More than 20 million cubic yards of sediment, enough to build 2,000 acres of land, was taken from the bottom of the Mississippi River and pumped into wetland areas along the lower channel — a record amount of dredged material moved to marshes in a single year.
While that doesn’t mean 2,000 acres were formed because some of the land remains under water, it does represent a significant addition to a rapidly eroding lower river marsh land, navigation representatives say.
“The state master plan doesn’t have any projects in this area so we’re kind of left to our own devices to protect the channel,” said Sean Duffy, executive director of the Big River Coalition. “We’re the only game in town.”
The state does have a 50-year master plan for coastal restoration, but officials have said in the past that the lower “birds foot” delta below Venice is not stable enough to justify widespread restoration efforts and money can be spent on projects upstream that will last longer.
U.S. Army Corps of Engineers officials claim maintaining a rock and marsh edge along the navigation route that runs through Southwest Pass is vital to the health of the navigation channel where almost 500 million tons of cargo gets transported each year. Without this edge, the river water slows down and dumps more sediment, increasing the need to dredge.
“The more streamlined you can have it, the better it is for self-maintaining,” said Michelle Kornick, Mississippi River operations manager with the Corps.
Storms also can cause bigger problems for the navigation channel without the maintenance, Duffy added.
That concern got navigation groups such as the Associated Branch Pilots and Duffy to meet with the Corps to talk about what options are available to use dredged material to help shore up these wetlands that were becoming open water.
Although use of the dredged material in the marshes has been done since 1976, it wasn’t until 2009 when circumstances changed, allowing more dredged material to be used in this beneficial way.
There are two dredges used on the river — the cutterhead and the hopper. A cutterhead dredge is anchored into place and, like a large lawnmower, slices sediment and pumps the loosened dirt through a pipe to a marsh area. The hopper pumped sediment into the dredge boat to be hauled away. But because it empties through the bottom of the boat, it has to be dumped in open water — often not the best option for marshland.
For years, bar pilots — who guide ships safely through the mouth of the river — were wary of the cutterhead dredge because it can’t be moved easily like the hopper if a problem arises, Duffy said. The cutterhead dredge also was the more expensive option.
However, in 2009, the cost of using the different dredges were about the same so the Corps, Big River Coalition and the bar pilots association decided to give the cutterhead a chance.
“This is all done because we want to be a part of restoring that too and protect that channel,” Duffy said.
The work started with building 46 acres in 2009 and increased each year as the safety concerns of the anchored dredge faded. In 2009, there were five places where the bar pilots’ concerns prevented the cutter head dredge from being used. Now, concern remains in only one area, Duffy said.
The pilots, Duffy said, also saw the advantage of the cutterhead dredge because it gives a much cleaner cut for the navigation channel.
“Over the last five- or six-year period, the pilots have come to appreciate it,” he said.
In addition, he said, the pilots can watch as land gets built with the dredge material, fostering more support for the practice. The bar pilots’ cooperation is essential for the program to work because parts of the navigation channel must be closed to travel while the dredge is working.
“It is helping, I hope, show that the large amounts of dredge material being created each year along the coast can be a large and important part of restoring/preserving our coast,” said Tim Osborn, regional navigation manager with the National Oceanic and Atmospheric Administration Office of Coast Survey.
Follow Amy Wold on Twitter, @awold10.