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Will The Levees Hold?

Posted at 9:26 AM, May 30, 2019

The Mississippi River and its associated tributaries have been running over flood levels all year. A number of different events, starting with a wet fall in the nation’s midsection, and above normal snowfall this winter, didn’t allow the rivers to drop to normal levels before the spring thaw. Then, incredible rainfall totals over much of the southeast and the Tennessee Valley in February. Next, snow melt and heavy rain in the upper reaches of the Missouri Valley starting in late March, and persistent flooding along the Illinois and Mississippi Rivers in the Midwest in April. The Tennessee River flooding has subsided, but in Nebraska and Iowa the Missouri River is back up, and residents in Illinois and Missouri are preparing for yet another near record crest on the Mississippi River. Now, the Arkansas River running from Tulsa to Little Rock is experiencing record flooding. All of this water is coming here.

Arkansas River Flooding Near Tulsa, OK May 2019-Courtesy KRJH

The Mississippi Basin levees have been holding the water back for a half a year now. As of this writing, there is no end in sight. Levees are meant to hold the rivers back for days or weeks, not months or years. It’s not a natural landscape. These levees can soak up water, and water can filter under the levee system as well. At first, when this happens, you’ll get either sinkholes, or sand boils. From what I learned during the 1993 flood in the Midwest, if water is leaking through the levee and it’s relatively clear, it can be plugged with sandbags. If the water contains mud, rocks, and other debris, it could indicate that the levee is failing. In 1993, as well as the 1973 and 1927 floods, levee failures were catastrophic to many cities and towns. Those failures also saved a few cities by lowering water levels upstream and relieving pressure similar to what the Bonnet Carre and Morganza Spillways are designed to do.

Levee Break Elsberry, MO June 2008-Courtesy FEMA

Unfortunately, this may already be happening. There are spots along the levees that the Army Corps of Engineers are concerned about. It’s hard to imagine how extensive the levee system is along the Mississippi River. Now think about all of the tributaries. It seems it’s nearly impossible to monitor all of it. And it’s not all under the jurisdiction of the Army Corps of Engineers. All along the rivers there is levee oversight run by individual communities, parish/county authority, and even rural levee boards. This was a particular problem in the upper Mississippi Valley in 1993 and continues today. The longer the water stays up, the more risk there is for a failure. Fortunately there was a considerable amount of money allocated by the federal government following the 2011 flood to strengthen the levee system, but there’s no guarantee.

Levee Breach East Carroll Parish May 2011 Courtesy: Louisiana Governor’s Office

The good news with the opening of the Morganza Spillway. The levees that corral the water into the Atchafalaya Basin are dry. The levee system that runs from Morganza southward to Ramah and beyond are okay. Water levels in the Basin are elevated, but nothing that would saturate levees. The western side is okay too. Levees on the east side of the Atchafalaya River across from Melville and Krotz Springs aren’t dealing with the waters like the Mississippi. As the water flows southward, it will pile along the Henderson levee southward to the Wax Lake Outlet and Berwick. But, if the flooding continues for months, instead of weeks, there may be issues. There will be even more concern for the levee system along the Mississippi River as each day above flood stage is a new record. Hopefully the levels will eventually return to normal as the weather patterns change for the summer because the levee system isn’t designed to hold water forever.