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| Titel |
Characteristics and controls of variability in soil moisture and groundwater in a headwater catchment |
| VerfasserIn |
H. K. McMillan, M. S. Srinivasan |
| 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 ; 19, no. 4 ; Nr. 19, no. 4 (2015-04-17), S.1767-1786 |
| Datensatznummer |
250120682
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| Publikation (Nr.) |
 copernicus.org/hess-19-1767-2015.pdf |
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| Zusammenfassung |
Hydrological processes, including runoff generation, depend on the
distribution of water in a catchment, which varies in space and time. This
paper presents experimental results from a headwater research catchment in
New Zealand, where we made distributed measurements of streamflow, soil
moisture and groundwater levels, sampling across a range of aspects,
hillslope positions, distances from stream and depths. Our aim was to assess
the controls, types and implications of spatial and temporal variability in
soil moisture and groundwater tables.
We found that temporal variability in soil moisture and water table is
strongly controlled by the seasonal cycle in potential evapotranspiration,
for both the mean and extremes of their distributions. Groundwater is a
larger water storage component than soil moisture, and this general
difference increases even more with increasing catchment wetness. The spatial
standard deviation of both soil moisture and groundwater is larger in winter
than in summer. It peaks during rainfall events due to partial saturation of
the catchment, and also rises in spring as different locations dry out at
different rates. The most important controls on spatial variability in
storage are aspect and distance from the stream. South-facing and near-stream
locations have higher water tables and showed soil moisture responses for
more events. Typical hydrological models do not explicitly account for
aspect, but our results suggest that it is an important factor in hillslope
runoff generation.
Co-measurement of soil moisture and water table level allowed us to identify
relationships between the two. Locations where water tables peaked closer to
the surface had consistently wetter soils and higher water tables. These
wetter sites were the same across seasons. However, patterns of strong soil
moisture responses to summer storms did not correspond to the wetter sites.
Total catchment spatial variability is composed of multiple variability
sources, and the dominant type is sensitive to those stores that are close to
a threshold such as field capacity or saturation. Therefore, we classified
spatial variability as "summer mode" or "winter mode". In "summer
mode", variability is controlled by shallow processes, e.g. interaction of
water with soils and vegetation. In "winter mode", variability is
controlled by deeper processes, e.g. groundwater movement and bypass flow.
Double streamflow peaks observed during some events show the direct impact of
groundwater variability on runoff generation. Our results suggest that
emergent catchment behaviour depends on the combination of these multiple,
time varying components of storage variability. |
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