Assessing the accuracy of the results of upstream and downstream river data in estimating environmental flow using PHABSIM model (Case study: Azad Dam basin)

Rivers are one of the most vulnerable ecosystems in the world, so determining and providing the minimum environmental flow to maintain their ecological functions, as well as maintaining the health of river ecosystems is a very complex issue in terms of: scientific and technical, managerial, executive and finally social and economic. In order to determine the environmental flow of Azad River, which is one of the most important rivers in Kurdistan Province, the present study was conducted using the PHABSIM model. In this study, the accuracy of upstream river data in comparison with the dam downstream river in estimating environmental flow was tested. In this regard, data on suitable water depth, appropriate water velocity and suitable substrate index for fish index species in January, February and March 2016 and April and May 2017 were used as model input data. The results showed that in the method of using upstream data, the amount of water requirement calculated for April and March is equal to 6.7 m3/s and 4.7 m3/s, respectively. And the same amount of need according to the data of the Azad River is equal to 4.4 m3/s and 4.2 m3/s, respectively, while the minimum flow rate of the river in the period 1987 to 1389 is equal to 7.327 m3/s and 7.779 m3/s. This indicates that the data obtained from the summing method of water requirement of upstream is closer to the minimum flow in the period 1987 to 2010 compared to the estimated environmental flow in the Azad river.