COMPARISON OF VARIOUS FLOOD FREQUENCY-DISTRIBUTIONS USING ANNUAL FLOOD PEAKS DATA OF RIVERS IN ANATOLIA

The two-parameter log-normal, three-parameter log-normal, smemax, two-step-power, log-Boughton, Gumbel, general extreme-value, Pearson-3, log-Pearson-3, log-logistic, and Wakeby distributions were applied to the annual flood peaks series greater-than-or-equal-to 30 observations of 45 unregulated streams in Anatolia. The parameters of most of these distributions were estimated by methods of. (1) moments; (2) maximum-likelihood; (3) probability-weighted moments. Methods of entropy, Bobee, and mixed-moments also were employed for the log-Pearson-3 distribution. Average values and standard deviations of the absolute relative differences of the 0.01, 0.001, and 0.0001 exceedance-probability peaks computed from 3333 and 1000 synthetically generated series of 30- and 100-element lengths, respectively, from the peaks by the base distribution used in generating the synthetic data revealed that the three-parameter and two-parameter log-normal, and the Gumbel distributions predicted these extreme right-tail events better than the other distributions.