Estimating T-year flood confidence intervals of rivers in Coruh basin, Turkey

The aim of this study is to determine the most suitable probability distribution for estimating T-year flood confidence intervals of the rivers in Coruh basin, Turkey. For this purpose, 10 different distributions, which are widely used in hydrologic frequency analysis, were fitted to annual maximum flows of nine gauging stations located in critical parts of the basin, and parameters of these distributions were estimated using the method of maximum likelihood. In order to determine the most suitable distributions at each station, Akaike's information criterion, modified Akaike's information criterion, Bayesian information criterion, Kolmogorov-Smirnov and chi-square goodness-of-fit tests were applied. According to evaluations of these tests, two-parameter lognormal, Gumbel and generalised Pareto appeared to be the most suitable distributions. Then, these distributions were used for the estimation of T-year's flood confidence intervals (10, 20, 50, 100 and 200 years). Finally, the performances of the distributions were compared and discussed with regard to its application on the stations.