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Floods and Flood Control

FLOODS AND FLOOD CONTROL

FLOODS AND FLOOD CONTROL. Floods are caused by the excessive accumulation of water over a short time in a specific area and may arise naturally or because of human factors. In the United States, floods can occur in any season and geographic region, and can be destructive to human property and life.

Types of Floods

Floods in the United States are of several types. Regional floods occur when winter or spring rains, often with snowmelt, inundate river basins over large areas. Heavy precipitation, snowmelt, and impervious frozen soils caused the March 1936 New England flood and the January 1996 winter flood in the northeastern United States. Flash floods are rapid rises in water of high velocity associated with intense or extended rainfall. Desert arroyos, along with urban and mountainous areas with steep topography and impervious surfaces, are prone to flash floods. A flash flood in Willow Creek, Oregon, destroyed the town of Heppner on 14 June 1903, resulting in 225 fatalities; in June 1972, rain in excess of fifteen inches in five hours caused flash floods in Rapid City, South Dakota, causing 237 deaths. Ice-jam floods occur on frozen rivers. Rising river water produces ice floes that create dams in shallow channels, causing water to back up; ice-dam failure releases a torrent of water downstream. Destructive ice-jam floods occurred in February 1981 in the Delaware River of New York and Pennsylvania and at the confluence of the Mississippi and Missouri Rivers in Illinois and Missouri in December 1989.

Storm-surge floods occur when water is pushed ashore by winds generated by severe storms. Extensive storm surge was caused by Hurricane Camille along the Gulf Coast in August 1969 and Hurricanes Dennis and Floyd in North Carolina in September 1999. Dam-and levee-failure floods occur when a structure is overtopped or destroyed by heavy flows, causing a flash flood. The infamous Johnstown Flood of 31 May–1 June 1889, a major nineteenth-century flood, occurred when an earthen dam on the Little Conemaugh River in Pennsylvania gave way, unleashing a torrent that caused twenty-two hundred deaths. Debris, landslide, and mudflow floods occur when mud, rocks, or logs dam a river channel; flash flooding occurs when the dam is breached. The eruption of Mount St. Helens caused a mudflow flood on 18 May 1980 that resulted in sixty deaths and untold property destruction along the Toutle and Cowlitz Rivers in Washington State.

Property and Human Losses

Property damage from floods in the United States averaged an estimated $5.9 billion yearly from 1955 to 1999. The most costly flood in U.S. history was the Great Flood of 1993, involving the Mississippi and Missouri Rivers, which caused economic losses of around $20 billion in nine states. Other costly floods of the twentieth century include the eastern North Carolina flood (Hurricanes Floyd and Dennis) in September 1999 ($6 billion); Red River Flood in North Dakota and Minnesota in April and May 1997 ($2 billion); May 1995 floods in south-central states (from $6 billion to $8 billion); floods from January to March 1995 in California ($3 billion); floods from December 1996 to January 1997 in the Pacific Northwest


($2–3 billion); and June 1972 floods (Hurricane Agnes) in the northeastern states ($3.2 billion). Five states led the nation in average estimated yearly flood losses from 1955 thorough 1999: Pennsylvania ($682 million), California ($521 million), Louisiana ($320 million), Iowa ($312 million), and Texas ($276 million). Pennsylvania alone sustained over $2.1 billion in damages from Hurricane Agnes in 1972, making it the worst natural disaster in the state's history.

The United States averaged 110 flood-related deaths yearly from 1940 though 1999. The greatest flood-related loss of life occurred in September 1900 when a storm-surge flood devastated Galveston Island, Texas, causing six thousand deaths. Other fatal floods of the twentieth century include the statewide flood of March and April 1913 in Ohio, resulting in 467 deaths, and the storm-surge flood of September 1938 in the Northeast, causing 494 deaths. Storm-surge floods have historically caused the greatest flood-related fatalities in the United States because of storm ferocity and the large population densities in coastal zones. Vehicle-related flood fatalities, usually caused by flash floods, have increased sharply in recent years. Of the 320 flood-caused deaths recorded in 1998–2001, 177 (55 percent) were vehicle-related.

Flood Control Measures

Human fatalities and property losses prompted extensive flood control efforts in the United States during the nineteenth and twentieth centuries. Artificial levees were first built to contain floodwaters in New Orleans in 1726 and became the favored flood control method along the Mississippi River in the 1800s. Recognizing both the economic potential and destructive force of the Mississippi River, Congress established the Mississippi River Commission on 28 June 1879 to formulate flood control and navigation policies for the river. The Army Corps of Engineers, dominant on the commission, favored a levee-based policy of flood control for the Mississippi, and by 1895, the federal government was sponsoring levee construction along the river. During the Great Flood of March though June 1927, the Mississippi overflowed its banks and destroyed levees in 170 counties, causing an estimated $230 million in damage and more than three hundred fatalities. This event renewed congressional efforts to control Mississippi River floods, resulting in the Federal Flood Control Acts of 1928 and 1936. These acts authorized construction of a system of levees, dams, and reservoirs to confine the river to a single channel. Between 1932 and 1955, channelization efforts straightened the normally meandering Mississippi River by 146 miles, and by 1990, twenty-six dams and thousands of miles of dikes and levees hemmed the river. An extensive effort was made to control river flows and floods nationwide in the twentieth century, often in conjunction with hydroelectric development. By 1990, only forty-two free-flowing rivers longer than 125 miles, out of an original total of 3.2 million miles, occurred in the conterminous United States.

In the twenty-first century, floods are pragmatically viewed as both beneficial and destructive. Floods can be used to restore fish and wildlife habitat degraded by flood control projects. In March 1996, the first artificial flood in the United States was conducted on the Colorado River (dammed in 1963) to rebuild sandbars and restore habitat for endangered fishes. Though the effort was considered a success, studies done in 2002 show that the river has returned to its pre-flood state, prompting calls for additional floods.

BIBLIOGRAPHY

Barry, John M. Rising Tide: The Great Mississippi Flood of 1927 and How It Changed America. New York: Simon and Schuster, 1998.

Lauber, Patricia. Flood: Wrestling with the Mississippi. Washington, D.C.: National Geographic Society, 1996.

McCullough, David. The Johnstown Flood. New York: Simon and Schuster, 1987.

McNeill, J. R. Something New under the Sun: An Environmental History of the Twentieth-Century World. New York: Norton, 2000.

McPhee, John. The Control of Nature. New York: Farrar, Straus, and Giroux, 1989.

Charles E.Williams

See alsoDisasters ; Engineers, Corps of ; Johnstown Flood ; River and Harbor Improvements .

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