Five-Part Project to Ease New Orleans Flooding
Designed and constructed by the U.S. Army Corps of Engineers (USACE), the project spans almost two miles and is broken up into five contracts, each with different general contractors. Discovery of subsurface material, the design of a complex siphoning system and coordination with local businesses have proven difficult, but the project is still on schedule.
Five ‘Big Easy’ Pieces
The $100-million project aims to improve drainage in the New Orleans suburbs of River Ridge and Harahan. Kazem Alikhani, director of the Jefferson Parish Public Works, says the idea for the project arose following a May 1995 flood that overwhelmed the canals and flooded thousands of homes. Post-disaster investigations found that pumping from River Ridge and Harahan to the Mississippi River instead of to Lake Pontchartrain could dramatically improve drainage.
The Southeast Louisiana Urban Flood Control Project (SELA) was founded in 1996 as a result of the disaster with the aim of completing more than 50 flood-control projects by 2017. As one of those projects, Pump to the River will cut three miles off the distance water has to travel, thus reducing volume and easing flows in the Soniat Canal. “The new [route] will tremendously lower the stage of the Soniat Canal and will significantly improve drainage in the Harahan and River Ridge area,” says Alikhani. “It will be a big improvement for flood protection in the area.”
The project spans almost 10,000 ft from the foot of the Soniat Canal to the Mississippi River. The system starts with the $10.7-million intake basin (SELA 09a) that takes water from the Soniat Canal and Mazque Ditch to a transition box culvert in the Harahan Pump Station. It is being constructed by Veteran’s Contractors Group JV LLC and consists of 600 linear ft of underground culvert.
The $29.4-million pump station project (SELA 09) broke ground in September 2011 and is roughly 80% complete. It is being constructed by MR Pittman Group and consists of three 400-cfs vertical diesel pumps that push the water on its trek to the river. After leaving the station, the flow runs into the 1,600-ft north discharge tubes (SELA 07a) and then to the 4,500-ft south discharge tubes (SELA 07b) being constructed by Conti Enterprises for $23.8 million. The entire system ends at the discharge basin (SELA 07c), a $24.4-million project being built by B&K Construction Co. It consists of 2,000 linear ft of steel pipe, a pile-supported concrete discharge basin and a cathodic protection system.
Rachel Calico, project manager at USACE, says it took careful planning to divide up the project and ensure that all the contractors were in sync. While they managed their own individual parts, they all needed to communicate where the segments met or overlapped. The Corps has also been working closely with Jefferson Parish, the city of Harahan and the Louisiana Dept. of Transportation and Development as well as local businesses affected by the construction.
“It’s a big site, and there are a number of [contractors] involved, but we haven’t had any major issues. It has been going very well with all involved,” Calico says.
Laying drain pipe may be relatively simple, but the long distance, large volumes and elevation changes demanded some complex engineering. To accommodate a large flow of water over such a long distance, the Corps called for 84-in.-dia pipes. The piping is being fabricated off site and transported to the jobsite in 20-ft to 50-ft segments, Calico says.
While most of the piping is laid through prescribed rights-of-way, there are some areas where work is affecting private property and causing long-term road closures. In other areas, heavy construction with pile drivers and excavators is happening near businesses and homes.
“We’re having to deal with some property owners, but we’ve done a good job of publicizing the work,” Alikhani says. “You’re going to have some inconvenience with a project like this, but [homeowners and businesses] in the area understand it’s important.”
Calico says there has also been some surprises on the project. One was the discovery of a 190-ft-long sunken barge along the banks of the Mississippi near the discharge basin. B&K employed a specialized dive and recovery team to remove it from the site. That delayed the schedule by a month, but the contractor has since made up the time by laying pipe in the ground faster than anticipated.
“It was a nerve-wracking process,” Calico says. “A diver had to cut [the old barge] with a torch, and they removed it piece by piece. It could have been a much bigger problem, but we’ve got good contractors who know how to get these things done.”
Calico says they also encountered some difficulty when driving the 500 60-ft piles for the pumping station. A tough layer of debris and sand was causing some of the wooden piles to split. MR Pittman Group and the Corps devised a method of pre-drilling the holes, filling them with water and installing steel cone points at the base of the piles.
“It initially gave us some grief and there was a learning curve, but once we came up with the right method, it was smooth sailing from there,” Calico says.
Engineering a Pump System
One particular challenge of the project design was moving water over such a great distance and then lifting it over the 26-ft-tall Mississippi River levee.
Stefan Miller, a mechanical engineer with the USACE, helped design the siphoning system. Where a typical pump station may have a 100-ft discharge tube, the long span to the river required special planning and hydraulic engineering. The system requires water to be pushed upward, from a low point of 15 ft below sea level, to 17 ft above sea level at the top of the levee.
“It’s the same principle as siphoning, but [the water] needs some help along the way,” Miller says. “The water is draining to a higher level than you are coming from.”
The pipes run on a slight incline toward the river before rising sharply to clear the levee. Miller says once water reaches the other side, it helps siphon the rest of the water over the top. The Corps created a scale model using water flow and volume to determine what it would take to prime the pipe. Miller says they then worked with a manufacturer to construct customized pumps to move the water at the right velocity. With such large pipes and the weight of the water moving across the levee, the design required the contractor to first widen and fortify the levee with concrete supports. After pipes are laid across the levee, they will be placed back underground for the span to the discharge basin.
Miller says the key to making the siphon work is to keep the pipe filled with water and eliminate air pockets. This was accomplished by designing the system with numerous shutoff and release valves. In the case of a big rain, the streets will drain to the pump station, which then starts to fill the pipe with water. Once the pipe is filled up to the levee, the system is primed and siphoning can start.
“It was a little complicated in that sense,” Miller says. “You don’t want air trapped in the pipe. We did a lot of studies to see what it would take to prime [the pipe]. If the pump isn’t pumping hard enough and you have air, it won’t work.”
Despite a few delays and engineering challenges, Calico says the project is on track for a 2017 completion.