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| Titel |
Calibration of a transient transport model to tritium data in streams and simulation of groundwater ages in the western Lake Taupo catchment, New Zealand |
| VerfasserIn |
M. A. Gusyev, M. Toews, U. Morgenstern, M. Stewart, P. White, C. Daughney, J. Hadfield |
| 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 ; 17, no. 3 ; Nr. 17, no. 3 (2013-03-19), S.1217-1227 |
| Datensatznummer |
250018834
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| Publikation (Nr.) |
 copernicus.org/hess-17-1217-2013.pdf |
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| Zusammenfassung |
| Here we present a general approach of calibrating transient transport models
to tritium concentrations in river waters developed for the MT3DMS/MODFLOW
model of the western Lake Taupo catchment, New Zealand. Tritium has a known
pulse-shaped input to groundwater systems due to the bomb tritium in the
early 1960s and, with its radioactive half-life of 12.32 yr, allows for
the determination of the groundwater age. In the transport model, the
tritium input (measured in rainfall) passes through the groundwater system, and
the simulated tritium concentrations are matched to the measured tritium
concentrations in the river and stream outlets for the Waihaha, Whanganui,
Whareroa, Kuratau and Omori catchments from 2000–2007. For the Kuratau
River, tritium was also measured between 1960 and 1970, which allowed us to
fine-tune the transport model for the simulated bomb-peak tritium
concentrations. In order to incorporate small surface water features
in detail, an 80 m uniform grid cell size was selected in the
steady-state MODFLOW model for the model area of 1072 km2.
The groundwater flow model was first calibrated to groundwater levels and
stream baseflow observations. Then, the transient tritium transport MT3DMS model was
matched to the measured tritium concentrations in streams and rivers, which
are the natural discharge of the groundwater system. The tritium
concentrations in the rivers and streams correspond to the residence time of
the water in the groundwater system (groundwater age) and mixing of water
with different age. The transport model output showed a good agreement with
the measured tritium values. Finally, the tritium-calibrated MT3DMS model is
applied to simulate groundwater ages, which are used to obtain groundwater
age distributions with mean residence times (MRTs) in streams and rivers for
the five catchments. The effect of regional and local hydrogeology on the
simulated groundwater ages is investigated by demonstrating groundwater ages
at five model cross-sections to better understand MRTs simulated with
tritium-calibrated MT3DMS and lumped parameter models. |
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