How a hydroelectric plant wrecked the ORCC plan

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Hans (Einstein) was not as famous as his father. But he was the world expert on river sediments. He advised the Corps of Engineers (Corps) on the design of the Old River Control Complex (ORCC) in the 1950s. He thought the Corps would take his advice. He was wrong.

The Corps built the ORCC to keep the Mississippi River from changing course down the Atchafalaya River. It’s about 50 miles upstream from Baton Rouge. It controls the Mississippi’s flow and diverts 23% to the Atchafalaya as ordered by Congress (1954 Flood Control Act) and thence straight to the Gulf near Morgan City. It leaves the remaining 77% in the main channel to meander to the Gulf at New Orleans.

Hans knew the natural law of sediment transport concentrates sediments in a meandering river when part of its flow is diverted. And that the concentrated sediments would fall out, clog the channel, create a bottleneck, and slow the Mississippi’s flow to the Gulf. And that this would cause higher and longer floods upstream.

He sought to minimize these effects by the careful design of the ORCC and by siting it to divert flow from the river’s sediment-rich strata. He was right about the design and the siting. Sedimentation was negligible for 27 years from 1963 when ORCC started up to 1990. Then the Corps ignored his advice and the natural law of sedimentation to collaborate on a hydroelectric power plant.

Private investors built the plant and made a deal with the Corps to put it just upstream of the ORCC and for the Corps to send sediment-lean flow through its turbines to the Atchafalaya instead of the sediment-rich flow it had sent through the ORCC. Han’s couldn’t know this would happen.
But he could have predicted the result: sediments concentrated in the river’s main channel, fell out, clogged it just below ORCC, and slowed its discharge to the Gulf. The river rose, floods got higher and much longer inside the levees with little or no increase in rainfall.

In 2015 there was a step-change increase in flood duration. The increase became obvious to landowners inside the levees in 2016. Floods were 2-3 times longer in the five years after 2015 vs before. There was no increase in the frequency of floods (rainfall events).

The Corps knew that sediments were increasing in 2005 when it made the first measurement of the river channel after the power plant began operating. By 2015 Corps measurements showed the channel width had shrunk by 50% and the channel depth, by 33%. The Corps knew this was happening and that it would continue and make floods ever higher and longer .

But the Mississippi River Commission (MRC) generals told Mississippi’s Secretary of State, other landowners, and me the flooding was due to more rain when we testified about flood damage in 2016-17. No mention of sediments. We didn’t learn that sediments were the cause until 2018. Why did the Generals hide the real cause?

The Corps deal with the power plant is a liability and an embarrassment. The Generals may have been ordered to hide it. The Corps is supposed to control floods and mitigate flood damage. Its deal with the power plant makes both worse.

The Corps has a Memo of Understanding (MOU) with the company that owns the plant. It requires the Corps to send sediment lean flow to the plant. It also requires the owner of the plant to dredge sediments the plant causes. The company doesn’t dredge. The Corps doesn’t enforce the MOU or dredge the sediments itself. It seems strangely indifferent to the consequences of its decisions.

We learned the real cause of the floods after LSU’s Dr. Xu published a report in late 2017 based on changes in Corps morphology measurements (channel dimensions) cited above. It showed that sediments had clogged the channel below ORCC and made it much smaller (bottleneck) since 1990. He said the bottleneck would cause the river to rise and change course in a big flood.

In 2019, the Corps published a little-noticed updated flow line study. It predicts hundreds of miles of levees from Greenville to New Orleans will overtop in a big flood. The last time that happened was the great flood of 1927.

Reality has confirmed that Dr. Einstein was right about Nature’s sediment transport law and the consequences of violating it. And that he was wrong to think the Corps would obey it. So disaster looms ever sooner as a result of Corps decisions — which seem inconsistent with the mission Congress gave it (1928 Flood Control Act): don’t let another 1927 flood happen. It looks like Corps’ decisions are leading to another great flood.

Who made the decisions about the power plant? And the decision not to dredge the sediments, and the decision not to build a relief structure to take the top off of floods, and the decision not to tell landowners inside the levees the cause of their flooding, and the decision not to warn landowners outside the levees about the increasing risk and inevitability of levees overtopping. The Corps is a bureaucracy subordinate to other
bureaucracies and to Congress. Authority and responsibility are diffuse. No one takes responsibility for bad decisions. No one is solely to blame for the flooding inside the levees and the coming flood disaster outside the levees. The buck doesn’t stop with the Mississippi River Commission Generals. They follow orders too. It seems the buck doesn’t stop anywhere. That’s the problem.

We don’t know the names of the Generals, politicians, and bureaucrats who made the decisions now. But we will learn them after the levees overtop.

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