Application of Peaks Over Threshold Method in Flood Frequency Analysis in Seyhan Basin

Flood frequency analysis is a statistical method that is used to obtain the amounts of flow corresponding to certain recurrences or probabilities in rivers. In this way, the design and economic evaluation of hydraulic structures is provided. In this study, flood frequency analysis was performed for the station numbered 1801 and located in Seyhan Basin by using peak values over an assigned threshold. Threshold value was determined through four different methods that include threshold selection plot, mean residual life plot, dispersion index plot as well as the method based on the mean and standard deviation; and autocorrelation analysis has been tested to determine whether the peaks obtained above the threshold are independent. Generalized Pareto distribution which is frequently used in partial duration series was applied and tested against the historically observed series. Uncertainty analysis was performed by determining the parameters of the Generalized Pareto distribution and the confidence intervals over the calculated flood flows of 2, 5, 10, 25, 50 100, 200, 500 and 1000 years. Finally, flood quantities with the recurrence intervals of 2, 5, 10, 25, 50, 100, 200, 500 and 1000 years were computed and compared to the corresponding quantities obtained from the annual maximum series. According to the results, it was observed that, the differences between the flood estimates obtained by peaks over threshold method and the analysis of annual maximums were bigger for the smaller recurrence intervals and the differences were relatively small for large recurrence intervals (500 and 1000 years).