The U.S. Army Corps of Engineers is preparing for the Mississippi River to reach some of its highest water levels in recent years in New Orleans and Baton Rouge.
According to forecasts, the river is expected to crest at 40.5 feet in Baton Rouge around Friday and 16.5 feet in New Orleans on Saturday.
To help prevent widespread flooding, the Corps did a test opening of the Bonnet Carre Spillway near LaPlace on Monday.
Residents across South Louisiana are being urged to follow updates from the Corps and local emergency management offices as water levels evolve over the coming days.
Host Karen Henderson spoke with Louisiana State Climatologist Jay Grymes to learn more about the Corps’ flood fight protocols.
This interview was edited for length and clarity.
KAREN HENDERSON: Jay, the Corps tested the Bonnet Carre Spillway in LaPlace on Monday to make sure it's ready if it needs to be open to help avoid any flooding. Where's all this water coming from and what areas of the state are most at risk?
JAY GRYMES: The river has been rising for a while now. All of this water is coming downhill, so to speak, out of the northern states. In fact, lots of your listeners may remember the significant flooding that they had up in Kentucky, Tennessee, parts of the Midwest. Well, that water takes as much as two weeks or so to get down here, and that's been generating this rise along the Mississippi. So, we've got flood warnings on the Mississippi through most of the reach of the Mississippi, and that extends from north of Baton Rouge through Baton Rouge and down towards New Orleans. Now it's important to remember when we talk about flooding on the Mississippi and we talk about flood stages on the Mississippi, we're generally not incorporating the levees. So for example, Baton Rouge is expected to go to “major flood.” Yet that'll still be well below the tops of levees for Baton Rouge. So the reality of the situation here is that for the vast majority of us high water on the Mississippi not only is something we can expect every spring, but it's just not likely to be that big of a deal.
HENDERSON: Still, the US Corps of Engineers is looking at testing the Bonnet Carre Spillway, and we know there's the Morganza Spillway. These are tools to relieve pressure on our levees and how likely are these to be used because they're needed.
GRYMES: Let’s talk about it. What we're talking about is when the water gets exceptionally high, it also starts to move at a fairly quick pace down the Mississippi River, and it's actually the rate of flow, not so much the height of the water that the Corps is trying to control. Now, without getting too caught up in the numbers, it's 1.25 million cubic feet per second. When the river reaches that flow rate, that's where they consider opening, or at least a partial opening of Bonnet Carre, and that seems like it's at least a decent chance of happening. The Corps is already in flood fight phase 1, and what that typically means is two inspections per week up and down the entire stretch of the levee just checking for things like seepage, sand boils, and other little incidental problems along the levee, not enough to be a concern for anybody. And in fact, when they find these problems, they deal with them instantly. Now over the next day or the next couple of days, they're probably going to go to flood fight stage 2, and that's when the river in New Orleans gets to 15 feet and steadily rises. The thinking is that the river is certainly going to get above 15 feet, so the Corps are getting ready. This is just being proactive, staying on top of the potential for some minor problems along the levee.
HENDERSON: Jay, currently, are there any flood warnings that have been issued due to the water that we know is coming or that has been coming?
GRYMES: We do have flood warnings at Red River Landing, which is up north of Baton Rouge. There are flood warnings for Baton Rouge, for Donaldsonville. So up and down the Mississippi River, there are sites that are under flood warnings that are in flood technically. But again, the key here is to remember that terminology can be a little bit misleading because even though the river is technically in “flood,” it is still readily contained by the levee system. So it's not as if communities along the Mississippi have to worry about real flooding. When we talk about flooding on the Mississippi, in most instances, the impact there is on river commerce.
HENDERSON: What’s the history, Jay? When's the last time the Bonnet Carre has been opened and can you talk to us about the environmental impact from the spillway?
GRYMES: So the last time the Corps had to use the Bonnet Carre was back in the spring of 2020. So it's been a few years. It’s also worth remembering that between about 2016 and 2020, there were multiple openings. So the river goes through ebbs and flows in terms of its spring crests. In that period of years from 2016 to 2020, our spring crests were unusually high. When we open the spillway, we're shunting a lot of fresh water and also sediment and maybe a little bit of agricultural runoff out of the Mississippi into Lake Pontchartrain, and that's where we can start to see environmental impacts to the lake system because that surge of freshwater changes the salinity of the lake. It has an impact on oyster and shrimp fishermen. So there is an impact. Generally, now the good news this year is I think that the opening of Bonnet Carre will be brief enough and limited enough that the environmental footprint will be fairly minor, maybe almost insignificant.
HENDERSON: Now, what do you expect to see as we move through this week and when do you believe that the flood threat will be over?
GRYMES: So it looks like the crest of the high water will be the last few days of April, somewhere between the 25th and 26th. That's where we're expecting the crest to pass Baton Rouge, and then it typically takes about one day for that crest to move from Baton Rouge down to New Orleans. Now, that doesn't mean that the water is gonna drop off rapidly, but this crest is going to be a relatively short event, just a couple of days. Now, keep in mind the Mississippi typically is high in the spring anyway. So this is, again, not all that unusual that we're looking at high water on the Mississippi. The unusual aspect of it is that it's going to be high enough that the Corps has to consider using the Bonnet Carre as a diversion to take a little bit of that pressure off of the levees as that water moves past the Crescent City.
