Basic concepts for the linear model of ground water level recession.

Area of Science:

• Hydrogeology
• Geophysics
• Environmental Science

Background:

• Groundwater level recession analysis is crucial for understanding aquifer behavior.
• Rorabaugh's method provides a framework for analyzing exponential decay in groundwater levels.
• Definable outflow boundaries, like rivers or lakes, are key to applying linear recession models.

Purpose of the Study:

• To illustrate Rorabaugh's method for displaying groundwater level recession.
• To assess the accuracy of the linear model with varying outflow boundary conditions.
• To identify factors causing deviations from linear recession and impacting hydraulic diffusivity estimates.

Main Methods:

• Utilized three finite-difference simulations to model groundwater flow and recession.
• Simulated an ideal Rorabaugh case with a uniform outflow boundary.
• Simulated cases with sloping and complex outflow boundaries to test model accuracy.

Main Results:

• The linear recession model is accurate for ideal and simple sloping boundaries when water levels are referenced to the nearest boundary point.
• Complex boundary shapes and sloping boundaries introduce nonlinearities and errors in hydraulic diffusivity estimation.
• Early-time groundwater head profiles after recharge can exhibit nonlinear behavior, affecting recession analysis.

Conclusions:

• Rorabaugh's linear recession model is effective under specific conditions, particularly with uniform or simple sloping boundaries.
• Accurate application requires careful consideration of the outflow boundary's geometry and the reference point for water level measurements.
• Deviations from linearity highlight the complexity of groundwater systems and the need for advanced analysis in certain scenarios.