A New Explicit Solver for MODFLOW Enabling Small Time Step Simulations.

Area of Science:

• Hydrology
• Hydrogeology
• Computational Modeling

Background:

• Surface water (SW) and groundwater (GW) models like MODFLOW and HEC-RAS simulate SW-GW interactions.
• Individual models have limitations in capturing the full complexity of these interactions.
• Model coupling addresses shortcomings but faces challenges with temporal scale disparities.

Purpose of the Study:

• Introduce a novel explicit solver (EXP1) for MODFLOW 2005.
• Enable GW modeling at small time steps (e.g., 15 minutes) to match SW models.
• Reduce runtime and computational burden for GW simulations.

Main Methods:

• Developed the EXP1 solver for MODFLOW 2005 with an integrated stability criterion.
• Evaluated EXP1 against the Preconditioned Conjugate Gradient (PCG) solver.
• Tested across 1D, 2D, and 3D model scenarios.

Main Results:

• EXP1 demonstrated efficiency and accuracy in predicting groundwater heads and water budget.
• Achieved runtimes up to 33% shorter than the PCG solver.
• Maintained less than 0.4% discrepancy in water budget compared to PCG.

Conclusions:

• EXP1 effectively facilitates groundwater simulations at small time steps.
• The solver bridges the temporal scale gap between SW and GW models.
• Offers a computationally efficient and accurate solution for coupled SW-GW modeling.