Day 7: Levees, Flooding - Intentional and Otherwise, and the Lock & Dam System
When the Waters Rise: Ins and Outs of the Mississippi River Levee System
The idea sounds simple: If you don’t want a river flooding your town or farm field, just build a ridge high enough to keep it out. The hydrology is much more complicated, however, and towns and cropland once thought safe from the whims of the Mississippi now routinely see 100- or 500-year floods swamp the land behind the levees. What are some weaknesses in the system and what are projections for future high-water scenarios? Are the levees designed to prevent flooding actually making things worse?
Pushing the Problem Downstream
We gathered in Hannibal, MO to hear about the levee system that stands between the town and the next big flood. For years, residents fought various iterations of Army Corps flood-control proposals that called for building up levees all along the Upper Mississippi except for St. Charles, Lincoln and Pike Counties. Instead, buyouts of flood-prone properties were proposed. While those plans never passed, some upstream levee districts have moved ahead anyway – like the one right across the river. Tasked with protecting the farmland and small communities on their side of the Mississippi, some Illinois levee districts routinely break federal law and raise the height of their levees, pushing water onto downstream communities and spurring them to, in turn, raise their own levees. We discussed what’s at stake in these “levee wars,” and what it’s like to live in a community having flood waters shoved its way.
When the Levee Breaks – On Purpose
Established in 1964 with funds from the purchase of migratory waterfowl stamps, The Clarence Cannon National Wildlife Refuge covers 3,750 acres of Mississippi River floodplain and is almost entirely surrounded by a levee. But here the idea is to let some water back on to the land. A pump station is used to create seasonal flooding that mimics natural flow patterns to restore floodplain habitat and benefit migratory birds.
Locks, Dams and Really Large Ships: Managing Water Levels and Mitigating Floods
Alton, IL is home to the largest developed floodplain north of New Orleans – nearly $19 billion in industrial, commercial and residential assets – which sits behind a floodwall built to provide a 500-year flood level of protection. We spent the afternoon at the Melvin Price Lock and Dam, which, completed in 1994 to replace an aging Lock and Dam 26, is the newest structure in the system. We learned how the Lock and Dam system tries to manage water levels and shipping and recreational expectations, and hear concerns about aging infrastructure and why commercial navigation interests would love longer locks. We also got a behind-the-scenes tour of the Melvin Price Lock and Dam.