A Watershed Year
Anatomy of the Iowa Floods of 2008
Publication Year: 2010
In June 2008, the rivers of eastern Iowa rose above their banks to create floods of epic proportions; their amazing size—flowing in places at a rate nearly double that of the previous record flood—and the rapidity of their rise ruined farmlands and displaced thousands of residents and hundreds of businesses. In Cedar Rapids, the waters inundated more than nine square miles of the downtown area; in Iowa City, where the flood was also the most destructive in history, the University of Iowa’s arts campus was destroyed. By providing a solid base of scientific and technical information presented with unusual clarity and a wealth of supporting illustrations, the contributors to this far-reaching book, many of whom dealt firsthand with the 2008 floods, provide a detailed roadmap of the causes and effects of future devastating floods.
The twenty-five essays fall naturally into four sections. “Rising Rivers, Spreading Waters” begins by comparing the 2008 floods with the midwestern floods of 1993, moves on to trace community responses to the 2008 floods, and ends by illuminating techniques for forecasting floods and determining their size and frequency. “Why Here, Why Now?” searches for possible causes of the 2008 floods and of flooding in general: annual crops and urban landscapes, inflows into and releases from reservoirs, and climate change. “Flood Damages, Flood Costs, Flood Benefits” considers the complex mix of flood costs and effects, emphasizing damages to cities and farmlands as well as potential benefits to natural communities and archaeological sites. “Looking Back, Looking Forward” lays out approaches to managing the floods of the future that are sure to come.
While the book draws most of its examples from one particular region, it explains flooding throughout a much larger region—the midwestern Corn Belt—and thus its sobering yet energizing lessons apply well beyond eastern Iowa. By examining the relationships among rivers, floodplains, weather, and modern society; by stressing matters of science and fact rather than social or policy issues; and by addressing multiple environmental problems and benefits, A Watershed Year informs and educates all those who experienced the 2008 floods and all those concerned with the larger causes of flooding.
Published by: University of Iowa Press
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Preface and Acknowledgments
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In early June 2008, my husband and I left our home near Iowa City to visit our grandchildren and their parents in Switzerland. The skies were crystalline blue and cloudless, the air fresh. Crossing the Coralville Reservoir on the way to the airport, I commented that the water level was unusually high, but gave the matter no more thought. By the time our plane landed and we had slept off ...
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In June of 2008, the rivers of eastern Iowa rose above their banks to create floods of epic proportions (fig. I-1). Onlookers noted not only their amazing size—the flow through Cedar Rapids for example reaching 140,000 cubic feet per second (cfs), nearly double the earlier record flood flow in 1961—but also the rapidity of their rise. Each day posed new and previously unimaginable ...
Section I: Rising Rivers, Spreading Waters
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Nature speaks to us in many ways. We watch, listen, and try to understand. Songbirds returning in the spring tell of homecoming and new life. Whales sing of ocean swells and planetary migrations. Some voices, like those of Arctic mammals swimming toward melting ice floes, speak of a planet where conditions seem to be changing too rapidly for their own ...
1. What Causes Floods in Iowa?
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All rivers flood. In fact, they flood with surprising regularity—almost every year or two (Leopold et al. 1964). Some floods are harmless and almost go unnoticed, with water barely spilling out of the river’s banks. Others are natural disasters that draw national attention. Iowa experienced such a disaster not long ago. Floodwaters destroyed homes and businesses, shut down city services, disrupted travel in the ...
2. Why Were the 2008 Floods So Large?
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In June 2008, eastern Iowa experienced some of the worst flooding ever recorded. Floods, commonly defined as river waters overflowing their banks, devastated cities and the countryside alike. Some 1.2 million acres of Iowa’s agricultural land was affected by floodwaters.1 From a plane, it was difficult to decipher the main channel of many rivers. The confluence of the Iowa and ...
3. Iowa City and the Flood
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In times of flooding, communities engage in a flurry of activities that test the limits of everyone involved. Extreme demands and rapidly changing circumstances may produce chaotic conditions that hamper a community’s ability to respond. Advance planning and focus are crucial if the government is to carry out its primary responsibilities to its citizens: protect the safety of residents ...
4. The University of Iowa and the Flood
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The University of Iowa and the city of Iowa City were founded together in the 1840s. They have always shared a common main street that runs along a ridge on the east bank of the Iowa River. The university and the city have grown together, now occupying both the east bank ridge and the hills to the west and the river valley in between. Among the university buildings erected ...
