modification of tennant and wetted perimeter methods in simindasht basin, tehran province

Environmental flow requirement (efr) is defined as the flow that is necessary to ensure the existence of habitats in water resources systems. efr is defined in rivers as flow index commonly. tennant method is the most popular hydrological method in rivers and based on the historic flow data. the most common method of hydraulic rating method is the wetted perimeter method. habitat simulation techniques attempt to assess environmental flow requirements on the basis of detailed analyses of the suitability of instream physical habitat. investigation of the relationship between simple approaches and physical habitat simulation approach and presentation of new recommendations based on the hydraulic and hydrological data can be very useful in estimation of environmental flow in planning phase of river projects. main objective of present research are modification of tennant and wetted perimeter methods and providing more reliable recommendations in simindasht basin in tehran province which rainbow trout is dominant species. based on the results, in april to september 60% of mean annual flow (maf) and in october to march 120% of maf can provide sustainable habitats approximately. also common wetted perimeter method estimates efr more than real instream flow need of target species. this method will assess the suitable value for environmental flow on 86% of the maximum wetted perimeter approximately. but based on physical habitat analysis mean suitable environmental flow will be assess in 63% of the maximum wetted perimeter. hence modification of wetted perimeter based on physical habitat analysis can reduce instream flow need significantly