Changing river’s channels impacts Mississippi flooding
Flood control engineering along the Mississippi River during the last century has caused floods to increase in magnitude when they do happen, according to an article published in a leading scientific journal and co-authored by a researcher at Southern Illinois University Carbondale.
The article, published April 4 in the journal Nature, argues that climate patterns, such as El Niño and others, also strongly affect flooding trends.
But changing the river’s channels, through confining it with levees, has greatly amplified flooding when it does occur.
Jonathan Remo, associate professor of geography and environmental resources at SIU, co-authored the article on the study, which examined the physical record for the last 500 years of flooding along the river.
The researchers focused on the river from about Cairo south to Vicksburg, Miss.
The researchers used a technique known as paleoflood reconstruction to gain information about flooding from before records were kept, stretching back to 1500.
The methods involved examining sand left behind by the river in floodplain lakes during flooding events centuries ago.
Using radio carbon dating techniques, researchers were able to tell the age of the organic material that accumulates on top of each new sand deposit left by a flood, giving them a relative date for each flood.
An expert in flooding and river management, Remo contributed further to the project by using knowledge gained from a nearly $300,000 National Science Foundation-funded study that examined the flooding record left behind in tree rings along the Mississippi River and its principal tributaries.
His method involves taking core samples from trees that in some cases are more than 300 years old, and examining the sample under a microscope.
Once those flood years were established, they could be compared to the carbon-dated sediment samples, further confirming the accuracy of the methods.
“Some of the trees date back to the latter half of the 1600s to the 1700s, many of them located in the Missouri bootheel,” Remo said.
“When you look at the sample under a microscope, the years that involved flooding have different shape than other years.”
Remo said flood protection engineering during the last century has increased the magnitude of flooding once those systems are breached or topped because such systems make the water run higher.
“So the flooding is worse when it does happen,” he said.
Remo said the study’s findings give policy makers and scientists a much better picture of flood variability along the Lower Mississippi River.
“I hope the information will help us ensure our flood mitigation systems are able to protect us from current and future flood hazards,” Remo said.