Osmosis: A cause of apparent deviations from Darcy's law

Recent evidence for deviations from Darcy's law at very low gradients provides a reminder that the origin of similar deviations reported during the last three decades has not been fully clarified. In most of these studies, the potential significance of osmosis was not considered. This review of the existing evidence shows that osmosis causes intercepts in flow rate versus hydraulic gradient relationships that are consistent with the observed deviations from Darcy's law at very low gradients. Moreover, it is suggested that a natural cause of osmosis in laboratory samples could be chemical reactions such as those involved in aging effects. This hypothesis is analogous to the previously proposed occurrence of electroosmosis in nature generated by geochemical weathering reactions.