Base Flow Estimation in Tireh Dorood River in order to EnvironmentalFlow Assessmen

Commonly used environmental flow evaluation techniques range in complexity. Some requires stream flow records alone, and some accounts for the habitat requirements of individual species life-stages and physical characteristics of the stream. Hydrological based methods for environmental flow assessment are the first step in planning for environmental allocation in developing countries. For determining environmental needs in a water ecosystem knowledge of the minimum discharge is needed that in hydrology named base flow. Determining it needs to hydrograph separation. For this purpose 30 years daily flow data of Tireh Dorood hydrometery station, on Tireh LorestanRiver was selected. Base flow calculated for daily data from 1982-2011 using BFI, Recursive Digital Filter and HYSEP methods. Results show that base flow in this river forms between 74 -78 % of stream flow. Comparing methods using error measures shows that sliding limit method and Lyne and Hulic method with filter index of 0.9 are suitable methods for base flow separation in Tireh River.