Cross-Sectional Models of Groundwater Flow: Review and Correction for Transverse Flow

Area of Science:

• Hydrogeology
• Numerical modeling
• Geoscience

Background:

• Cross-sectional (2D) groundwater models are vital for simulating complex processes often too detailed for regional 3D models.
• Extracting 2D models from 3D models presents challenges in preserving regional flow patterns due to property and stress translation.
• Existing methods struggle to maintain accuracy when simplifying 3D groundwater systems into 2D cross-sections.

Purpose of the Study:

• To develop and evaluate a methodology for maximizing head agreement between 2D and 3D groundwater models (MODFLOW).
• To address challenges in translating hydraulic properties and stresses from 3D to 2D models.
• To improve the consistency and predictive capability of extracted 2D groundwater models.

Main Methods:

• A methodology was developed for averaging hydraulic properties and stresses from 3D to 2D MODFLOW models with rectilinear grids.
• Lateral flow was incorporated as inflows/outflows in 2D models, requiring input from the 3D model.
• Pumping stresses from the 3D model were redistributed to adjacent cells in the 2D model to mitigate simulation errors.

Main Results:

• Initial concordance between 2D and 3D transient heads was generally poor.
• Incorporating lateral flow significantly improved model agreement.
• Pumping redistribution showed minimal improvement in the case study but substantial gains in simpler, localized pumping scenarios.

Conclusions:

• The presented methodology offers a straightforward approach for creating 2D cross-sectional models consistent with 3D parent models.
• Lateral flow incorporation is crucial for improving 2D/3D head agreement but limits 2D model independence.
• Further research is needed for methodologies applicable to 2D models oblique to 3D grids.