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Approximate Soil Water Movement by Kinematic Characteristics
Author(s) -
Smith Roger E.
Publication year - 1983
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1983.03615995004700010001x
Subject(s) - kinematic wave , kinematics , richards equation , péclet number , flow (mathematics) , mechanics , nonlinear system , diffusion , convection , soil water , movement (music) , water flow , mathematics , geotechnical engineering , geology , mathematical analysis , soil science , physics , classical mechanics , thermodynamics , surface runoff , ecology , quantum mechanics , biology , acoustics
Using the Richard's equation in the Fokker‐Planck nonlinear diffusion form, unsaturated soil water flow may be treated as a diffusion‐convection wave process. If ∂θ/∂z is assumed a function of θ alone, the unsaturated flow equation may be solved by the method of characteristics, and when ∂θ/∂z becomes sufficiently small, the Peclet number is assumed large enough to treat unsaturated flow kinematically. Changes in θ with depth in the soil profile are treated as waves, moving downward. Advancing and receding “waves” are treated differently in the approximate analytical technique described here, with advancing wetting fronts described by kinematic “shocks.” The method is compared to the complete solution to Richard's equation for a complex rain pattern and found to predict well the location of deeper moving fronts and also general θ patterns. The kinematic method is also shown to apply to root water extraction zones and to layered soil situations.