Changing Planet

Mississippi Floods Can Be Restrained With Natural Defenses

The destruction of 35 million acres of wetlands — an area the size of Illinois — in the upper Mississippi River basin has increased flood risks to cities and farms downstream. One way to protect against floods has stood the tests of thousands of years: the ecosystem of wetlands and flood plains natural to big rivers.  Instead of letting this ecological infrastructure degrade further, U.S. federal and state authorities should work to expand and rebuild it.

Water levels were extremely high along the Mississippi and other central U.S. rivers on April 29, 2011. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite acquired the top image on April 29, 2011, and the bottom image exactly one year earlier. (NASA images courtesy MODIS Rapid Response Team, Goddard Space Flight Center. Caption by Michon Scott.)


As riverboat casinos close along the lower Mississippi River as a precaution against disastrous flooding, another form of river gambling is coming under the spotlight — the bet that levees will be able to safeguard cities and farms from the rising floodwaters surging south through America’s heartland toward the Gulf of Mexico.

Already the federal Army Corp of Engineers has had to make a decision even the biblical King Solomon would have agonized over.  To try to avert a levee failure that would swamp Cairo, Illinois, a town of 2,800 people at the confluence of the Mississippi and Ohio rivers, the Corps decided to blast a two-mile hole in the levee at Birds Point, Missouri.  The breach will relieve pressure, at least temporarily, on the levee protecting Cairo, but is expected to inundate 130,000 acres of rich Missouri farmland and some 90 homes.

On May 2, 2011, in an effort to spare Cairo, Illinois, the U.S. Army Corps of Engineers used explosives to breach a protective levee near the confluence of the Ohio and Mississippi Rivers. As predicted, the two-mile hole in the levee flooded 130,000 acres of nearby farmland. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite captured these images of the area on May 3, 2011 (top), and April 29, 2011 (bottom). Both images use a combination of visible and infrared light to increase constrast between water and land. Water ranges in color from electric blue to navy. Vegetation is green. Clouds are pale blue-green and cast shadows onto the land surface below. (Images courtesy MODIS Today, Space Science and Engineering Center, University of Wisconsin-Madison. Caption by Michon Scott.)


Unfortunately we’re likely to see more breached, failed and overtopped levees in the future, because for several reasons, the deck is increasingly being stacked against the Mississippi’s levees being able to provide the protection of life and property they once did.

Over the last three-quarters of a century, while engineers were building hundreds of miles of flood-control structures along the river’s banks, the water-holding wetlands in the Mississippi watershed were being drained and filled to make room for more farms and homes. Illinois, Indiana, Iowa, Missouri and Ohio have each lost more than 85 percent of their wetlands.  Minnesota, where the Mississippi originates, has lost a whopping 9.3 million acres of wetlands, 62 percent of its pre-industrial total. All together, eight states of the upper Mississippi basin have lost 35 million acres of wetlands, an area the size of Illinois.

Those wetlands worked like a giant sponge: they absorbed rainwater and then released it slowly to nearby streams or the groundwater below.  In this way, they mitigated floods and made the job of levees that much easier. But with these natural protections largely gone, levees have been left to do all the work.

The levees have also disconnected the river from its floodplain, eliminating another crucial piece of natural flood protection.  Before the levees were built, Mississippi floodwaters would overtop the river’s banks and spread out over the floodplain’s marshes and forested wetlands.  By confining the river to its channel, the levees effectively put floodwaters in a straight jacket, causing the river to rise higher and flow faster.  The Corps decision to explode the levee at Birds Point effectively allows the river to reclaim part of its historic floodplain, but at great cost to the farm families living in the “spillway.”

Lastly, the likelihood of destructive floods is increasing as climate change pushes rainfall and hydrologic extremes outside their expected range. Depending on rainfall over the coming weeks, some areas could experience their second or third “100-year flood” in 17 years.  The Mississippi Emergency Management Agency expects the river to rise almost three feet higher than it did during the severe flooding of 2008, when local levees failed after several months of rain.  Officials are forecasting the river to crest at 53.5 feet on May 18 at Vicksburg, Mississippi, which would be the highest flood stage recorded there since the catastrophic flood of 1927.  During the Great Midwest Flood of 1993, 92 river locations set new record crests and 1,083 levees either failed or were overtopped.

