The purpose of the Upper Mississippi River System Flood Frequency Study was to update the discharge frequency relationships and water surface elevations for the Mississippi River and Illinois River above Cairo, Illinois, and the Missouri River downstream from Gavin’s Point Dam. Five Corps Districts participated in this study effort—Omaha, Kansas City, St. Paul, Rock Island, and St. Louis. The Corps prepared existing flow frequency data for the upper and middle reaches of the Mississippi River in 1979. Existing flow frequency relationships for the Missouri River were developed in 1962. The water surface elevations have been published and are by government agencies, local communities and private citizens for purposes of land use planning, floodplain regulation and mapping, etc.