Simulating Funnel‐Type Preferential Flow and Overall Flow Property Induced by Multiple Soil Layers

Abstract

AbstractFunnel‐type preferential flow was observed in Plainfield sand (sandy, mixed, mesic Typic Udipsamment) of central Wisconsin. The objective of this paper was (i) to develop a numerical model based on the Richards equation and finite element scheme to simulate this preferential flow in a soil profile with inclined layers, and (ii) to determine flow properties in a soil with funnel‐type preferential paths. The model was first validated by testing against two‐dimensional (2‐D) laboratory results and then used to simulate water flow patterns in hypothetical 2D soil profiles made of medium sand with multiple randomly distributed, inclined coarse layers. The following results were found from the numerical experiments; (i) funnel‐type preferential flow paths could be deterministically simulated if soil layering structure, hydraulic conductivity of the overall profile, and threshold potential of the embedded coarse layers were known; (ii) distribution of the vertical component of flux was determined by the funneling effect along the upper coarse sand lenses. The lenses located in deeper parts of the profile would only influence macrotortuosity of the preferential flow paths; (iii) funnel‐type preferential flow paths were determined not only by soil structures and textures but also by water application rate; and (iv) although funnel‐type preferential paths were very complex, the vertical component of flux could be very simply described by two stochastic parameters—the mean and standard deviation of a log‐normal distribution after the flow paths became stationary.