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Titel |
Geologic controls on groundwater discharge in large tropical rivers: an environmental tracers approach |
VerfasserIn |
J. Batlle-Aguilar, G. A. Harington, M. Leblanc, P. G. Cook |
Konferenz |
EGU General Assembly 2012
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 14 (2012) |
Datensatznummer |
250059239
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Zusammenfassung |
Tropical rivers supply large volumes of fresh water, making them attractive opportunities for
new irrigation development, particularly to mitigate the impacts of drought in other regions.
Many tropical rivers are perennial, with flow maintained during drier months by
groundwater discharge. Determining the locations and fluxes of groundwater discharge to
these rivers is required to maintain their ecological value under future management
decisions.
In tropical areas, like northern Australia, the climate is characterized by two distinct
seasons; on average about 90% of annual rainfall occurs in the “wet season”. The Mitchell
River, located in tropical north Queensland (Australia), was sampled at the end of two dry
seasons. Preliminary reconnaissance sampling of the upper half of the catchment in October
2010 provided ion chemistry, radon (222Rn), chlorofluorocarbons (CFCs), helium (4He), and
87Sr/86Sr data that were interpreted to infer locations – and potentially different sources –
of water discharging into the river. Then in October 2011 the Mitchell River was
synoptically sampled by helicopter every 5 km along a 350 km reach. Water samples
were taken from the main river channel and major tributaries for ion chemistry,
222Rn, tritium (3H) and 87Sr/86Sr ratio, and many of these sites were flow gauged.
Simultaneously, groundwater samples were taken from existing bores completed in different
geologies.
Hydrochemical, isotopic and hydrometric results all indicate that water from different
sources, related to different geologies, contribute to maintain the river flow at the end of the
dry season. Surface water or groundwater with very low residence time mostly
contributes in the upper part of the catchment, while discharge of older groundwater is
important in downstream reaches, where aquifers of the Great Artesian Basin (GAB)
outcrop. Applying a longitudinal 1D model we are able to demonstrate the spatial
variability of groundwater contribution to the dry season flow of the Mitchell River. |
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