Estimating base-flow to assess environmental flow in the rivers of arid and semi-arid regions (Case study: Shamkan river, Sabzevar)

Base-flow is the percentage of river flow which is associated with groundwater discharge and demonstrator of the extent of groundwater participation in total runoff. Therefore, base-flow has an important role in hydrological and water resources researches such as quantitative and qualitative water resources assessment, hydrologic modelling, calibration and validation of these models and also evaluating the environmental water requirements in different regions. In present research the daily data of river flow for the period of 30 years is selected to evaluate base-flow in Shamkan River which is located in Sangerd catchment. The daily base-flow is calculated during the years of 1987 to 2016 using BFI, Lyn and Hollick, Eckhart and Local Minimum methods. Due to the lake of observation base-flow data, the BFI method is considered as the base method and the results of other methods were compared with the results of the mentioned method. The results indicated that the estimated base-flow by different methods is averaged between 71 to 81 percent of the river flow. The results of error criteria showed that Lyn and Hollick method with the filter parameter of 0.95 is the most suitable method to separate base-flow in the case study. While the Eckhart method with the filter parameters of 0.99 and 0.995 have had highest RMSE and MAE values and also had the lowest Nash-Sutcliff values.