Floods on the Mississippi River are getting more frequent and more severe. But scientists warn that the infrastructure meant to protect towns and farms against flood waters is making the problem worse.
A series of analyses have helped confirm what engineers have posited for more than a century: that earthen levees built along the river are increasing flood risk for everyone, and especially hurting those who live across from them.
"When a new or larger levee is built there is often hew and cry, and if there isn't, there should be," says Nicholas Pinter, a geologist and the associate director of the Center for Watershed Sciences at the University of California, Davis.
"What you're doing in many cases is taking a flood plain out there — it can be 5 [or] 6 miles wide — and you're forcing the water that would otherwise spread across that area to go through a narrow passageway." As the passageway gets narrower, the water flows faster and higher.
The resulting floods are more severe than they would have been without the levees, which then drives people to build more levees, driving a "hydrologic spiral" of flooding, levees, more flooding and higher levees.
Levee hazards are not a new idea. In 1852 an engineer named Charles Ellet Jr. wrote a report for the federal government in which he warned that confining the Mississippi River to a narrow channel caused the water to "rise higher and flow faster."
But despite 19th century warnings, levees quickly became the go-to solution for controlling the river. After the great flood of 1927, Congress required the U.S. Army Corps of Engineers to build a massive system of levees and dams on the Lower Mississippi.
A study published earlier this year attempted to quantify the effect of that infrastructure on flooding. The authors examined river-adjacent sediment and tree rings going back 500 years, and found that floods have become significantly more severe and frequent in the last 150 years.
Increased precipitation from climate change, combined with the effects of levees and dams, have "elevated the current flood hazard to levels that are unprecedented within the past five centuries," the authors write.
But the hydrologic spiral is a powerful thing.
Doubling down on levees
Faced with major floods every other year along some stretches of the Upper Mississippi, which has historically had fewer levees than the lower part of the river, many floodplain managers have built up levees and flood walls, even though doing so will only make the problem worse in the long-term.
An investigation by ProPublica, The Alton Telegraph and The Center for Investigative Reporting found drainage districts in Missouri and Illinois are lobbying to reduce federal flood regulation, paving the way for more and higher levees in communities that want them.
A model released earlier this year by the U.S. Army Corps of Engineers showed that a handful of drainage districts north of St. Louis aren't waiting for permission; they have already raised their levees above the level authorized by the Corps.
The largest of them, the Sny Island Levee Drainage District in Illinois, raised its levees in response to a flood in 2008, which was the second largest flood ever recorded on the Upper Mississippi. "In a flood fight, you raise your levees at least two feet higher than the forecast crest, and we did that," explains the drainage district superintendent, Mike Reed.
After the water receded, the district decided to leave the extra sand where it was to protect against the next flood, even though that violated federal height regulations. In 2015, the Army Corps announced it would withhold future federal funds for maintaining the overbuilt levees.
Reed says the drainage district assesses about $2 million each year from local land owners to pay for the levee system, and that the investment has paid off.
"We have calculated that since 2001, almost $1 billion in damages has been prevented by our levee system, just in the Sny," says Reed. "So, it works. It's difficult, it's hard work, it's tough, and it's 24/7. But that's what you have to do."
But multiple studies show overbuilt levees are increasing flood risk for people on both sides of the river. An analysis released earlier this year found the Sny levees have increased the height of the river during floods, pushing water into towns and farms across the river, as Eli Chen of St. Louis Public Radio has reported.
'They're sending the water our way'
"They're sending the water our way, and there's nothing we can do about it," says Al Murry, the emergency manager for Pike County, Mo. The county has been hit with multiple so-called 100-year floods in the last decade, destroying crops on Murry's side of the river while the other side stayed dry.
"You know, every year you just spend enormous amounts of money. It makes a mess out of a lot of property. A lot of crops are going wasted," he says.
Murry, who is a former fire fighter, says he thinks the Sny levees are indicative of short-term thinking and poor risk assessment. "People are greedy. That's a lot of what's going on on this river right now. It's not good for anyone."
Indeed, people who study the river say levees can also increase long-term flood risk for the farmers who pay to be protected by them.
"Just because you live behind a great, big, strong levee does not mean that there's no chance of getting flooded," explains Pinter. "There are two types of levees: those that have failed and those that will fail."
When tall levees fail, the people who live and work behind them are less likely to be carrying adequate flood insurance. That's because when levees are high enough to protect against floods with a one percent chance of occurring in any given year, the federal government no longer requires homeowners living behind them to carry flood insurance.
Risk is similarly obscured in the crop insurance market. Farmers behind the Sny levees are paying half as much to insure fields along the Mississippi River as their neighbors across the river are, explains crop insurance salesman Matt Jones. "It's based on flood risk, and the area behind the levee is considered lower risk," he says.
Since crop insurance is a federally subsidized program, if the levee-protected fields are ever inundated, much of the cost would be born by taxpayers. "When they do have a catastrophic flood, it's going to be a big loss," says Murry. "It's going to be huge. It's going to affect the cost of living. And everybody's going to pay for it."
