Study area
Karun River watershed located in the south-west of Iran with an area of 23,250 km2 is part of the Persian Gulf watershed. The elevation varies between zero near sea level to more than 4000 m in the mountains. There are 83 river flow gauges on the Karun River and its branches. The longest data set belongs to Ahwaz station near Ahwaz city from 1950 and Fig. 1 shows the river flow histogram in that station (Jamab, 1999). There are two dams constructed on the river and the first station above the upper dam, Karun 1, is the Shaloo bridge station. Since the data at this station are not affected by the dam, they were selected for this research. Monthly river flow data in this station from 1933 to 2001 were used for evaluating the proposed method. The
monthly average river flow is 826.2 cubic meters per month. The minimum and maximum monthly average flows are 334.81 and 1763.18 in September and March, respectively.