Impacts of 1993 floods on the Upper Mississippi and Missouri River Bhowmik, N. O. 1995. Impacts of 1993 floods on the Upper Mississippi and Missouri River Basins in the USA. Pages 127-154 in the Proceedings of the International Joint Seminar on Reduction of Natural and Environmental Disasters in Water Environment, Seoul National University, Seoul, Korea, July 18-21, 1995. Reprinted by the National Biological Service, Environmental Management Technical Center, Onalaska, Wisconsin, August 1995. LTRMP 95-R005. 28 pp. (NTIS #PB95-267555) ABSTRACT The 1993 Flood on the Upper Mississippi and Missouri Rivers is now considered the largest flooding event on these river basins. Not only were many miles of the rivers flooded, but there was also a significant amount of flooding to the interior of the country. More than 420 counties in all the midwestern states were declared disaster areas. Stages were exceeded many locations, hundreds of levees either failed or were overtopped, more than 500 scour holes developed, the rivers scoured their beds at numerous locations, sediments were deposited at many other locations, and the rivers attempted to create new channels and/or cutoffs during the peak periods. This paper is not intended to summarize the various factors associated with this flood. A number of excellent reports have been published on the 1993 flood, and readers are referred to these reports for further information. They are: Bhowmik et al., 1995, 2nd Edition; Illinois Department of Energy and Natural Resources, 1994; Chrzastowski et al., 1994; Interagency Floodplain Management Review Committee, 1994; Interagency Floodplain Management Review Committee, Part V, 1994; U.S. Army Corps of Engineers, 1994a, 1994b, 1994c; and Dowgiallo, ed., 1994. So many articles in newspapers, journals, and popular magazines have been written about the flood that it would be almost impossible to cite all of them. It is worth noting that the International Water Resources Association published a special issue of Water International in December 1994 on "The Great Flood of 1993" that features seven articles prepared by various experts, including an editorial by Bhowmik and Demissie (1994). The main topic covered in this paper is the impact of the 1993 flood on erosion, scour, sediment transport, channel alternation, sedimentation, and water qualities of both rivers. A very brief summary will be included to inform the readers about the background of this flood. KEYWORDS flood, Mississippi River, Missouri River, sedimentation, flood impacts