USA: A better way to decrease disastrous flooding on the Mississippi River
By Willy Blackmore
Life in davenport, Iowa, revolves around the Mississippi River. Downtown overlooks the broad waterway here, where, due to a bend, the 2,300-mile-long river flows east to west rather than north to south. The extensive parks along the waterfront host baseball games and music festivals, and tourists disembark mid-cruise to visit breweries, museums, and shops. The Mississippi is usually a source of pride, but this spring locals watched it with wariness. The fat, brown river began to swell in March, the muddy water advancing farther into the city with each passing day, driven by snowmelt and heavy rain. Within a week the water level had climbed nine feet, and it didn’t stop. It surged past 15 feet—flood stage, when water spills into areas not usually inundated—and kept going, cresting at a record-high 22.7 feet on May 2.
As the water rose, it drowned the parkland lining the city’s nine-mile riverfront. The torrent turned the band shell and baseball stadium into islands, and transformed the crowns of shade trees that dot what is usually acres and acres of grass into emerald buoys. Nearly a trillion gallons of water pooled in Nahant Marsh, a restored wetland just west of downtown. One of the temporary HESCO barriers—movable metal structures that stave off river water—abruptly gave way in late April, flooding a few blocks of the business district and sending emergency responders scrambling to evacuate buildings. More than seven weeks passed before the water receded to below 18 feet, trouncing the previous 31-day record.
Davenport is just one of dozens of communities in eight states along the Mississippi that saw historic flooding this past spring and summer, a series of disasters that caused more than $2 billion in damages and killed at least three people. Levees were breached along the river, which swelled to seven miles wide in one place, flooding towns and farmland from Wisconsin to Louisiana. Barges that transport corn and soybeans destined for export were kept off of the Mississippi for months, and this year’s harvests may be hampered due to widespread rain-related delays in planting.
Flooding has always been a part of life in the Mississippi basin, but we have engineered a river primed to over ow dramatically—a problem that climate change is already making worse. We’ve transformed the grasslands and wetlands that naturally absorb rainwater into farmland and towns, and installed walls and levees along the river, cutting it off from historic floodplains. When the pressure of trillions of gallons of extra water builds, we’ve left the river no choice but to jump its banks when and where it can.
One reaction is to shore up and expand the system of floodwalls and levees. In April, at a meeting of the Mississippi River Commission, U.S. Army Corps of
Engineers Major General Richard Kaiser noted that in response to the historic flooding, many people were calling for a system of levees and barriers similar to that on the Lower Mississippi. “Maybe this event is something that will help trigger that,” he said.
Davenport is taking a different approach. It’s Iowa’s largest city on the Mississippi and one of the few without a permanent floodwall. Instead of relying on hard barriers that hold back the torrent and increase pressure on the system, it depends on its riverfront parkland and marsh to act as a release valve. Aside from the breached HESCO barrier, all went according to plan this year. “Building a floodwall, a solid-structure floodwall, it pushes problems downriver,” says Mayor Frank Klipsch, where the growing volume of water overwhelms the next town—and beyond.
As the destruction wrought by this year’s flooding has made clear, the old ways aren’t working. Momentum is building for more natural flood control in riverfront communities and throughout the Mississippi basin. These ventures hold the promise not just of safeguarding Midwest cities but of restoring habitat increasingly critical to wildlife as temperatures rise.
Between April and June, storms roll into Iowa like clockwork. The air grows heavy with humidity, and ashes of lightning and shuddering thunder signal the drama of the coming deluge. “We’ve always had these spring and summer thunderstorms,” says Gene Takle, the former director of Iowa State University’s climate science program. “They move over from Nebraska and hit the state of Iowa at about six o’clock at night, and instead of dying out, they intensify.”
The weather system may be predictable, but in exceptionally wet years, the destruction caused by flooding is anything but. In May 1844, storms led to immense flooding on the Mississippi, which was then an almost completely wild river. With no levees or floodwalls to retain it, the river swelled as wide as 15 miles in some places and crested at 41.4 feet.
A few years later Congress passed the Swamp Land Acts of 1849 and 1850, which provided funding for levee development. The bills transferred federally owned wetlands to states, which drained and sold them; millions of acres became farmland. Amid the ensuing flurry of levee construction, there was some concern that it might back re: An 1852 War Department report noted that “water that was formerly allowed to spread over many thousand square miles of low lands . . . is, therefore, compelled to rise higher and ow faster.” The warning wasn’t heeded.
