No abstract

Preferential flow is common in clay or expansive clay soils, involving water bypassing a large portion of the soil matrix. Dye tracer experiment and numerical modeling are used to simulate the surface runoff and subsurface preferential flow patterns influenced by the soil fracture network of a relatively steep hillslope system (slope angle equals to 10 degrees). The result of the experiments indicates that part of the water is infiltrated through cracks, leading to the delay of the initial runoff-yielding time and reduction of the discharge of the surface runoff. The soil water flow is mainly in the matrix when the intensity of precipitation is low. With the increasing of precipitation, soil water movement may become in the form of preferential flow through cracks. In addition, the nonuniformity of soil water infiltration and the depth of the average water infiltration increase as the precipitation intensity increases. To this end, the complete coupling model was established by using the surface-matrix-crack (SMC) model to simulate water flow within discrete fracture as well as to simulate water flow in the soil matrix based on the concept of dual permeability using the traditional Richards' equation. In this model, the "cubic law" of fluid motion in cracks within smooth parallel plates and the two-dimensional diffusion wave approximation to Saint-Venant equations with momentum term ignored (two-dimensional shallow water equations) were used. The model divides soil water infiltration into two forms and uses the overall method to calculate the exchange of water between the crack networks and matrix regions as well as the exchange water between surface runoff and infiltration water. Results indicate that the SMC model has better performance compared with the traditional equivalent continuum model when those models are used to simulate the surface runoff movement and the soil water movement in the presence of cracks.

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.

No abstract

According to the available geological data and monitoring data, the completely weathered phyllite slope dilates and softens under the condition of continuous rainfall, which is then prone to instability failure. The indoor artificial rainfall test was carried out through the construction of the slope model, and the soil moisture sensor, pore water pressure sensor and matric suction sensor were used to study the variation laws of moisture content, pore water pressure and infiltration line at the back edge, slope body and the foot of the slope under continuous heavy rainfall. According to the sensor data and recorded information, with the influence of heavy rainfall over a long period of time, the water content and pore water pressure increased firstly, then decreased, and finally stabilized. The infiltration line moved from the top, the surface and the foot of the slope to the slope body, and shallow slip failure occurred in the shallow layer of the slope body., 0 Web of Conferences https://doi.org/10.