Jackson Jambalaya

The Corps has managed to do that — so far. But its latest flow line study predicts a repeat. The study, completed in 2019 and quietly shelved, predicts that hundreds of miles of main line levees from Greenville to New Orleans will overtop in the theoretical worst flood (Project Flood) they are designed to hold. In fact, the study predicts that levees will overtop in lesser floods like the ones in 2011 and 2019 — when they happen again. Why? Mississippi River Floods are due to two things: weather (25%) and flood control projects (75%) according to a 2018 study of floods going back 500 years. Scientists from Woods Hole Oceanographic Institute concluded this based on analyses of core samples of sediments left by earlier floods. Coincidentally, some core samples were from Lake Mary, an oxbow lake near the Old River Control Structure (ORCC). I have seen and written about increased flooding at my farm there since 2016.

I said the longer and higher floods were due to the Corps’ failure to discharge more flow to the Gulf at its downstream flood control projects. The Corps said it’s more rain — acts of God. It’s both. But the Corps didn’t and doesn’t mention that God had lots of help from Corps flood control projects. One of the worst offenders is its Old River Control Complex about 14 miles below my farm and 50 miles above Baton Rouge. It is primarily responsible (75%?) for recent and future floods — including those that will overtop the levees.

The Corps’ help is an unintended consequence of its good intentions. It built ORCC as directed by Congress (1954 Flood Control Act) to delay a developing shift (avulsion) anticipated around 1975 of the Mississippi River to the Atchafalaya and thence to the Gulf near Morgan City. When that course change happens, it will destroy everything in its path. It will also shut down the New Orleans port, Mississippi River commerce, and the refinery and petrochemical complexes from Baton Rouge to New Orleans. It will be a disaster worse than the great 1927 flood.

The ORCC has delayed that catastrophe for 50 years. Its flood control structures contain the Mississippi’s flow and divert 23% down the deep, swift Atchafalaya straight to the Gulf 150 miles away and 77% to the Gulf 350 miles away via the meandering main channel choked with sediments. Gravity will eventually send all the flow down the shorter, straighter, swifter route — in a big flood that will overtop levees too.

Perversely, the Corps and Mother Nature will make that flood happen sooner than planned. Why? Because sediments have caused a bottleneck in the main channel below ORCC sooner than planned — for two reasons. One, the Corps acquiesced to the addition of a power plant at ORCC in 1990. And two, a record-high flood in 2011.

The power plant changed ORCC’s flows and increased sedimentation in the main channel. And the 2011 flood concentrated the sediments just below ORCC at a bottleneck in the river there. LSU’s Dr. Xu reported the bottleneck in a 2017 paper. It slows the Mississippi’s flow and makes floods higher and longer. He predicted that the higher floods (more flood for the same or less rain) will cause the river to avulse down the Atchafalaya in a future big flood. The Corps’ 2019 flow line study predicts higher floods.

We began to see more frequent, longer, and higher floods inside the levees at my farm in 2016 — due to the bottleneck. There was a step change increase then in flood durations and heights and in the damage they cause. Such step changes in flood patterns and other natural phenomena indicate changes in underlying physical forces and their future effects. In other words: expect more flood for the same or less rain.

It’s likely the Corps’ 2019 flow line study that predicts hundreds of miles of levees overtopping actually understates future flood risks. That’s because it is based on river flow dynamics and channel geometry that existed before the step change. It’s outdated, and its dire predictions are probably unrealistically optimistic. This is confirmed by the longest flood ever in 2019 after the flow line study was done. It made the bottleneck even worse.

The Corps has a dilemma. It can continue to deny that sediments at the ORCC it operates are the primary cause of increasing flooding and are accelerating the inevitable course change there. And watch it happen. And try to evade responsibility for the destruction it causes. Or it can try to reduce the existing sediment bottleneck, shut down the power plant to remove the primary source of future sediments, and try to mitigate damage from the avulsion that may happen anyway. It can mitigate avulsion damage by limiting and controlling the avulsion flow. It can do this if it makes the avulsion happen at a better location. There is a better location 13 miles upriver from ORCC where the levee failed in the 1927 flood.

It’s the Widow Graham Bend in the Mississippi River. The Corps can build a control structure there to take the top off of floods and send part of their flow SW to the Atchafalaya below ORCC. It will reduce flood crests and avulsion risk at ORCC. It will also shorten flooding inside the levees, lower crests and overtopping risks, reduce Yazoo basin backwater flooding, and maintain river commerce and the viability of New Orleans and Baton Rouge. The flow it sends to the Atchafalaya will be just a fraction of the flow if the river avulses at ORCC. It’s a good trade- off.

It may take 10 years to build that structure. We should have started yesterday. There may still be time to prevent a catastrophe at ORCC and miles of levee overtopping.

But not if we keep on dawdling.