When is porous-media flow preferential? A hydromechanical perspective

Both, preferential flow and dispersive flow (the latter is usually expressed with the Darcy-Richards Equations) are approached with kinematic wave theory. The kinematic wave assumption, iota = beta gamma(alpha) (where iota [LT(-1)] is volume flux density, beta [LT(-1)] is conductance, gamma [L(3)L(-3)] is moisture participating in the flow process, and alpha is a dimensionless exponent) is validated against data from an infiltration-drainage experiment, performed on a reconstituted soil sample containing artificial macropores. It is proposed that the exponent alpha may serve as a measure to assess the degree of preferential flow. The model is then applied to four hydrographs obtained from infiltration-drainage experiments at various rates, using a dual-porosity medium made of artificial soil aggregates. The exponent alpha decreased with increasing application rates of water input to the surface, indicating the dynamic aspect of preferential flow.