Techniques for estimating magnitude and frequency of floods on rural unregulated streams in New York State excluding Long Island

Techniques are presented for estimating the magnitude and frequency of floods at ungaged sites on unregulated rural streams in New York, excluding Long Island. The discharge-frequency data and basin characteristics of 220 stream-gaging stations in New York and adjacent States were used in developing multiple linear regression equations for floods ranging in recurrence interval from 2 to 100 years. Separate equations were developed for northern, southeastern, and western New York. Standard errors of estimate of the 100-year flood range from 32.9 percent in the southeastern region to 42.8 percent in the western region. Drainage area is the independent variable needed in all equations; other variables needed, depending on region, are main-channel slope, storage index, and mean annual precipitation. A method is given for obtaining improved discharge-frequency relationships at gaged sites by weighting log-Pearson type III and regression estimates according to their variances. Basin characteristics, log-Pearson type III statistics, and regression and weighted estimates of the frequency-discharge relationship, are tabulated for the gaging stations used in the regression analyses. (Kosco-USGS)