تعيين الگوي توزيع زماني بارشهاي كوتاه مدت در استان تهران

The choice of a design for rainfall is a basic step in many common used methods for estimation of flood design. Knowledge of the time distribution or temporal pattern of rainfall in heavy storms is of paramount importance in solving certain hydrological problems such as the design of urban storm sewer systems. This knowledge is also useful in studying soil erosion and flood potential of various types of storms, as well as in advancing our understanding of the physics of the atmosphere with regards to precipitation. After a complete literature review, in our present study, the temporal patterns of rainstorms were derived for 13 rain gauge stations by Fluff method in Tehran province. By this method, at first, all storms were grouped into four according to the characteristics of homogeneity as 1, 2, 6 and 12 hours group. Then each cluster of storms was divided into four groups depending on whether the heaviest rainfall occurred in the first, second, third or fourth quarter of storm periods. For each cluster of storms, predominant quartile storms were assigned by means of frequency analysis. After wards, the temporal pattern curves were generated as probabilistic terms in order to provide many design requirements. The results revealed that the heaviest rainfall occurred close to the center of storms durations in Tehran province. The results also showed that second and third quartile storms are predominant in most recording rain gauge stations and storms durations.