Flux and Water Content Relation at the Soil Surface
1985
Parlange, J.-Y. | Hogarth, W. L. | Boulier, J. F. | Touma, J. | Haverkamp, R. | Vachaud, G.
A general analytical equation is presented which relates the surface water content and surface flux. The result is obtained for general soil properties and arbitrary dependence of the flux on time. The equation is approximate but optimal at least in the short time limit. Its accuracy is assessed by comparison with numerical and experimental results for Grenoble sand and when the surface flux is constant. The analytical and numerical results differ by a small amount which would however be significant if the analytical result was used to predict the time at which a certain water content is reached at the surface, for instance the value of time at ponding. It is shown that the numerical solution has an intrinsic error in the short time limit. This suggests that the analytical result may be more accurate than the numerical solution. This is reinforced by the good agreement between the numerical results and an earlier approximate analytical solution which is known to be often inaccurate, for instance if it is used to estimate the value of the sorptivity. Finally, careful experimental observation shows closer agreement with the analytical result than with the numerical solution.
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