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Traditional and New Methods to Describe Multimodal Soil Water Characteristics

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Pp. 181-184 in Preferential Flow, Water Movement and Chemical Transport in the Environment, Proc. 2nd Int. Symp. (3-5 January 2001, Honolulu, Hawaii, USA), eds. D. D. Bosch and K. W. King. St. Joseph, Michigan: ASAE  701P0006.(doi:10.13031/2013.2110)
Authors:   F. Kastanek
Keywords:   Multimodal soil water characteristics, spline interpolation, soil water hydrology

The first step to describing soil water behavior by differential equations frequently consists of the representation of the relationship between soil-water-content and soil-matric-potential (soil water characteristic) by a mathematical functional relationship. For proper shaped (unimodal) curves the van Genuchten equation and for some kinds of special curves the Brooks and Corey equation show excellent fit. But there are same examples (bimodal shaped soil water characteristics) with questionable results. To overcome discrepancies between measured data and approximation by traditional equations, considerable improvement was achieved by the introduction of the concept of superimposing more (two or three) van Genuchten equations - the multi-van Genuchten model. But there are some more alternatives for superimposing different equations which show reasonable results. Moreover splines have been proposed some time ago, but they have not been accepted till now. The introduction of a new concept applying virtual data points makes the splines the most versatile method for circumstances where other methods fail.

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