Numerical Study of the Influence of Horizontal Spatial Distribution of Macropores on Water Infiltration

The existence of macropores acutely enhances the capacity of soil to conduct water, gas, and chemicals. The capacity of macropores to transport water extremely depends on their spatial characteristics. However, the effect of the horizontal spatial distribution of macropores (especially the position characteristics of macropores) on water infiltration is still ambiguous. Therefore, this study utilizes the approach of numerical simulation to investigate the general pattern of the effects of horizontal spatial distribution characteristics of macropores (such as number, pore size and position) on water infiltration. Given the limitations on the ability to characterize the macropore position from the existing spatial characteristic parameters of macropores, two new statistical parameters (spatial dispersion, γ, and spatial deviation, γ*) are established to characterize the position relationships among macropores and between the macropores and the observation area, respectively. The results show that the larger the macropore number and the more uniformly macropores are distributed, the greater the soil permeability and the preferential flow degree, while the pore size hardly affects the water transport. Additionally, comparison between number and position effects reveals that the macropore number is the dominant factor when the macropore number is relatively small, but this relationship will reverse when the macropore number is relatively large. This study provides a novel meals to investigate the effect of macropore position on water infiltration, and emphasizes that besides the macroporosity, number and position are also significant for quantifying soil permeability.