Comparison between Low Flow Indices Using FL Approach and Low Flow Frequency Curve (A Case Study of Gharesou River Catchment)

Selection of low flow is necessary for water resource management, water supply planning, and watershed ecosystem restoration. In this study, FL approach was used, which is based on minimum flows and flow duration curve (Q80) categories. This approach was compared with the conventional 7Q10 approach used in low flow selection. For this purpose, the daily flow series from Gharesou catchment was applied. Low flow frequency analysis related to 7Q10 approach was done by fitting various distribution functions and using three frequency software, including HYFA, SMADA, and Easy fit. The results of both approaches show that low flows increased as time elapsed and the recurrence probability of low flow increased while the recurrence interval of low flow decreased as time elapsed. In addition, a low flow decline from 1971 to 2000 observed as 1.57 m3/s and 2.46 m3/s for 7Q10 and FL approaches respectively. The 7Q10 approach lead to selecting extremely low flows (approximately zero). The FL approach used in this study, could result in selecting low flows, considering role of the environment and minimum flow to protect the ecosystem of the catchment.