A Spatially Periodic Solute Boundary for MT3DMS and PHT3D

Area of Science:

• Hydrogeology
• Computational Hydrology
• Environmental Engineering

Background:

• Hyporheic zone models often assume spatial repetition for simplification.
• Existing solute transport codes (MT3DMS, PHT3D) lack boundary conditions for spatial periodicity.
• Simulating flow and transport under repeating bedforms requires specialized boundary conditions.

Purpose of the Study:

• To develop and implement a spatially periodic boundary (SPB) for solute transport.
• To ensure compatibility with existing SPB for groundwater flow (MODFLOW).
• To enable accurate simulation of hyporheic zone processes under spatially periodic surface features.

Main Methods:

• Developed a solute SPB compatible with MODFLOW's flow SPB.
• Utilized a block-centered finite-difference approach for implementation.
• Discussed necessary source code modifications for MT3DMS and PHT3D.
• Compared multi-bedform and single-bedform models to evaluate performance.

Main Results:

• The new solute SPB performs well in hyporheic zone models.
• Effective in situations with minimal dispersive effects.
• Suitable for conditions with limited lateral seepage flux in the underflow regime.
• Successfully simulates groundwater flow and transport under repeating surface features.

Conclusions:

• The developed solute SPB is a valuable tool for hyporheic zone modeling.
• Enhances the simulation of solute transport under spatially periodic conditions.
• Provides a method for more realistic modeling of groundwater systems with repeating bedforms.