Bigger Pie Forum Chairman Kelly Williams authored this post.
The Mississippi River is going to change course (avulse) to the Atchafalaya at the Old River Control Complex (ORCC) above Baton Rouge and discharge to the Gulf near Morgan City, LA. Gravity will send it down this shorter, steeper path in a big flood — maybe the next one. Course changes happen about every 1,000 years when the channel clogs up with silt, flow slows, and floods get higher. The last one happened around the 12th century. The Corps of Engineers said the next one would happen around 1975 at the junction of the Mississippi, an old riverbed, and the Atchafalaya. Congress told the Corps to stop it (1954 Flood Control Act). So the Corps built the ORCC there to control the river. It diverts 23% of the Mississippi’s flow to the Atchafalaya and then straight down to the Gulf 150 miles away near Morgan City. It sends the other 77% via the meandering main channel 315 miles to the Gulf below New Orleans. That was the flow split in 1950 when the river showed signs of avulsing. Engineers thought that maintaining that split would delay the avulsion indefinitely — although they knew it would increase sedimentation in the main channel and eventually create a bottleneck there. The ORCC has delayed the avulsion for 50 years. It has protected New Orleans, Baton Rouge, the refineries and petrochemical complexes there, the nation’s grain exports and port and river commerce, and the E-W highway, rail, pipeline, and transmission line corridors, and the Atchafalaya basin. It has permitted billions of investments and development in the meantime. All of this will be at risk if the inevitable avulsion occurs at the ORCC. It will destroy everything on its way to the Gulf at Morgan City. It will leave New Orleans and Baton Rouge stranded on a saltwater estuary and will shut down river commerce.
In 2017, LSU’s Professor Xu said it’s just a matter of time now when he reported a huge sediment bottleneck just below the ORCC. The bottleneck developed sooner than expected due to the addition of a power plant at the ORCC in 1990 and the record-high flood in 2011. The power plant decreased the ORCC’s flow control capability and greatly increased sediments. And the 2011 flood moved the sediments to the bottleneck. The result: flooding in the Natchez reach tripled after 2015. Increased sediments in the main channel also decrease sediments in the Atchafalaya. So the main channel gets higher, and the Atchafalaya gets deeper. This increases the differential (head) between the water level in the main channel at flood stage and the water level in the Atchafalaya. The force of this head of falling water will cause massive erosion and destruction when the full flow of the Mississippi avulses down the Atchafalaya. It will be greater than 20 Niagara Falls. It will carry millions of tons of sediments at the ORCC and drop them along the way to the marsh below Morgan City. It will destroy highways, pipelines, railroads, transmission lines, and everything in its path. There is a better location for the avulsion. It can reduce avulsion destruction. It is the Widow Graham Bend about 13 miles above ORCC where levees failed in the 1927 flood. It’s just across the river from my farm where flooding has tripled since 2015. That step change in flooding portends looming disaster. (The Corps’ latest flow line study does too.) If the inevitable avulsion happens at the Widow Graham location, it will be less destructive. The head is lower there. The river at flood stage vs the ground outside the levee there is not as high as is at ORCC vs the deep Atchafalaya channel. The force of the falling water there will be less. Much less. So the avulsion will be less destructive. And its flow can be managed and increased gradually — not suddenly and catastrophically. There are also fewer sediments there to be swept down to the Atchafalaya and onto the Gulf. And the distance (about 20 miles) to the Atchafalaya provides room for levees, overflow channels, weirs, and other structures to channel and direct the flow. The avulsion volume at Widow Graham can also be increased or decreased to maintain navigation. This could allow Baton Rouge and New Orleans to transition to a new flow regime. Entrenched interests strongly oppose changing the existing flow regime on any schedule. Or preparing for Mother Nature to change it. Or even thinking about changing it. Reminds me of Scarlet O’Hara: “I’ll think about that tomorrow.” But not thinking about it today may cause the greatest river disaster in history. The risk and destruction of avulsion at ORCC steadily increases as the bottleneck grows and the river rises. It may take 10 years to complete an avulsion control project there. If it’s completed before that inevitable big flood event, it can save lives and billions if not trillions in damages. It can prevent a catastrophe at ORCC and permit a gradual transition to a new flow regime that satisfies the law of gravity — if not the 1954 Flood Control Act. It’s time for action, not more wistful not thinking and more studies. When the river does avulse, catastrophically or under control, its flow to the Gulf will increase, and its height (stage) will decrease for the same volume of flow. This will reduce flooding inside the levees, backwater flooding in the Delta, and the risk of levees overtopping from Greenville to New Orleans that the Corps now predicts. Natural avulsions are Mother Nature’s way of rebooting rivers. We can help her do the next one — at the right place. If we start now.
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4 comments:
And we all know you can't fool Mother Nature-
But I thought Gubmint was the problem, not the solution
We should divert some of the trillions we are spebding on welfare and also sending to Israel and Ukraine, and do a moonshot river project like the PRC did with the Yangtze River in China. Include the Pearl River too. Hell, we named the Pearl River and Canton after Chinese (Cantonese)
I was told that during the historic 1973 Mississippi River flood, ORCC oscillated (shook back and forth) at a rate that wouldn't allow anyone to stand upright on it. There were some engineers who thought it was going to give way at any moment, and that was 53 years ago. Just think about the wear and tear the structure has endured in the intervening years.
It's only a matter of time.
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