M Dehghazadeh - M.Sc. graduated, Watershed Management Dept., Ferdowsi University of Mashhad
J Ahmadi - Ph.D. Student at Dept, Rehabilitation Arid and Mountainous Area, University of Tehran

Today one of the most important issues in water resources management is allocating water resources betweendifferent sectors. Environmental flows describe the quantity, timing, and quality of water flows required tosustain freshwater and estuarine ecosystems as well as the human livelihoods and wellbeing that depend onthese ecosystems. General methods for determining environmental flow requirements include habitatsimulation, hydrological and hydraulic methods, as well as comprehensive and combined methods. In thisstudy, a hydraulic method (wetted perimeter) and hydrological methods (FDC) were used to determineenvironmental water requirement. In the wetted perimeter method, the critical point was determining the waterrequirement using three approaches; Slope of curve Method (SM), Maximum curvature Method (CM) andIdeal Point Method ۱ (IPM۱). The results of SM and IPM۱ are in range proposed by the Tennant method (۱۰-۳۰% Mean Annual Runoff). The results revealed that the Tennant method was evaluate the environmental flowpoorly. The hydraulic method only determines the wetted perimeter basically arose to assess the suitableaquatic environment for fish, and does not consider other components of the ecosystem. Also, minimumenvironmental requirement in Tessman method was ۰.۹۸𝑚۳⁄𝑠. The wetted perimeter, Tessman and Tennantmethods are not recommended for the study area. According to the results, values obtained from FDC shiftingmethod, due to consideration of ecological management conditions is preferred in comparison to othermethods. Therefore, environmental flow requirement of Zarringol River which is in the environmentalmanagement class C was estimated ۰.۹۳ 𝑚۳⁄𝑠 on average (۴۵.۳% MAR). It is recommended that studies becarried out on the minimum environmental flow requirement.

environmental flow requirement, FDC shifting, Tennant, Wetted perimeter, Tessman