Estimation of Water Balance Components by Simulating River flow Using SWAT Model (Case Study: Balkhlochai Watershed)

Sustainable use of fresh water resources and analysis of the hydrological behavior of the basin for water resources management requires knowledge of the state of water balance components. The main goal of the research is to estimate the water balance components of the Balkhlochai catchment area with an area of 567 square kilometers. Therefore, necessary information such as meteorological parameters, monthly discharge, as well as required maps were prepared and introduced to the model. In order to test and validate the model, SUFI2 algorithm was used. The period of 2003 to 2013 was considered for the validation period and 2014 to 2018 for validation. The results showed that the Nash-Sutcliffe and explanation coefficients were 0.52 and 0.60 respectively for the validation period and 0.60 and 0.65 respectively for the validation period. Also, the balance components of the basin showed that 69% of precipitation enters the atmosphere through evaporation and transpiration. About 16% enters waterways as surface runoff, lateral flow, and return flow, and 15% of it also infiltrates. The results of the research show the good performance of the SWAT model in simulating the water balance of the Balkhlochai watershed. One of the most important reasons for the decrease in the efficiency of the model can be attributed to the incompleteness of the snow melting coefficients, the less compatible initial assumptions of the model, for the simulation of water flow at high altitudes and frozen layers, and the lack of necessary information regarding the simulation of underground water cited.