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
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.