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| Titel |
Geostatistical investigation into the temporal evolution of spatial structure in a shallow water table |
| VerfasserIn |
S. W. Lyon, J. Seibert, A. J. Lembo, M. T. Walter, T. S. Steenhuis |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 10, no. 1 ; Nr. 10, no. 1 (2006-02-15), S.113-125 |
| Datensatznummer |
250007919
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| Publikation (Nr.) |
 copernicus.org/hess-10-113-2006.pdf |
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| Zusammenfassung |
| Shallow water tables near-streams often lead to saturated, overland flow
generating areas in catchments in humid climates. While these saturated
areas are assumed to be principal biogeochemical hot-spots and important for
issues such as non-point pollution sources, the spatial and temporal
behavior of shallow water tables, and associated saturated areas, is not
completely understood. This study demonstrates how geostatistical methods
can be used to characterize the spatial and temporal variation of the
shallow water table for the near-stream region. Event-based and seasonal
changes in the spatial structure of the shallow water table, which
influences the spatial pattern of surface saturation and related runoff
generation, can be identified and used in conjunction to characterize the
hydrology of an area. This is accomplished through semivariogram analysis
and indicator kriging to produce maps combining soft data (i.e., proxy
information to the variable of interest) representing general shallow water
table patterns with hard data (i.e., actual measurements) that represent
variation in the spatial structure of the shallow water table per rainfall
event. The area used was a hillslope in the Catskill Mountains region of New
York State. The shallow water table was monitored for a 120 m×180 m
near-stream region at 44 sampling locations on 15-min intervals. Outflow
of the area was measured at the same time interval. These data were analyzed
at a short time interval (15 min) and at a long time interval (months)
to characterize the changes in the hydrologic behavior of the hillslope.
Indicator semivariograms based on binary-transformed ground water table data
(i.e., 1 if exceeding the time-variable median depth to water table and 0 if
not) were created for both short and long time intervals. For the short time
interval, the indicator semivariograms showed a high degree of spatial
structure in the shallow water table for the spring, with increased range
during many rain events. During the summer, when evaporation exceeds
precipitation, the ranges of the indicator semivariograms decreased during
rainfall events due to isolated responses in the water table. For the
longer, monthly time interval, semivariograms exhibited higher sills and
shorter ranges during spring and lower sills and longer ranges during the
summer. For this long time interval, there was a good correlation between
probability of exceeding the time-variable median water table and the soil
topographical wetness index during the spring. Indicator kriging
incorporating both the short and long time interval structure of the shallow
water table (hard and soft data, respectively) provided more realistic maps
that agreed better with actual observations than the hard data alone. This
technique to represent both event-based and seasonal trends incorporates the
hillslope-scale hydrological processes to capture significant patterns in
the shallow water table. Geostatistical analysis of the spatial and temporal
evolution of the shallow water table gives information about the formation
of saturated areas important in the understanding hydrological processes
working at this and other hillslopes. |
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