Uncertainty Assesment of Hydraulic Conductivity Parameter in MODFLOW Model using Monte Carlo and RPEM Method (Case study: AliAbad plain of Qom)

In groundwater modeling, an array of factors are the cause of deviation between estimated results and observed data which demonstrate uncertainty in groundwater resources system. In this study, with the aim of investigating the uncertainty of groundwater flow model in Ali Abad plain of Qom with the area of 1712 km2, the parameter of hydraulic conductivity as the most important source of uncertainty was used to analyze the parametric uncertainty. For this purpose, in order to simulate ground water level, different uncertainty ranges in 90% of confidence interval of hydraulic conductivity was investigated by Monte Carlo method and the uncertainty assessment criteria were used to quantify the uncertainty. Eventually, the most appropriate uncertainty range was defined. The Rosenblueth’s Point Estimation Method (RPEM) was used to reduce the calculation process and time and then its performance for analyzing the parametric uncertainty was compared to Monte Carlo method using assessment criteria. Results showed that the most appropriate uncertainty range with RPEM and Monte Carlo method for hydraulic conductivity was obtained by increasing of 40% and reduction of 30% of this parameter. RPEM method showed a better performance account for 43% compared to Monte Carlo method.