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Surface‐zone flow along unsaturated rock fractures
Author(s) -
Tokunaga Tetsu K.,
Wan Jiamin
Publication year - 2001
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/2000wr900242
Subject(s) - imbibition , geology , permeability (electromagnetism) , geotechnical engineering , fracture (geology) , flow (mathematics) , wetting , saturation (graph theory) , petrology , water flow , vadose zone , relative permeability , porosity , mineralogy , materials science , mechanics , composite material , groundwater , chemistry , biochemistry , botany , germination , physics , mathematics , combinatorics , membrane , biology
Although fractures in rock are well recognized as pathways for fast percolation of water, processes which permit fast flow along unsaturated fracture pathways remain to be identified and understood. Earlier aperture‐based models of flow in partially saturated fractures permit fast flow only through a continuous network of locally saturated segments. Film flow was recently identified as a mechanism capable of sustaining fast flow along truly unsaturated fractures when the matric potential is very close to zero. Another mechanism for fast flow along unsaturated fractures is introduced in this study, “surface‐zone flow,” which can be important when the permeability of the rock along fractures (fracture skin) is significantly greater than that of the bulk rock matrix. In such systems the fracture surface zone provides low resistance pathways through which fast flow (relative to the bulk matrix rock) can occur, even when the fractures are at very low water saturation. Initial experimental tests of surface‐zone fast flow were performed. Surface‐zone fast imbibition of water was measured on a welded tuff and a rhyolite. However, because (1) imbibition rates are also strongly influenced by rock wettability, (2) these initially air‐dry rocks exhibited finite contact angles upon exposure to water, and (3) we lack methods to reliably measure permeabilities of thin regions on rock surfaces, quantification of permeability contrasts was not possible in these initial tests.