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Scientists set out to answer a question that has plagued them since Hurricane Katrina

Land near the Davis Pond Diversion in St. Charles Parish, LA  (John Snell) Land near the Davis Pond Diversion in St. Charles Parish, LA (John Snell)
(WVUE) -

Only miles from the mouth of the Mississippi River, a giant container ship heads out to sea, cruising past one of the few spots where the great river runs free of levees.

Here, Alex Kolker of the Louisiana Universities Marine Consortium pilots a small boat into the marsh, pulls out a boring tool, and digs down into the earth.

"You can take a look at the kind of soil structure," Kolker said as he examined a sandy cross section of time.  

"Sand is a very solid substrate for a marsh to build land on," Kolker said.  "It doesn't compact much and it's often very resistant to erosion."

In 1862, here in Cubit's Gap, an oysterman carved an opening  in the river bank. 

Sediment that poured into the bay created more than 75 square miles of land in less than a century. 

"It was the river, creating beauty and doing what she does," said Natalie Peyronnin, Director of Science Policy for the Environmental Defend Fund's Mississippi Delta Restoration effort. "It was amazing."

Cubit's Gap continues to build land today and researchers believe it holds lessons for Louisiana's ambitious plans to duplicate the river's land-building powers with man-made sediment diversions.

Skeptical commercial fishermen point to the smaller freshwater diversion at Caernarvon on the Plaquemines-St. Bernard Parish Line. 

After Hurricane Katrina wiped out hundreds of square miles of land in a matter of hours, even some scientists argued Caernarvon made the marsh more vulnerable to storm surge by converting salt water marsh to fresh grasses. 

Kolker and his colleagues come to a completely different conclusion, arguing that Cubit's Gap acts like a large sediment diversion.

Kolker paints the marshes here as practically immune to erosion-- with the strongest soils-- in areas that are almost completely fresh.

"These marshes also had the most organic sediments (largely decaying roots), the soils were relatively salty, and structurally these were the weakest soils we measured," Kolker said.

He believes the "pattern of wetland loss and wetland gain has nothing to do with salinity and it has everything to do with proximity to the river."

Farther from the river, the study finds the marshes saltier and flimsy.

"The more sediment that the wetlands get from the river, the more resilient they can actually be," Peyronnin said.

The stakes could scarcely be higher.

The state's Coastal Protection and Restoration Authority plans to spend $2 billion on the first two of the diversion projects, one on each bank of the river in Plaquemines Parish.  

In yet another spot in the parish, dubbed Mardi Gras Pass, the river has blown through its east bank in what environmentalists see as a sort of "free" river diversion.

"Having just this complete blowout of water doesn't fit into the plan," said Plaquemines Parish President Amos Cormier, echoing the concerns of fishermen who blame the an onslaught of fresh water for ruining their catch.

Cormier, at the very least, wants some kind of control structure to regulate the flow and suggests Plaquemines is being used as a guinea pig. 

"Why, in Plaquemines, are we going to let things go on their own?"  

Other critics want Mardi grass pass closed entirely and argue the state is using unproven science to back up the spending of billions of dollars on diversions.

They point out that never before has man attempted to build new land on such a large scale by diverting a river. 

"It has been done before," Peyronnin counters, pointing to Cubit's Gap. "The difference between what we're trying to do is build a structure that we will manually open and close."

She said the state will manage the system as opposed to being a more natural system.

"But we see Mother Nature, when we let her go in places like Cubit's Gap, she builds beautiful land, she builds productivity and she builds resilient land."

Critics question the modern river's land-building powers since studies show the Mississippi River is only about half as muddy as it was just over a century ago.

Countless locks and dams in other parts of the country trap much of the sediment flow. 

While diversion opponents want more emphasis on dredging to build land instantly by pipeline, scientists counter dredging accounts for more of the spending in the state's coastal master plan.

However, they argue only the river can sustain land whether built naturally or artificially.

"A lot of the land in this area is stable and building and that's because it's receiving water from the Mississippi River," Kolker said. 

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