There is a choice on what steps to take either when or before high water from the Mississippi River again runs through Louisiana.
Either let the river go in its natural direction, or make decisions now that change how the river is managed, says Paul Kemp, vice president and director of Audubon’s Gulf Coast Initiative.
Dredging sediment in the lower river is just forestalling the inevitable — the Mississippi River is getting shorter.
There are a number of signals that the river is changing and that the approach to managing the river needs to change as well, Kemp told the Governor’s Advisory Commission on Coastal Protection, Restoration and Conservation on July 13.
A map of land loss in coastal Louisiana, the delta of the Mississippi River, shows the large areas of land loss are located where the most sediment from the river is allowed to flow into the marsh, he said.
Relative sea level rise — a combination of sinking land and rising water — means the Gulf of Mexico is moving inland.
At LSU, scientists have access to a scale model of the Mississippi River used to test where sediment and water would flow if certain changes were made to the river.
For instance, the scale model has been used to examine where sediment in the river would go as relative sea level rise occurs.
“We found when we raised sea level (in the model), the sand deposition moved upstream,” Kemp said.
Also, he said, the volume of material dredged from the lower river has decreased in the past decade — a possible result of sediment falling out of the river upstream.
In addition, measurements show that more water is going out of the river system farther upstream in Louisiana.
Passes upstream of Head of Passes, near the mouth of the Mississippi River, are flowing more water out of the main river stem, he said. Two passes alone are taking out 20 percent of the flow, he said.
Passes below Head of Passes, meanwhile, are receiving less of the river’s flow, he said.
“The river is changing. It’s not static,” Kemp said. “We’re having to come up with a dynamic approach to a dynamic river.”
Even with more sediment falling out of the river farther upstream, there is still a sediment issue at the mouth of the river, but that sediment is building up in a different way than it has in the past, Kemp said.
“This is a symptom of a changing situation,” Kemp said.
Sandbars are building up at the side of the river and some pop up from the river bottom, which forces dredging to keep the navigation lanes open, Kemp said.
“It’s sort of like ‘whack a mole’ out there,” Kemp said.
We need to change the way we’re dredging, Kemp said.
“This 1930s-era approach is wearing out, essentially,” Kemp said. “These things are all related.”
The flood of 1927 grabbed the attention of the nation and prompted the federal government to pass the Flood Control Act of 1928. This act authorized the Mississippi River and Tributaries project, managed by the Mississippi River Commission. The project continues today with the construction of levees, operation of floodways and channel improvements to enable the river to carry more water during floods, according to the commission’s website.
Kemp said opportunities exist to manage a shorter river that would help improve navigation, provide for deeper draft and a more-sustainable coast. However, in the meantime, the evidence of a changing river system is clear, he said.
“We’re seeing these things and they’re not real subtle,” Kemp said. “And we should be talking about it, and we’re not.”
Amy Wold covers the environment for The Advocate. She can be reached at email@example.com.