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.]