Comparison of Base Flow separation methods from daily flow hydrograph (Case study: Upstream of Boostan dam catchment In Golestan province)

Base flow is a part of flow that comes from aquifer. This section of flow is important in water resource management and hydrologic researches for e.g. in precipitation-runoff modeling and water quality evaluation. Also base flow is used calibration and validation of these models. By dividing base flow on total flow, the Base Flow Index (BFI) is derived, that shows the amount of ground water portion in total flow. The aim of this research was to choos the best method of hydrograph separation and estimating base flow. 21 years daily recharge data of Tamar station in upstream of Bustan dam in Gorganrood river catchment was separated by Local minimum, fixed interval, Sliding interval and Recursive Digital Filter (RDF) or BFLOW algorithm by filter coefficients same as 0.9, 0.925, 0.95, 0.975, 0.99. Results were compared with recession curve by MAE, RMSE and Nash & Sutcliffe coefficient (E). This comparison showed that RDF by filter coefficient of 0.9 was the most suitable method for hydrograph separation in this region and 89% of total flow was base flow.