The floods of May 1943 in Illinois

In May 1943, Illinois was subjected to a series of flood that reached major intensities in the central part of the state but decreased to minor intensity--less than the maximum for the year--in the northwestern and extreme southern part. All records were broken on lower Illinois River and on its triibutaries entering from the east, from Sangamon River south, as well as on Kaskaskia River. These floods were the result of rain during the storm period May 6-21. At no place did it rain continuously for 24 hours and in most places the limit was about half a day. An appropriate description is a series of showers that produced a series of floods on small streams. As the rains continued, the ground became more nearly saturated and the ratio of runoff to rainfall increased. As the small streams entered larger ones, with their peaks arriving at different times, the channel storage of the larger streams smoothed out the minor peaks so that the very large streams had only one peak. The magnitude of channel storage in Illinois River and its adjoining lakes is emphasized by the fact that the peak discharge at Meredosia, lasting about 44 hours, was no greater than the peak discharge of Sangamon River at Oakford, 123,000 second-feet, that lasted about an hour.