Evidence from a number of field sites suggests that water seepage through fractured unsatu- rated zones may proceed, in part, by means of fast preferential flow paths. This paper presents conceptual and numerical models which aim at developing an understanding of water seepage behavior in such media, and exploring conditions for fast preferential flow. Water seepage has been numerically simulated in heterogeneous fractures, which were conceptualized as two-dimen- sional heterogeneous porous media. Flow was found to proceed in dendritic patterns along preferential paths, giving rise to such features as localized ponding and bypassing.
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