For the past 150 years a titanic struggle has been underway between the human occupants of the Mississippi River system and its floods. A flood of some type occurs somewhere in this giant basin each year, and every 2 to 10 years a massive flood encompasses a fourth or more of the 3.2 million km2 basin. Humans first tried to control the floods with structures: channel straightening, levees, dams, and reservoirs; but after 100 years and the expenditure of billions of dollars, losses to property and lives continued to grow. Efforts since the 1950s to encourage land-use changes in flood-prone areas and the use of flood insurance often have been thwarted by government relief payments to flood victims, plus a continuing human desire to ignore the threat and reside in floodplains. Only 10% of the residents of flooded areas in the massive floods on the Mississippi and Missouri Rivers in 1993 and on the Ohio River in 1997 had flood insurance. Ever growing urban sprawl in the floodplains, intense use of the rivers for shipping, dense surface transportation networks in the floodplains, and major cities and industrial complexes built along major rivers help keep the basin highly vulnerable to today's floods.

The river system brings enormous economic value to the United States, but interests in protecting and enhancing the natural environment of the river are commonly in direct conflict with economic interests, and flood mitigation is often caught in the middle of the debate about how to manage the river system to satisfy all interests. The massive 1993 flood losses and responses, costing $18 billion, brought about needed changes in crop and flood insurance. The huge and costly

Handbook of Weather, Climate, and Water: Atmospheric Chemistry, Hydrology, and Societal Impacts, Edited by Thomas D. Potter and Bradley R. Colman. ISBN 0-471-21489-2 © 2003 John Wiley & Sons, Inc.

infrastructure built to control the major rivers for floods and navigation is aging and is beginning to need replacement. This offers an opportunity for more correctly handling flood mitigation to satisfy the complex mix of economic, human, and environmental interests (Shabman, 1994). However, if the past is a predictor of the future, this seems unlikely, but we do know one thing about the future—major record-setting floods will continue to occur.

Thirteen lessons emanating from the recent struggles between humans and floods include:

1. After massive expenditures to control flooding, flooding in the Mississippi River system is still the most costly natural hazard of the region.

2. Floods occurring at various scales, from localized flash floods to enormous basin-scale floods cannot be controlled, although existing control works help to reduce losses.

3. Forecasting and warning of floods have improved, leading to a reduction in lives lost, but people still are killed due to failure to understand the risks or to receive warnings.

4. Surface and river transportation systems suffer major damages and costly delays.

5. Communities suffer costly damages to water and sewage treatment plants and huge costs for postflood cleanup, and many flood-prone communities consciously chose to not construct adequate flood protection systems.

6. Flooding in suburban areas is increasing, due to construction in questionable areas, a lack of control on residential and commercial developments with inadequate stormwater control systems, and a lack of regional plans for managing flood waters.

7. Millions of individuals continue to risk flood losses by failing to purchase flood insurance, relying on government relief, and simply not appreciating their risk.

8. Environmental impacts of floods are mixed—the worst relate to soil erosion and river pollution by chemicals—but flooding generally helps floodplain ecosystems.

9. Agricultural impacts from floods can be enormous, particularly if the floods occur during the growing season.

10. Government relief for flood victims and communities remains a major response that often acts to discourage doing the right things in floodplains.

11. Rivers will reclaim their floodplains in extreme floods, and it is wise to work with the river and not against it in deciding where and how to build levees and in rebuilding other control structures such as the aging lock-and-dam system.

12. Future use of the floodplains of the Mississippi River system will require a careful balance between controlling for natural variations for navigation and flood protection purposes or for benefits to the ecosystem.

13. In sum, the nation's policy philosophy about flood mitigation must change: The nation needs to move beyond reliance on political responses and solutions to inappropriate uses of floodplains. Individuals must assume responsibility for their locational decisions, not the government, and future government policies must stand firm over time.

To understand the floods of this huge river system, and the impacts the floods create, requires background information about the physical and human setting of the river system. This setting has its roots in the basin's physical formation and configuration and the history of settlement and ensuing development of the basin. Today's impacts of flooding integrate many decades of massive, costly efforts to mitigate flooding in the Mississippi River system.

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