Methods of estimating flood magnitudes for recurrence intervals of 2, 5, 10, 25, 50,100, 200, and 500 years are described for rural streams in Alabama that are not affected by regulation or urbanization. Flood-frequency characteristics are presented for 198 gaging stations in Alabama having 10 or more years of record through September 1991, that are used in the regional analysis. Regression relations were developed using generalized least-squares regression techniques to estimate flood magnitude and frequency on ungaged streams as a function of the drainage area of a basin. Sites on gaged streams should be weighted with gaging station data that are presented in the report Graphical relations of peak discharges to drainage areas are also presented for siter along the Alabama, Black Warrior, Cahaba, Choctawhatchee, Conecuh, and Tombigbee Rivers. Equations for estimating flood magnitudes on ungaged urban streams (taken from a previous report) that use drainage area and percentage of impervious cover as independent variables also are given.
