Frequency of the 1993 flood in the upper Mississippi River Basin

The frequency of the 1993 flood in the upper Mississippi River Basin is characterized by applying Bulletin 17B and L-moment methods to 111 unregulated watersheds in the basin. The analysis indicated that the 1993 flood was primarily a 10- to 50-year event on unregulated watersheds less than about 50,000 square kilometers. Of the 111 stations analyzed, the L-moment and Bulletin 17B methods were used to identify 24 and 30 stations, respectively, that had recurrence intervals greater than 50 years, and 13 and 16 stations, respectively, that had recurrence intervals greater than 100 years for the 1993 flood. Because the magnitude and duration of precipitation was substantial over a major part of the basin, the 1993 flood was greater than a 100-year event on the larger watersheds such as the Missouri River downstream from Rulo, Nebraska, and a reach of the Mississippi River from Keokuk, Iowa, to St. Louis, Missouri.