Shaan Patel
1993 Mississippi Flood
Introduction
* Most devastating flood in U.S.A history in the Summer of 1993. * The Mississippi River at St. Louis, Missouri, was above the flood stage for 144 days between 1st April and 30th September, 1993. * Approximately 3 billion cubic meters of water overflowed from the river channel onto the floodplain downstream from St. Louis. * Seventeen thousand square miles of land were covered by floodwaters in a region covering all or parts of nine states, which were: North Dakota, South Dakota, Nebraska, Kansas, Missouri, Iowa, Wisconsin, Minnesota and Illinois.
Causes
Natural Causes: * The region received higher rainfall than normal precipitation during the half of 1993. Much of the area received over 150% of normal rainfall and parts of North Dakota, Kansas and Iowa received more than double their typical rainfall. * The ground was saturated because of cooler than normal conditions during the previous year, due to less evaporation. So less rainfall was absorbed by soil and instead more ran- off into streams and rivers. * Individual storms frequently dumped large volumes of precipitation that could not be accommodated by local streams. * The river system had been altered over the previous years by the draining of the riverine wetlands and the construction of levees. * The abnormal weather was due to the weather conditions: * Warm moist air from the Gulf of Mexico collided with cold dry air, from Canada over the Midwest * When the warm air cooled it lost the moisture it carried as rain. * A high pressure system over the Southeast blocked the flow of Jetstream, resulting in a constant stream of storms over the Midwest. * For 2 months, June and July, the weather patterns in the U.S.A were overcome by this high pressure system
Human Causes: * Urbanisation of the Flood Plain, which reduced infiltration rates * Poorly built Levees * The channelization of the river, especially at St.Louis.Effects:Primary Effects * 50 people died * 62,000 families were evacuated * 72,000 homes were flooded * 70% of levees were damaged * Nine states were effected ; floodwater stretched from Memphis in the south to Minneapolis in the north covering 23 million acres. * 55 towns were wrecked and some areas never recovered. The town of Valmeyer, Illinois, was abandoned after the floods and rebuilt on higher ground. *
