was the most economic, the one we could get in place the quickest,” Gilmore said.

Under the terms of the contract, Shaw got to make the selection, Gilmore said, but added “there is no sense” the corps would have gone in a different direction.

The flood protection authority didn’t object at the time, either, Turner said, because the original plans called for the barge gate to remain closed except when repairs to the sector gate would be required — about once every 10 to 15 years.

“The whole reason for a second gate there is to have a way for commercial traffic to pass while they close the main gate for periodic maintenance,” Turner said. “So, the second gate — in this case the barge gate — wouldn’t be opened except during those rare instances.

“So it was not a problem then, because it would never be open during storm season.”

It became a big problem, Turner said, when the corps announced a change of plans in 2008: The barge gate would have to remain open all the time, and would be closed only for hurricanes.

Gilmore said that change of plans was based on two pieces of new research that came to the corps’ attention after planning was well under way:

The speed of the tidal currents through the 150-foot wide sector gates caused safety concerns for marine operators, and the corps’ environmental section finished research showing the opening was not large enough to allow adequate passage of estuarine species, primarily fish larvae.

The information about currents wasn’t available earlier, Gilmore said, because it didn’t show up on computer simulations.

“Computer models can only tell you so much,” he said. “We had a good idea of what we thought would happen, but once we actually had a physical model [a video simulation] for the maritime traffic [operators] to actually get in with a full screen and actually try to pilot this, that’s when we thought there might actually be some issues.

“So all this came up in the design phase.”

Gilmore did not say why the environmental concerns were not raised earlier.*

Both problems could be solved, the corps decided, by leaving the nearly 200-foot wide barge gate open full-time.

Gilmore said no alternatives were considered because “we were too far down the design path to actually change. We would never have met our construction schedule if we changed our design at that point.” And anyway, the corps was confident the barge gate would not compromise the system, he said.

The flood protection authority has no such confidence.

Turner said the sudden decision by the corps to create a second, full-time 190-foot opening in the defensive perimeter caused serious anxiety that was heightened when his agency recognized how tricky it is to operate. Closing the gate requires its many moving parts to mesh perfectly and takes 9.5 hours.

Those anxieties have only grown with each of the repeated setbacks the corps has suffered in trying to get the system to work without failing.

On one attempt, the barge’s cement bottom landed on a piece of scrap metal and fractured. Other closings have ground to a halt when moving parts failed to work properly. And recently the corps discovered that corrosion had eaten into iron parts of the system, which needed to be replaced — less than a year after it was first installed.

Shaw is responsible for some of the repairs, while the corps will foot the bill for others that have been determined to be off-contract adjustments, Gilmore said.

Of equal concern is the narrow range of tidal currents in which the huge structure can work properly. Gilmore said the outer limit for confidently closing the barge is about a half-mile per hour. That’s not an unusual flow in the intracoastal waterway, and far below the speeds that occur when a tropical storm begins affecting the gulf.

It means the gate has to be closed 96 hours — four full days — before a storm in the gulf is expected to begin effecting conditions within the intracoastal waterway, Turner said the corps has told him.

Tidal flow is so grave a concern that the corps has resorted to using the Seabrook gate — 10.2 miles away, at the Lake Pontchartrain end of the Industrial Canal — to mitigate the problem. Closing Seabrook reduces the current in the intracoastal waterway, providing a longer interval in which to close the barge gate.

Gilmore said his team is currently working on strengthening some of the moving parts so the current parameter can be increased. And he insisted the barge gate troubles are nothing unusual for any large construction project the corps undertakes.

“That’s just a product of actually finalizing construction and trying to operate this thing, to work out all the little kinks,” Gilmore said. “The first couple of times we tried to operate each of these gates, things pop up.

“We are very confident once we get all these kinks worked out that, with proper training not only us but the local authorities will be able to operate this gate.”

Turner shakes his head in dismay, contemplating the problems the barge gate poses to his job making sure there are no holes in the city’s flood defense as a storm approaches.

While Turner said the flood authority is confident that Col. Edward Fleming, the corps’ local commander, will honor his pledge not to hand over the system until all its parts are working properly, he is concerned about the problems his agency will face with the complicated, seldom-used barge gate design.

“What happens when a storm blows up just off the coast in 72 hours, as has happened in the past?” he asked. “What happens if that thing is open and the tide is already running faster than the parameters? What do we do then? What happens is we can’t close Seabrook?”

He’s already working on answers to his own questions.

The flood authority plans to have a SCUBA diver and tug boat on stand-by throughout hurricane season to address at least two of the risks posed by the barge gate.

“We’ll need to get a diver down there to make sure there is no debris on the bottom so we can sink the barge without cracking it,” he said.

“And we’ll have a tug and a tug boat operator on standby so if that thing doesn’t work properly, we can put a line on it and somehow drag it closed.

“So, no, I’m not confident this thing is going to work as designed. It worries me. Like I said, it keeps me awake at night.”

*Correction: The original version of this story misstated the name of the Hurricane Storm and Damage Risk Reduction System and also of the Southeast Louisiana Flood Protection Authority – East. It also incorrectly stated that Gilmore said why environmental concerns weren’t raised earlier; he did not explain this.

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