Comparative evaluation of environmental flow assessment: Contrasting habitat simulation and hydrological methods in the Beshar River, Iran

In the past few decades, water infrastructures and exploitation programs have increased in arid and semi-arid areas of Iran. Therefore, environmental flow assessment with Nature-based solutions is an important issue to preserve and restore the river and lake ecosystems. This study compares conventional hydrological methods, and habitat simulation approaches with regard to the habitat suitability of native cyprinid fish species of the Beshar River located in the southwest of Iran. The results showed the highest agreement between physical habitat simulation (PHS) with Tennant method Optimum range (60–100 % of MAF) and Outstanding (60 % of MAF) for high water season and 40 % of MAF for low water season) classes for the hydrometry stations in this area. Whereas, Fair or degrading class of Tennant method officially suggested by Iran's Ministry of Energy for downstream of reservoir dams does not meet desired habitat of target fish species. Moreover, the high water and low water seasons of Tennant method will be matched with spawning of adult and growth stages (larval, fry and juvenile) of target cyprinid species in this arid region. The results show that the Good class of Tennant method is the most compatible with minimum environmental flow based on PHS for three cyprinids target species for the Beshar River. This hybrid approach to estimate environmental flow based on both simple hydrologic methods and habitat requirements perspectives of native species are recommended for semi-arid regions of developing countries under human regulation of the riverine systems by dam construction.