HR: 10:55h
AN: H22B-03    [Abstracts]
TI: Infiltration Flow Path Distributions in Unsaturated Rocks
AU: * Tokunaga, T K
EM: tktokunaga@lbl.gov
AF: Lawrence Berkeley National Laboratory, 1 Cyclotron Road, ms 70-108B, Berkeley, CA 94720 United States
AU: Olson, K R
AF: Lawrence Berkeley National Laboratory, 1 Cyclotron Road, ms 70-108B, Berkeley, CA 94720 United States
AU: Wan, J
AF: Lawrence Berkeley National Laboratory, 1 Cyclotron Road, ms 70-108B, Berkeley, CA 94720 United States
AB: Spatial distributions of infiltration flow paths through rock formations are complex networks that determine flow velocities, control rates of natural geochemical reactions in the subsurface, as well as rates of contaminant transport to underlying groundwater. Despite these important consequences, distributions of infiltration paths and locally fast seepage rates through rocks are not well understood. Laboratory-based studies on fractured rocks cannot easily be conducted on systems large enough to include sufficient fracture network complexity, so that inferences of field-scale flux distributions cannot be reliably made. Field-based studies to date have permitted quantification of only a small fraction of the flow distribution, typically while imposing extremely high fluxes, and therefore have not allowed comprehensive delineation of flow distributions expected under natural recharge. Based on hydraulic scaling considerations, we hypothesize that unsaturated flow path distributions in rock deposits will be similar to those occurring in fractured rock formations under low overall infiltration rates. Talus rock deposits and mine waste rock piles control flow and transport into their respective underlying groundwaters. All of these reasons motivated infiltration experiments in rock packs. Experiments have been conducted on 4 different rock types and system scales ranging from 1 to 46 rock layers. Our experiments showed that infiltration through rocks conforms to no previously reported behavior in soils, and that flow paths do not progressively converge into fewer and fewer flow paths. Instead, a fundamentally different hydraulic structure develops, having an exponential (geometric) flux distribution, with the characteristic scale determined by the characteristic rock size. Although the phenomena are very different, the evolution of flow path distributions and local seepage rate distributions is predictable based on a statistical mechanical model for energy distributions. Our experiments and model are consistent with the available data on natural recharge flow paths in deep unsaturated fracture rocks at Yucca Mountain. Funding of this study was provided by the Geosciences Research Program, Basic Energy Sciences, U.S. Department of Energy.
DE: 1831 Groundwater quality
DE: 1848 Networks
DE: 1875 Unsaturated zone
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting