Why “Improving Conveyance” Doesn’t Work

It Causes More Flooding

Taming the Mighty Mississippi May Have Caused Bigger Floods

Human meddling with the river is blamed for most of the rise in flood levels, but the role of climate remains unclear

By Stephanie Pappas, Scientific American, April 10, 2018


Now a new study raises the possibility much of the effort humans have put into trying to control the mighty river has paradoxically made its large floods more destructive. The magnitude of so-called 100-year floods—massive inundations defined as having a 1 percent chance of occurring in any given year—has increased 20 percent in the past five centuries on the lower Mississippi, researchers reported this month in Nature. The bulk of the increase has been in the last 150 years, when human engineering of the river has been most intense. “We’ve channelized the river, we’ve straightened it,” says Samuel Muñoz, lead author of the new study and an assistant professor of marine and environmental sciences at Northeastern University. “We’ve made the gradient steeper, and we’ve encased the river in concrete mats and lined it with levees.”

The resulting physics is straightforward, Muñoz explains. With little leeway to meander and limited floodplain to spread over, the waters of the Mississippi in places are corralled into a relatively narrow chute, making peak flows higher than they would be otherwise. Muñoz and his colleagues estimate about 75 percent of the increase in 100-year-flood magnitude is due to river engineering, with the rest attributable to natural climate cycles. The study was not able to factor in the influence of anthropogenic climate change effects, though, leaving open the question of how much rising flood levels are driven by engineering and how much by a warming climate.

Read the rest of this article in Scientific American.

Aerial view of water diverted from the Mississippi River flooding Krotz Springs, Louisiana, on May 20, 2011. Credit: Julie Dermansky Getty Images for Scientific American

4 thoughts on “Why “Improving Conveyance” Doesn’t Work”

  1. Janice Walden says:

    This has been long understood and contested along the Mississippi. Read John Barry’s historical account, “Rising Tide”.

    1. Yes. Thank you, Janice. Rising Tide is an excellent history and resource and one of the books recommended on our Books and Articles page.

    2. William D. Justice says:

      Hello Janice…….I have the book and will be reading it soon……My experience has always proven that if there is a backup in a drainage system of any kind, it can be eliminated by removing the bottleneck……..Naturally of course, the system downstream of the bottleneck when removed must have enough capacity to handle the increase flow.



  2. William D. Justice says:

    Did the engineering and actual work include:

    Increasing the river flow rate capacity by dredging and excavating along the entire length of the river proceeding from the upper river to the outlet into the Gulf of Mexico.

    Adding required, additional detention areas along the river to to compensate for the increasing river flow volume and capacity differentials proceeding from the upper river to the outlet to the gulf.

    If this was all engineered and done properly, then I remain puzzled as to why unexpected flooding is occurring.

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