lesson 15-2 - 1 Background Ten years ago, the upper Missis-...

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Unformatted text preview: 1 Background Ten years ago, the upper Missis- sippi River Basin in the Midwest- ern United States experienced the costliest fl ood in the history of the United States. The fl ood came to be known as The Great Flood of 1993. The Mississippi River drains approximately 40 percent of the continental United States (approxi- mately 1.25 million square miles) --all or part of 31 States, and two Canadian provinces, Ontario and Manitoba (fi g. 1). During the sum- mer of 1993, extremely high rain- fall fell on the upper Midwest. An abnormally persistent atmospheric weather pattern consisting of an almost stationary jet stream was positioned over the central part of the Nation during this time. Moist, unstable air fl owing north from the Gulf of Mexico converged with unseasonably cool, dry air moving south from Canada. The magnitude and severity of the resulting fl ood event was overwhelming. The areal extent, intensity, and long duration of the fl ooding makes this one of the greatest natural disasters ever in the United States. At least 48 people lost their lives as a result of this extreme fl ood (Interagency Floodplain Management Task Force, 1994). Over 500 river fore- cast points in the Midwest were above fl ood stage at the same time. Nearly 150 major rivers and tribu- taries fl ooded. Banks and chan- nels of many rivers were severely eroded, and sediment was depos- ited over large areas of the Missis- sippi River fl ood plain. Economic damages approached $20 billion (National Oceanic and Atmo- spheric Administration, 1994). Le- The Great Flood of 1993 on the Upper Mississippi River10 Years Later By Gary P. Johnson, Robert R. Holmes, Jr., and Loyd A. Waite The Mississippi River will always have its own way; no engineering skill can persuade it to do otherwise...- Mark Twain in Eruption Figure 1. Upper Mississippi River Basin in the United States. The Arch in St. Louis, Missouri: taken close to the peak of the Great Flood of 1993 on the upper Mississippi River. 2 vees were broken, farmland, town, and transportation routes were destroyed, and more than 50,000 homes were damaged or destroyed (Josephson, 1994). Water-quality threats to public health and safety were of paramount concern. These threats included contamination of drinking-water supplies, disrup- tion of wastewater-treatment plant operations, failure of septic sys- tems, and risks associated with the inundation of facilities that handle hazardous materials. Precipitation From June to August 1993, rainfall totals surpassed 12 inches across the eastern Dakotas, south- ern Minnesota, eastern Nebraska, Wisconsin, Kansas, Iowa, Mis- souri, Illinois, and Indiana. More than 24 inches of rain fell on central and northeastern Kansas, northern and central Missouri,...
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This note was uploaded on 09/14/2009 for the course ISS 731 taught by Professor A.arbogast during the Summer '09 term at Michigan State University.

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lesson 15-2 - 1 Background Ten years ago, the upper Missis-...

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