Escape from New Orleans
Project improves drainage, lengthens hurricane evacuation route

By Sam Barnes

Residents along the new extended route for West Napoleon Avenue in New Orleans will get more than a new four-laned road. They'll get a way out.

Boh Bros. Construction Co. LLC of New Orleans will give the area a vital hurricane evacuation route and dramatically improve stormwater drainage when it finishes the $11.8 million road and canal project this summer.

The West Napoleon extension is the only active project in the Crescent City area funded by the Louisiana Department of Transportation and Development's four-laning program and connects to existing Napoleon Avenue to the east.

DOTD Secretary Kam Movassaghi said the project is one of many begun during the last year as part of a renewed initiative to complete the state's Transportation Infrastructure Model for Economic Development.

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"The $3.5 billion program (to be completed by 2010) will widen 500 miles of state highways to four lanes on 11 project corridors," Movassaghi said.

Most significant to the everyday lives of residents near West Napoleon is the drainage work, which requires the widening and paving of the existing canal in the median. The paved canal will reduce friction and therefore improve the flow of stormwater through the flood-prone area.

Boh Bros. superintendent Bill Moulton expected the project to be completed a full year ahead of schedule.

"We broke ground in May and should complete the project in July, but the required completion date is not until the fall of 2005," Moulton said.

He credited the project's impressive progress to a dose of good weather and "doing everything every day."

"It comes down to the method of construction that we use," he added. "We complete an entire 40-ft. section every day by managing multiple crews. The pile drivers drive sheet piling, the excavation crew digs, the carpenters erect forming, the rod busters place reinforcing steel and we pour our concrete and backfill. We then break the forms, pull the sheet piles and move on down."

The key is keeping the entire crew busy all day, every day.

"To get maximum productivity out of your labor you have to be forming and pouring a section each day," he added. "If you don't finish the entire sequence on a given day, the next day you're not as productive because you'll have a crew with nothing to do." Boh crews are completing about 160 ft. of canal a week, with a maximum of 200 ft. during weeks with "perfect weather conditions."

As with any canal job, the weather doesn't merely delay progress - it stops it dead in its tracks.

"On other jobs, a thunderstorm comes along and a crew finds cover under an overpass or somewhere, then resumes work when it's over," Moulton said. "With canal work, a storm floods you out and you send everybody home for the day. You then pump the water out and hustle when you come back in."

When crews broke ground at the site late last spring, they began paving the canal from east to west, driving sheet piles along a 1,000-ft.-long section of canal and bracing 200 ft. with struts and wales to create the cofferdam. An earthen dam is moved about 200 ft. down the canal each week to keep the site dry, when possible.

Boh Bros. chose to create 40-ft. of paved canal per day even though engineers allowed for up to 60 ft. per day.

"Doing 60 ft. a day would would have required a larger crane (than the 60-ton crane currently being used) and that would have taken up vital space," Moulton said. "We had to have sufficient access around the crane."

Ultimately, the canal will be deeper and its bottom will be narrower, while the width at the top of the canal will remain the same. Excavators are removing more than 26,000 cu. yds. of material, all of which is being re-used by Jefferson Parish.

On the canal bottom, Boh Bros. is placing a layer of geotextile fabric and a 4-ft.-thick layer of limestone, followed by the pumping of 12 in. of concrete for the 27-ft.-wide canal bottom and 14 in. of concrete for the walls. More than 7,500 cu. yds. of concrete supplied by Carlo Ditta Inc. of New Orleans is being placed for the canal.

All of the concrete is reinforced with steel.

"We pour from sheet pile to sheet pile for our bottoms and use a metal wall system for the flume walls," Moulton said. Relief grates are installed every 60 ft. in the canal bottom to relieve hydrostatic pressure, thus reducing water pressure from beneath the canal.

While the paved canal bottom will improve drainage flow, the paved walls of the canal will support the new roadway and prevent erosion.

Jefferson Parish engineer Mark Drewes said a section of Napoleon will be 2 ft. higher than surrounding neighborhoods to bring the road bed to the elevation required for a hurricane evacuation route.

To accommodate the heightened elevation, Boh Bros. will connect new concrete pipes to five existing pump stations to transport stormwater from low-lying areas into the canal.

"The subdivisions are so low that it inverts the flow in the pipes. The pipes are at a lower elevation than the water in the canal," Drewes said.

During a high-water event, flapgates on the concrete canal pipes prevent water from backing out of the canal and the pump stations then "lift" the water into the canal.

"Once the pressure in the canal becomes greater than the pressure in the pipe, the flapgate shuts and the pump stations kick on," he added. "This works until the water flows over the canal top. If that happens, there's nothing that can be done."

That's happened seven times in 15 years, but parish and state officials hope having the canal deeper and lined with concrete will improve the flow enough to reduce the likelihood of a major flood event.

Drewes said the new lanes of Napoleon Avenue will provide further flood protection by acting as a protective berm around the canal.

Other drainage-related work requires the placement of about 7,700 ft. of reinforced concrete pipe and the construction of more than 150 catch basins. The pipe will run beneath the new lanes of Napoleon Avenue and connect to the parish's existing drainage system.

"We went back about 60 ft. from the intersections, built new catch basins and tied into existing drain lines," Moulton added. "Basically, there is a pipe leading out of the catch basin to a collection box, and out of that one pipe goes to the pump station and one pipe goes to the canal."

More than 200 ft. of 72-in.-diameter pipe is being installed where neighborhood streets intersect West Napoleon. All of the RCP pipe is being supplied by Hanson Concrete Pipe of Baton Rouge.

Other pipe is made of PVC and ties the concrete drain lines to manholes in the street.

In areas where the new roadway comes too close to pedestrian paths or residential properties, a Boh Bros. crew forms and pours concrete retaining walls.

"We've done one of these so far, but there could be more to come," Moulton said. "The parish decides where they want them."

Moulton said the summer completion date would be achieved barring a significant weather event.

"It's all about the weather," he added. "We have a system in place that will get the job done more than a year ahead of schedule, but it's all in Mother Nature's hands."

Editor's Note: This is the first story in a two-part series on the extension of West Napoleon Avenue in New Orleans. This story focuses on the project's drainage canal work, while the second story - to be published in the May issue - will focus on road construction.

Useful Resource

For more information about drainage improvement projects in the New Orleans area, go to: http://www.swbno.org/drainagerehabilitation.html