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| Titel |
On the trail of double peak hydrographs |
| VerfasserIn |
Núria Martínez-Carreras, Christophe Hissler, Laurent Gourdol, Julian Klaus, Jérôme Juilleret, Jean François Iffly, Jeffrey J. McDonnell, Laurent Pfister |
| 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 |
250131916
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| Publikation (Nr.) |
 EGU/EGU2016-12369.pdf |
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| Zusammenfassung |
| A double peak hydrograph features two peaks as a response to a unique rainfall pulse. The
first peak occurs at the same time or shortly after the precipitation has started and it
corresponds to a fast catchment response to precipitation. The delayed peak normally starts
during the recession of the first peak, when the precipitation has already ceased. Double peak
hydrographs may occur for various reasons. They can occur (i) in large catchments when lag
times in tributary responses are large, (ii) in urban catchments where the first peak is often
caused by direct surface runoff on impervious land cover, and the delayed peak
to slower subsurface flow, and (iii) in non-urban catchments, where the first and
the delayed discharge peaks are explained by different runoff mechanisms (e.g.
overland flow, subsurface flow and/or deep groundwater flow) that have different
response times. Here we focus on the third case, as a formal description of the different
hydrological mechanisms explaining these complex hydrological dynamics across
catchments with diverse physiographic characteristics is still needed. Based on a
review of studies documenting double peak events we have established a formal
classification of catchments presenting double peak events based on their regolith structure
(geological substratum and/or its weathered products). We describe the different
hydrological mechanisms that trigger these complex hydrological dynamics across each
catchment type. We then use hydrometric time series of precipitation, runoff, soil
moisture and groundwater levels collected in the Weierbach (0.46 km2) headwater
catchment (Luxembourg) to better understand double peak hydrograph generation.
Specifically, we aim to find out (1) if the generation of a double peak hydrograph is a
threshold process, (2) if the hysteretic relationships between storage and discharge are
consistent during single and double peak hydrographs, and (3) if different functional
landscape units (the hillslopes and the plateau) equally contribute to the generation
of delayed peaks in double peak hydrographs. We found evidence of catchment
storage being a dominant control on the delayed peak activation. The amount of this
storage threshold was consistent over a 3-year period. Hillslopes were connected to
the stream at low discharge values, whereas the plateau contribution to discharge
was significant when storage reached a certain threshold value. The latter seems
to trigger the generation of the delayed peak in the double peak events. We also
observed a non-linear relationship between storage and discharge, which leads to
hysteretic relationships between both variables. During single peak hydrographs
and first peaks in double peak hydrographs discharge increases faster and peaks
before catchment storage, resulting in counter-clockwise hysteretic loops. This
was explained by the fact that these runoff peaks are generated by precipitation
falling directly into the stream or near stream locations, and/or by the contribution
of water flowing through preferential flowpaths that quickly reached the stream
network. When catchment storage exceeded the threshold for the generation of double
peak hydrographs, events showed clockwise hysteretic loops. It is the stored water
in the catchment that will peak first and consequently generate the delayed peak
in the hydrograph as a result of the capacity exceedance of a subsurface storage. |
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