Free coastal project? Or a threat to navigation?
Coastal activists question Army Corps plans to partially close Neptune Pass
NEW ORLEANS (WVUE) - Charter boat captain Ryan Lambert scoops up a handful of Mississippi River mud a couple of miles from the river in Quarantine Bay.
Here, on the east bank of Plaquemines Parish, sediment pours into nearby bays, converting parts of them to land.
Several decades ago, the Mississippi blew through the river bank to create a new cut. Barely the size of a bayou a few years ago, the channel has grown rapidly following a high-water event in 2019.
The U.S. Army Corps of Engineers estimates Neptune Pass, as it is called, now has a width of 850 feet and captures 16 percent of the river’s flow.
“We’ll have a free diversion,” said Lambert, who for years has been a vocal supporter of the state’s plans to divert the river into the marsh with the aim of building new land. “It’s already growing land like crazy with no manipulation.”
However, the Corps sees issues with Neptune Pass and its rapid growth.
“We know we have impacts to navigation,” said Corps spokesman Ricky Boyett. “It has to be addressed.”
As more water veers into the pass, engineers say, the flow in the main channel slows. That causes sand to drop to the bottom, potentially making it more difficult for large ships to navigate the river.
“The increase began after the high water of 2019,” Boyett said, “but in the last few years, we’ve seen a rapid expansion.
“What the end result would be -- left uncontrolled -- we don’t know. That would require some study and evaluation.”
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The Corps first wants to stop the new pass from gouging out more of the river bank.
As early as next month, the Corps plans to put down a blanket of rocks where the channel begins, to stop the erosion. Then, about half a mile into Neptune Pass, engineers plan to install some kind of rock barrier or structure mostly below the surface, allowing for some water flow and boat traffic.
“If we did something to completely cut it off, you’re changing this dynamic that has slowly built over time immediately, and you can cause unintended consequences,” Boyett said.
Boyett says more study is needed to ensure that, by cutting the flow in Neptune Pass, they don’t simply push more water into another cut in the Mississippi somewhere upriver or downriver.
“It just kind of takes my breath away,” said Erin Sandefur, a coastal activist seeing the new delta for the first time.
Coastal advocates want the Corps to leave it alone, suggesting the pass is like having a free coastal restoration project.
“I mean, all you have to do is look at the historical map and see how much we’ve lost,” said another activist, Polly Glover. “We simply can’t lose any more.”
That new delta has been the subject of some controversy, with skeptics questioning whether land-building truly takes place here.
Boyett points out that the channel itself was once land.
“We need to know where that sediment went,” Boyett said. “Is that the sediment that’s kind of creating a new delta? So, you’re not really getting plus-land, you’re just getting a redistribution. Or, is it a situation where the sediment from the river truly is building land.”
Lambert, who has watched the new delta form over the last couple of decades, needs no convincing.
“I want to manage it like God made it,” Lambert said. “If you let Mother Nature do what she does, it’s gonna grow back. We’re the ones that ruined it. We built the levees.”
The Corps says it only intends to go back to the amount of water flowing through the pass in 2018.
Corps hydrologists estimate the average flow at Neptune Pass to be 96,000 cubic feet per second, making it the equivalent of the 15th largest river in the U.S.
At its peak flow during high-river events, hydrologists estimate the flow at up to 200,000 cfs. For perspective, the design flow for the Bonnet Carre Spillway operating with all the bays open is 250,000 cfs.
“Whatever we do, we’re going to be looking at restoring what was (prior to 2019), not just closing it off,” Boyett said.
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