Instead, the federal government massively expanded flood control after the Great Mississippi Flood of 1927, which left 27,000 square miles of land underwater, more than 700,000 people displaced, and at least 250 people dead. During the next great flood, in 1993, fewer than 50 people died but more area flooded than in 1927: 400,000 square miles and at least 75 towns were completely inundated, and some communities were never rebuilt. Levees and reservoirs built by the Army Corps of Engineers prevented more than $19 billion in potential damage, according to a federal report, commissioned by the Clinton administration, on the causes and effects of the flood. But hundreds of levees on the Mississippi and Missouri Rivers were also breached or overtopped. The report’s authors highlighted the need for more research into the role of natural landscapes for absorbing and minimizing floods—an approach promoted by a growing consensus of scientists and community leaders today.
The report doesn’t mention climate change, but Gerald Galloway, who coordinated the investigation, says that the signs were all there. “Things were happening in the ’93 flood that gave an indication that things were not going well,” he says, “that weather was not operating in a normal fashion.”
It’s now understood that even back in 1993, those evening storms—the result of warm, moisture-laden air pushed up from the Gulf of Mexico by the low-level jet stream—were already changing. In the past 30 years, about 20 percent more precipitation has fallen between April and June than during the same period in any of the previous 90 years; Iowa saw more rainfall in the 12-month period ending this spring than during any similar span in 124 years. The trend toward wetter, more frequent storms will continue if carbon emissions aren’t significantly reduced. According to the Fourth National Climate Assessment, heavy downpours that today happen once every 20 years will occur two to three times as often across much of the Upper Mississippi by 2100.
“The Gulf of Mexico starts to warm up in the spring—that’s natural. The low-level jet stream is always there—that’s natural,” Takle says. “It’s the increase in global temperatures that is increasing the intensity.” When water temperatures in the Gulf are higher, more water evaporates into the air, producing higher concentrations of humidity over the Midwest. That feeds the same old storms a huge influx of moisture, resulting in rainfalls of seven or eight inches instead of two or three. There’s still the possibility of low-precipitation years, Takle says, but “it’s going to be less and less likely that we’re going to get a relatively dry, or what was considered a normal, year.”
The question now is whether we’ll continue to double down on hard infrastructure or finally heed the warnings and rethink flood control. “The challenge,” says Galloway, “is are we prepared to deal with this?”
While neighboring cities have built floodwalls in the past half century, Davenport has opted to maintain its river view instead. The city nixed a plan in the 1980s to build a $34 million floodwall with support from the federal government, and instead bought out low-lying properties and beefed up its natural areas to act as a buffer. After the 1993 flood, it again opted against permanent flood barriers.
In the aftermath of this year’s flooding, the city is undertaking a thorough review of its flood-response plans. “What this disaster has shined a light on is the fact that we need to be even more prepared than we already are,” says Kyle Carter, executive director of the Downtown Davenport Partnership, a nonprofit focused on economic development. While the local business community, which bore the brunt of the flooding, isn’t clamoring for a floodwall along the waterfront—it would, for one thing, ruin the vista—some residents support building a permanent structure.
Mayor Klipsch is determined to keep an open riverfront and expand natural storage along the river. He’s not alone. The Mississippi was still well above flood stage in Iowa when he and the mayors of 89 other river communities released a statement calling for more natural infrastructure in response to the ongoing disaster. By and large, they say they have the support of their constituents. “In years past, if you wanted to stay mayor, you couldn’t talk about anything but a floodwall or a levee,” says Colin Wellenkamp, executive director of the Mississippi River Cities and Towns Initiative, an association of 90 mayors. “Times have changed.”
While Wellenkamp says Davenport’s miles of parks and wetlands are the envy of many riverfront towns, more and more are adding their own green infrastructure. Arnold, Missouri, for instance, already has a floodable, 68-acre riverfront park that’s just up the Meramec River from its confluence with the Mississippi; now it’s buying up adjacent properties with an eye toward transforming the empty lots into floodable space. The plan protects both Arnold and its downstream neighbor, Kimmswick, which could be devastated if Arnold opted for a floodwall.
