The Danger of Endangered Rivers

An endangered river is dangerous—the Cedar River proved that exactly two years ago this week.

In June 2008 massive storms hit parts of southern Minnesota and eastern Iowa, sending the Cedar into a destructive frenzy of historical proportions. As it happens, while taking a break from reading A Watershed Year: Anatomy of the Iowa Floods of 2008 the other day, I ran across the announcement that the main “character” in the book, the Cedar, has just been named one of the nation’s most endangered waterways by the group American Rivers. “Outdated flood management and poor watershed planning” were cited as the reasons for the ranking.

The Cedar has its headwaters in southeast Minnesota’s Dodge County, and it flows through some of our richest farmland before cutting a wide, crescent-shaped swath through a major part of eastern Iowa. That makes we Minnesotans partially responsible for the tremendous damage and heartache the Cedar has caused our neighbors downstream.

The Cedar has experienced a “500 year flood” twice during the past 15 years—giving that part of Iowa two of its worst river-related catastrophes. When the river went out of its banks in 1993, people thought they’d never see anything like it again in their lifetimes. But in 2008, it did happen again. Virtually all of eastern Iowa was affected, but the area around Iowa City and Cedar Rapids was perhaps the worst. At one point the water flow through the latter city reached 140,000 cubic feet per second, nearly double the earlier record flood flow in 1961.

Homes, businesses and institutions were wrecked and lives ruined. The floods also did a major number on farmland. In fact, part of the damage caused by that flooding can be traced back to farmland, or, more accurately, how it is managed. As Laura Jackson and Dennis Kenney write in A Watershed Year: “A drop of rain that falls in Iowa has a 63 percent chance of falling on a corn or soybean field. If we look just at northern Iowa, where farming is most intensive, that probability rises to 88 percent.”

In July, August and September, all those corn and soybean fields provide plenty of ground cover. But the flood occurred in mid-June, when row-cropped fields have yet to develop a good canopy that can protect the land’s surface from torrential rains. Water dropping from the sky can be like a hydraulic hammer on bare ground: the power of raindrops on one acre of land in the Midwest is equal to the energy found in 20 tons of TNT. The root systems of row crops are also not well established in mid-June, leaving fields vulnerable to the scouring effect of flood waters.

Soil scientists estimate that a soil erosion rate of around five tons per acre annually is “tolerable,” meaning a farmer can maintain crop productivity as long as the rate doesn’t rise higher. Five tons roughly translates to the thickness of a dime uniformly covering an acre of land. According to  A Watershed Year, the 2008 floods loosened as much as 50 tons per acre in some Iowa townships. That ain’t chump change.

It’s also not surprising. Various studies have shown that storm events are major sources of farm field erosion. In a landmark 1997 paper published in the  Journal of Soil and Water Conservation, soil scientists pointed out that in fact such storm events are the major cause of soil erosion. The authors of the paper went on to argue that land management systems must be adjusted to deal with such erosion events. That doesn’t mean that a significant amount of soil isn’t lost on a routine basis. But big storm events can accelerate things considerably, particularly if they come at just the wrong time—when crops are short and provide very little ground cover, for example. And relatively recent changes in our climate seem to favor spring and early summer storm events (more on that later).

Let’s face it: when a storm event of that magnitude hits an area, even the best ag conservation practices aren’t going to be enough to prevent some above-normal erosion. We certainly saw that in southeast Minnesota and southwest Wisconsin during the flooding that took place in August 2007. But the theme that emerges from the various essays in A Watershed Year is that there are steps we can take to mitigate such damage.

Much of Iowa, like southern Minnesota, has had its wetlands, deep-rooted prairies and other natural areas replaced by intense plantings of row crops that only cover the soil a few months out of the year. That makes the land much less hydrologically resilient, write Jackson and Keeney. They, as well as other authors in A Watershed Year, recommend bringing perennial plant systems back to key parts of the landscape to help slow down and soak up water.

This doesn’t mean establishing a blanket of bluestem from Austin to Iowa City and banning farming in the Cedar River watershed. Great strides have been made in recent years to utilize managed rotational grazing, diverse crop rotations and other sustainable systems to balance agricultural production with environmental protection on working lands.

Returning perennials to key, particularly sensitive portions of agricultural watersheds can produce impressive results. For example, Jackson and Keeney cite an Iowa study where prairie strips covering just 10 to 20 percent of a field were able to reduce sediment loss by 95 percent, according to preliminary results. Modeling research right here in Minnesota has shown that diversifying portions of intensely row-cropped watersheds in the western and southeastern part of the state can vastly improve water quality, while returning some balance to the hydrological cycle.

It’s also time to examine whether a major land use like agriculture is prepared to meet the challenges of a changing climate. As A Watershed Year points out, one new climate wrinkle is that we’re getting our precipitation in a different manner. Nice steady showers that have a chance to soak in without creating damaging runoff are increasingly rare. That means conservation methods and structures such as conservation tillage and terracing may not be able to handle these intense, infrequent storm events. As soil scientist Jerry Hatfield once told me: “We have conservation measures that were built for a climate scenario we no longer have.”

There’s no doubt changes in land use can help make rivers like the Cedar less dangerous. But A Watershed Year also points out the limits to what humans can do. In fact, I found the book’s argument that we should stop treating floods as “abnormal events” its most intriguing proposal—and perhaps its toughest to accept.

“Floods are what rivers do,” writes Cornelia Mutel in the book’s introduction. “Floods are one component of the water cycle, a process as ancient and necessary as any of nature’s cycles…Floods become a problem only because we choose to live and place objects of value in a river’s extended channel—that is, in its floodplain.”

That reminds me of a passage in John McPhee’s classic geology tome, Annals of the Former World. At one point he quotes geologist Anita Epstein describing how change on the landscape is not always as slow and constant (think glaciers) as we might think. “The evolution of the world does not happen a grain at a time. It happens in the hundred-year storm, the hundred-year flood,” Epstein tells McPhee.

When put in that context, it makes it easier to accept that maybe we shouldn’t be issuing building permits or raising corn in every last acre of bottomland. As Kamyar  Enshayan, the director of Center for Energy & Environmental Education at the University of Northern Iowa who happens to be a member of the Cedar Falls City Council told the Washington Post: “Cities routinely build in the flood plain. That’s not an act of God; that’s an act of City Council.”