Sunday, November 09, 2008

Project aims to restore Mississippi river flow and aquatic life behind diversion dikes

Memphis Commercial Appeal [link]
By Tom Charlier, Sunday, November 9, 2008

With its Sahara-like dunes and outcroppings of sun-bleached shells that hinted at a richer past, the acreage stretching out behind Ron Nassar and John Rumancik on a crisp fall morning had all the hallmarks of an ecological desert.


Biologist Leighann Gipson surveys the scene near a Mississippi River dike targeted for relief to restore aquatic habitat up and down the river. Photo: Mike Maple/The Commercial Appeal

This area just upstream from Downtown Memphis used to be a back channel of the Mississippi River -- a place where young fish could find refuge before plunging into the swift current, and where migrating shore birds could swoop in for a quick meal of tiny crustaceans.

But today, it's 11 miles of mostly sand.

"You can see what's happening to the river," said Nassar, coordinator of the Lower Mississippi River Conservation Committee. "You're converting it from aquatic to terrestrial habitat."

The problem lies with the navigation dikes -- stone walls up to a mile long -- erected by the Corps of Engineers to divert the Mississippi's water away from back channels and into the main river where barges navigate. Although they've kept the navigation channel deep enough for barges, the dikes have dried up many of the critical side chutes and channels behind islands.

But now, through a comprehensive program known as

"Restoring America's Greatest River," the corps and a group of other federal and state agencies are working to undo the damage. They've identified 239 projects along 954 miles of the river between Cairo, Ill., and the Gulf of Mexico to improve aquatic habitat and recreational opportunities.

Two years ago, in the initial project of the restoration campaign, the group reopened a secondary channel behind Island 63 in Coahoma County, Miss.

In a $200,000 project now under way, a contractor is creating large notches in seven dikes that blocked channels behind Loosahatchie Bar and nearby islands near the Arkansas side of the river across from DeWitt Spain Airport in Memphis. To make the notches, trackhoes and bulldozers peel away rocks weighing up to 5,000 pounds.

Until now, water flowed into the secondary channels only when the river was high. When low stages occur during summer, water gets trapped behind the dikes and eventually dries up or withers into stagnant pools, in which fish are doomed.


The Corps of Engineers and the Lower Mississippi River Conservation Committee are putting notches in navigation dikes on Loosahatchie Bar and Redmond Chute near Memphis to restore river flow behind the dikes. Photo: Mike Maple/The Commercial Appeal

Biologists over the years have noted a decline in the diversity in the age groups and sizes of some fish found in the river. It's been attributed in part to the loss of the secondary channels, which newly spawned fish need to safely forage and grow before entering the main river.

Once the notches are in place, the river will scour away some of the sand, creating channels that will have some flow at least 97 percent of the time.

Rumancik, a biologist for the corps, said the builders of the dikes in past decades shouldn't be faulted for not foreseeing the damage.

"Nobody ever thought what might be the impacts because the river was so big and huge," he said.

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