5. Linn County and the Flood
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A neat rectangle in eastern Iowa, Linn County (population 200,000) is the state’s second most populous county and one of its largest manufacturing centers. The Cedar River flows across the county from northwest to the southeast, cutting through its largest city, Cedar Rapids (population 125,000). During the 157 years before 2008, the Cedar River flooded often. In 1851 ...
6. Forecasting a Record Flood
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In Iowa, nearly everyone has used weather forecasts to make everyday decisions— such as how to dress for the day, or whether it is time to plant crops. We know that weather forecasts are not perfect. But from our everyday experience, we also know that forecasts do not have to be perfect to be useful. In contrast, the public looks at river forecasts only when a river is expected to overflow its banks ...
7. Estimating Flood Frequency
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Soon after the 2008 floods in Iowa reached their peak, the media labeled them as 100-year floods or 500-year floods. What exactly do these terms mean, and how do they apply to Iowa’s floods of 2008? These terms are expressions of the extreme magnitude of the 2008 floods and the frequency with which they are expected to occur. Flood frequency is expressed in several ways ...
Section II: Why Here, Why Now?
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Although floods are natural processes, humanity has not entirely come to terms with this idea. Instead, since the earliest written records, people have tried to explain flooding and extreme natural events in other ways. Flood myths of worldwide deluges, often with common themes, appear widely in early writings from around the world. Consider Noah and ...
8. The Hydrologic Footprint of Annual Crops
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Given the question of agriculture’s potential contribution to the 2008 floods, one might ask what would have happened had the same weather patterns occurred before the 1830s, when native vegetation still dominated the landscape. Would extreme flooding have occurred then, and if so, would these earlier floods have resembled those of today? Would their extent and magnitude have ...
9. The Hydrology of Urban Landscapes
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In urban areas, the altered landscape significantly reshapes the hydrologic cycle, which describes the flow of water over and through the earth’s surface. Broadly summarized, the cycle follows water from the atmosphere down to the ground as rain or snow. Once on the ground, precipitation may return to the atmosphere through evaporation or transpiration, held by vegetation, or ...
10. The Coralville Dam and Reservoir: Design and Operation
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The Coralville Dam was constructed in the 1950s by the U.S. Army Corps of Engineers (Corps) and put into operation in September 1958. The earthfilled dam is 1,400 feet long, 100 feet tall, and 650 feet wide at the base.1 The dam created the Coralville Reservoir, a large body of water that under normal conditions—when the water surface is at 683 feet elevation above mean sea ...
11. The Dam and the Flood: Cause or Cure?
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“Fortunately,” Iowa City historian Irving Weber wrote in 1985, “since the Coralville Dam and Reservoir have been installed, the Iowa River has been under control and the area no longer suffers disastrous floods.” The floods of 1993 and 2008 have since proven Weber wrong. He also might have known better. The Coralville Dam, with a storage capacity of 435,300 acre-feet (when the reservoir is at 712 feet elevation at ...
12. Was Climate Change Involved?
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Did climate change feed into the severe 2008 floods? This is a provocative question. The science of attributing specific climate features to global climate change is new and controversial, especially when applied to weather extremes at the regional or local scale. It is far more defensible to assert that particular global physical factors, such as volcanoes, fluctuations in solar output, greenhouse ...
Section III: Flood Damages, Flood Costs, Flood Benefits
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From time immemorial, humans have been drawn to rivers and settled along their banks. Rivers provided the water needed by people and their livestock and also attracted game for the taking. Fertile alluvial soils often abounded here. People used the rivers as transportation corridors and as a source of power for mills that ground grains and cut lumber ...
13. Flood Effects on Archaeological Sites
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People have lived in Linn and Johnson Counties for over 10 millennia. For most of that time, the only records of their presence are the archaeological remains of villages and campsites where they lived and worked, and the cemeteries and mounds where they buried their dead. Although artifacts like arrowheads and pottery sherds can be found virtually anywhere, most such finds ...
14. Flood Effects on Modern Communities
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The 2008 floods can be measured, described, and studied, their causes sought, and certain types of their effects measured. But these efforts give little vision of the magnitude of flood impact on modern residents: displaced families and lost homes, family treasures, and jobs. Many aspects of these damages will never be recorded. However, they can be sensed to a small degree in statistics ...
15. Economic Losses from the Floods
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Flooding in Iowa was one of the largest natural disasters in the U.S. in 2008. While from a national accounting perspective (Mattoon 2008) the 1993 floods in the upper Midwest were larger in scope and damages, the 2008 flooding appears to have caused more damage and losses for Iowa communities and individuals. The most severe flood damages occurred in communities along the ...
