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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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Preprints
https://doi.org/10.5194/hess-2020-143
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/hess-2020-143
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  14 Apr 2020

14 Apr 2020

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A revised version of this preprint is currently under review for the journal HESS.

Using multiple methods to understand groundwater recharge in a semi-arid area

Shovon Barua1, Ian Cartwright1, P. Evan Dresel2, and Edoardo Daly3 Shovon Barua et al.
  • 1School of Earth, Atmosphere and Environment, Monash University, Clayton, Victoria 3800, Australia
  • 2Agriculture Victoria, Department of Jobs, Precincts and Regions, Bendigo, Victoria 3554, Australia
  • 3Department of Civil Engineering, Monash University, Clayton, Victoria 3800, Australia

Abstract. Understanding recharge in semi-arid areas is important for the sustainable management of groundwater resources. This study focuses on estimating groundwater recharge rates and understanding the impacts of land-use changes on recharge in a semi-arid area. Two adjacent catchments in southeast Australia were cleared ~180 years ago following European settlement; in one of these catchments eucalypt plantation forest was subsequently established ~ 20 years ago. Chloride mass balance yields recharge rates of 0.2 to 61.6 mm yr−1 (typically up to 11.2 mm yr−1). The lower of these values probably represent recharge rates prior to land clearing, whereas the higher likely reflects recharge rates following initial land clearing. The low pre-land clearing recharge rates are consistent with the presence of groundwater that has residence times that are up to 24,700 years (calculated using radiocarbon) and the moderate to low hydraulic conductivities (0.31 to 0.002 m day−1) of the clay-rich aquifers. Recharge rates estimated from tritium activities and water table fluctuations reflect those following the initial land clearing. However, recharge rates estimated using water table fluctuations (15 to 500 mm yr−1) are significantly higher than those estimated using tritium renewal rates (0.01 to 89 mm yr−1; typically < 14.0 mm yr−1). The higher recharge rates from the water table fluctuations approach the long-term average annual rainfall (~ 640 mm yr−1) and are unlikely to be correct given the estimated evapotranspiration rates of 500 to 600 mm yr−1. While it is difficult to examine the uncertainties associated with the water table fluctuation method, it is likely that a reduction in the effective specific yield due to the presence of moisture in fine-grained soils results in the water table fluctuation overestimating recharge rates. Although land-use changes increased recharge rates, the preservation of old groundwater indicates that present-day recharge is generally modest, which is likely to be the case in semi-arid regions of southeast Australia.

Shovon Barua et al.

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Shovon Barua et al.

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Short summary
We evaluate groundwater recharge rates in a semi-arid area that has undergone land-use changes. The widespread presence of old saline groundwater indicates that pre-land clearing recharge rates were low and present-day recharge rates are still modest. The fluctuations of the water table and tritium activities reflect present-day recharge rates; however, the water table fluctuation estimates are unrealistically high, and this technique may not be suited for estimating recharge in semi-arid areas.
We evaluate groundwater recharge rates in a semi-arid area that has undergone land-use changes....
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