Abstract: Preferential flow is a common flow pattern of infiltrated rain and irrigated water in unsaturated soils, and characterizing preferential flow is always a hot topic of soil hydrology researches. In this research, the wavelet packet entropy, including the Shannon entropy and logarithmic energy entropy, was used to characterizing the preferential flow heterogeneity under different infiltration conditions. The research results were compared with those characterized by matrix entropy and fractal characteristic parameter to show the feasibility of applying wavelet packet analysis to preferential soil water flow. The results show that: 1) the wavelet packet entropy is capable of characterizing the heterogeneity of preferential flow patterns; 2) the heterogeneity of preferential flow increases firstly and then decreases as the infiltration amount increases; 3) the heterogeneity of preferential flow increases steadily as the experimental scale increases within this research.

Key words: preferential flow in soil, wavelet packet entropy, experiment scale, heterogeneity, dye tracer