Diverting the Mississippi River south of New Orleans could create up to 470 square miles of new land over the next 100 years, according to a new computer model.
That’s an important finding for the Mississippi Delta, which has been losing about 17 square miles of land to the sea each year since 1940.
Although the river’s water naturally carries sediment southward from Minnesota to the Gulf of Mexico, levees built below New Orleans in the early 20th century have upset the natural balance between soil loss and sediment deposition. As a result, the waters at the end of the river flow fast and deposit sediments over the continental platform, draining into the Gulf of Mexico.
"What this model shows is that we can, to a large degree, match future land loss by making these diversions," said David Mohrig, a geologist at the University of Texas-Austin and a co-author of the study with Wonsuck Kim, who first published their findings in the journal Eos, the weekly newspaper of the American Geophysical Union.
How do they figure?
Researchers say the loss of land could be stopped by making two cuts, on opposite sides of the river, in levees 93 miles downstream from New Orleans. That way, nearly half the river’s water would spill out through those cuts, depositing sediment on each side of the river channel. As a result, new land would be created, reversing the alarming trend that would see 45 percent of the area vanish into the sea if nothing changes.
Other scientists have proposed similar solutions in the past, but critics have their reservations. Some say dams in the upper Mississippi have reduced the water’s sediment content so much that it’s not possible to rebuild the delta. Others say restoration is not possible, given the current sinking rate of the delta and future sea-level rise.
Mohrig said his model offers proof of a solution. "Until we put together this model, there was a lot of debate that wasn't substantiated by anything but by intuition," he said. "We needed to move from having very soft impressions of what could be done to making predictions that can actually be tested."