In Cape Girardeau, Missouri, an effort to remove flood-prone homes has been underway since 1993, and the city project is replacing a low-lying former residential area with parkland. Grafton, Illinois, meanwhile, completed a small wetland project similar to Nahant Marsh and is already considering expanding it. Restoring these natural areas also creates habitat. Even as the sandbag wall protecting the Nahant visitor’s center inched higher, wildlife abounded within the 305 acres of cattails, sedges, and wild flowers. A Bald Eagle duo hatched chicks, a rare occurrence in the city, and a breeding pair of Sandhill Cranes returned to the marsh for the fourth year in a row. Prothonotary Warblers, whose populations have plummeted globally around 40 percent since the 1960s, nested in riverside boxes in the shade of the flooded woods. Beavers, once extirpated from Iowa, plied the floodwaters. When it comes to flooding, attention has long been focused on reducing risk at the river’s edge. But as storms worsen in the coming years, protecting communities will mean looking beyond riverfronts, to the source of all that potentially destructive water.
Like farmers across the Midwest, Hans Schnekloth’s planting was interrupted by storm after drenching storm this spring. From his tractor, he’d watch water pool between corn and soybean rows on his farm in eastern Iowa, forming rivulets that swept away the soil and nutrients he depends on—despite his efforts to reduce runoff. Every spring, he and his father plant new seeds in the remnants of the previous year’s crop on their 2,800-acre farm. In this no-till system, the decaying roots funnel water into the earth instead of over the soil. To catch more runoff, they also seed their streambanks with grass. “But when you get three inches of rain in half an hour,” Schnekloth says, “it doesn’t hold up.”
Those rivulets end up in streams that have been straightened, eroded, channelized, or all the above. Hemmed off from natural floodplains, the brimming streams eventually feed into the mighty Mississippi.
Historically, the Great Plains acted like a gigantic sponge when it rained. The upper Midwest was blanketed in tallgrass prairie, dotted with small lakes and wetlands. Instead of what Schnekloth saw this spring, rainwater moved slowly through the dense plants, seeping into the ground. Any excess fed into the oxbows and vast wetlands alongside rivers, or in the small marsh or boggy spot in every swale between hills.
Then farmers plowed under the prairie and drained the wetlands, forever altering the way the Midwest floods. Today, less than .1 percent of Iowa’s tallgrass prairie remains, and more than 90 percent of its historic wetlands have been lost—a stark transformation replicated across the Midwest. “This changed land cover from prairie to row crop has increased the probability of the same amount of rainfall causing a higher degree of flooding,” says Keith Schilling, Iowa’s state geologist. Three inches of rain historically might have resulted in one inch of runoff, compared with two today.
We’ll never restore all of the lost prairie—but we might not need to. Planting swaths of native vegetation amid crops may dramatically increase the amount of water absorbed, according to mounting evidence from Iowa State researchers. Converting just 10 percent of a field to prairie strips—30-foot-wide strips of grasses and wild flowers—reduces runoff by 42 percent. It also prevents nearly all sediment and nutrients from washing into waterways. Visit a prairie strip after a major storm and you’ll see a line of fresh deposited soil, its escape stymied by the dense vegetation.
Only 576 acres of prairie strips have been planted amid some 5,000 acres of Iowa cropland. But more farmers are adopting the practice, which was highlighted in the Fourth National Climate Assessment as an adaptation that could make agriculture resilient to more intense rains. Converting a tenth of an acre to prairie strips costs less than $40 per acre, and the perennials take about three years to establish themselves.
The benefits go beyond flood control, says Lisa Schulte Moore, co-founder of the STRIPS (Science-based Trials of Rowcrops Integrated with Prairie Strips) project at Iowa State. She’s found 51 native plant species in prairie strips, compared with 13 in acres with crops alone—diversity that supports wildlife from pollinators to raptors. Fields with prairie strips support twice as many birds and bird species, including Common Yellowthroats and Dickcissels, as fields of corn or soy alone. Grassland birds will be among those hardest hit by climate change, according to Audubon’s new climate report, so prairie strips could help them hang on. What’s more, healthy native grasslands with diverse plant species act as a natural carbon sink, so installing prairie strips on a grand scale might ultimately help pull more carbon dioxide out of the air and store it in the ground.
Schulte Moore says the difference prairie strips make is audible. On a June visit to an Iowa cornfield, “you could hear the leaves rustling in the wind, but otherwise it was just quiet.” On a nearby field with a prairie strip, “there were bees buzzing, there were crickets chirping, there were different species of birds singing, and butterflies flying among the flowers.”
In Davenport, by June the floodwater was receding from Nahant, where the insistent warbler chicks chirped as Bald Eagles scanned for sh. Downtown, most business had resumed, and cleanup was underway at riverside parks. It’s just what the city is striving for in these increasingly uncertain times: life carrying on.