Performance Assessment of Numerical Solutions in Groundwater Simulation (case study: Birjand aquifer)

The extensive knowledge of groundwater resources' status has double importance for the planning of the sustainable future in the arid regions. Strictly, without an efficient model with accurate simulation, it is impossible to have a good understanding of groundwater behavior. Since groundwater modeling in real problems comprises irregular boundaries, heterogeneity, anisotropy, and conceptualization, there exist many challenges in the simulation process. Due to proper acceptable performance, this study aims to present a proper framework to simulate groundwater flow based on Finite Difference (FD), Finite Element (FE), and Meshfree (Mfree) methods. The governing equation of groundwater flow was discretized through FD, FE, and Mfree approximations, and their performance was examined in two case studies: hypothetical case and field study. The findings of this study revealed that the Mfree has more applicability than others because some noticeable challenges were found in the simulation process of the FD and FE. Comparison of analytical solutions and simulated values in the hypothetical aquifer indicated that all methods are compliant. In terms of the RMSE criterion, the Mfree, FE, and FD were evaluated respectively, 0.005, 0.016, and 0.018 m. However, the numerical methods' act, especially the mesh-based methods (FD and FE) in the field study, becomes less accurate. Performance assessment of the FD indicated that this method has good ability in a simple test case with regular geometry, while in an aquifer with irregular geometry associated with isotropy and heterogeneity, its accuracy is greatly diminished. So that, the RMSE for FD methods in field study was evaluated 1.77 m. The same results may be obtained from the FE method, such that its RMSE was obtained 0.36 m. Investigations of this study showed that the FE needs time-consuming preprocessing practices to implement in the different aquifer. The results of the Mfree application indicated that this method is more efficient than others due to its very high flexibility in irregular geometry with isotropy and heterogeneity issues. The RMSE for the Mfree in the field study obtained 0.26 m.