This report outlines methods by which the magnitude and frequency of expected floods of any recurrence interval from 1.1 to 50 years can be determined at most points in the Colorado River basin.
Composite frequency curves were drawn showing the relation of the mean annual flood to floods having recurrence intervals from 1.1 to 50 years. Other curves express the relation of the mean annual flood to basin characteristics. In the northern part of the basin (north of about lat 37° N.) both drainage area and mean altitude were important factors influencing the magnitude of the mean annual flood. Only drainage area was used as an independent variable in the southern part of the basin.
By combining data from the composite frequency curves and curves showing the relation of the mean annual flood to basin characteristics, flood-frequency curves can be drawn for streams in the report area not materially affected by regulation or diversion within the range and recurrence interval defined by base data.
Some of the larger streams in the basin do not lend themselves to regional analysis. These streams are given special treatment in this report. Owing to the paucity of streamflow data, flood-frequency relations are not defined in some of the more arid parts of the report area.
