comparison of regional flood analysis methods in central alborz region

one of the most appropriate approaches for flood forecasting is using peak discharge data of hydrometric stations in each region. however, lack of such stations or short duration of data in most parts of the country, make it necessary to use some alternative methods in order to estimate the flood discharge properly. one of these approaches is regional flood analysis method that in a region using observation discharge data in separate points, it calculates relevant regional flood models. these approaches give us possibility at a region without gauging station with similar and homogenous hydrological condition to estimate flood discharge for different return periods with acceptable accuracy. in this research three methods of regional flood analysis including index flood, multivariate regression and hybrid method were considered in 20 watersheds of central alborz region. after taking into account, the hypothesis and limitations of each method, the results were compared with observed flood discharges using rmse and mbe. considering the hypothesis and validation of multiple regression model indicated it is not appropriate. finally index flood method in return periods of 2, 5 and 10 years and hybrid method in return periods of 50 and 100 years proved higher accuracy in the whole region and no difference between these two methods in return period of 25 were shown.