Floods in Nebraska on small drainage areas, magnitude and frequency

Abstract

Flood hazard information is needed for small streams as well as for large ones. This report explains methods of defining the magnitude and frequency of floods in Nebraska on uncontrolled and unregulated streams which have about 300 square miles or less of drainage area contributing to surface runoff. Composite frequency curves defined for two flood regions express a ratio of floods with recurrence intervals ranging from 1.1 to 25 years to the mean annual flood. Curves for 10 hydrologic areas were defined to show the relation of the mean annual flood to the contributing drainage area, A flood-frequency curve can be drawn from these two sets of curves for any site in the State within the range of drainage area and recurrence interval that is defined by the base data and not materially affected by the works of man. The two sets of curves are based on all available pertinent data from records of 5 or more years' duration. This report includes a tabulation of maximum flood peaks at gaging stations used and at a number of miscellaneous sites which have less than 300 square miles of contributing drainage area.