Evaluation of empirical relationships for estimation of instantaneous peak flow Discharge in western catchments of IRAN

One of the most important parameters in design of hydraulic structures is the instantaneous peak discharge. In this research, 20 empirical formulas that have been developed all over the world to estimate the peak discharge are evaluated in 26 hydrologic stations of western catchments of Iran. Instantaneous peak discharge data during a 42 year period at these stations were selected. Frequency analysis was performed on these instantaneous peak discharges by eight probability distribution functions, and after the best fit test, the instantaneous peak discharges with return periods of 2, 5, 10, 25, 50, 100, 500 and 1000 year were estimated by Log Pierson type III distribution. Homogeneity test of catchments under study was also done by Dalrymple method. Linear and non-linear regression analyses were done and the empirical formulas were calibrated for the region, and then the best formula was recommended. For the recommended models, the mean error for 20 to 1000-year return periods was between 21.67% and 34.67%. Among the most important results of the study is the inaccuracy of Fuler formula in estimating the instantaneous peak discharge in western catchments of Iran.