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| Titel |
Transit times from rainfall to baseflow in headwater catchments estimated using tritium: the Ovens River, Australia |
| VerfasserIn |
I. Cartwright, U. Morgenstern |
| 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 ; 19, no. 9 ; Nr. 19, no. 9 (2015-09-08), S.3771-3785 |
| Datensatznummer |
250120802
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| Publikation (Nr.) |
 copernicus.org/hess-19-3771-2015.pdf |
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| Zusammenfassung |
| Headwater streams contribute a significant proportion of the total flow to
many river systems, especially during summer low-flow periods. However,
despite their importance, the time taken for water to travel through
headwater catchments and into the streams (the transit time) is poorly
understood. Here, 3H activities of stream water are used to define
transit times of water contributing to streams from the upper reaches of the
Ovens River in south-east Australia at varying flow conditions. 3H
activities of the stream water varied from 1.63 to 2.45 TU, which are below
the average 3H activity of modern local rainfall (2.85 to 2.99 TU). The
highest 3H activities were recorded following higher winter flows and
the lowest 3H activities were recorded at summer low-flow conditions.
Variations of major ion concentrations and 3H activities with
streamflow imply that different stores of water from within the catchment
(e.g. from the soil or regolith) are mobilised during rainfall events rather
than there being simple dilution of an older groundwater component by event
water. Mean transit times calculated using an exponential-piston flow model
range from 4 to 30 years and are higher at summer low-flow conditions. Mean
transit times calculated using other flow models (e.g. exponential flow or
dispersion) are similar. There are broad correlations between 3H
activities and the percentage of rainfall exported from each catchment and
between 3H activities and Na and Cl concentrations that allow
first-order estimates of mean transit times in adjacent catchments or at
different times in these catchments to be made. Water from the upper Ovens
River has similar mean transit times to the headwater streams implying there
is no significant input of old water from the alluvial gravels. The
observation that the water contributing to the headwater streams in the
Ovens catchment has a mean transit time of years to decades implies that
these streams are buffered against rainfall variations on timescales of a
few years. However, impacts of any changes to land use in these catchments
may take years to decades to manifest themselves in changes to streamflow or
water quality. |
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