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Most available methods for unit hydrographs (SUH) derivation involve manual, subjective fitting of a hydrograph through a few data points. The use of probability distributions for the derivation of synthetic hydrographs had received much attention because of its similarity with unit hydrograph properties. In this paper, the use of two flexible probability distributions is presented. For each distribution the unknown parameters were derived in terms of the time to peak(tp), and the peak discharge(Qp). A simple Matlab program is prepared for calculating these parameters and their validity was checked using comparison with field data. Application to field data shows that the gamma and lognormal distributions had fit well.