Estimating design probable maximum precipitation using multifractal methods and comparison with statistical and synoptically methods case study: Basin of Bakhtiari Dam

摘要

The probable maximum precipitation which is defined as the maximum precipitation at a particular location for a given duration is used as a design criterion for major dams. The assumptions of deterministic consideration and an upper limit to probable maximum precipitation have been repeatedly criticized by hydrologists. Nowadays, multifractal method which strongly contains physical bases can be used to improve the probable maximum precipitation. In this research, the universal multifractal model was used to estimate the design probable maximum precipitation for specified exceedence probability in basin of Bakhtiari Dam, southwest Iran, and its results were compared with statistical and synoptically methods. The results revealed that the return period of statistical and synoptically probable maximum precipitation, estimated for the different durations, are about 10~9 and 10~3-10~4 years, respectively; also, over periods ranging from 1 to 7 days, the ratios of design probable maximum precipitations, estimated based on multifractal method for return period of 10~3-10~9 years, to statistical and synoptically probable maximum precipitation estimates ranged from 0.61 to 1.1 and 1.33 to 2.37, respectively. These results indicated that the multifractal method can be used to reasonably estimate the probable maximum precipitation.