Comparing three approaches to determine environmental flow for Harou river in Ardabil province

To meet flow requirement of streams, it is necessary to allocate some part of stream flow to own stream, aiming to ensure stability of aquatic life. The underlying reason for it is that utilizing the ecosystems and ecological services such as water supply of streams should not endanger their ecological potential in having a sustainable life. The main objectives of environmental flows for all major rivers and streams applying three rainfall-runoff modeling, hydrologic approach, and indicators hydrologic alteration, and comparing the find outs. Base flow approach is based on the idea that the driest month-mean flow is sufficient for aquatic life except the aquatic life needs additional flow for their spawning and reproduction. To conduct the base flow approach, tank model, has been applied. In flow duration method, flow data of a given river or stream is analyzed in order to estimate the discharge value relate the stream flow amount to the percentage probability that the daily flow will be exceeded over a long-term base period without regard to the sequence of the flow events. Findings of the present study suggest that in this catchment tank model results are reliable, as their Nash-sutcliff criteria measure higher than 0.5. The results indicated that according to the environmental flow estimation of Flow duration curve method, environmental flows is 0.191 m3/s in the study area.