The effect of fracture properties on preferential flow in carbonate-derived laterite from karst mountainous agroforestry lands

Karst mountainous agroforestry significantly enhances the formation of soil fractures. However, there are still some uncertainties regarding the effects of these soil fractures on water flow in carbonate-derived laterite. Therefore, a series of laboratory column infiltration and blue dye-tracing experiments were designed to evaluate the effects of fracture burial depth (15, 25, 35 cm), configuration (V: V shape; 1: vertical bar shape) and inclusions (S: sand grain; R: rock fragment) on preferential flow processes in carbonate-derived laterite. The Green-Ampt model with effective hydraulic conductivity was applied to determine the hydraulic properties of soils containing fractures. The results show that the fracture configuration had a larger influence on the soil infiltration, while the responses of soil infiltration were not sensitive to the fracture burial depth. In the 1R15 treatment, the dye distribution was not uniform, as evidenced by two significantly different staining regions. All three parameters (dye coverage, uniform infiltration depth, and preferential flow fraction) to quantify the contribution of preferential flow showed that the preferential flow fraction was highest in the 1R15 treatment. Furthermore, Brilliant Blue was not a suitable quantitative tracer for water movement in carbonate-derived laterite that contains fractures. The effects of the fracture properties, including configuration and inclusions, on preferential flow cannot be neglected for karst mountainous agroforestry land management.