There’s palpable concern among industrial owners that this year’s record rise in Mississippi River levels is not an isolated event. Some have begun to entertain scenarios where flooding is a recurring phenomenon, even as they must plan for billions of dollars in investments along the waterway.
A recent study by a researcher with The Water Institute of the Gulf in Baton Rouge seems to lend credence to this fear, as it shows that flood-stage peaks are getting higher, and the river is remaining high for longer periods of time.
The city of Baton Rouge established a new record in May, marking 136 consecutive days with the Mississippi at or above the flood stage of 35 feet, a depth it surpassed and maintained through mid-summer. That broke the previous record set during the Great Flood of 1927, according to the National Weather Service, although the most recent flood was more significant in terms of the sheer volume of water.
That’s problematic for companies building mega-facilities in St. James Parish and elsewhere, as it could prevent pre-assembled modules and other structures from passing beneath the Crescent City Connection in New Orleans due to inadequate “air draft.” In fact, Wanhua Chemical worries that river heights in 2020-21 could block the passage of modularized units needed for its methylene diphenyl diisocyanate (MDI) manufacturing facility. The units will be manufactured in Yantai, China, and shipped to the site.
“It will be important to plan these large module movements to avoid high Mississippi River levels,” says Jim Newport, Wanhua Chemical’s general manager in St. James Parish, in a written statement. “Wanhua will continue to monitor projected river levels and plan site work and large module movements accordingly.”
Is this a trend?
Alex McCorquodale, a retired UNO professor and current senior technical adviser at The Water Institute, says his recent examination of 90 years worth of U.S. Army Corps of Engineers data makes clear that while high river levels are a cyclical occurrence, the peaks in the cycle are getting higher and greater in volume.
“If I was someone in industry planning long-term, I would plan for an increase in those high stage events at least for the next decade,” says McCorquodale, who has spent more than 50 years in hydrology, solving challenges in rivers, lakes and the Gulf of Mexico.
During his research, concluded in early 2019, McCorquodale studied river stages and flows since 1930 (the oldest available data) to extrapolate potential causes—whether that be a cyclical trend, climate change or some combination of both. He was commissioned by the Environmental Defense Fund in Washington, D.C., to perform the work as part of a broader study by Natalie Snider, senior director for EDF’s Coastal Resilience program, into the future need for diversion structures and canals.
In gathering data from the Corps’ Tarbert Landing gauge downstream of Old River, McCorquodale noticed an alarming trend—the peaks in the cycle are getting higher. “The opening of the Bonnet Carré Spillway has gone from an average of seven years between openings to about half that,” he says. “It’s opening twice as often in the last 20 years as it as it did over the entire 90-year period.”
Something else to consider: Some of the older data was gathered when the Atchafalaya River diversion canal was plagued with log jams and limited capacity. “Only since the late 1950s has 30 percent of the flow gone into the Atchafalaya. That’s a change that should have reduced the flow into the Baton Rouge and New Orleans areas.”
That could mean that recent rises in river levels are more than just a cyclical occurrence. “This latest series of floods is much higher in terms of volume,” he adds, “and the number of peaks is higher than in the historical record.
“Imagine this as a wave. We’ve had three waves since 1930, and each time the frequency of the highest part of that wave is greater and the volume of water is greater. We’re seeing this up and down change, but we’re seeing that the peaks are getting higher.”
One note of optimism: McCorquodale predicts the current cycle should peak this year or next, followed by a gradual reduction in frequency over the next decade.
A costly problem for industry
Sean Duffy, executive director of the Big River Coalition, an advocacy group in Metairie, says the maritime industry takes a big hit when the river hits flood stage and the Corps restricts ship traffic.
He blames a plethora of incomplete flood control projects for exacerbating the problem, going back to the Flood Control Act of 1928. “I’m not a scientist,” he says, “but I hope that after this record flood it will become more of a priority and that science will play a role in dealing with what will likely be an ongoing problem as precipitation levels continue to increase.”
Recent shoaling—a buildup of river sediment—in Southwest Pass has been a particular concern, as it blocks larger vessels from entering and exiting the river. “We went down to a drab 40-foot draft,” Duffy adds. “If you have a ship that’s coming in from 45 feet and they limit it to 40, they’re leaving behind $5 million worth of cargo, or about $1 million a foot.”
Complicating matters, shoaling is greater when the river is higher. “The rate at which the sediment and sand is coming down increases in years we have high water,” says Clint Willson, director of the LSU Center for River Studies. “As a result, the Corps is having to dredge a lot more this year than they have on average over previous years.”
Interestingly, rising sand deposits might even be worsening the problem. “Sand is depositing farther up river from Baton Rouge, which might be leading to some increased water levels.”
For petrochemical plants, an inability to pass beneath the Crescent City Connection remains the biggest worry. “All of a company’s benefit cost analyses for a project are based upon a time schedule,” Willson says. “They need to start producing product and their concerns are 12 or 36 months out because they’re not getting their shipments.”
What is the cause?
It’s difficult to put the blame squarely on climate change, McCorquodale says, as there could be a number of other reasons for the rise in river levels. Developments up and down the river and an increase in urbanization are two possibilities. “The Mississippi Basin is so large that there’s not one thing you can point to and say, ‘This had a significant impact on river levels.’”
Still, there are other factors that suggest climate change is at least one of the causes. For one, the Great Lakes system is at a 100-year high. “This suggests that there is increase in water supply, e.g. more rainfall and snow melt,” McCorquodale says.
For its part, the LSU Center for River Studies provides a collaborative and innovative space for people to think about such problems through its long-term modeling of the Mississippi River Basin. While the center isn’t currently researching trending data or making projections about future river levels, “we’ve obviously seen an increase (in river levels) over the last 15 to 20 years,” Willson says.
Nonetheless, no one should hit the panic button just yet. “Something that climate scientists and others need to understand is that there are just certain things that happen over 10- to 12-year periods that balance out over the long term,” he adds.
More than ever, Willson feels additional investment in new river infrastructure is needed to stave off the issues that higher river levels will bring. That’s an admittedly difficult thing to convince taxpayers to fund. “It’s not a sexy topic,” he adds, “but we have to start rethinking how we’re going to plan our communities and our infrastructure from a resiliency standpoint, since the return on a dollar you spend on flood mitigation has a 10-fold benefit during a flood.”