Comparison of methods for estimating base-flow in relation to total river flows of Behesht-Abad basin

Loss function is an internal module in HEC-HMS model. In combinations with transfer function it provides a continuous rainfall-runoff. Baseflow, as a repetitive for groundwater, also will be included to total flow. Behesht-Abad basin is among those areas where due to the hydrodynamic characteristics of groundwater, base-flow plays a significant responsibility in the shape of hydrograph.  Since HEC-HMS is a component-based hydrological model, it allows user to select the type of internal functions. Each of which requires different input data. For instance for base-flow there exist a number of methods that could be selected optionally.  The aim of this study was to evaluate different methods for base-flow methods for the case of Behesht-Abad Basin. In this study, time series of temperature, precipitation, discharge, and evaporation and transpiration for the period of 1998 to 2015 were used to calibrate the HEC-HMS model. Model was tested against a number of base-flow methods.Results showed the constant monthly and bounded recession methods were performed better   with Nash Sutcliffe efficiency coefficient 0.64 at 0.69 in the calibration and validation, respectively. The visual and statistical interpretation of observed and simulated hydrographs indicated that   bounded recession generally has exhibited better performance. The high sensitivity of the model to type of base-flow shows groundwater plays a key role in the study area.