Floods Are Not the Problem

Rivers will do what rivers do. Historic flooding of the Mississippi River shows that our approach to flood control hasn't worked and can have effects far beyond the limited area of a floodplain. The consensus of scientists around the world is that we are in a period of rapid global climate change, which makes working with rivers—instead of against them—increasingly important. Some places will get more intense rainstorms, while others may get less frequent summer rains. Still other areas may get winter storms with less snow and more rain, producing immediate runoff instead of storing water for spring. These and other changes may increase flooding, and, in some cases, may also increase drought.

In many cases, flood management practices are based on dam or levee projects that do not incorporate all we now understand about river processes. They try to control the river. Many years of experience with dam and levee systems have shown their limitations. Though dams and levees may be necessary in some cases, more often a larger suite of tools is available. We suggest instead that a better solution is to work with the natural tendencies of the river: retreat from the floodplain by preventing future development and sometimes even removing existing structures; accommodate the effects of floodwaters with building practices; and protect assets with nonstructural measures if possible, and large structural projects only if absolutely necessary.

To help decide on the best (cheapest, longest lasting, most beneficial, and so on) project choice to control destructive floods or enhance our water resources, we should answer six questions:

1. What values or assets do you want to protect or enhance?

2. What are the apparent risks or opportunities for enhancement? 2 Floodplain Management

3. What is the range of risk-reduction or opportunity-enhancement strategies available?

4. How well does each strategy reduce the risk or enhance the resource?

5. What other risks or benefits does each strategy introduce?

6. Are the costs imposed by each strategy too high?

Only after answering all six questions will we find the optimal strategy.

Lessons from the Mighty Mississippi

The Mississippi watershed stretches from Canada to the Gulf of Mexico between the Rockies and the Appalachians. The Mississippi River and its tributaries drain all or part of thirty-one states and two Canadian provinces over 1 million square miles. Major tributaries include the Minnesota, Wisconsin, St. Croix, Iowa, Skunk, Des Moines, Illinois, Ohio, Missouri, and Arkansas rivers.

As early as the 1800s, Mississippi River flooding created a problem for adjacent cities and farms, as well as for the river traffic that transported a good deal of American commerce.

Many engineers of this time were educated at West Point and assigned to the U.S. Army Corps of Engineers (called USACE or the Corps). For a variety of reasons, the Corps was given the job of "fixing" the floods along the Mississippi. Levees were the weapon of choice. In the short term, the levees protected productive floodplains from being retaken by the river and actually created valuable land. By 1858, more than a thousand miles of levees had been built. These produced the typical feedback loop: levees gave floodwaters a narrower reach to flow through, making floods higher, requiring even higher levees.

The USACE continues to manage flood control for the Mississippi River. Many policy decisions were made when the watershed and our explanation of river processes were very different, and are still in effect today. The natural alluvial valley of the Mississippi is a wide swath of forest and grassland that allowed the river to roam across it, producing constantly shifting meanders. Frequent flooding left silt on the land, which provided rich farmland for early settlers. This very activity of the river—its wandering, which left such rich earth—is exactly the problem it posed for cities along the river. Urban areas need rivers to stay in a fixed location. The levees-only policy was based on a fundamentally wrong tenet: that by confining the river within levees the erosive power of the water would be redirected to the bottom of the channel. Using levees was supposed to force the river to scour its channel, making it deeper and allowing it to carry high flows without flooding. This scouring and deepening never happened.

Today, little of the Mississippi valley is in its natural condition. Forests made way for farms and cities and even much of the floodplain is urban, channeling rain to the river ever faster. This increases the height of floodwaters and requires higher levees. Though there are increasing numbers of projects that enhance outlets and impoundment to contain these high flows, most of the focus remains on levees. The result has been catastrophic flooding.

1926–1927

By 1926 the USACE had pursued a levees-only policy on the Mississippi for several decades, going so far as to seal off many natural outlets. The effect should have been clear: through the years, similar amounts of water in the river produced higher and higher floods. Still the policy continued, ultimately leading to a catastrophic flood of the lower Mississippi. Places in the upper watershed like Helena, Montana, saw intense snowfall in the winter of 1926–1927. Pittsburgh, Pennsylvania, and Cincinnati, Ohio, flooded in January 1927. March snow fell from Colorado to Tennessee. For months, record precipitation fell on the basin, ultimately reaching the river. In response the river ran high, flooding tributaries and the main channel.

Upper tributaries flooded first, starting in September 1926. Officials knew that water would eventually flow through the lower Mississippi, where 800 miles of levees were the only defense against the stream. The Corps inspected and reinforced weak spots, but the levees did not hold.

The first to break were those on tributaries, built and maintained by state governments or private contractors. The Corps continued to insist that no levee built to federal standards had ever broken. On April 16, 1927, that changed.

Over the next weeks, the Mississippi flooded 27,000 square miles over seven states, home to nearly 1 million people. In some spots, the river ran more than sixty miles wide. The last floodwaters did not recede until August. For nearly a year, one part or another of the Mississippi watershed had languished under floodwaters.

The official death toll of 246 certainly...