Floods of April-May 1969 in upper Midwestern United States

Abstract

The 1969 spring floods in upper Midwestern United States can be attributed primarily to an exceptionally heavy blanket of snow which accumulated during the period December 1968 through February 1969. March precipitation was light, but at the end of the month water content of snow on the ground was as much as 8 inches in some parts of the area. Unusually heavy rains in the fall of 1968 throughout the area, and as much as 3 inches of localized spring rain in the Red River basin during the period April 7-10, 1969, accentuated the flooding. Flood data are presented for 285 gaging sites in this report. Peak stages and discharges exceeded previous known maxima in the upstream tributaries of the Red River of the North, upper Minnesota River basin, upper basin of West Fork Des Moines River, and the James, Vermillion, and Big Sioux River basins. In many other basins the 1969 floods were the second highest in many years of record. Recurrence intervals exceeded 50 years for 71 of the 178 sites for which recurrence intervals were computed. Flood-crest elevations and flood profiles show the peak stages expressed in mean sea level at many points in the Mississippi, Minnesota, Red, Souris, West Fork Des Moines, Rock, and Little Rock River basins. Sediment discharge data obtained in a small part of the lower Minnesota River basin indicated varying yields during the month of April ranging from 26 to 396 tons per square mile. Aerial photography during the flood was obtained in a number of river basins. The river reaches which were photographed are tabulated and the location of the photographs indicated. Flood damages were estimated to be about $147 million in the six States of North Dakota, South Dakota, Minnesota, Iowa, Wisconsin, and Illinois. Eleven lives were lost to the flood, more than 23,000 persons were forced from their homes, more than a million acres of rich agricultural land were inundated, and thousands of culverts and bridges were washed out on highways and secondary roads.