Floods of Insight: Learning From the 1927 and 2011 Mississippi River Floods

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Published on May 25th, 2011  |  Discuss This Article  

Left: Catastrophic levee breach at Mounds Landing on Mississippi River, 1927; Right: opening of Morganza Floodway, 2011

The Mississippi River flood of 2011 has forced agonizing decisions upon those tasked with managing the river and protecting people and property from floods. Facing record or near-record river levels, the US Army Corps of Engineers and the Mississippi River Commission gave orders to open several “floodways” in order to reduce pressure on the levees that protect communities and farms along the lower Mississippi River (see photo above on right and photos at end of post). These floodways are portions of the river’s historic floodplain that were designated in the 1930s to serve as relief valves should the river reach certain flood levels. By allowing floodwaters to surge out onto their historic floodplains, the floodways make it less likely that other levees—including those that protect New Orleans and Baton Rouge—will fail or be overtopped.

What makes the decision to use the floodways agonizing is that they are not empty lands. Roughly 300 people live in the New Madrid Floodway, farming its rich soil, and more than 20,000 may be impacted by floodwaters in the Morganza Floodway.

The anxiety, disruption, and loss experienced by people in the floodways cannot be ignored and this flood raises important questions about the most effective ways to handle the occasional losses when the floodways are used (more on that below).

But the emotional images, and the underlying drama of Cajun homes going under water to save New Orleans, should not obscure important lessons from this flood nor distract from discussion of critical questions about the future.

First, it must be noted that these floodways are part of a carefully designed flood-management system and that the system is working. (It should also be noted that the system was designed strictly for flood control and navigation and not for the environmental values of river and floodplains–more on that below as well.)

From a flood-management perspective, the Army Corps of Engineers can take pride in the fact that it learned lessons from the historic Mississippi River flood of 1927 and that the system designed based on those lessons is managing a similar flood with dramatically different results.

What happened in 1927? An area the size of South Carolina was inundated for months, displacing 600,000 people from their homes.

Despite the massive volume of floodwaters, New Orleans remained dry in 1927. The same process that saved New Orleans then—floodplains acting as relief valves for the levee system—will also keep New Orleans dry this year.

But that relief-valve process played out in a starkly different way in 1927 and the comparison puts into perspective the river managers’ difficult decisions to use the floodways this year and the impacts of those decisions.

In 1927 New Orleans was spared when dozens of upstream levees failed, allowing floodwaters to spread out on their historic floodplains and lowering the river to a safe level as it coursed through the city. Although New Orleans avoided disaster, hundreds died in the floods upstream. The reported death toll is almost certainly a gross underestimate and it is likely that thousands of poor, mostly African-American, floodplain residents were drowned and swept beyond recovery or the attention of official statistics.

The levee failures that saved New Orleans also shattered the existing paradigm of river management that held that levees alone could contain all floods. In addition to excessive faith in levees, the flood-management system prior to 1927 had been constructed in a piecemeal manner. Learning these lessons, the Corps designed a comprehensive flood-management system for the Mississippi River and its major tributaries.

These two massive floods—and the whole-river approach adopted in the wake of 1927 that proved effective in 2011—have much to teach us about safe and sustainable flood management:

  • Planned or unplanned, rivers will access their floodplains during the biggest floods; intentional and anticipated flooding is far less disruptive than unintentional levee breaches or failures.
  • Therefore, allowing the river to access some of its floodplain is a critical component of a safe and resilient system.
  • River managers should learn from past floods and incorporate insights into subsequent plans.
  • The most effective flood-management systems consider the river system as a whole: the main river, its tributaries, dams and levees, and floodplains.

Although the flood-management system on the Mississippi has performed remarkably well in 2011, we should still ask what river managers can learn from this most recent flood and how they can continue to improve the overall system. And we can also ask what other rivers can learn from the Mississippi.

One key lesson lies with the social challenge of using the floodways when needed. Media coverage has focused primarily on the drama of the decision and the trauma of those affected, which may diminish the demonstration value that this system of floodways has worked to avoid potential disaster. Further, this emphasis may complicate future decision making to operate the system, as the Chief of Engineers observed after the New Madrid floodway was used in 1937 (the only time prior to this year): “No flood plan is safe if it is based on deliberately turning floodwaters upon the homes and property of people, even though the right to do so may have been paid for in advance.”

State and federal agencies should initiate a dialogue on potential mechanisms to reduce the social conflicts triggered by using the floodways. Similarly, managers from other rivers that already have floodways, or are considering adding them, should explore a full set of options that can reduce the social stress of using floodways when needed.

Second, although the flood-management system is working, it is operating close to its limits.  For a variety of reasons, including the extensive loss of upstream wetlands and floodplains that store and slow floodwaters, floods of an equivalent volume of water rise higher today than they did decades ago. Large floods appear to be happening with increasing frequency in the Mississippi Basin.  Because climate change forecasts suggest that the volume of floods in the Mississippi may become larger, it is prudent to ask whether the system needs more release valves and other improvements, such as strengthening levees in heavily populated areas.

Finally, the Mississippi flood system was designed in the late 1920s, many decades before floodplains’ full spectrum of values was well-documented or appreciated. Today we understand that floodplains provide diverse benefits for wildlife, fisheries, and clean water and, because they can hold back floodwaters, reconnecting floodplains to rivers can be part of the solution for reducing flood risks.

In the spirit of learning from past problems to improve floodplain management, demonstrated after the 1927 flood, today we can seek further improvements to the Mississippi flood management system. A comprehensive approach to floodplain management today—whether ongoing refinement of the Mississippi system or undertaken for the first time in a different river—should strive for a river-floodplain system that can provide its full range of values to people and nature.

(Left image credit: Archival Photography by Steve Nicklas; Right image credit: Lagoshep via Creative Commons license; Images below: the first shows the confluence of the Ohio and Mississippi Rivers in April of last year (not flooding); the second shows the same location on April 29th of this year, with extensive flooding.  Note the area marked “floodway” showing the New Madrid Floodway. The third photo is from 5 days later after the floodway has been activated by intentionally breaching the northern levee. Photo credit Nasa Earth Observatory).

 

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