On water seepage and fast preferential flow in heterogeneous,unsaturated rock fractures
Evidence from a number of field sites suggests that waterseepage through fractured unsaturated zones may proceed, in part, bymeans of fast preferential flow paths. This paper presents conceptual andnumerical models which aim at developing an understanding of waterseepage behavior in such media, and exploring conditions for fastpreferential flow. Water seepage has been numerically simulated inheterogeneous fractures, which were conceptualized as two-dimensionalheterogeneous porous media. Flow was found to proceed in dendriticpatterns along preferential paths, giving rise to such features aslocalized pending and bypassing. Fast preferential flow can occur from'external' (non-uniform boundary conditions) or 'internal' mechanisms(heterogeneities), or a combination thereof. A most effective conditionfor fast preferential flow is the presence of sub-horizontal barriers ofsignificant length. Limited parameter variation studies have shown strongdependence of seepage patterns on fracture permeability and applied flowrate. The temporal evolution of seeps proceeds on a vast range of timescales. This casts doubt on the applicability of steady-state conceptsfor water migration in unsaturated zones of fractured rock whereinfiltration is episodic. An approximate invariance of seepage behaviorwas derived for simultaneous space-and-time scaling, suggesting thatseepage patterns should appear more vertically elongated as the scale ofobservation is increased. Numerical simulation experiments have confirmedthis invariance, as well as its limits of applicability.
- Research Organization:
- Ernest Orlando Lawrence Berkeley NationalLaboratory, Berkeley, CA (US)
- Sponsoring Organization:
- USDOE Director, Office of Science
- DOE Contract Number:
- AC02-05CH11231
- OSTI ID:
- 902127
- Report Number(s):
- LBNL--38883
- Journal Information:
- Journal of Contaminant Hydrology, Journal Name: Journal of Contaminant Hydrology Journal Issue: 3-4 Vol. 30; ISSN JCOHE6; ISSN 0169-7722
- Country of Publication:
- United States
- Language:
- English
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