SIMULATING FUNNEL-TYPE PREFERENTIAL FLOW AND OVERALL FLOW PROPERTY INDUCED BY MULTIPLE SOIL LAYERS

Funnel-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 pr operties in a soil with funnel-type preferential paths. The model was first validated by testing against two-dimensional (2-D) laboratory re sults 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 num erical experiments: (i) funnel-type preferential flow paths could be d eterministically simulated if soil layering structure, hydraulic condu ctivity of the overall profile, and threshold potential of the embedde d coarse layers were known; (ii) distribution of the vertical componen t of flux was determined by the funneling effect along the upper coars e 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 s tructures and textures but also by water application rate; and (iv) al though funnel-type preferential paths were very complex, the vertical component of flux could be very simply described by two stochastic par ameters - the mean and standard deviation of a log-normal distribution after the flow paths became stationary.