The Mississippi river flows past New Orleans, Louisiana, at an average rate of about 17,000 cubic metres per second, carrying more than a hundred million tonnes of sediment from the middle of the US into the Gulf of Mexico each year. Standing along its shore on land made of such sediment, I watch the silt spin in brown eddies in the river. That mud might soon be put to use.
A construction team not far downstream from where I stand has begun cutting a channel across the narrow strip of land that separates the river from Barataria Bay 鈥� an arc of shallow water polluted by the Deepwater Horizon oil spill in 2010. The project 鈥� called the Mid-Barataria Sediment Diversion 鈥� will redirect about 8 per cent of the Mississippi鈥檚 total flow into the bay, reuniting the river and its wetlands, which were separated by levees put in place a century ago.
鈥淭his is one of many projects that are needed to restore the landscape,鈥� says at the Louisiana Universities Marine Consortium, a state research group. If completed, the project would be among the largest ecosystem restoration projects ever undertaken in the US, both restoring the wetlands and forming new land on Louisiana鈥檚 coast.
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According to assessments by the US Army Corps of Engineers, the deposited sediment would build 25 square kilometres of new land within the first decade as it piles up in mudflats and plants take root. By 2050, as much as 70 square kilometres of land would form in the new delta. Accounting for further erosion and rising seas, the Corps projects a net gain of about 40 square kilometres by 2070.
That is a pittance against the more than 5000 square kilometres of Louisiana鈥檚 coast lost in the past century. But proponents see Mid-Barataria and other proposed sediment diversions as essential to addressing the root of the problem: levees cutting off the supply of fresh sediment to wetlands. Accelerating sea level rise adds urgency, with of the state鈥檚 coastal wetlands at risk of drowning by 2070 on our current emissions trajectory. 鈥淭his is our last chance as a coast,鈥� says at Tulane University in Louisiana.
Environmental advocates have unsuccessfully lobbied for sediment diversions for half a century. But the $2.9 billion project on Barataria Bay became more than a pipe dream only after funds for coastal restoration became available from legal settlements related to the Deepwater Horizon disaster, the largest marine oil spill in history.
The fresh sediment would help restore wetland habitats for birds, as well as the many species of fish that spawn there. The new land would also buffer New Orleans and other coastal communities from increasingly powerful storms and rising seas. According to one , the new soil could also sequester more than a million tonnes of carbon. 鈥淚t鈥檚 one of the most sustainable, long-term ways to build land,鈥� says Kolker.
But there are downsides. The freshwater is expected to disrupt lucrative oyster and shrimp fishing in the bay, which took off after the levees were constructed in the 1930s and the water grew saltier. The decrease in salinity would also that live primarily in the bay. And even as the new land would protect people further inland, the added water in the bay would raise flooding risk for adjacent communities in Plaquemines parish.
For these reasons, the project has been embattled by legal challenges. Plaquemines parish sued the state to halt construction, which began in August 2023. After briefly restarting, it was paused again on 26 February and remains stalled. The state agency building the project said it is committed to building the diversion, but the pause has raised doubts about whether it will be completed.
鈥淲e don鈥檛 know yet what is going to happen eventually, but I fear the worst,鈥� says T枚rnqvist, who sees the sediment diversion and other projects like it making the difference between an orderly retreat from Louisiana鈥檚 coast and 鈥渃omplete chaos鈥�. To not reconnect the river with its wetlands would be to give in to the sea, he says. 鈥淭hat鈥檚 basically like a surrender.
