Efficiency Assessment of Baseflow Separation Methods in Gol-Gol Catchment, Ilam

In this research, the baseflow at the Gol Gol station, as a part of the Ilam dam watershed from 1991 to 2015, was separated from the entire river flow. For this purpose, WETSPRO methods, one-parameter and two-parameter numerical filters for continuous flow with porous and rocky aquifers, and using flow index and WHAT software with different filtration coefficients were used. To compare the methods and to select the most appropriate method, BFI index was used as an observational baseflow. Based on the results obtained, the baseflow occupies a major part of the total flow. The mean of the total flow rate was 1.945 m3/s and the mean of the baseflow index was 1.445 m3/s, which indicates the permeability of the watershed. RMSE, MAE, and Nash-Sutcliffe criteria were used to evaluate the efficiency of the methods. The results showed that the Lyne and Hollick method based on WHAT software had the best result and then followed by Eckhart for continuous flow with a porous aquifer with a significance level of 0.742, mean 1.250 m3/s, with a confidence level of more than 95%. Therefore, the Eckhart method can be considered suitable for continuous flow with a porous aquifer with a filter coefficient of 0.990 due to the proximity of the mean baseflow in it to the mean of the baseflow index.