16. How Did the Floods Affect Farmland?
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Iowa’s farmland is defined by its soils, which are among the most fertile, productive, and deepest in the world. For centuries these soils were protected from damage by intense rainfall by lush perennial prairie cover, wetlands, and forests. Today our highly productive soils produce food, feed, fiber, and fuel for the world, and about two-thirds of Iowa is covered with annual row crops ...
17. What's in Your Floodwaters?
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When people think about flooding, they recall the destructive nature of the water or, for those unlucky enough to have had homes or businesses inundated by floodwater, the muddy mess that it left behind. In many Iowa communities hit by the June 2008 floods, buildings were coated with muck and sand after the floodwater receded. That material, which we will call by the general name ...
18. Air Quality Hazards
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During times of flooding, waterborne hazards are obvious, but few think about the dangers that might be drifting through the air. Yet floods produce airborne hazards that often linger long after the flooding has ended. Floods produce airborne chemical health hazards when previously contained toxic substances are released into the environment, and microbial hazards when post-flood conditions promote the growth ...
19. Flood Effects on Natural Communities
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Floods bring tremendous damage to human communities in the form of swamped homes, ruined businesses, inundated farms, wrecked bridges, and devastated lives, so it is difficult to imagine that the same floods might renew and restore natural communities of plants and animals. But while the water that fills a basement is destructive, water that fills a dried wetland creates habitat for ...
Section IV: Looking Back, Looking Forward
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As long as water has cycled around our planet and fallen to its surface, rivers have risen above their banks to flood surrounding lands. And as long as people have wandered the earth, they have dealt with these rising flows. For eons, human communities have worked to build walls to protect flood-prone areas, or to deepen and straighten river channels, or to hold ...
20. When (Not If) the Big One Comes
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The Iowa floods of 2008 once again reminded us of a basic truth: if you live in a floodplain, sooner or later you’ll get flooded. And once again the floods of 2008 reminded us that a 100-year flood is just an intermediate-sized flood. Much larger floods can and do occur with some regularity. Homes, businesses, and facilities protected to a 100-year flood level are still vulnerable to flood ...
21. Watershed-Based Flood Management
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The Iowa floods of 2008 remind us that we live in an interconnected system: the watershed. Each watershed, or drainage basin, collects the runoff (and anything the runoff carries) from a region’s land area and feeds it through streams and rivers. Consideration of the entire watershed in flood planning is critical because the areas that flood are determined by watershed conditions upstream ...
22. Flood Barriers
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Flood barriers have been heavily featured in news stories and discussions involving the 2008 floods on the Iowa and Cedar Rivers. Permanent and temporary flood barriers were used to combat flood damage during the event. But in many cases, these barriers were overtopped or failed, causing significant damage to public and private property. Following the event, flood barriers became ...
23. Managing Urban Runoff
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As I described in chapter 9, urban landscapes and new urban development increase the volume of stormwater runoff by expanding the proportion of land covered with impervious surfaces. This increased urban runoff certainly contributed to Iowa’s 2008 flooding. But because of Iowa’s relatively small total coverage by urban areas, urban runoff could not have been a major contributor ...
24. Perennial Farming Systems That Resist Flooding
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A drop of rain that falls on Iowa has a 63 percent chance of falling on a corn or soybean field (NASS 2007). If we look just at northern Iowa, where farming is most intensive, that probability rises to 88 percent (figure 24-1). Is this droplet likely to contribute to flooding? To answer this question, let’s trace the course of three hypothetical raindrops. The first drop, falling in summer when crops are actively growing, soaks into the earth, is absorbed ...
25. The Great Flood of 1993: Did We Learn Any Lessons?
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In July 2008, following the Midwest floods, the United States Senate Environment and Public Works Committee held a hearing to review what had happened and what might be improved in management of flood risk (U.S. Senate 2008). The chairman of the committee, Senator Barbara Boxer, questioned whether any lessons had been learned from the floods of 1993 and asked the Hon. John ...
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My office window overlooks the Iowa River in downtown Iowa City. Sometimes I glance up from work to see flocks of gulls the size of small clouds swooping over the water, or dozens of feeding swallows, or soaring bald eagles searching for fish. Once, even here in the city, an otter bobbed in the water below my window. Often people fish along the river’s gravel shores, chatting and hauling ...
Notes on Contributors
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Page Count: 272
Publication Year: 2010