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Coastal News Roundup: Predicting Floods On The Mississippi River

May 10, 2019
Originally published on May 10, 2019 2:32 pm

Towns along the Upper Mississippi River are dealing with some of the worst flooding they’ve ever seen. Busted levees. Flooded downtowns. What does that mean for us in Louisiana? When should we be concerned, and when should we not be?

WWNO’s Travis Lux called up Jeff Graschel, hydrologist at the Lower Mississippi River Forecast Center in Slidell, Louisiana to get those answers, and more, for this week’s Coastal News Roundup.

 


The following transcript has been edited for clarity:

Q: In recent weeks, the Upper Mississippi River has been flooding like crazy in places like Iowa and Missouri. When I see something like that I tend to get nervous because I know that water will eventually wash through Louisiana on its way to the Gulf of Mexico. Are we going to see a big spike in water levels in Louisiana from this Midwestern flooding?

We’re really not going to see any impacts, or the river going to higher levels when that water actually reaches us in the Baton Rouge/New Orleans area. It takes quite a lot of time for that water to make its way down here. We’re probably still looking at several weeks before we’re to see any of that water make it down to the Baton Rouge/New Orleans area.

We do have a rise coming down the Mississippi River at this time and we are going to see another couple more feet of rise on the lower part of the river, but that’s really because of the rainfall we’re looking at over the next few days -- not actually the flooding you’re seeing in Missouri and Iowa at this time.

Q: When it rains in the Midwest -- if there’s flooding up there -- it seems like sometimes that has an effect down here and sometimes it doesn’t. Can you tease out why that is?

You can kind of look at it from an Interstate perspective, like cars and stuff. The Missouri River is like two lanes. The Mississippi is another two lanes. The Ohio is probably 6 lanes. Four lanes of that is the Ohio, and two lanes of it are the Tennessee and Cumberland Rivers. So we have like a 10-lane interstate system down here [on the Lower Mississippi River].

When you’re looking at areas like the Missouri in Iowa, you’re looking at maybe two to three lanes in those areas. So really if you want the whole highway to be crowded with cars, you’d really have to have all those [upstream] lanes filled up in order to really have problems on the lower part of the river.

Q: What about river predictions in general? Has it been getting easier or more difficult to make predictions about river levels?

The technology has changed to allow us to do a better job modeling and forecasting of the MississippI River. One of the key ingredients is being able to know how much rainfall you’re going to have in a period of time. Our weather models have improved over the years to do a better job. But one of the areas that’s still a little hard for us is to predict exactly how much rain we’re going to get and exactly where that location will be.

If that rainfall misses just one or two basins, that could play a big role in whether your river goes up or down. There’s still a lot of uncertainty with forecasting rivers because of the challenge we have of being able to forecast the placement and the exact amount of rainfall.

The Coastal News Roundup airs on Fridays at 7:45 a.m. and 4:44 p.m. on WWNO in New Orleans and WRKF in Baton Rouge.

Support for the Coastal Desk comes from the Walton Family Foundation, the Greater New Orleans Foundation, the Foundation for Louisiana, and local listeners.

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