Flood Risk Rising on the Mississippi River?
The Mississippi River is perhaps the U.S’s most visible and enduring example of an altered river. Where the Upper Mississippi River was once free flowing with islands, backwaters, and wide floodplains to support diverse fish and wildlife, it is now a series of pools, created by an extensive lock and dam system. The Mississippi’s conversion to a “working river” that can support barge transportation was achieved by the U.S. Army Corps of Engineers’ (Corps) extensive work to manipulate and harness the river’s natural flow, functions and features.
In addition to the 29 locks and dams on the River, the Corps maintains a 9 foot deep navigation channel on the river using “river training structures” like chevrons, wing dikes, and bendway weirs. (see photos). These structures are placed in the river to help the river self- scour and reduce the need for dredging. Between 1980 and 2009, the Corps built at least 380 new river training structures in the Middle Mississippi, including 40,000 feet of wing dikes and bendway weirs between 1990 and 1993. The Corps built at least twenty-three chevrons between 2003 and 2010.
The Corps frequently argues that these new structures are more cost effective and create a more diverse stream bed, which can be environmentally beneficial. However, the Corps’ St. Louis District office has not documented any adverse or beneficial impacts, relying on mostly models and a handful of surveys that do not fully support the Districts’ claims that these structures are eco-friendly. Despite the addition of so many new structures to the river, the Corps has not updated their environmental impact statement since 1976.
Even more concerning for many riverside communities along the Mississippi River are concerns that adding these structures to the river bottom is significantly increasing flood levels. At least 51 peer-reviewed scientific studies demonstrate that river training structures are significantly increasing the risks of floods for riverside communities. These structures have increased flood levels by up to 15 feet in some locations and 10 feet in broad stretches of the river where these structures are prevalent. Despite the evidence of increasing flood risk, the Corps denies the validity of these claims.
In 2011, the Government Accountability Office – the independent federal watchdog agency – investigated the use of river training structures and recommended [PDF] that the Corps update its Environmental Impact Statement to assess the environmental impact of river training structures on the river. While the Corps’ St. Louis District has decided to undertake an Environmental Impact Statement [PDF], it is not planning to address the critical flood risk concerns that have been raised about these river training structures. Instead, the Corps plans to continue to build new structures while this study is being completed.
The Corps’ St. Louis District is currently accepting comments on the scope of their Environmental Impact Statement. This is the public’s opportunity to tell the Corps what they should consider while performing this study. Please join American Rivers and members of the Nicollet Island Coalition in telling the Corps to:
- Stop building new river training structures.
- Evaluate all of its activities on the Upper Mississippi River and Illinois Waterway.
- Invite the National Academy of Sciences to evaluate impacts of river training structures on floods.