Comparison of the environmental flow assessment methods involving case studies of Karaj and Talar Rivers

Environmental flow is explained as the period of time, quantity and the amount of required water for maintaining the water, fresh, the river’s ecosystem, human beings’ welfare and the life depending on the water. The main goal of this paper is to investigate and compare the hydrological methods including Tennant, aquatic flow, Tessman, analysis of the flow duration curve and the flow duration curve shifting (FDC shifting) in determining environmental flow of two rivers from two different prime basin of Iran, Karaj and Talar rivers with data of 59 and 63 years, respectively. According to the results, the flow duration curve shifting approach for its consideration to different ecological classes, attention to natural flow shifting and the efforts of maintaining this shifting in its own suggested environmental flows, has priority over other approaches and it is also more precise in comparing with others. Therefore, the environmental needs of Karaj and Talar rivers in the classification of environmental management C (the preservation of river’s least environmental condition) are assessed equal to 4.77 m3/s which is 38 percent of the average annual flow and 1.81 m3/s, equal to 24 percent of the average annual flow of each river, respectively.