1999 Fiscal Year Final Research Report Summary
Fingered flow occurred in the unsaturated soil
| Project/Area Number |
09660263
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Irrigation, drainage and rural engineering/Rural planning
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| Research Institution | Saga University |
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Principal Investigator |
CHO Hiroyuki Department of Agricultural Sciences, Saga University, Assistant Professor, 農学部, 助手 (90136599)
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| Co-Investigator(Kenkyū-buntansha) |
INOUE Mitsuhiro Tottori Univ., Arid Land Research Center, Associate Professor, 乾燥地研究センター, 助教授 (90032309)
TORIDE Nobuo Department of Agricultural Sciences, Saga University, Associate Professor, 農学部, 助教授 (70212074)
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| Project Period (FY) |
1997 – 1999
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| Keywords | unsaturated soil / preferential flow / wetting front / fingered flow / glass beads / water retention curve / water movement / solute transportation |
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| Research Abstract |
When fingered flow occurs during ponding infiltration in a fine-coarse-textured profile, a thin wet zone forms directly below the textural interface (induction zone). During the onset of wetting front instability, a thin induction zone develops from which many small fingers grow initially. Subsequently, a few of these fingers become dominant; they continue to grow at the expense of the remaining fingers which stagnate. Two possible mechanisms govern this process: (1) the pressure head gradient required to laterally transport water from any location at the soil surface to the nearest finger is such that the water entry value of the dry soil is exceeded at some distance from a finger, thus causing another finger to fully develop at that point, and (2) the flux density strongly amplified wavelength of perturbations of the wetting front or the pressure head. Finger spacing in the former case is determined by the properties of the induction zone, and in the latter case by the flux conducted by an individual finger as well as the water supply rate.
In order to investigate flow in the induction zone, and nature and extent of the interaction between the induction zone and the fingers, we performed two-dimensional experiments using a glass-bead porous medium. Pressure heads in the induction zone and the fingers were monitored by microtensiometers. We made small disturbances (notches) at various intervals in the textural interface to trigger finger formation and change the number of fingers occurring at first.
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