Simple predictions of maximum transport rate in unsaturated soil and rock
Article first published online: 22 MAY 2007
Copyright 2007 by the American Geophysical Union.
Water Resources Research
Volume 43, Issue 5, May 2007
How to Cite
2007), Simple predictions of maximum transport rate in unsaturated soil and rock, Water Resour. Res., 43, W05426, doi:10.1029/2006WR005372.(
- Issue published online: 22 MAY 2007
- Article first published online: 22 MAY 2007
- Manuscript Accepted: 21 FEB 2007
- Manuscript Revised: 12 FEB 2007
- Manuscript Received: 24 JUL 2006
- Unsaturated zone;
- vadose zone;
- preferential flow
 In contrast with the extreme variability expected for water and contaminant fluxes in the unsaturated zone, evidence from 64 field tests of preferential flow indicates that the maximum transport speed Vmax, adjusted for episodicity of infiltration, deviates little from a geometric mean of 13 m/d. A model based on constant-speed travel during infiltration pulses of actual or estimated duration can predict Vmax with approximate order-of-magnitude accuracy, irrespective of medium or travel distance, thereby facilitating such problems as the prediction of worst-case contaminant traveltimes. The lesser variability suggests that preferential flow is subject to rate-limiting mechanisms analogous to those that impose a terminal velocity on objects in free fall and to rate-compensating mechanisms analogous to Le Chatlier's principle. A critical feature allowing such mechanisms to dominate may be the presence of interfacial boundaries confined by neither solid material nor capillary forces.