This report presents methods by which the magnitude and frequency of expected floods for most streams in Oklahoma can be determined. Flood data were used to define flood-frequency curves applicable to the State. Composite frequency curves were drawn showing the relation of mean annual floods to floods having recurrence intervals from 1.2 to 50 years. In some areas, it was found that the slope of the composite frequency curve varies with the drainage area. An adjustment curve was defined for use in conjunction with the composite curve for these areas. Other curves express the relation of the mean annual flood to drainage basin characteristics. By combining data from the composite and mean annual flood curves, flood-frequency curves can be drawn for streams in Oklahoma not materially affected by the works of man. Neither of the above two types of curves should be extrapolated beyond the range defined by base data. Frequency curves presented in this report were based on analysis of flood records collected at gaging stations having 5 or more years of record not materially affected by regulation or diversion.
