Use of hydrological and ecohydrological methods for the assessment of river environmental flow to protect aquatic animals and aquatic ecosystem

The survival of aquatic life and natural habitats requires the preservation of rivers as the most important aquatic ecosystems. Climate change, dams, overfishing, and water pollution have put rivers, aquatic ecosystems, and fish which are biological indicators at risk in recent years. all around the world, various hydrological methods are used to improve the ecological environment, maintain the natural flow regime, and protect the ecological diversity of the ecosystem. In this study, hydrological and eco-hydrological methods (FDC Shifting, Arkansas, Tessman, Tennant, and ABF) were used to estimate the environmental flow of the Darreh-Rood River at the Moshiran hydrometric station in Ardabil province, based on statistical period of 30 years. The average environmental water requirement in the aquatic base flow method and the Tennant method were 1.51 and 1.63 m3/s, respectively, which are not suitable approaches due to the excluding of seasonal changes and severe monthly flow changes without modifications. The flow duration curve shifting method with an average environmental flow requirement of 3.67 m3/s was better than other methods due to the bio-management class in accordance with the conditions of the region. Furthermore, this study discovered that in the lack of complete ecological data, hydrological indicators and environmental classes in flow duration curve shifting approach could be used to estimate environmental flow requirements.