Using Ecologic-Hydraulic-Hydrologic Methods for Evaluating Environmental Flows in Rivers

The assessment of environmental flows in a river ecosystem is a new practice in Iran. The main aim of the present study was to use different Eco-hydraulic-hydrologic methods to determine the environmental flow requirements in a typical perennial river. The ecological needs of the transboundary Zab River (located in the northwest of Iran) were investigated in three different reaches along the 160 km length of the river course using the hydraulic-wetted perimeter method (and taking advantage of the two different algorithms of slope method and maximum curvature), the synthetic habitat simulation method, and the water quality control method. The results were compared with those obtained from different echo-hydrologic methods. It was found that the FDC Shifting method (considering Class B: ecologically important rivers despite water resources development) is well adapted to the conditions in the upper reaches of the river (Derabkay Khaneh). The synthetic Eco-hydraulic method is to be recommended for the middle and downstream reaches (Grezhal and Pol–Sardasht) providing the ecological requirements of the Barbus Capito fish (as the bio– indicator species) are met. The mean annual flows in the three river reaches are determined as 2.3, 7.6, and 7.9 m3/s, respectively. The potential monthly flow rates are also proposed for preserving the riverine life