Following that devastating 1993 flood, estimated to cause $16 billion in damages and considered among the worst natural disasters in U.S. history, James Baker, the Administrator of the National Oceanographic and Atmospheric Agency at the time, wrote: “Although the Great Flood of 1993 has caused devastating human, environmental and economic impacts, the lessons learned will guide us in providing improved services and benefits to the nation in the future.”

But fifteen years later, when the 2008 flood hit, there was little evidence of lessons learned. Instead of calling floodplains and wetlands back into active duty, officials in the region had permitted even more floodplain development. According to Nicholas Pinter of Southern Illinois University in Carbondale, 28,000 new homes and 6,630 acres of commercial and industrial development have been added on land that was under water in 1993.  By one reckoning, more homes and businesses have been built in the Mississippi floodplain in the St. Louis metropolitan area since 1993 than in all the time before then.

Clearly, public safety and good sense call for a change of course.  While upgrading levees is important, engineering fixes alone will not suffice. According to ecologists Donald Hey and Nancy Philippi, despite the massive construction of levees throughout the upper Mississippi Basin during the 20th century, annual average flood damage during that time more than doubled.

What is needed is a comprehensive plan to add ecological infrastructure to complement engineering infrastructure -specifically to expand wetlands and re-activate floodplains so as to mitigate future flood risks.

Following the Great Flood of 1993, U.S. researchers estimated that restoration of 13 million acres of wetlands in the upper portion of the Mississippi-Missouri watershed, at a cost of $2-3 billion, would have absorbed enough floodwater to have substantially reduced the $16 billion in flood damages.  Re-establishing wetlands would contribute other benefits, too. Besides helping control floods, wetlands recharge groundwater, filter out pollutants and provide habitat for birds and wildlife. Prairie potholes alone provide the breeding habitat for 50-70 percent of ducks in North America.  About half of the continent’s bird species depend in some way on wetlands.

Unfortunately, U. S. protection of wetlands has diminished in recent years. Two Supreme Court cases (decided in 2001 and 2006) and subsequent guidance from federal agencies have classified wetlands that supposedly are “geographically isolated” from navigable waters as deserving of less protection under the federal Clean Water Act.  These decisions, which defy sound science, have placed more than 20 million acres of wetlands at additional risk nationwide, threatening to reduce water quality, habitats and flood protection.

Instead of letting the nation’s ecological infrastructure degrade further, federal and state authorities should work to expand and rebuild it.  Cadres of ecological engineers should join civil engineers in shoring up the nation’s flood defenses.  Re-creating wetlands and re-activating floodplains in strategic locations will result in a more robust and resilient flood protection system.  With more extreme weather and devastating floods likely in store in the decades ahead, public safety and economic security depend on enlisting Nature’s defenses along with our engineered ones.


Sandra Postel is director of the Global Water Policy Project and lead water expert for National Geographic’s Freshwater Initiative.  She is the author of several acclaimed books, including the award-winning Last Oasis, a Pew Scholar in Conservation and the Environment, and one of the “Scientific American 50.”

[This post has been reformatted for Water Currents.]

Sandra Postel is director of the Global Water Policy Project and author of Replenish: The Virtuous Cycle of Water and Prosperity. From 2009-2015, she served as Freshwater Fellow of the National Geographic Society. Sandra is also co-creator of Change the Course, the national water stewardship initiative awarded the 2017 US Water Prize for restoring billions of gallons of water to depleted rivers and wetlands. The recipient of several honorary degrees, she works to bridge science, policy, and practice to promote innovative ways of securing water to meet both human and ecosystem needs.
  • Ben Guyot

    There is a reason that when I was a kid (50+ years ago) that “the bottoms” around our area were mostly “woods”. They were a “hunter’s playground” when dry and “Mom Nature’s sponge” when wet. Mature trees were the “harvest” every 10-20 years when “thinned” by local “loggers”. The open areas which were farmed were owned/produced under the old adage of “harvest a crop in three of every five years” and you are making money. Return to the “old ways” and get rid of overbearing “greed” when new owners want an instantaneous, continuous return on a land investment. The “old guys” took pride in the “long haul” on family land and did not abuse “the bottoms”.

  • Steve O

    Another possible outcome of this catastrophic flooding is that the river will breach the Old River Control Structure and change course. Permanently. The new course will enter the Gulf of Mexico about 65 miles west of New Orleans.

    The Mississippi River has changed course about once every thousand years and is due for another. The drainage of wetlands that Sandra points out here has only accelerated the date for the next one. It might be 2011.

  • Jon H

    It would be nice if the article provided some information on the value of the development in those wetlands. That way we could see how the $16 billion in damages and money spent on levees stacks up against the economic value of the land.

