Effect of isolated fractures on accelerated flow in unsaturated porous rock
Article first published online: 2 DEC 2003
Copyright 2003 by the American Geophysical Union.
Water Resources Research
Volume 39, Issue 12, December 2003
How to Cite
2003), Effect of isolated fractures on accelerated flow in unsaturated porous rock, Water Resour. Res., 39, 1326, doi:10.1029/2002WR001691, 12., , and (
- Issue published online: 2 DEC 2003
- Article first published online: 2 DEC 2003
- Manuscript Accepted: 17 SEP 2003
- Manuscript Revised: 25 AUG 2003
- Manuscript Received: 27 AUG 2002
- unsaturated flow;
- fractured rock;
- preferential flow
 Fractures that begin and end in the unsaturated zone, or isolated fractures, have been ignored in previous studies because they were generally assumed to behave as capillary barriers and remain nonconductive. We conducted a series of experiments using Berea sandstone samples to examine the physical mechanisms controlling flow in a rock containing a single isolated fracture. The input fluxes and fracture orientation were varied in these experiments. Visualization experiments using dyed water in a thin vertical slab of rock were conducted to identify flow mechanisms occurring due to the presence of the isolated fracture. Two mechanisms occurred: (1) localized flow through the rock matrix in the vicinity of the isolated fracture and (2) pooling of water at the bottom of the fracture, indicating the occurrence of film flow along the isolated fracture wall. These mechanisms were observed at fracture angles of 20 and 60 degrees from the horizontal, but not at 90 degrees. Pooling along the bottom of the fracture was observed over a wider range of input fluxes for low-angled isolated fractures compared to high-angled ones. Measurements of matrix water pressures in the samples with the 20 and 60 degree fractures also demonstrated that preferential flow occurred through the matrix in the fracture vicinity, where higher pressures occurred in the regions where faster flow was observed in the visualization experiments. The pooling length at the terminus of a 20 degree isolated fracture was measured as a function of input flux. Calculations of the film flow rate along the fracture were made using these measurements and indicated that up to 22% of the flow occurred as film flow. These experiments, apparently the first to consider isolated fractures, demonstrate that such features can accelerate flow through the unsaturated zone and should be considered when developing conceptual models.