Investigation of hydrological methods of Environmental Flow Determining for Protected River Kashafrood in Mashhad area

Iran is faced with limited freshwater resources and, on the other hand, is facing increasing demand for water for various uses. One of the most important challenges in planning water resources is the determination of the environmental flow in the rivers. The environmental flow describes the time, quality, and amount of flow needed to maintain the aquatic ecosystem. Protected rivers are widely protected with a high conservation value, aimed at preserving and restoring plant habitats. Protected areas are suitable environments for conducting educational and environmental studies. Protected River Kashafrood is part of the Qara-e-Ghom basin of Iran located in the northeast of the country and in the north of Khorasan Razavi province. The basin has 15650 km of area. To maintain ecosystems in this area, it is essential to determine the minimum environmental flow. Today, various methods for estimating the environmental flow of the river are presented in the world, which hydrological approaches are the most widely used ones. In this paper, the environmental flow of the Kashafrood Protected River is estimated on the basis of the 39-year statistical period in the Olang Asadi station using hydrostatic methods of Tessman and Transmission curve continuity flow (Smakhtin). The required flows were obtained and then, using SWOT analysis, according to the internal and external characteristics of each method, the most suitable approach for determining the environmental flow of Kashafrood River was presented. The minimum environmental flow in the Tessman method was 1. 57 and in Smakhtin method, the continuity curve was 1.85. Using the SWOT analysis, internal and external evaluation matrices of the internal and external assessment matrix were used to convey the continuity curve of 3.64 and 3.53, which was selected as the appropriate method in comparison to the method.