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Work of 19th century geologist could help with Louisiana coastal restoration plans

The New Orleans skyline can be seen in the background from the Davis Pond Diversion site on the west bank of the Mississippi River (Source: John Snell) The New Orleans skyline can be seen in the background from the Davis Pond Diversion site on the west bank of the Mississippi River (Source: John Snell)
NEW ORLEANS, LA (WVUE) -

Engineer Dennis Lambert was researching an ancestor's role in early drainage projects in New Orleans when, at the Tulane University archives, he stumbled upon some long-forgotten work of a 19th century geologist.

Marie Joseph Raymond Thomassy, a geologist from France, might have been the first expert to suggest diverting the Mississippi River into the marsh as a means of building land.

"He was the originator of it in the 19th century," Lambert said.  "It had been used in the 18th century in Italy."

Thomassy and other scientists from his day were not thinking about coastal restoration. It was thought New Orleans, desperate for a solution to repeated yellow fever epidemics, might benefit from filling in parts of the swamp. Lambert points to one of Thomassy's maps that depicts changes near the mouth of the river.

"It's all in French," he said.  "This map right here is very interesting because it shows the change in the delta from 1839 to 1851."

Still connected to the river, the delta grew as the Mississippi spilled over its banks and belched mud and sand from the annual spring snow melt. While the modern plans call for large structures and guide levees, Thomassy also envisioned more than simply a cut in the river. His plan, circa 1860, called for strategically positioning "colmates" - levees or small islands - to slow the water flow and trap tiny bits of soil.

"This was thought about without computers and modeling," Lambert said.  "It was sort of human intuition to try to use the river."

The Civil War came along and the method was never used, an idea lost to history. 

Today, 21st century conflicts pose new obstacles, especially the opposition of commercial fishing interests skeptical about the notion of pouring massive amounts of polluted Mississippi River water into the basins.

"Some people are just vehemently opposed to diversions no matter what kind of control you could implement in the outfall area," Lambert said.

He believes that some application of this old technique could find its way into the design of diversions. One example might already exist in the Davis Pond fresh water diversion on the west bank near the Jefferson-St. Charles Parish line. Bren Haase, Coastal Planning Director for the Coastal Protection and Restoration Authority, points out natural features in Davis Pond trapped sediment.

"What we're sitting in right now is a colmate," Haase said during a recent tour of the site.   

Even though Davis Pond was designed only to deliver fresh water to marsh and push back salt water from the gulf, about 8 inches of land has built up in places since the diversion opened in 2002.

Haase said terraces or other features could be used to slow sediments moving through the diversion and target land-building spots.

"We are certainly open to looking at that as we move forward with the diversions that are planned."

The firm Lambert works for, COWI North America, has done extensive engineering on coastal projects, including the planned diversions along the Mississippi.

"I think there should be consideration and targeting these areas" where modern colmates could be used," Lambert said.  "How it's done exactly I don't even think I have worked out in my head."

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