Modeling plot scale dye penetration by a diffusion limited aggregation (DLA) model

Solute transport in the unsaturated zone often occurs in preferential flow paths. There are several reasons for this, e.g., water repellency, the occurrence of fissures and cracks, animal burrows, decomposed root threads etc. The resulting flow patterns often display a fractal resemblance which is difficult to predict using conventional transport models. A way to preserve the fractal property of observed data is to use the diffusion limited aggregation (DLA) model concept. In the present paper we use dye infiltration data to further develop the DLA model concept as applied to solute movement in soils. The DLA model is first calibrated against detailed field observations of dye infiltration. The model is shown to give a good description of observed mean and variance of dye penetration. After this, the calibrated model is verified against independent data from a nearby plot. The model is shown to reproduce observed dye patterns in a satisfactory way also at the verification plot.