Despite a century of massive investment in flood control structures throughout the Upper Mississippi River Basin, flood damages have increased. Indeed, it could be argued that it is because of our emphasis on structural solutions, rather than ecological solutions, that we now face these damages. Clearly new solutions need to be explored.

The Wetlands Initiative believes the solution requires new thinking about the way we use our floodplains. Rather than immediately discharging water downstream after a precipitation event, we need to store that water on and in the ground for days, if not weeks. We need to restore the natural hydrology of the unleveed 100-year flood zone while reconnecting much of the leveed floodplain to its parent river. In short, we should be returning the floodplain to its basic functions—holding floodwaters, improving water quality, and supporting rich, biodiverse habitats.

The Army Corps of Engineers uses sandbags and portable floodwalls to hold back floodwaters in Hannibal, Missouri, on June 18, 2008 (left). The Wetlands Initiative proposes a more natural solution—using more wetlands (right) to slow down and store floodwaters and using leveed areas to store water.

To assess what it would take to implement this solution, the Wetlands Initiative (TWI) and its partners conducted a study, funded by the McKnight Foundation, to determine how much of the 100-year flood zone was existing or drained wetlands. Called Flood Damage Reduction in the Upper Mississippi River Basin: An Ecological Alternative, the study estimated the potential storage capacity of the floodplain if leveed lands and restored wetlands were pressed into providing the services of flood storage.

TWI began with an analysis of the 100-year floodplain within 77 counties of Iowa, Illinois, Minnesota, Missouri and Wisconsin. Within this study area, we identified the hydric soil, wetland, land use, and leveed areas. Our study area covered 24% of the total 100-year flood zone of the five states. These data were then used to extrapolate landscape characteristics for the entire area of the five states in the basin. We concluded that:

• Almost 7 million acres (37%) of the 18.4 million acres in the 100-year flood zone in the five-state region were wetlands prior to European settlement.
  
• Approximately 4 million acres of these former wetlands have now been drained for row crops (3 million acres) and for pasture (1 million acres). This means that nearly 60% of the former wetlands on the 100-year flood zone are now used for agriculture.
  
• Federal levees isolate approximately 2.3 million acres (13%) of floodplain from their parent rivers.

Restoration Strategy

Based on these findings, TWI estimates that restoring the 4 million acres of former wetlands—land now used for row crops or grasslands—could significantly relieve flood problems in the basin. By holding 3 feet of water in restored wetlands as well as in existing wetlands, we could acquire approximately 16.5 million acre-feet of flood storage. [An acre-foot is the volume of water that fills one acre of land at a depth of one foot.] We also could use land currently behind levees to store floodwaters. By adding spillways to the top of existing levees, 23 million acre-feet of floodwaters could be stored, assuming that they hold 10 feet of water during a flood event.

Hence, by replumbing our landscape—restoring water-holding wetlands on unleveed land and using our leveed areas to receive floodwaters—we could increase flood storage in the five state area by almost 40 million acre-feet of water. This volume is comparable to the 39 million acre-feet (as measured at St. Louis) that is credited with causing the damage in the Mississippi River Flood of 1993.

Our strategy is possible, but would require changes to our land use and subsidy practices. Rather than paying landowners to recover from damage after flooding, we would need to develop mechanisms that pay landowners to receive floodwaters. At the same time, urban or residential development behind leveed areas would need to cease. Although some farming on the floodplain might continue, rather than assuming that flooding is a rare event that needs to be avoided, farmers would treat flooding as an event to be expected and one from which benefits can be gained. Our study estimated that the economic benefit from converting cropland in the floodplain to wetland flood storage would be $500 million per year!¹

In addition to alleviating flooding and flood damage, restored wetlands would provide important water quality and wildlife benefits. For example, restored wetlands could support more than 150 bird species, including 60 that are of high conservation interest, whereas farm fields in our study supported only 50 bird species—only 8 of high conservation concern. Similar increases in other wildlife are likely.

Background

Flooding and, more importantly, flood damages have increased over the past century. Whereas early in the century (1904-1933) annual flood damages averaged $1.4 billion in the United States, by late in the century (1964-1993), this average rose 150% to $3.5 billion. In the 1993 flood in the Upper Mississippi River system nearly 150 major rivers and tributaries flooded, levees were broken, more than 50,000 homes were destroyed, and drinking-water supplies were contaminated. Economic damages reached nearly $16 billion. 

As flood damages have increased, so has federal spending on flood control. By 2004, the U.S. Army Corps of Engineers had spent more than $156 billion nationwide on flood control projects, usually levees.

Yet, these control efforts cannot overcome centuries of wholesale drainage. Ditches, drain tiles and pumps have been constructed or installed to develop flood-prone land into farms, homes, and cities. As a result, low lying areas that once stored floodwaters no longer retain water. Instead, excess water rapidly drains off the land and is emptied or pumped into the rivers.

Levees confine floodwaters to a narrow channel, increasing both the velocity and stage of flow—the former increases the erosive power of the river and the latter increases flood stage and, thereby, flood damage. Levees often give citizens a false security and developers a ‘license to build’ on the floodplain. In the St. Louis area, more than $2.2 billion worth of new development has occurred on land that was underwater during the 1993 flood (St. Louis Post-Dispatch, July 7, 2003).

The artificial drainage system in the basin also contributes to another serious problem—nutrient pollution in the river and the Gulf of Mexico. More than 7 million pounds per day of agriculture fertilizer containing nitrogen and phosphorous runs off farm fields  in the upper Midwest and flows quickly downstream through the man-made channel of the Mississippi River. These nutrients fuel algal blooms in the Gulf, which, when they decompose, deplete the oxygen supply. The resulting dead zone is deadly to marine life and damaging to the Gulf economy.

Yet wetlands can naturally process and store nutrients. By restoring wetlands in the Upper Mississippi River Basin, we could improve water quality in the river system while providing needed flood storage.

Financing Wetland Restoration

To advance this ecological solution, we need a means to finance it. The Wetlands Initiative is now developing such a strategy, called “nutrient farming,” which could fuel large-scale wetland restoration by creating a market to pay for it. The Illinois River Nutrient Farming Pilot Project at Goose Pond, Illinois, will create a 1,300 acre demonstration and research site.

Partners in this study included the Audubon Society, University of Missouri-Columbia, National Wildlife Federation, and the Sierra Club of Wisconsin.

¹Economic benefit was computed as the savings from reduced crop damage and subsidy payments, plus income from other wetland benefits (e.g., recreation), minus the loss of rental income for cropland, plus wetland construction and operating costs.