File talk:Wrc.svg

Plots seem to be based on wrong equation

Five years ago somebody noticed at de:Diskussion:Bodenwasserspannung#Diagrammbeschriftung that the curves in this figure are at least one order of magnitude off. I tried to reproduce the graphs based on the equation and parameters given in the reference:
Ad-hoc-AG Boden (2004-09-17). Verknüpfungsregel 1.18 – Parameter für das Modell einer stetigen Funktion der θ(ψ)-Beziehung (in German) (PDF, 242 KiB). Staatlichen Geologischen Dienste und BGR. Retrieved on 2015-07-29.
and I my graphs look completely different. I also checked that the equation in this reference coincides with Eq. [2] and [3] from the original paper by M. Th. van Genuchten from 1980. Then I realized that the equations given here in the file description here are wrong: because of $x\cdot \exp(m)\neq x^{m}$ they are not the same as in the reference – and this is a bigger problem than just a matter of scaling. With this wrong equation I can reproduce the behaviour in this file, which makes me feel sure that this figure is based on the wrong equation. I'm going to generate a new SVG-file with en:GNU Octave based on the equation from the reference and upload my version as a new file to Commons. Or should I rather upload my file as a new version of this file? --DufterKunde (トーク) 22:23, 3 August 2015 (UTC)

I've discussed this issue with the original author via e-mail and created a corrected version from the scratch. I just uploaded this new version and also fixed the typo in the description of the formula. Qualitatively, the new plot also matches the printed diagrams in textbooks as for example Karl-Heinrich Hartge, Rainer Horn (1999), “Abschnitt 4.4–4.6, insbes. Abb 4.9”, in Einführung in die Bodenphysik, 3rd edition, Stuttgart: Ferdinand Enke Verlag, ISBN 3-432-89683-2, pages 130 much better than the old one. --DufterKunde (トーク) 15:54, 13 August 2015 (UTC)