Federal Levee Effects on Flood Heights Near St. Louis

A physical model of the Middle Mississippi River was used to perform quantitative analyses of Federal levee effects on flood heights. Contrary to some opinions of the general public, these tests showed that today's stage-frequency relationship at the St. Louis gage is not greatly different than that existing prior to the onset of man's changes, beginning in the 1820's. Federal levees do result in increased flood heights upstream of the protected area, but these increases are offset by flood reductions resulting from Federal flood control reservoirs. The model tests also found that the key historical flood discharges of 1844 and 1903, used in current levee design, may be overestimated by up to 33%.