A BATTLE IS TAKING PLACE on the Mississippi River involving conservation groups, the US Army Corps of Engineers, the Federal Emergency Management Agency, and local drainage districts. The issue? The height of some of the levees along the river, which one group claims is causing excessive flooding and erosion for properties downstream.
The height of the levees—earthen structures designed to protect farms and buildings along the river from flooding when the water level rises—is limited by federal law. A few years ago, as reported in a recent article in the Wall Street Journal, the Army Corps of Engineers surveyed the levees along a 200-mile stretch of river and discovered that 40% of them were higher than they should be, by as much as 4 feet.
Now a conservation group, the Great Rivers Habitat Alliance, is asking FEMA to make at least one drainage district lower its levees. If that isn’t done, the group says, FEMA should penalize the district by taking away federal flood insurance from the landowners whose property those levees protect.
However, the district in question—the Sny Island Levee and Drainage District in Illinois—says FEMA and the Corps of Engineers approved the levees back in 2004. The district says they are exactly the height they need to be to protect against a 100-year flood, which was the requirement for local landowners to qualify for lower flood insurance premiums in the first place.
It’s an old question: Do structures designed to prevent flooding and erosion—levees, seawalls, groins, and jetties—actually cause more damage to adjacent land? Many experts say that they do, especially in coastal environments, either by deflecting wave energy or by trapping the sand that would otherwise move horizontally along the shoreline. That’s why some coastal states prohibit or severely restrict the building of hard-armor structures for erosion control. When the rules are set by individual cities or coastal protection agencies rather than by the state, the piecemeal nature of the barriers that are constructed can create more problems than they solve.
The situation along the river is a bit different, but the same principles apply. If the rising water has nowhere to go as it flows downstream, it increases in volume and does more damage than it otherwise would as soon as it finds a break—or in this case, a lower levee. On a smaller scale, the same thing occurs in many urban channels that are lined with concrete or riprap for only part of their length; the water’s volume and velocity increase, and erosion in the unarmored portion downstream is much greater than it would have been if there were no armoring at all.
In the ongoing Mississippi River fight, the Corps of Engineers has sided with the conservation group and wants the Sny district’s levees to be lowered. The Corps can’t deny the district’s members flood insurance—the National Flood Insurance Program is under FEMA’s purview—but it has said that if the district’s levees should be damaged in a flood, the district won’t receive federal funds to help repair them. That decision has serious implications for the other areas whose levees also exceed the allowed height—and perhaps eventually for areas with other types of flood protection structures like seawalls.
