The sediment that builds up in the bed of the Mississippi River has long been a challenge, requiring constant dredging by the U.S. Army Corps of Engineers to keep the channels clear for maritime traffic.
But that sediment also has been an underutilized resource, the very material that should be building and sustaining the wetlands and coastline in southeast Louisiana.
Over the past year, the Corps has reused more sediment from the Mississippi to aid coastal restoration projects than in the past, taking roughly 9 million cubic yards of material from the bottom of the river to create wetlands near Southwest Pass.
That amounts to reusing about 60 percent of the sediment dredged from the river, a significant milestone for the agency’s efforts to put what was once considered waste material into coastal restoration efforts.
“Back then it wasn’t a matter of developing or restoring coastal habitats,” said Ed Creef, an environmental resource specialist with the Corps. “That was before the coastal land-loss situation was as dire and extreme as it is now.”
The material dredged by the Corps was used to create about 850 acres of wetlands, or about 1.3 square miles. Another 400 to 700 acres of marsh are expected to be created under contracts put out earlier this fall.
“We want to use as much dredged material as feasible to offset that coastal land loss,” Creef said.
Using dredged material to rebuild wetlands is, essentially, a solution to a man-made problem, for much of the damage to coastal wetlands near the Mississippi River can be traced back to the building of levees along the river.
While the levees have stopped the regular flooding of communities along the banks of the river, they also have prevented those floodwaters from carrying sediment out to replenishes the marshes and wetlands along the coast. Combined with other factors, including the oil and gas exploration that cut through and destroyed many of the wetlands, the levees have led to significant coastal erosion.
Roughly 1,880 square miles of land have washed away over the past 80 years, and another 1,750 square miles are predicted to disappear over the next half-century, according to the state Coastal Protection and Restoration Authority.
The Corps uses two types of dredges to keep the river channel at its authorized 45-foot depth, a challenge in a river that can create 6-foot-high underwater shoals overnight.
Generally, the more common have been hopper dredges, which move through the river sucking sediment into their holds. That material is then dumped in open-water areas.
In recent years, however, the Corps has made more use of cutter head dredges, which use arms that end in eggbeater-like attachments that stir up and suck the sediment from the river, Creef said. That material is then fed into a pipeline that empties in an area where land is to be created, he said. The increasing use of cutter dredges comes, in part, from budgetary constraints on the Corps. The cost of dredging has gone up and the agency’s budget has declined, a situation that has allowed larger shoals to develop than in the past, Creef said.
Because cutter head dredges are typically more stationary than other dredges, it makes more sense to use them on larger shoals, he said.
CPRA Chairman Jerome Zeringue said his agency has encouraged the Corps to reuse as much sediment as possible and is working with maritime groups and others to push for more funding for both dredging and reusing the sediment it produces.
“Essentially, they don’t want it in the river and we don’t want it in the river either. It should be placed in the wetlands,” Zeringue said.
The use of sediment from the river plays a significant role in the CPRA’s efforts, he said.
Half of the state’s $50 billion, 50-year coastal master plan is dedicated to restoration projects, and roughly two-thirds of those will depend on dredging, Zeringue said.
The CPRA has spent $223 million on a variety of projects involving about 31.8 million cubic yards of pumped sediment that have yielded about 13.4 miles of barrier islands and 31.9 miles of beaches and headlands, according to the agency.
In the works is a $102 million plan that would involve building a long-distance pipeline that would start in Plaquemines Parish and allow sediment to be pumped to where new wetlands are needed, Zeringue said. As the work proceeds, segments would be added to the pipe to allow the material to be pumped farther away, eventually making its way through Jefferson and Lafourche parishes.
“It’s a critical resource needed to rebuild and sustain our coast,” he said.
Follow Jeff Adelson on Twitter, @jadelson.