Posted on February 20, 2023
A contentious channel formed off the Mississippi River has begun to build new land off Plaquemines Parish’s east bank, according to research published Tuesday.
Debate over the future of Neptune Pass began last spring after the river scoured out what has become one of the largest new distributaries to form on the lower Mississippi in decades.
The U.S. Army Corps of Engineers has since begun to look at closing the 850-foot-wide crevasse over navigation concerns. With the creation of Neptune Pass, nearly a third of the river’s flow has been redirected, and a slower main stem forced the Corps to do emergency dredging in the Mississippi River Ship Channel.
But Louisiana’s Coastal Protection and Restoration Authority and environmental advocates argue the channel presents an opportunity to balance shipping needs with coastal restoration if new land is being built.
And according to a new report, Neptune Pass is actually building some land – a rare occurrence on the state’s rapidly sinking coastline.
Alex Kolker, a geologist with the Louisiana Universities Marine Consortium, and co-author Dallon Weathers crafted a “sediment mass balance study” and ultimately budgeted all the mud that’s been deposited. They found that over one-sixth of a new delta formed in Quarantine Bay was likely built by introducing muddy river water.
The rest of the sediment settled in the bay after the force of the river widened what was once Bayou Tortillion.
Kolker and Weathers used a mix of tools – ranging from soundwaves and drone lasers to satellite imagery – to map the current state of Neptune Pass, compare it to its old size and measure the new growth in Quarantine Bay as part of the “sediment mass balance” study. They also plan to gather more data with core samples once they receive permits.
Geologist Alex Kolker (left), surveyor Dallon Weathers (right) and local councilmember Richie Blink discuss the future of a channel growing on the east bank of Plaquemines Parish, while docked on the marshes bordering it on June 6, 2022.
Kolker added that the use of some of the new mapping technology could lead to a wider range of error as they continue their calculations.
“I hope whatever is done with Neptune Pass is done based on the best available science, and we’re trying to do our best to give them a piece of that best available,” Kolker said.
The research was funded by CPRA and the National Wildlife Federation, one of the environmental groups in a larger coalition advocating for coastal restoration in Louisiana.
Both state officials and environmental advocates hope the Corps will take the 9-month-long research project into consideration as it crafts its final environmental analysis of closing the channel.
Jim Pahl, a senior staff scientist with CPRA’s planning and research division, said the state understands the difficulty in negotiating a plan that avoids increased dredging costs without sacrificing the potential to keep building land.
“That’s obviously the friction,” Pahl said. “Land building’s great, but if the land building comes at the expense of increasing the burden of maintaining the navigation channel, how do we weigh that?”
National Wildlife Federation coastal scientist Alisha Renfro echoed Pahl, stating Kolker’s research shows that leaving the channel open has “real ecosystem benefits.”
“At the end of the day, the question really becomes how do we balance all the needs in this area?” she said.
In September, the Corps’ draft environmental assessment seemed to lean toward fully closing the channel with a stone structure that would restrict the water flowing through Neptune Pass to a 100-foot-wide, 10-foot-deep opening. The state and advocacy groups hope to see that change to allow more water to flow through – even if not at the current volume.
Kolker said he presented his findings to the Corps and plans to continue to refine his research over the next year before ultimately publishing in a peer-reviewed journal.
The Corps is expected to release its final assessment of the channel and its closure within the next few weeks.
