modflow

Mathematical simulation of groundwater resource systems is one of the essential tools in managing these valuable resources and calibration of the groundwater simulation models is the time-consuming, and complicated step of these systems. Automated calibration, developed in recent years by researchers with different algorithms, is one of the effective methods to overcome these computational problems. On the other hand, lack of field data in terms of time and space and the hydrological and hydrogeological complexities leads to many uncertainties in the calibration results. The SUFI-II algorithm is an uncertainty-based automatic calibration method that is capable of calibration and uncertainty analysis of numerical simulation models. In this paper, for the first time, this algorithm is used to calibrate and analyze the uncertainty of hydrodynamic parameters (hydraulic conductivity and specific yield) of the MODFLOW model. The results of model implementation for the Ardabil plain groundwater model (Northwestern Iran), indicate an average of 62 percent of the observation data within the 95 percent confidence interval. Finally, the best intervals of parameters are determined for the hydraulic conductivity and specific yield by the proposed approach. Also, the calibration of the groundwater model has been carried out using PEST. According to the results, the root-mean-squared error (RMSE) value in this case (RMSE = 3.37) is higher than the SUFI-II method (RMSE = 1.86), which indicates better performance of the SUFI-II algorithm than the PEST model.

Exchanges of water and solute between stream flow and flow through river bed porous media are known as hypoerheic exchanges. Hyporheic exchanges transfer water and nutrient to the organism lived in the hyporheic zone, so affect ecological conditions and food cycle. One of the important factor effects on these exchanges is pressure gradient along the bed form. Riffle-pools are geomorphic features of rivers which pressure gradient along them drive hyporheic exchanges and recently considered in river restoration projects. The goal of this study is to compare the hyporheic flux and residence time of flow within sediment bed, in 2D and 3D riffle-pool. For reaching this goal, the surface flow simulated with OpenFAOM and then the results of pressure along bed form, set as a boundary condition on groundwater model (MODFLOW software). The results show that, by increasing bed form amplitude, hyporheic exchanges flux increases by 26 percent for both 2D and 3D models, and residence time decreases by 36 percent for 2D and 41 percent for 3D models. Also, comparison of 3D riffle-pool with equal 2D model shows that hyporheic exchanges flux and residence time increase by 3% and 4%, respectively.