By AMY WOLD
Advocate staff writer
November 13, 2012
The mouth of the Mississippi River is moving north, and unless preparations are made in advance for those changes, the impact could be devastating, speakers at a recent coastal conference said.
However, the changes also present opportunities for navigation and coastal restoration, said Paul Kemp, vice president of the Louisiana Audubon Society’s Gulf Coast Initiative.
Waiting for the navigation system at the mouth of the river to “break” is not the way to handle the problem, especially when it’s known that it’s going to happen, Kemp said.
As with the levees in New Orleans, it’s clear that it’s more expensive to react to disaster than to prepare for it, he said during the “Answering Fundamental Questions about Mississippi River Delta Restoration” symposium on Tuesday, Oct. 9 and Wednesday, Oct. 10 at LSU.
“If you know that’s happening, you can actually get in front of it and take advantage of it,” Kemp said. “It’s not all bad.”
Knowing that the river is changing means there are opportunities to not only get more sediment into eroding coastal marshes, but to also make navigation channels in the river more stable in the future.
“The option of doing nothing is not there,” Kemp said. “The river is going to change regardless.”
David Rogers, a professor in the Department of Geological Sciences and Engineering at Missouri University of Science and Technology, said the problem could come up in a scenario where there is a big flood one year followed by a dry year. During the dry year, there might not be enough flow to flush out sediment deposited during the high flow years — which could cause problems.
If this happens, those who navigate the river are going to be “beating on the doors” of Washington, D.C., to get some kind of fix in place and fast. This will lead to “combat engineering” and not to a long-term solution that has been thought out, Rogers said.
“If you shut down all this commerce coming out of the Mississippi River for even two months, that’s a big deal,” Rogers said.
Kemp said that with the subsidence, or the sinking of sediment, in the delta at the mouth of the river combined with a sea level rise, the river is now pushing to exit the channel farther north than where it exits at the southwest pass navigation channel.
Kemp pointed to aerial photos from a flood in 1985 where the plume of sediment can be seen primarily coming out of the delta area farther downstream. However, similar aerial photos of the 2011 flood show the same plume of sediment starting to flow out of the channel about 15 miles upstream from where it did in 1985, he said.
“In some ways, the mouth of the river is not out here anymore,” Kemp said, pointing to the map. “The river actually wants to exit at Venice rather than the Southwest Pass.”
In addition to the aerial photos, Kemp said, more of the river is now flowing through old crevasses, which are cuts in the natural river bank, than it did in the past.
“It’s related to these subsidence rates,” he said. “The river is actually filling in on the lower river and spilling over the sides.”
Sean Duffy, executive director of the Big River Coalition representing deep draft navigation interests, said Kemp has talked with navigation representatives several times and seems to understand their needs. Duffy said Kemp is willing to work toward combining navigation and restoration efforts for the benefit of both.
Kemp said there are opportunities to not only make the Mississippi River more stable for navigation, but to also use the river more efficiently for coastal restoration purposes.
A study, which is being done in partnership between the state and the U.S. Army Corps of Engineers, is looking at those issues.
The Mississippi River Hydrodynamic and Delta Management Study was authorized by congress in the Water Resource Development Act of 2007 as part of the Louisiana Coastal Area Program. The LCA Program outlined short-term and long-term projects in Louisiana to focus on coastal restoration efforts.
The hydrodynamic part of the study will look at what resources are available in the Mississippi River in terms of water, sediment and nutrients and where these resources can be found in the river. The second part of the study will look at how the river can be managed for navigation, flood control and the addition of ecosystem restoration, said Tim Axman, senior plan formulator with the New Orleans Corps of Engineers district.
“The depositing areas in the river are moving upstream,” he said.
Darrel Broussard, corps senior project manager for the Mississippi River Hydrodynamic and Delta Management Study, said the hydrodynamic part of the study, which includes identifying the resources in the river and determining where they’re located, will take three years to complete. However, some results will be available in about a year and those can be used in the delta management portion of the study, he said.
Editor’s note: This article was changed on Nov. 13, 2012 to correct the dates of the coastal restoration conference.