  • John Rumpler

    Thank you for highlighting a root cause of this week’s tragic flooding along the Mississippi River. The good news is that right now, we have an opportunity to do something to preserve nature’s flood-prevent systems. Just last week, U.S. EPA and the Army Corps of Engineers proposed a guidance document that would restore Clean Water Act protections for millions of acres of wetlands across the nation. Your article reinforces our conclusion that the flood prevention benefits of such a measure would be dramatic. To find out how to support this effort, please visit our website at

    John Rumpler, Senior Attorney
    Environment America

  • […] featured an essay by Sandra Postel, Freshwater Fellow of the National Geographic Society, “Mississippi Floods Can Be Restrained With Natural Defenses” : The destruction of 35 million acres of wetlands — an area the size of Illinois — in […]

  • […] (Read more about how we can mitigate Mississippi River flooding in National Geographic Freshwater Fellow Sandra Postel‘s most recent blog post: “Mississippi Floods Can Be Restrained With Natural Defenses.”) […]

  • Bayougirl

    I grew up in South Louisiana and the threat of the Mississippi changing course was ever-present in our lives. My father had a business in Amelia, LA, which was threatened by the 1973 floods. We were always afraid of a breach in the levees or the scouring under the ORCS finally causing a collapse of the control system. Although I now live far away both in miles and altitude from the River and the bayous, with family and friends still at the mercy of the River, the spectre of Momma Nature getting what she wants haunts me. As the saying goes, “water always finds its way.”

    It’s amazing how little we hear about the potential for the River to change course in the media these days. Any journalist who reports on this story should read John M. Barry’s fabulous book “Rising Tide.”

  • Steve W Zwick

    Thank you for an excellent and simple summary of a complex phenomenon. I’d like to pick up on Jon H’s point and see if anyone has explored the use of payments for ecosystem services to rebuild degraded wetlands. The US has a viable community of mitigation bankers who are adept at restoring degraded wetlands to offset new development, but these floods make it clear that wetland restoration is often a more economic use of land than is farming. We touched on this in Mississippi Learning: Flood the Plains – and Spare the Disaster?, which we posted yesterday. I just added a link to Ms. Postel’s excellent piece, and would be curious to see if anyone else is thinking along the same lines we are.

  • GoodCheer

    To expand on what ‘Jon H’ stated:

    If we develop 35 million acres of wetland, and the consequence is a $17B flood every 6 years, then the cost of developing each of those acres is $81/year in flood damage. (I think that’s a pretty generous assessment of flooding costs, but I don’t have any better numbers). That almost makes it seem worth it. I assume at least some of those acres are delivering more than $81/year in GDP.
    Of course the problem is transferring the benefit seen by those on the upstream development to the farmers and homeowners who bare the costs of the flood.

  • Dan Branton

    This is all poppycock! The MRT Project is doing exactly what it was designed to do. Birds Point floodway is in US Law to breech at a set elevation at Cario (61Feet). The Morganza spillway/floodway also is opened when the river gets to a certain stage at Baton Rouge. The same with Bonnet Carre above New Orleans. The river will go down then all you environmentalist will get all excited about the dead zone in the gulf, which is another sham. You want to take the richest land in the world from unwilling sellers who have been on this land for generations to satisfy some elite desires. Go jump in the river!

  • […] River might just mean not farming, developing or building in flood plains and allowing “natural defenses” to exist. Wait, developers could lose money? Never mind. [Ecosystem […]

  • […] spring, the Mississippi River is broadcasting a message loud and clear: it’s time to put nature back into the water equation.  […]

  • […] of the independent Global Water Policy Project, explains in her article for National Geographic (…) why the floods can be restrained with natural defenses.  Over 35 million acres of wetlands have […]

  • […] building durable food systems and smarter water management.  And it involves strategically rebuilding our ecological infrastructure – including wetlands, floodplains and watersheds – so as to enlist nature’s help in […]

  • flood defence

    For anyone living in a flood-prone area, flood protection is always a must. Although you can’t always depend on a flood happening, it’s important to depend on a service that can stop a flood at any time.

  • […] Mississippi Floods Can Be Restrained With Natural Defenses […]

  • Jona Cris Peredo

    Thank you for the information, it will greatly help the land investors.

  • […] lessened by strategically re-building the basin’s ecological infrastructure – in particular, by bringing water-absorbing wetlands back into action in the upper […]

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