<p>This study examines the sensitivity of one-dimensional transient flow in variably saturated bi-layered and multi-layered soils through a parametric analysis based on Richards’ equation. Several soil–water retention models, van Genuchten, Brooks-Corey, and Gardner, are employed to assess how variations in key parameters, including hydraulic conductivity, inflow rate, interface position, and layer thickness, affect pressure head distributions. Sensitivity analyses using the Morris and Sobol methods are performed to quantify the relative influence of these parameters under three representative scenarios: the capillary-barrier effect, a bi-layered paddy field system, and unsteady infiltration in a multi-layered soil column. The results show that the hydraulic conductivity of the coarse layer primarily controls pressure conditions at the interface, while the thickness of the fine layer strongly influences the pressure head near the soil surface. Inflow rate and interface position further modulate the overall pressure profiles. Model predictions are validated against analytical solutions and experimental observations, demonstrating strong agreement and confirming the robustness of the proposed framework. Overall, these findings underscore the importance of accurate parameter estimation in soil–water flow modeling and provide practical insights for improving soil and water management strategies.</p>