Analysis of Hydrological and Hydraulic Aspects in Designing Ideal and Optimal Environmental Flow Regime for Conservation of Qarasoo River Ecosystem

A good understanding of the river natural flow regime plays an important role in many hydrological studies. In integrated water resources management, it is necessary to determine the environmental flow in river systems that affect the health of river habitats, water-dependent systems and aquatic life. In the present study were calculated and evaluated hydrological methods (Tennant, Q50 and Q90, Esmakhtin, flow duration curve shifting (FDC Shifting), Texas and Water Quality) and hydraulic (Wetted Primer) estimating the environmental flow of the Qarasoo River in different months of the year. Based on the results of this study, for the protection of the Qarasoo River in the minimum acceptable environmental conditions, FDC Shifting method in management class C with a flow of 0.96 m3/s (53 Percent Mean Annual Flow) in this study due to the consideration of biodiversity management classes and the proper adaptation of the pattern changes within the year of environmental flow and the mean annual flow and its flexibility with respect to changes in the monthly flows river under study. On the other hand, the efficacy, flexibility and effectiveness of the Tenntant, Q90 and Smakhtin methods are not sufficient to protect the river habitat under study due to an inappropriate estimate environmental flow. Also, comparison of water allocation for environmental flow with Wetted Primer and Tennant methods in the studied river showed that shortage of flow is observed in summer and winter seasons (river flow is less than environmental flow). Finally, it was concluded that other environmental flow methods provide values above 20% of the mean annual flow, which provide better flow protection for the river habitat. It is noteworthy that the Wetted Primer and Tennant methods, with assigning a more portion of the river flow regime to the environmental segment, should be used with caution in summer. The optimal environmental flow regime will be effective when released and provided in the river at the appropriate time to continue bio-activities, river habitat performance and the preservation of the river bed morphological conditions.