Regression equations are provided for estimation of flood magnitude and frequency on unregulated and unurbanized streams in Pennsylvania. Frequency-discharge profiles are shown for regulated reaches on eleven major streams. These regression equations and discharge profiles enable the design engineer to estimate flood-frequency characteristics for almost all streams that drain more than 2 square miles.
Ten regression models for eight flood-frequency regions consist of regression equations that relate floods for recurrence intervals of 2.33, 10, 25, 50 and 100 years to readily determinable drainage-basin characteristics. Individual equations include no more than two of the following drainage-basin characteristics as independent variables: drainage area, channel slope, percent of area which serves for storage of surface water, and index of average annual excess precipitation.
Standard errors of estimate for regression equations applicable to drainage areas of more than 15 square miles range from 16 to 33 percent. For smaller drainage areas, the highest standard error of estimate is 56 percent. The equations do not apply to streams whose drainage basins are highly urbanized or extensively strip mines; neither do they apply if runoff from more than 15 percent of the drainage basin upstream from the site of interest is regulated.
Peak discharges for recurrence intervals of 2.33, 10, 25, 50, and 100 years, as attenuated by installed and planned reservoirs, are presented for the principal regulated streams by means of discharge-frequency profiles.
Tables of drainage basin characteristics and discharge-frequency distributions are appended.
