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A simple treatment of physical nonequilibrium water flow in soils
Journal article   Peer reviewed

A simple treatment of physical nonequilibrium water flow in soils

P.J. Ross and K.R.J. Smettem
Soil Science Society of America Journal, Vol.64(6), pp.1926-1930
2000
DOI: https://doi.org/10.2136/sssaj2000.6461926x
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Abstract

Water flow in soils with sufficiently large aggregate size or pore-class heterogeneity may exhibit a nonequilibrium between the actual water content and that given by the water retention curve. The result is deeper penetration of infiltrating water than predicted using classical infiltration theory. Models of this process usually divide the soil into two or more exchanging flow regions. A simpler treatment is possible by combining Richards' equation with a dynamic description of the approach to equilibrium. We present a first-order time constant equilibration model of infiltration into a hypothetical structured soil and use the model to describe published outflow responses to constant rate rainfall on six large, undisturbed cores. Using measured hydraulic properties and varying only the A and B horizon time constants, the model was fitted to cumulative outflow from one particular soil core that had measured time domain reflectometry (TDR) water contents at the 0.05- and 0.5-m depths recorded during the experiment. Cumulative outflow was fitted using time constants of 4 and 5 h for A and B horizons, respectively, and this also gave good agreement with TDR measured water contents. Cumulative outflow and runoff from a further four of the six cores was described using the same A and B horizon time constants and varying only the macropore hydraulic conductivity. The remaining core contained a decayed root, which conducted water rapidly with little opportunity for lateral exchange. A description of cumulative outflow required both the macropore hydraulic conductivity and the time constant to be altered.

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Collaboration types
Domestic collaboration
Citation topics
7 Engineering & Materials Science
7.133 Geotechnical Engineering
7.133.986 Unsaturated Soil Mechanics
Web Of Science research areas
Soil Science
ESI research areas
Agricultural Sciences
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