A Reproducible R–Fortran Toolkit for Groundwater Flow and Contaminant Transport Modeling in Watershed Applications

ABSTRACT: Uncertainty and calibration are major challenges in hydrologic and hydraulic analysis, especially in watershed applications involving groundwater flow and contaminant transport. This study presents an integrated modeling framework for comprehensive simulation of groundwater flow and contaminant transport, with automated calibration and sensitivity analysis capabilities. The framework extends traditional Fortran-based modeling by incorporating the statistical, numerical, and visualization strengths of the R environment. In the proposed approach, the Fortran code is executed within R, while the Fortran program employs a finite-volume time-splitting method to discretize the governing equations of groundwater flow and contaminant transport. Integration with R statistical packages improves model calibration, sensitivity evaluation, and visualization of groundwater contamination results. To illustrate the applicability of the framework, two test cases of groundwater flow and contaminant transport through porous media were conducted. Results demonstrate the accuracy, efficiency, and enhanced visualization capabilities of the integrated system. Ultimately, the framework is intended to support three-dimensional analysis of pollution plume evolution in heterogeneous media and to investigate interactions among multiple contaminant sources in watershed systems.