Regional flood frequency analysis of the Firat and Dicle basins in Turkey using l-moments approach and plotting-position method for maximum flow values

For the design of hydraulic structures such as dams, bridges, waterways, the maximum flood flow over the life of the project should be estimated. This peak value is estimated based on the values of the observed annual instantaneous maximum flow series. Several methods are used to estimate the maximum flow value, such as the L-moment and plotting position methods. Regional flood frequency analysis was performed in this study to the annual maximum flow series recorded previously in the Euphrates and Tigris basins in Turkey by using the L-moments method to estimate probability distribution parameters. The homogenous region was identified by using the L-moments method, and in different regions the Generalized Extreme Value, Generalized Normal, Generalized Pareto, Pearson Type 3, Generalized Logistic, and Wakeby distributions have been applied by using the Xtest software. The accuracy of the estimated quantiles is assessed through the regional L-moment algorithm. The extreme value distribution is found to be appropriate in the Fırat basin and normal distribution for Dicle basin in Turkey. Key Words: Regional flood frequency analysis, L-moments, plotting-position , Fırat basin, Dicle basin.