Mississippi River carries enough sand for 600 years of wetland building

quote:

---

Mississippi River will carry enough sand needed to build new Louisiana wetlands for at least 600 years, new study says

By Mark Schleifstein, NOLA.com | The Times-Picayune
on April 20, 2014 at 3:33 PM, updated April 20, 2014 at 7:24 PM

The lower Mississippi River should carry enough sand during the next six centuries to supply the needs of sediment-capturing diversions proposed for Louisiana to rebuild wetlands, according to a scientific letter published online Sunday in Nature Geoscience.

“Our evidence indicates that the sand supply from the Mississippi River is stable and sustainable,” said the paper. “This sediment is available to build deltaic land via engineered diversions, designed to capture sand deep in the Mississippi River channel.”

Rice University geologist Jeffrey Nittrouer and University of South Carolina water-resources engineer Enrica Viparelli reviewed 40 years of sediment sampling data at locations on the Mississippi below major dams built in the 1950s on the Missouri River to conclude that the amount of sand carried by the river when it reaches Louisiana has remained steady, even though the amounts of lighter organic and clay particles have been significantly reduced.

“Our modelling shows that it will require several centuries for this zone of degradation to reach, and thus limit sand supply to, the Mississippi River delta, so as to form channel morphologies with diagnostic features indicative of limited sand supply,” the paper said.

That’s important because the heavier sand granules are more likely to build land when deposited in open water areas by diversions than lighter organic and clay particles that make up the largest portion of sediment that the river carries.

“Sediment is the life-nourishing resource to any delta because it builds a stable platform on which vegetation colonizes,” the paper said. “Despite the dominance of mud versus sand supplying the Mississippi delta, it is the sand that builds the landscape framework,” according to the study in the peer-reviewed journal.

Such a process is happening with the expansion of the Wax Lake delta at the bottom of the Atchafalaya River, which carries 30 percent of the Mississippi’s flow.

---