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Reinforcing of canal at parish line set to start
Floodwall along Vintage Drive will seal off gate for pedestrians
Thursday, March 23, 2006
By Sheila Grissett
East Jefferson bureau


Almost $4 million worth of sheet piling has been manufactured in Virginia and is ready for delivery to Louisiana, where most of it will be used to bolster a misshapen section of canal floodwall on the Jefferson-St. Charles parish line, federal engineers said Wednesday.

 

Before the sheet piles can be driven, a process that officials said should start in mid-April, a grassy berm on the land side of the existing wall will be raised another 5 feet. That work will begin next week. All the work is expected to be finished by the start of hurricane season June 1.

 

An Army Corps of Engineers contractor is expected to use about 900 of the steel sheets -- each a half-inch thick and 60 feet long -- to build a protective barrier along about 1,600 feet of leaning floodwall on either side of the Vintage Drive pedestrian gate, as well as the gate itself.

 

"For anyone who cares, it will close off that gate," said Mervin Morehiser, corps project manager for the Lake Pontchartrain and vicinity hurricane protection system.

 

The new wall is the pièce de résistance of a corps plan to provide an extra line of defense this storm season for that section of the West Return Canal wall that dips and sways on both sides of the Vintage gate in Kenner.

Workers will begin spreading and compacting mud next week that will be hauled to the site from a Bonnet Carre Spillway borrow site, Morehiser said.

 

Sheet piling will then be driven through the new berm and deep into the ground to better separate the drainage canal, St. Charles Parish wetlands and Lake Pontchartrain from the heavily developed neighborhoods of northwest Kenner.

A 2-foot-wide space between the old and new walls will be filled with dirt for additional stability, and a concrete apron will be poured on the land side of the new wall to help protect against erosion if water comes over the floodwall during tropical weather, Morehiser said.

 

The apron will be about 10 feet wide and will follow the downward curve of the berm, Morehiser said. Neither the wall nor the new berm will be built atop the bicycle and walking path, which is part of an 11-mile asphalt trail that runs along the entire East Jefferson lakefront between St. Charles and Orleans parishes.

 

"But I'm afraid the equipment that we'll use out there will damage the path," Morehiser said. "I just don't see any way around it."

Wobbly wall

 

Although subsidence could be to blame for distortions in the wall, which a state engineer said have gotten a bit more pronounced since Hurricane Katrina, corps officials have said they don't know exactly what has caused some sections of the wall to sink or lean -- some to the east, some to the west.

 

But what the corps does know is that this piece of the structure was built in the late 1980s and early 1990s as an I-wall, which means a single sheet pile was driven about 11 feet deep, then tied with steel into a decorative, concrete cap to form the floodwall.

 

With the exception of two very short stretches of floodwall, most of the rest of the wall between the north end of Louis Armstrong International Airport and the lake was built as sturdier, more expensive T-wall. A T-wall rests on deeper sheet piling and depends on horizontal bracing to help keep the sheets from moving when stressed by high water.

 

I-walls in the London Avenue and 17th Street canals failed during Katrina, even though the floodwalls were not overtopped.

Even as a team of corps and independent engineers continues investigating those failures and devising new standards for future construction, the corps is taking remaining I-walls out of play by adding floodgates in the 17th, London and Orleans Avenue canals, and bracing the Vintage wall for the storm season ahead.

More info required

 

Al Naomi, senior manager of the Lake Pontchartrain project, said in January that the corps would replace the Vintage wall with new T-wall once the hurricane season ends in November, but he was unable Wednesday to provide an exact timeline.

Naomi said a replacement wall cannot be designed until investigating scientists using up-to-date information and new computer modeling finish calculating just how high all levees and floodwalls in the region should be.

 

"We have to apply new standards they come up with, assuming there will be some, so that we don't spend millions of dollars on a new concrete and steel structure that doesn't provide the protection it's supposed to provide," Naomi said.

"It could turn out that there are new standards that call for a whole new wall or even a new alignment if we had to build much higher," he said. "And if that happened, it would be bigger than just one wall."

 

Conversely, if the analysis indicates that only the Vintage gate needs replacing, that would be addressed.

"We just don't know yet," Naomi said. "But this temporary fix will take care of the Vintage wall this season while we're waiting for the reanalysis of the entire system."

 

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