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Floodplain Management

A New Approach for a New Era

ISLAND PRESS

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 underestimates the true number of casualties. Additionally, more than 130,000 homes were lost and 700,000 people were displaced. In today's dollars, estimated property damage totaled $5 billion.

The 1927 flood changed river policy, but it had other long-lasting effects on American society.

• Herbert Hoover's substantial flood relief efforts propelled him into the White House.

• The lack of preparation and the generally reprehensible flood relief efforts were a factor in Huey Long becoming governor in Louisiana, shifting political power away from the elites who had ruled New Orleans and its environs for generations.

• The destroyed economy of the delta region and deplorable treatment of many African Americans during the flood added to the Great Migration of African Americans out of the South and to northern cities. As many as 50 percent of Mississippi delta country African Americans moved north within a few years of the flood.

• Before the great flood, government did not provide relief services to victims of floods or other catastrophic events. President Coolidge refused to get involved, voicing the traditional opinion that government aid demeaned its recipients and that communities should take care of their own. The enormous scale of the 1927 catastrophe required a federal approach. From that time on, though the programs have changed considerably, the federal government has been expected to take care of its most unfortunate citizens in a catastrophe.

Flood control policy changed unalterably. The vastness of destruction discredited the idea of using only levees. The Corps had to come up with a new way to keep the Mississippi from flooding and destroying the inhabitants along its banks. Under the Flood Control Act of 1928, levees remained key but were supplemented with meander cutoffs, flood outlets, reservoirs upstream and on tributaries, and other measures. By 1936 the Mississippi River had twenty-nine locks and dams, hundreds of runoff channels, and a thousand miles of levees.

At the same time, development continued within the watershed, changing forestland to farmland and farmland to cities, altering the basic ecology and hydrology of the watershed.

1993

In 1927, the lower Mississippi took the brunt of flooding. In 1993, water overwhelmed the upper watershed. Significant flood control changes made after the 1927 and subsequent floods were supposed to prevent catastrophic flooding. They did not. For example, the Corps shortened the river by more than 150 miles by creating cutoffs that eliminated a series of sharp curves. These initially lowered flood heights 15 feet but the river has regained one third of these cutoffs.

In 1993 precipitation and runoff were intense in the western part of the Mississippi's basin along the Minnesota, Iowa, Des Moines, Kansas, and Missouri rivers. Saturated soils in the Midwest contributed to record runoffs for these and other streams. At St. Louis the river flowed more than 50 feet above flood stage for more than three months. Nearly 150 major rivers and tributaries were at flood stage at the same time.

In the summer of 1993, floodwaters killed fifty-two people, damaged more than 1,000 levees (only 20 percent of federal levees were damaged, as opposed to 80 percent of local levees), destroyed 50,000 homes, and forced the evacuation of 70,000 people. Flooding affected more than 27,000 square miles. At least seventy-five towns were completely under floodwater. The dead zone in the Gulf of Mexico at the mouth of the Mississippi, in which low oxygen levels cannot support life, expanded. Total flood damage estimates ran as high as $20 billion. The USACE estimated that flood-control structures prevented an additional $19 billion in damage.

After the flood, more than 300 homes were moved to safer ground and 12,000 homes were bought and razed at a cost of more than $150 million. The empty lands were then dedicated to parks and wildlife habitat that could be used as temporary reservoirs in future floods. Levees were rebuilt, sometimes to higher and better standards. At least four entire towns considered moving to higher ground.

2008

Many analysts looked at the Mississippi watershed and levees after the 1993 floods. Human development has changed the natural characteristics of the basin. Most of the wetlands have been drained, cities cover much of the floodplain, and vast swaths of the basin used to be grassland with deep roots that would draw in water. Now agricultural land has been drained and tiled to keep it from flooding. All this means more water runs more quickly into rivers throughout the basin.

