Sensitivity Analysis and Validation for Numerical Simulation of Water Infiltration into Unsaturated Soil

Area of Science:

• Soil Science
• Hydrology
• Computational Modeling

Background:

• Liquid water flow in unsaturated soils is crucial for understanding hydrological processes.
• Richards' equation is the governing equation for water movement in unsaturated soils.
• Accurate simulation of soil water infiltration requires sensitivity analysis of model parameters.

Purpose of the Study:

• To develop a FORTRAN code for simulating isothermal liquid water flow in unsaturated soil.
• To perform a sensitivity analysis of Richards' equation using normalized sensitivity coefficients.
• To investigate the influence of various parameters on water infiltration in Yolo light clay.

Main Methods:

• Developed a FORTRAN code to solve Richards' equation using the finite-difference method.
• Employed one-at-a-time (OAT) and elementary effects (EE) methods for sensitivity analysis.
• Calculated normalized sensitivity coefficients based on hydraulic functions for matric suction and hydraulic conductivity.

Main Results:

• The elementary effects (EE) method provided insights into parameter linearity and oscillating sign effects.
• Boundary volumetric water content and saturated volumetric water content were identified as the most sensitive parameters.
• Spatial discretization size (Δz) significantly influenced model output, despite other parameters showing high sensitivity or uncertainty.

Conclusions:

• The developed FORTRAN code effectively simulates water infiltration in unsaturated soils.
• Sensitivity analysis is vital for understanding parameter influence and model behavior.
• Parameter interactions and their combined effect on model output are critical for accurate simulations.