Investigation of a Monthly Water Balance and Valuemetric Estimation of the Filtered Base -Flow and Total Flow in Vanak Watershed

Base-flow can be considered as a part of stream-flow which is connected to discharged flow from aquifers. Due to high variations in rainfall values and other hydrological components in arid and semi-arid areas, watershed scale simulation of the flow is very important. Hydrological models are generally employed as an appropriate tool in this field of study. This work makes uses of use a distributed model called WetSpass-M to investigate water balance and estimate the total flow for Vanak watershed. This model was developed with the aim of simulating water balance in arid and semi-arid regions. Since the model focuses on spatial variations of hydrological components for a desired watershed, all inputs of this model are in the form of raster maps with an ascii format. The temporal resolution for grid inputs was set on a monthly scale except the number of rainy days. The performance of the model for total flow was measured with the Nash-Sutcliff coefficient, the values of 0.57 and 0.56 in both calibration and validation periods were obtained respectively. It also shows an efficiency coefficient of 0.52 for simulated baseflow in both periods. Thus the model result could be regard as an acceptable accuracy for both total flow and base-flow for Vanak watershed. Also a visual comparison of observed and simulated hydrograph demonstrated that model performed better in the case of total flow than filtered base-flow. The other conclusion that we draw from this visualization was low flows simulation were simulated slightly better than high flows. Additionally the results of simulation of water balance components in the study area has demonstrated that the highest portion of annual rainfall in water balance components of the watershed belongs to groundwater recharge.