The main stem of the Mississippi River and many of its tributaries are narrowly confined by levees. However, these are not part of a coordinated system. The USACE builds levees, state and local governments build levees, and private interests build levees. They are built to different standards, are maintained by different entities, and each levee is engineered independently of the others. No person or agency looks at the levees as a system, researching what effects new levees have on the river and how they may increase the pressure on existing levees, mandating and enforcing a maintenance schedule, or looking at the total effect of the levees as a whole on the dynamics of the watershed. Calls for such oversight after the 1993 floods went unanswered.

In June 2008, another massive flood overwhelmed the upper Mississippi basin, stunning many who believed that such an event could not happen after the lessons of 1993. Some called it the second 500-year flood in fifteen years, highlighting the problem of that terminology. A 500-year flood happens, on average, every 500 years. It's the "on average" part that causes confusion. While some researchers called them 500-year floods, others thought the 2008 flood could be a less frequent event, possibly a 200-year flood. It is possible that one or both of those floods could be 500-year floods if the watershed were in its natural state. However, with the massive amount of urban development (that continues to increase) along the Mississippi, it is unlikely that either flood would happen, on average, only every 500 years. We are very likely to see similar flooding in the twenty-first century.

The $2 billion of damage was small only compared to the catastrophe of 1993. The destroyed homes, flooded fields, and shutdown of the river to barge traffic were expensive both in terms of money and of human endeavors. As if further proof were needed, it became clear that no integrated flood control system exists for the Mississippi watershed.

Two divergent trends helped shape the amount of damage in this flood. On one hand, buildings were removed from tens of thousands of acres after 1993, leaving land that now can be flooded. That action substantially lowered the damage in 2008. On the other hand, people continued to view new and rebuilt levees as absolute protection, and thousands of acres of floodplain behind the levees became the site of new homes and businesses. When levees have overtopped or failed, these places have flooded. Even with the inadequacies of levees repeatedly demonstrated, the allure of rich, flat land close to the river and existing urban areas is too strong to stop development.

Fundamental Problems

Mississippi River floods show that our approach to managing floods and floodwaters is fundamentally wrong.

In our industrial society, we're used to "overcoming" nature with science and technology.

Don't want dirt on your clothes? Here's a new detergent. Have to travel 20 miles to get to work? Here's a bigger/smaller/ safer/more luxurious car.

But we don't really control nature, and an everlasting truth is rivers will do what rivers do. That's not to say that we have to live with the whims of floods, meandering channels, and droughts. These things can be ameliorated, but if not done correctly there will be unintended consequences—some of them quite serious.

There are good reasons for people to live in and use floodplains, but their use must be regulated by society. Floodplains are an integral part of life and need to be protected, if not for themselves then for the enhancement of humanity. The only way to conserve floodplains for the long term is to understand how they work, and to work with—not against—their natural processes.

In this book, we do not use the phrase "natural and beneficial processes" even though this is a long-standing expression in watershed management. The reason is simple. These processes are integral to effective management, not a separate and discrete module of it. Our philosophy is simple: natural processes are the starting point of any successful project and they must be considered and built upon at every step, not considered as an addendum after making plans.

Rivers convey, create, and conserve a number of values and assets. Some are natural, others are man-made. A couple might want to protect their streamside home, a conservation group might want to enhance riverine natural beauty and ecological benefits, and a city might want to use the river for a community water supply.

Each use affects the others and is affected by the others. The Columbia River, for example, provides scenic beauty that attracts tourists, an important part of the economy for the Oregon, Washington, and British Columbia communities along the river. It provides a spiritual element to Native American peoples in its watershed, as well as to others who feel a connection with nature. In addition, its water provides irrigation for farms and ranches, hydroelectric power for residents and businesses as far away as California, transportation for crops and manufactured goods, and habitat for endangered salmon and myriad other wildlife among many other riverine benefits.

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Excerpted from Floodplain Management by Bob Freitag, Susan Bolton, Frank Westerlund, J.L.S. Clark. Copyright © 2009 Island Press. Excerpted by permission of ISLAND PRESS.
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