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| Titel |
Comparison of subsurface connectivity in Alpine headwater catchments |
| VerfasserIn |
Giulia Zuecco, Michael Rinderer, Ilja van Meerveld, Daniele Penna, Marco Borga |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250129595
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| Publikation (Nr.) |
 EGU/EGU2016-9730.pdf |
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| Zusammenfassung |
| Saturation at the soil-bedrock interface or the rise of shallow groundwater into more
permeable soil layers results in subsurface stormflow and can lead to hillslope-stream
connectivity. Despite the importance of subsurface connectivity for streamflow and
streamwater chemistry, the factors controlling its spatial and temporal variability are still
poorly understood.
This study takes advantage of networks of spatially-distributed piezometers in five small
(<14 ha) headwater catchments in the Italian Dolomites and the Swiss pre-Alps to i) quantify
and compare the spatial and temporal variability of subsurface connectivity and its relation to
streamflow, and ii) assess whether the differences in connectivity between the catchments are
related to climatological or morphological characteristics of the catchments (e.g. the presence
of a riparian zone).
Shallow groundwater levels were measured for two years from spring to fall in 16 and 12
piezometers in the 14 and 3.3 ha catchments in the Italian Dolomites, and for four years from
spring to fall in 7-8 piezometers in three <1 ha Swiss pre-alpine catchments. Subsurface
connectivity was quantified by a graph-theory approach, considering linear connections
(edges) between the piezometers (nodes). A node was considered to be connected to
the stream when shallow groundwater was observed in the piezometer and it was
connected by the edges to the stream. Weights were given to each piezometer based on
Thiessen polygons to determine the area of the catchment that was connected to the
stream.
For the Swiss pre-alpine catchments the duration that nodes were connected to the stream
was significantly correlated to the local and upslope site characteristics, such as the
topographic wetness index, local slope and curvature. For the dolomitic catchment with the
largest riparian zone, the time that nodes were connected to the stream was correlated with
downslope site characteristics, such as the vertical distance to the nearest stream. The
temporal changes in the area of the catchment that was connected to the stream reflected the
streamflow dynamics for all catchments. Subsurface connectivity increased during rainfall
events but there was a short delay compared to streamflow, suggesting that other
processes (e.g. direct channel precipitation, runoff from near stream saturated areas)
contributed to streamflow at the beginning of the event. Groundwater levels declined
later and slower than streamflow, resulting in complex but mainly anti-clockwise
hysteretic relations between streamflow and the area that was connected to the stream.
Threshold-like relations between maximum connectivity and total stormflow and between
maximum connectivity and the sum of total rainfall plus antecedent rainfall were more
evident for the dolomitic catchments, where the riparian zone is characterized by
a groundwater table near the soil surface. A sudden increase in connectivity for
these catchments could represent the connection of hillslopes to the stream. These
preliminary results suggest that the delayed increase in subsurface connectivity relative
to streamflow is likely not affected by the presence of a riparian zone. However,
further analyses are needed to determine if the climate and/or morphology of the
catchments affect the observed relations between maximum connectivity and total
stormflow.
Keywords: subsurface connectivity; headwater catchments; groundwater; graph theory;
hysteresis. |
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