Reed insists the Sny's risk assessment is sound. "In an excess of 100 years we've had one levee breach," he says. He doesn't agree with data that shows levees increase flood risk. "A model is a theory. What actually is happening, to me, is more important that what a theory says."
Reed say people feel safe behind his district's levees, at least relatively so. But he admits, "Mother Nature is a tough thing to predict."
A previous photo caption in this story incorrectly stated that the flood wall in Hannibal, Mo., was constructed after the 1993 Mississippi River flood. The wall was built in 1992 and was temporarily built higher during a flood in 2008.
MARY LOUISE KELLY, HOST:
The Mississippi River is flooding more than it used to. One reason is an increase in intense rain from climate change. Another is the very thing that is supposed to prevent flooding. NPR's Rebecca Hersher reports the levees meant to protect farms and towns are actually making the problem worse.
REBECCA HERSHER, BYLINE: Mike Reed was born and raised on the banks of the Mississippi River in a small town called Hull, Ill.
MIKE REED: Hull was a family. Everybody knew everybody.
HERSHER: It's a farming community. Floods are a part of life, but the big floods, the ones that destroy entire livelihoods, were so infrequent in the 20th century that everyone here can name them - 1937, 1973 and 1993.
(SOUNDBITE OF ARCHIVED RECORDING)
UNIDENTIFIED PERSON #1: Channel 5, KSDK St. Louis...
HERSHER: In August of 1993, the water would not stop rising.
(SOUNDBITE OF ARCHIVED RECORDING)
UNIDENTIFIED PERSON #2: For days and for nights, volunteers worked to build a wall to hold back the water.
HERSHER: But nothing would keep it back. The river came right over the levees. Dozens of people died.
REED: The town that I grew up in and loved had 5 to 8, 10 feet of water in it.
HERSHER: Hull never really recovered. Reed is the floodplain manager for the whole drainage district now, and 25 years later, the memory of that disaster is clearly still painful.
REED: Flood fighting is very personal. You work hours and hours and hours and hours of daylight. You work all night. It's a very personal thing that you are trying to protect. And when you don't, it's tough.
HERSHER: So tough that after 1993, Reed and his neighbors took drastic measures so they would never lose another flood fight. Landowners started taxing themselves millions of dollars a year which they used to build up the levees between their fields and the river.
AL MURRY: You're in the country now. We drive pickups.
Emergency manager Al Murry drives me out to see one of the tallest levees - on one side, newly planted cornfields - on the other, a big mound of sand covered in grass. You can see where people piled up extra sand on the levee during a huge flood.
MURRY: See that grass line.
MURRY: Right there - that's what they put on in 2008, from that grass line up.
HERSHER: That's a lot.
It looks like 3 extra feet in some places, and it worked. It kept the fields dry. So they just left the extra sand even though it makes the levee higher than what's legally allowed by the Army Corps of Engineers.
MURRY: It's very obvious. They don't try to hide it.
HERSHER: The extra-high levees seemed good for this side of the river, but they're a big problem for Murry's hometown directly across the way. During floods, the water that would go onto these fields goes his way instead. He drives me across the bridge to show me.
MURRY: This is the old town. This used to be full of hotels and stuff.
HERSHER: Now most of the storefronts here in the town of Louisiana are empty, and roads are still ripped up, being repaired from the last big flood in 2008.
MURRY: Right where we're at right now is about 4 1/2 foot deep - yeah, a lot of water.
HERSHER: Farmers around here lost millions of dollars in crops. And another financial blow - the high flood risk means they pay twice as much for crop insurance as their neighbors across the river even though it's those same neighbors' levees that are partly to blame.
NICHOLAS PINTER: Essentially when you build a levee, you are dumping flood risk on your neighbors. That is, people on the other side of the river upstream and to a smaller extent downstream as well.
HERSHER: Nicholas Pinter is a geologist at the University of California, Davis. He says levees make the river a lot narrower than it would or should be.
PINTER: What you're doing in many cases is taking a floodplain out there. It can be 5, 6 miles wide. And you're forcing the water that it would otherwise spread across that large area to go through a narrow passageway.
HERSHER: The passage narrows. The water is forced higher. And so levees meant to protect against floods actually increase flood risk. It's true up and down the river. A recent study of the lower Mississippi found floods are more severe now than at any time in the last 500 years in part because of levees and dams on both sides of the river. Lowering or removing levees that protect farmland would reduce flood risk for everyone. European farm managers have been doing it for decades.
But as floods have gotten more severe on the upper Mississippi, many officials here have reacted by doubling down on levee construction. They're also lobbying Congress to give them more power over how high they can build, which is pretty frustrating for water manager Al Murry.
MURRY: People are greedy. That's a lot of what's going on on this river right now. We look at things yesterday and right now in this country, and nobody's willing to give up anything for the moment.
HERSHER: He says he has no plans to raise his levees. In the long term, it's a losing battle. Rebecca Hersher, NPR News. Transcript provided by NPR, Copyright NPR.