Viscosity—The weak link between Darcy's law and Richards' capillary flow |
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| Authors: | Peter F Germann |
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| Affiliation: | Geography Department, University of Bern, Bern, Switzerland |
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| Abstract: | Preferential flow, a term that includes macropore flow, non‐equilibrium flow, and finger flow, stands in well known conflict with Richards' ( 1931 ) capillary flow. Acoustic velocity experiments demonstrate that preferential flow moves independently from, faster than, and before capillary flow during gravity‐driven infiltration. Viscous flow in permeable media is briefly introduced to the point where Richards' ( 1931 ) particular treatment of viscosity turns out as the hydro‐mechanical bifurcation from general laminar flow. Preferential flow is expected during significant infiltration, however, spatio‐temporarily limited according to the viscous‐flow regime. Two ways of delineating capillary flow from viscous flow reveal minimum path widths of preferential flow in the range of about 20 μm. |
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| Keywords: | capillary flow non‐equilibrium flow preferential flow viscous flow |
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