Nonlinear Flow Process: A New Package to Compute Nonlinear Flow in MODFLOW.

Area of Science:

• Hydrogeology and Groundwater Modeling
• Computational Fluid Dynamics in Porous Media

Background:

• Standard MODFLOW simulations often assume linear flow, which is insufficient for many real-world aquifer conditions.
• Nonlinear flow, particularly following the Forchheimer equation, is prevalent in porous media with high flow velocities or complex structures.

Purpose of the Study:

• To develop and implement a new MODFLOW package, the Nonlinear Flow Process (NLFP), to simulate Forchheimer flow.
• To validate the NLFP package's accuracy and applicability across various hydrogeological scenarios.

Main Methods:

• Developed the NLFP package for MODFLOW-2005, employing an iterative modification of conductance to achieve effective Forchheimer conductance.
• Tested the package against four benchmark scenarios with available analytical solutions.
• Evaluated performance in a transient, larger-scale model with complex conditions.

Main Results:

• The NLFP package accurately simulates nonlinear flow, demonstrating correct implementation through benchmark scenarios.
• The tool performs well in complex, transient flow conditions, though convergence may be slower than standard MODFLOW.
• Compatibility with existing MODFLOW features (layer types, boundary conditions, solvers, wetting) was confirmed.

Conclusions:

• The NLFP package provides a valuable new capability for simulating nonlinear groundwater flow within MODFLOW.
• This tool is particularly suited for simulating flow in core samples, vuggy karstified aquifers, and near pumping wells.
• It expands the scope of MODFLOW applications to a wider range of hydrogeological environments exhibiting nonlinear flow behavior.