Infiltration Model Based on Traveling Characteristics of Wetting Front

This study presents a one-dimensional infiltration model based on the traveling characteristics of wetting front (TCWF) model. The TCWF model predicts the infiltration process by solving an ordinary differential equation linking infiltration rate and wetting front profile, which avoids numerically solving the highly nonlinear Richards equation and eliminates associated numerical difficulties. This is achieved by an assumption of normalized equality between flux and soil moisture within wetting front before the time when infiltration rate reaches steady value and traveling wave property of wetting front in the equilibrium state. With the two traveling characteristics, the TCWF model uses infiltration rate as input and back solves wetting front profile, time, and cumulative infiltration. We examine the accuracy and capability of TCWF model by comparing 48 infiltration cases with different setups of soil profile and infiltration conditions to the numerical solutions of the Richards equation for vertical infiltration and exact solutions for horizontal infiltration. Results demonstrate that the TCWF model can effectively capture the evolution of wetting front and predict infiltration. The TCWF model can be applied to any soil type, soil hydraulic model, and infiltration on any slope angle. Good agreements with maximum percent bias for cumulative infiltration of 3.525% are found in the vertical infiltration cases with initially dry and initially wet conditions and in the horizontal case with initially dry conditions. In the absence of gravity, the TCWF model slightly overestimates horizontal infiltration, especially under initially wet conditions. The developed TCWF model provides a simple and accurate approach to simulate infiltration.