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The Mississippi River Carries More Than Enough Sand to Rebuild Its Sinking Delta

The mighty Mississippi carries enough sand and silt to rebuild Louisiana's disappearing marshes for the next 600 years

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The Mississippi River carries enough sand downstream to keep Louisiana's sinking marshes afloat for the next 600 years, according to a new study published in Nature. This means that a plan to rebuild wetlands through sediment-capturing diversions could be viable, the Times Picayune reports. The sand would be captured from the deepest parts of the river through engineered diversions, and then repurposed in other places where the wetlands are being washed away. The Times Pic:

Some diversions could move as much as 250,000 cubic feet per second of freshwater laden with sediment into wetlands on the east and west sides of the Mississippi River, but would be operated at such high levels only during river flood years, which occur every three to seven years, when the river carries the greatest sediment load. At other times, scientists say, they'd be managed to benefit local fisheries as much as possible. 

The new Nature study is good news for those plans, proving that the diversion idea is indeed viable on the long term. The authors analyzed sediment samples taken over the past 40 years at various locations along the Mississippi. The flow of sand, they found, has remained steady over that period, despite the presence of dams on the Missouri River, which historically provided sand to the Mississippi.  

Here's the Times Picayune with more on the findings: 

The model indicates that the river’s flow mines sand from its bottom between Cairo, Ill., and the Louisiana-Mississippi border to make up for the sand lost on the Missouri, as evidenced by the near-steady levels of sand over the last 40 years at Tarbert Landing, Miss., which is just north of the Louisiana border.

The slow deepening of the river bottom that this process causes will eventually make its way downstream, reducing the amount of sand the river carries. But that slow process will result in only a 17 percent reduction of sand at the end of 600 years, the study concludes.

That sand, the study authors write, could "substantially mitigate land loss." That land loss is currently well underway. Indeed, the Delta is suffering from a "catastrophic drowning"—largely caused by human activities—that is turning thousands of square miles of wetlands into open water, the authors write. As the wetlands disappear, biodiversity goes with it, a loss that also impacts human livelihoods. Without wetlands, fish and crustaceans have fewer places to grow from juveniles into adults, meaning less of the delicious seafood that Louisiana and the rest of the Gulf Coast is known for. 

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