Experimental and numerical simulation of water movement in soil

Preferential flow refers to a flow transport pattern where water and solute flows around the soil matrix, contributing to accelerating velocity of movement in the soil; soil recharge occurs over the whole inlet boundary. Preferential flow is produced by a large number of macropores and fractures in the soil, such as root or worm holes, and is very important to groundwater recharge owing to its rapid movement. Using the reaction of iodine turning blue on contact with starch, outdoor tracer experiments of heterogeneous flow in clay loam for different scales and boundary conditions are designed, so that the heterogeneous flow patterns can be studied. Using experimental image analysis, the soil is divided into a matrix and a preferential channel network, formed by the spatial structure of the flow channels. An irregular flow network is established through random generation of angles, lengths, aperture and location coordinates of flow channels, in order to achieve an accurate description of preferential flow channels. According to the soil moisture of each layer obtained by tracer experiments, soil water retention curve and saturated hydraulic conductivity, soil moisture variation was simulated. The distribution of the channel network and models of water movement in the soil are used to undertake a quantitative analysis of the influence of preferential flow on soil water migration.