Experts discuss impact of Mississippi River diversion in Louisiana

There’s an idea in the general public that creating diversions of fresh water and sediment from the Mississippi River is just a matter of opening up the levee, putting in a structure and letting the river do the work of building land.

But it’s not that simple, Brig. Gen. Peter “Duke” DeLuca, commander of the Mississippi River Valley Division of the Corps of Engineers, told members of an expert panel on diversions at a meeting in Baton Rouge Wednesday.

The Expert Panel on Diversion Planning and Implementation is made up of 12 experts from around the country who have experience with Louisiana and Louisiana issues and who will meet at least three times a year over the next three years to help answer questions about the sediment diversions the state plans to build for coastal restoration.

The panel was set up by The Water Institute of the Gulf at the state’s request because of questions that surround how and where sediment diversions will be built and what their impact will be on the ecosystem and on coastal communities.

“We know our coastline was built through the deltaic processes,” said Kyle Graham, deputy executive director of the state’s Coastal Protection and Restoration Authority. The new diversions the state is planning to build will focus on helping reconnect the Mississippi River with the surrounding marshes, he said.

“A lot of what we’re asking this panel to do is to help guide us through some of those planning decisions,” Graham said.

The panel heard from scientists, environmental groups, state coastal agency representatives and the public during an all day meeting designed to provide an overview of current coastal restoration activities, the challenges of building diversions and possible questions the panel will be asked to address during the next few years.

During his presentation, DeLuca laid out the numerous considerations that the corps thinks will have to be included in the design and construction of these sediment diversions.

He said it’s important to manage expectations of what diversions from the Mississippi River can realistically do in the rebuilding land in Louisiana’s coastal zone.

About half of the land loss experienced in Louisiana is on the central and western side of the state, he noted, which is outside the Mississippi River influence. Any river diversion wouldn’t have an impact on half of the disappearing coastline, he said.

Then there’s the scale at which diversions could build land, he said. Although there has yet to be a sediment diversion built, there are several freshwater diversions, crevasses and channels that can be examined, he said.

One example proponents of diversions point to is the Wax Lake Outlet, a channel off the Atchafalaya River dredged in the 1940s for flood control purposes. By the 1970s, a delta started forming at the mouth of the channel and it’s been one of the few areas along the coast that has continued to grow instead of erode over the years.

However, he said, planners need to consider how much of the river it took to build that land, he said. Between 1983 and 2010, the Wax Lake Outlet built 250 acres of land a year using 10 percent of the Mississippi River’s flow through the Atchafalaya. Over that same time period, coastal Louisiana as a whole lost 10,600 acres per year, DeLuca said.

“We just don’t want to overpromise what we’re going to do here,” he said.