Simulation of water-table aquifers using specified saturated thickness

Area of Science:

• Hydrology
• Hydrogeology
• Numerical Modeling

Background:

• Groundwater flow simulation in unconfined aquifers is complex because saturated thickness varies with hydraulic heads.
• This variability complicates numerical modeling, often requiring iterative solutions.

Purpose of the Study:

• To review the theoretical basis of the specified-thickness approximation for groundwater flow models.
• To derive an error analysis for this approximation.
• To demonstrate its practical utility in complex hydrogeological scenarios.

Main Methods:

• Theoretical review of the specified-thickness approximation.
• Derivation of an error analysis for idealized conditions.
• Application and evaluation of the approximation on a complex test problem (transient and steady-state).

Main Results:

• The specified-thickness approximation yielded maximum drawdown errors of ~4% (transient) and ~20% (steady-state) of initial saturated thickness.
• Mean errors in steady-state simulations were approximately 5% of initial saturated thickness.
• The method significantly reduces computation time and enhances model stability.

Conclusions:

• The specified-thickness approximation is a valuable tool for accelerating groundwater model development, especially during calibration and sensitivity analyses.
• It facilitates convergence and is particularly useful for extensive model runs like uncertainty analysis and resource management scenario development.
• Despite potential criticisms, the approximation provides accurate results and substantial computational benefits in unconfined aquifer modeling.