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| Titel |
Hydraulic properties and inner structure of a relict rock glacier in the Eastern Alps, Austria |
| VerfasserIn |
Marcus Pauritsch, Gerfried Winkler, Andreas Kellerer-Pirklbauer, Steffen Birk |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250079533
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| Zusammenfassung |
| Water economic studies in 1990s documented the importance of the springs draining relict rock glaciers for water supply and human consumption as well as for the ecosystem in alpine catchments in the Niederen Tauern Range, Austria. Recent studies confirm the hydrologic importance and show that in the easternmost subunit, the Seckauer Tauern Range, more than 40% of the area above 2000 m a.s.l. and up to 20% of the area above 1500 m a.s.l. drain through relict rock glaciers. Thus, the hydraulic properties of these alpine aquifers are considered to be important controls on the hydrology of these areas. Nevertheless their hydraulic properties and their inner structure are still poorly understood. Our hydrogeological research is carried out at the Schöneben Rock Glacier, located in Seckauer Tauern Range, Austria. This rock glacier is presumably relict although patches of permafrost might exist particularly in the upper part of the landform. The rock glacier covers an area of 0.11 km² and drains a total catchment of 0.76 km² with a maximum elevation of 2282 m a.s.l.. The rock glacier consists predominantly of gneissic sediments (mainly coarse-grained, blocky at the surface) and extends from 1720 to 1905 m a.s.l.. Discharge of the rock glacier spring is recorded since 2002. Electrical conductivity and water temperature used as natural tracers are continuously monitored since 2008. Furthermore, a tracer test with simultaneous injection of the fluorescent dyes naphthionate and fluoresceine at two injection points (one close to the front and one close to the rooting zone of the rock glacier) was performed. Recession analysis of the spring hydrograph reveals similarities to the flow dynamics of karst springs. The results exhibit on the one hand a slow base flow recession indicating a high storage capacity and on the other hand sharp discharge peaks immediately after rainfall events referring to a high hydraulic conductivity. Applying different analytic runoff models, the hydrograph analysis provides two possible conceptual aquifer models: (1) an aquifer with multiple overlapping exponential runoff components and (2) a single homogeneous aquifer with a runoff following a power law function triggered by diverging recharge pulse durations. Best fits to the analysed hydrographs were achieved with a 25 days recharge pulse and a base flow coefficient of 0.002 1/d. The recession coefficients of the multiple exponential runoff components range from 0.04 to 0.001 1/d. The derived hydraulic conductivity indicates a sandy, poorly silty aquifer for the base flow component. The peak of the fluoresceine breakthrough curve was observed after approximately 90 days, fitting well to the reciprocal of the base flow recession coefficient. The spring responds within a few hours to recharge events with sharp discharge peaks and negative electric conductivity and temperature peaks. Discharge separation based on electrical conductivity data reveals that only 20% of the discharge peak is recently recharged water. The natural and artificial tracers thus support the hydraulic model of two diverging storage components building up the aquifer of the relict rock glacier. While a fine grained (sandy, poorly silty although with larger embedded blocks) inner zone provides the base flow component, a coarse grained, blocky upper zone lacking fine-grained sediments provides the fast run off component. |
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