Reversible flow advantages cited
By David J. Mitchell
River Parishes bureau
September 10, 2012
GONZALES — Ascension Parish government officials say a proposed Mississippi River diversion project in St. James Parish may be a way to blunt the kind of high storm surge seen after Hurricane Isaac.
Parish President Tommy Martinez and East Ascension Drainage Director Bill Roux would like the diversion project planned near Romeville to be reversible as part of a broader flood protection plan in the Lake Pontchartrain Basin.
Under that concept, water would flow not only from the Mississippi into the Maurepas Swamp, as currently designed, but also from the swamp into the river in times of high water in the lake basin, the officials said.
Surge from Hurricane Isaac moving in from the east almost swamped the Marvin J. Braud Pumping Station, a key pump station for Ascension Parish. At the same time, parish officials said the surge water blocks drainage of the Amite River Basin to the west and north after heavy rains.
Martinez said there needs to be a way to drain that surge water.
“We need to look at the whole basin and come up with a solution that affects Ascension, St. John the Baptist, St. Charles and St. James (parishes),” he said.
Roux noted that a levee project along the south side of the basin alone could raise the same kind of concerns for parishes on the northern side of Lake Maurepas and Lake Pontchartrain as have been raised about the post-Hurricane Katrina improvements in New Orleans.
“Water is going to go somewhere. You can’t squeeze it into a smaller space,” he said.
The Blind River diversion is designed to bring fresh water, nutrients and sediment into the Maurepas Swamp, which has been cut off from the river by the Mississippi levee.
The diversion is part of the Louisiana Coastal Area program and was authorized by Congress in 2007 under the Water Resources Development Act.
The recommended project calls for a 3,000 cubic feet per second gravity flow diversion structure on the Mississippi with a transmission canal and a diffuse distribution system into the Maurepas Swamp.
St. James Parish President Timmy Roussel said parish leaders have looked at the reversible concept before, but environmental regulators raised concerns about the quality and higher salinity of the brackish Lake Maurepas water. The Mississippi is used for drinking water downstream.
But Roussel said he believes a reversible diversion is “a viable option” if retention levees are built to protect populated areas.
Unanticipated flooding from Isaac in LaPlace, St. James and other River Parishes have created renewed urgency in building flood protection as well as drawn speculation that the billions spent to improve the New Orleans area’s flood protection pushed water onto those communities to the west.
National Weather Service officials have said their models show no evidence of this and the flooding was more likely due to the size, direction and slow speed of Isaac. The U.S. Army Corps of Engineers also disputes the claim but has agreed to study the issue.
Some River Parishes leaders are calling for accelerated action on building the long-in-the-planning West Shore Levee, which would provide 26 miles of protection from Montz in St. Charles Parish to the Marvin Braud station in Ascension.
The levee would largely track along the north side of Interstate 10, which had flooding during Isaac. Versions of the project, which have raised environmental concerns, have been discussed since the mid-1960s.
Steve Wilson, president of the Pontchartrain Levee District Board, said the levee can be designed to address concerns about cutting off wetlands from tidal flow.
Wilson said the full project can be built with about $500 million.
“It’s just our turn. We’ve got to finish the job,” Wilson said.
He said making the Blind River diversion reversible would require some sort of redesign to be able to move water toward the river.
Also, Wilson said, he does not see how a diversion in Romeville/Convent would help flooding in St. John because the surge water moved from the east to the west through the Lake Pontchartrain Basin during Hurricane Isaac.
Ricky Boyett, corps spokesman, said making the diversion reversible was brought up in discussions but never was a primary feature.
He said that project is still in the planning phase, and a hydraulic analysis would need to be conducted to see if a reversible flow would be beneficial.
Boyett added that corps officials noted that the probability of high water in Lake Pontchartrain and low water in the Mississippi is extremely remote and would happen only for a short time.
But Garret Graves, chairman of the state’s Coastal Protection and Restoration Authority and executive assistant to Gov. Bobby Jindal for coastal activities, said the state is trying to look more holistically at the basin and making the Blind River and nearby Hope Canal diversions reversible will be considered for their effectiveness.
“It’s absolutely something we will be looking at over the next few months,” Graves said.
The state’s coastal master plan has $1.6 billion in funding set aside for future projects and new concepts, he said.
But he also noted some considerations, including the water quality concerns and the possible need to build pumps to move the water into the river.
He said an important project to him, however, is putting control structures at the Rigolets and Chef Pass. They are Lake Pontchartrain’s main connections to the broader Gulf of Mexico and hurricane surge.
Graves said that project would not preclude the diversion concept, which could be another tool to prevent flooding from hurricanes.