Research on the change in soil water repellency and permeability in burned areas

Forest fire always results in the newly occurrence (or enhancement) of soil water repellency (SWR), and subsequent reduction in soil infiltration. It dramatically increases the surface runoff rate of a drainage basin. Under certain situation, especially the mountain area with high altitude and steep terrain, augmented surface runoff usually infiltrates the generation of debris flows. But little is known about the distribution of SWR and change in soil permeability in areas with high altitude. Based on the burned area with altitude ranging from 3029 to 4474 m in the Egu village of Yajiang county in Sichuan province, a set of water drop penetration tests and disk infiltration measurements are conducted to study the fire influence on distribution of the severity of SWR and soil permeability. The results indicate that great spatial heterogeneity of Hydrophobic strength of soil exists, and the influence depth of fire impact on SWR is up to 2 cm in the slightly burned area and 3 cm in the moderately and highly burned area. Soil permeability is inversely linked to the severity of water repellency, and the relationship between water drop penetration time and sorptivity and hydraulic conductivity of soil fallow the law of power function. The coefficient of variation in infiltration parameters increases with fire intensity, and part of the severely burned soil loses water repellency due to high temperature in fire and results in increase of saturated hydraulic conductivity. In contrast to hydrophilic soil, an obviously delay in infiltration is found find in the hydrophobic soil. The results of this work enrich the study of hydrological feature in burned areas and can provide the theoretical basis for the motivation of surface material in debris flow generation.