Diverting parts of the Mississippi would create up to 1000 square kilometres of new wetlands between New Orleans, Louisiana and the Gulf of Mexico, forming a vital storm surge buffer against hurricanes, researchers say. The formation of new delta lands could also help stem ongoing coastal erosion without disrupting important shipping traffic.

"The scientific and engineering barriers are easily overcome," says Gary Parker, a geologist and engineer at the University of Illinois in Urbana-Champaign, who developed the plan with colleagues. "The big issue is political will".

Details of the scheme were unveiled on Sunday at the annual meeting of the American Association for the Advancement of Science in Boston, US.

Breaching the levee

The proposed diversion would cut breaches into a levee some 150 km south of New Orleans, Louisiana, and 30 km above where the river empties into the Gulf of Mexico. With the diversions in place, flooding would cause the river to empty into shallow saltwater bays on either side of the river, releasing sediment-rich water to produce new deltas.

"You keep the sediment within the coastal boundary current that keeps it running along the shoreline, whereas now it gets ejected into the Gulf," adds Robert Twilley, of Louisiana State University in Baton Rouge, who worked with Parker on the project.

A similar plan, presented to the state of Louisiana and the Army Corps of Engineers in 2005, before Hurricane Katrina flooded much of New Orleans, never gained political support. "It was too bold, too aggressive, and too expensive," Twilley says.

Geological modelling

But researchers have since worked out how to model the effect of diversions in greater detail, providing better evidence that such an ambitious plan would be successful. Parker and Twilley used a model featuring a detailed picture of the amount of sediment coming down river, the volume of floodwater and the topography of the areas the sediment would fill.

Assumptions about the amount of new delta land that would appear were based partly on an analysis of the nearby Wax Lake Delta, which began forming in 1974 after flooding.

The team ran simulations factoring in varying rates of soil subsidence (1 millimetre to 10 mm) and rising sea level (2 mm to 4 mm per year). Depending on these variables, they estimate that between 700 and 1000 square km of new land would form over 100 years. Land is already being lost to coastal erosion in the state two to three times as quickly.

Twilley says the new delta land would provide significant storm surge protection – more than can be achieved through levies alone – for New Orleans.

Shipping not affected

But a major stumbling block for any plan to alter the Mississippi's flow is the potential disruption caused to shipping between the Gulf and New Orleans – one of the world's busiest ports. The proposed diversion would mainly take water during times of flood, leaving the river's shipping lanes untouched when they are needed most.

"This is achievable even given that navigation is the number one priority," Twilley says. The researchers plan to present their findings to members of Louisiana's state legislature in the coming weeks.

"The state has to say this is what we want to move forward and I feel confident they will do that," Twilley adds. "This is not cheap, but we have done bigger engineering projects in this country before."

Source : New Scientist Environment