Engineering system failures worry La. flood official
New Orleans — 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, installed after research showed it could not perform as originally planned and that might not be able to close unless another, distant gate is closed first?
And what if that gate still has not been operated successfully after almost a year of trials?
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 South 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,’’ he said.
The “barge gate” gets its name from its main element: a mammoth, concrete barge that is not so much a gate as an emergency dam to be used on a temporary basis during storms.
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.
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.
Their complaints are numerous: The corps backed off the operational parameters originally promised; closing it takes too long and is too complicated; and 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, 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.
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.
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 design found in channels the world over, thanks to its simplicity and efficacy: Two arms, mounted 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 the barge gate choice was based on budget and speed. 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.
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.
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.
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 hour before a storm in the Gulf is expected to begin affecting 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.
“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,” he said.
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.”
This story was reported by The Lens, an independent, nonprofit newsroom serving New Orleans at http://thelensnola.org/