Application of the PHABSIM model in Explaining the Ecological Regime of the River in order to Estimate the Environmental Flow and Compare with Hydrological Methods (Case Study: Gharasoo River)

Lack of appropriate allocation Environmental Flow, has been disrupts the vital activities of aquatic organisms, reduces communication between ecosystems, access to suitable areas for spawning and migrating aquatic. In this research, the environmental demand of Gharasoo River at the siahab station hydrometry was investigated at the entrance to the Gorgan Gulf. Were evaluated of In order to obtain the ecological requirement of Gharasoo River in Golestan province hydrological methods of Tenant, Tessman, Arkansas, Physical Habitat Simulation Model (PHABSIM) for species Capoeta capoeta gracilis. The findings of this research show method of Tenant by taking 30 % annual average flow for the spring and summer seasons, 10 % annual average flow for autumn and winter seasons suggests respectively quantities 0/57 and 0/19 cms. Methods of Tessman, Arkansas and Physical Habitat Simulation model Provide estimates environmental water requirement in equal order 0/856, 1/22, 1/63 cms. Also, there was a lot of difference among between the results of estimating the minimum required water requirement for the river using hydrological methods and providing minimum habitat conditions for indicator species using habitat simulation method and as regards the ecological and habitat conditions of the river are a completely dynamic situation.