I've been reading the Van Genuchten parameters, and it seems like S_s is set to (usually) the porosity of the medium.
e.g. Sand, S_s = 0.43, S_r = 0.045
The online FEFLOW help has default parameters of S_s = 1 and S_r = 0.0025
(http://www.feflow.info/html/help71/feflow/mainpage.htm#t=09_Parameters%2FMaterial_Properties%2Fflow_parameters.html)
Does the FEFLOW value account for porosity, or how does it actually work...?