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| Titel |
A comparison of particle-tracking and solute transport methods for simulation of tritium concentrations and groundwater transit times in river water |
| VerfasserIn |
M. A. Gusyev, D. Abrams, M. W. Toews, U. Morgenstern, M. K. Stewart |
| 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 ; 18, no. 8 ; Nr. 18, no. 8 (2014-08-20), S.3109-3119 |
| Datensatznummer |
250120440
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| Publikation (Nr.) |
 copernicus.org/hess-18-3109-2014.pdf |
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| Zusammenfassung |
| The purpose of this study is to simulate tritium concentrations and
groundwater transit times in river water with particle-tracking
(MODPATH)
and compare them to solute transport (MT3DMS) simulations. Tritium
measurements in river water are valuable for the calibration of particle-tracking
and solute transport models as well as for understanding of
watershed storage dynamics. In a previous study, we simulated tritium
concentrations in river water of the western Lake Taupo catchment (WLTC)
using a MODFLOW-MT3DMS model (Gusyev et al., 2013). The model was calibrated
to measured tritium in river water at baseflows of the Waihaha, Whanganui,
Whareroa, Kuratau, and Omori river catchments of the WLTC. Following from
that work we now utilized the same MODFLOW model for the WLTC to calculate
the pathways of groundwater particles (and their corresponding tritium
concentrations) using steady-state particle tracking MODPATH model. In order to
simulate baseflow tritium concentrations with MODPATH, transit time
distributions (TTDs) are necessary to understand the lag time between the
entry and discharge points of a tracer and are generated for the river
networks of the five WLTC outflows. TTDs are used in the
convolution integral with an input tritium concentration time series
obtained from the precipitation measurements. The resulting MODPATH tritium
concentrations yield a very good match to measured tritium concentrations
and are similar to the MT3DMS-simulated tritium concentrations, with the
greatest variation occurring around the bomb peak. MODPATH and MT3DMS also
yield similar mean transit times (MTTs) of groundwater contribution to river
baseflows, but the actual shape of the TTDs is strikingly different. While
both distributions provide valuable information, the methodologies used to
derive the TTDs are fundamentally different and hence must be interpreted
differently. With the current MT3DMS model settings, only the methodology
used with MODPATH provides the true TTD for use with the convolution
integral. |
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