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| Titel |
Drainage effects on the transient, near-surface hydrologic response of a steep hillslope to rainfall: implications for slope stability, Edmonds, Washington, USA |
| VerfasserIn |
G. Biavati, J. W. Godt, J. P. McKenna |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1561-8633
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| Digitales Dokument |
URL |
| Erschienen |
In: Natural Hazards and Earth System Science ; 6, no. 3 ; Nr. 6, no. 3 (2006-05-11), S.343-355 |
| Datensatznummer |
250003498
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| Publikation (Nr.) |
 copernicus.org/nhess-6-343-2006.pdf |
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| Zusammenfassung |
| Shallow landslides on steep (>25°) hillsides along Puget Sound have
resulted in occasional loss of life and costly damage to property during
intense or prolonged rainfall. As part of a larger project to assess
landslide hazards in the Seattle area, the U.S. Geological Survey
instrumented two coastal bluff sites in 2001 to observe the subsurface
hydrologic response to rainfall. The instrumentation at one of these sites,
near Edmonds, Washington, consists of two rain gauges, two water-content
probes that measure volumetric water content at eight depths between 0.2 and
2.0 m, and two tensiometer nests that measure soil-water suction at six
depths ranging from 0.2 to 1.5 m. Measurements from these instruments are
used to test one- and two-dimensional numerical models of infiltration and
groundwater flow. Capillary-rise tests, performed in the laboratory on soil
sample from the Edmonds site, are used to define the soil hydraulic
properties for the wetting process. The field observations of water content
and suction show an apparent effect of porosity variation with depth on the
hydraulic response to rainfall. Using a range of physical properties
consistent with our laboratory and field measurements, we perform
sensitivity analyses to investigate the effects of variation in physical and
hydraulic properties of the soil on rainfall infiltration, pore-pressure
response, and, hence, slope stability. For a two-layer-system in which the
hydraulic conductivity of the upper layer is at least 10 times greater than
the conductivity of the lower layer, and the infiltration rate is greater
than the conductivity of the lower layer, a perched water table forms above
the layer boundary potentially destabilizing the upper layer of soil.
Two-dimensional modeling results indicate that the addition of a simple
trench drain to the same two-layer slope has differing effects on the
hydraulic response depending on the initial pressure head conditions. For
slope-parallel flow conditions, pressure head is significantly reduced near
the drain; however, for transient, vertical infiltration in a partially
saturated soil, conditions consistent with those observed during monitoring
at the Edmonds site, the drain decreases the thickness of a perched water
table by a small amount. |
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