In most cases a two-for-one deal would be a money saver for both partners in a business arrangement.

That might not be the case when it comes to the area’s new $14.5 billion storm surge protection system.

Some 34.6 miles of the Army Corps of Engineers’ Mississippi River levees also serve as part of the new storm surge system the corps recently built with its partner, the state of Louisiana. But it turns out that two-fer could eventually end up saving the corps millions, at local taxpayers’ expense.

The hurricane protection system requires 21- to 23-foot levee heights, while the river levee system needs to be just 20 feet high. So when the natural, ongoing subsidence that plagues the area eventually pulls those levees below the specs for the hurricane protection design, the local levee authority must pay to raise them.

And that means the corps may never have to pay to lift its river levees  — because the local levee authorities will make sure they never sink so low.

“We have to maintain our specs to qualify for national flood insurance, so we have to do those repairs and lifts, ” said Bob Turner, regional director of the Southeast Louisiana Flood Protection Authority-East.

“And right now, we would have to pay all of those costs even though we’re basically doing the corps’ job of maintaining its (river levee) specs.”

Corps spokesman Ricky Boyett said Turner’s assessment was correct because maintenance of the two systems is covered under different congressional actions. The storm surge levees are governed by the  Hurricane and Storm Damage Risk Reduction System while the river levees come under the Mississippi River and Tributaries Projects.

The  Water Resources and Reform Act of 2014 allows the corps to cover 65 percent of such repairs for the storm surge protection system  through 2024 – but only if Congress has appropriated the funds.*

“And right now there are no such appropriations,” he said.

The Mississippi levees are a vital part of hurricane protection because storm surge can travel up the river channel. For example when Hurricane Isaac, a weak Category 1 storm, came ashore in August 2012 the river jumped 6 feet in four hours at the Carrollton gauge in New Orleans.* That posed no threat to the city because at that time the river level was actually 6 feet below mean sea level, common for the late summer. The river bottom here is actually lower than the nearshore Gulf.

However, if a 6 foot jump  had occurred in July when the river was at 15 feet above sea level – a record height for the summer – the river might well have flowed over even the storm surge levee heights for a few hours.

Fortunately that would require a bigger storm than Isaac because the stronger current of the higher river would push back against storm surge.

“We estimate if a storm the size of Isaac came ashore (with the river at 15 feet) the jump would be about only 5 feet,” Boyett said.

Even that would push the river past 20 feet. That’s why the specifications for storm surge protection requires the river levees to be higher than what is mandated to guard against a river flood – and why local levee officials have to keep an eye on subsidence.

The corps is currently raising about 15.5 miles of West Bank river levees to bring them up to the storm surge specs, a cost covered by current authorizations.

But Boyett said corps’ subsidence estimates indicate 3.5 miles of east bank levees will need a lift by 2021 -– two years before the FEMA will check the levees to make sure they still are high enough to qualify for federally-subsidized flood insurance.*

And by 2057 another 16 miles will need lifts, 6.5 miles on the West Bank and 9.5 miles on the east bank.

Maintenance of the storm surge protection system is paid for by local property taxes from Orleans, Jefferson and St. Bernard parishes.

*Correction: This story contained three errors when it was published. It said the Water Resources and Reform Act allows the corps to cover a portion of repairs through 2014. That date should have been 2024. It also said that about 3.5 miles of east bank levees would need to be lifted by 2012. That should have been 2021. Corps spokesman Ricky Boyett’s name was misspelled. And the estimate of river rise due to Hurricane Isaac was 10 feet, based on early estimates. The figure has now been refined to 6 feet.(Sept. 4, 2015)

Bob Marshall

From 2013 to 2017, Bob Marshall covered environmental issues for The Lens, with a special focus on coastal restoration and wetlands. While at The Times-Picayune, his work chronicling the people, stories...