"Phreatic Zone". Encyclopædia Britannica. Retrieved 7 June 2012.
drgan.org
Dynamics of Drainage and Viscous Fingering
in Transport in Porous Media Note that zones "behind" the drainage front are areas on the 'dry' (low-viscosity) (typically above / beyond the 'wet' zone).
thefreedictionary.com
"Phreatic Zone". TheFreeDictionary.com. Retrieved 7 June 2012.