A study of preferential flow in heterogeneous media using random walk particle tracking

We investigated the onset of preferential flow in heterogeneous porous media using the random walk particle tracking (RWPT) concept. The RWPT model is first used to analyze empirically the required number of particles to achieve accurate concentration distributions in two-dimensional homogeneous media and under uniform flow conditions. The analysis is then extended to randomly heterogeneous systems. By increasing the variance of log-normal hydraulic conductivity fields, the transition between homogeneous and preferential flows is observed. To analyze the degree of preferential flow in the porous media, we provide a diagram that consists of two dimensionless parameters: normalized travel time and distance. All the heterogeneous media synthetically generated show a linear relation in the diagram. The characteristic travel velocity increases with increasing heterogeneity. We found the diagram is a useful tool to analyze preferential flow.