Characterizing heterogeneity of soil water flow by dye infiltration experiments

The inherent heterogeneity of soil water movement, such as fingering flow, is still poorly understood. To address the flow heterogeneity issue, the objectives of this study are to: (1) investigate heterogeneity of soil water flow at different measurement scales and under different boundary conditions using dye infiltration experiments; (2) characterize the heterogeneity information included in different scales using the random cascade model, and (3) predict heterogeneous soil water flow over the measurement scales. Field experiments of dye infiltration included three measurement scales (three dye source surface areas of 25 × 25, 50 × 50, and 100 × 100 cm) and three hydraulic boundary conditions (three initial water ponding depths: 1.5, 2.5, and 5.0 cm at the soil surface). The random cascade model with a lognormal distribution was used to simulate the infiltration process in soils and different methods were applied to estimate the model parameters. Results based on the experimental data and the model simulations showed that the hydraulic boundary condition and the measurement scale were important factors to affect the flow patterns in soils. To accurately describe flow transport processes at different scales, it was necessary to consider heterogeneities in the vertical and horizontal directions. As the measurement scale increased, the effect of multi-dimensional heterogeneities on the flow processes in soils became more significant. Interdependency between flow paths also increased with the scale.