Browsing by Author "Bradd, J"

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    Groundwater response to heavy precipitation.
    (Australian Nuclear Science and Technology Organisation, 2003-04) Waring, CL; Bradd, J; Hankin, SI
    An investigation of the groundwater response to heavy rainfall at Lucas Heights Science and Technology Centre (LHSTC) is required under the conditions of Facility Licence F0001 for the ANSTO's Replacement Research Reactor. Groundwater continuous hydrograph monitoring has been used for this purpose. Hydrograph data from four boreholes are presented showing the rainfall recorded during the same period for comparison. The drought conditions have provided only limited cases where groundwater responded to a rainfall event. The characteristic response was local caused by saturated soil contributing water directly to the borehole and the falling head as the water was redistributed into the aquifer in a few hours. Hydrograph data from borehole near the head of a gully showed that groundwater flow from the plateau to the gully produced a peak a few days after the rainfall event and that the water level returned to its original level after about 10 days. The hydrograph data are consistent with an imperfect multi-layer groundwater flow regime developed from earlier seismic and geophysical data with decreasing rate of flow in each layer due to decreasing hydraulic conductivity with depth. The contrast in hydraulic conductivity between the thin permeable soil layer and the low permeable sandstone forms an effective barrier to vertical flow.
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    Sustainability of groundwater under climate change
    (International Atomic Energy Agency, 2003-05-19) Airey, PL; Henderson-Sellers, A; Bradd, J; Chambers, SD; Hughes, CE; Habermehl, MA
    One of the key commitments from the plan of implementation of the World Summit on Sustainable Development Johannesburg 2002 was to 'develop integrated water resources management and water efficiency plans by 2005'. In this paper, a detailed concept will be presented for assessing the sustainability of groundwater in warm arid and semi-arid areas challenged by climate change. The IAEA Global Network of Isotope Precipitation (GNIP) database is fundamental to the development of the concept which will be extended to the evaluation of climate change models. The concept will be evaluated with data from three recharge areas in the Great Artesian Basin, as well as aquifers in Central Australia, in the far north of the country and in Victoria. Experimental work is currently being extended to the Murray-Darling Basin. The role of the GNIP in the evaluation of climate change models is illustrated with data from the Amazon. Groundwater sustainability is achieved through balancing exploitation of the resource with recharge. As groundwater exploitation raises issues of demand management beyond the scope of this paper, the focus will be on recharge. Surface water infiltration is dependent on total rainfall within the intake areas, the seasonal distribution of rainfall, the rainfall intensity and the antecedent landscape conditions. Variation in total rainfall can be predicted without recourse to isotope data. However, effective recharge will only occur if the total monthly rainfall exceeds a threshold value. The above-mentioned concept involves predicting these threshold values from GNIP and groundwater isotope data. The evaluation of the concept with field data, and its incorporation into a predictive tool are the central themes of this paper. Four stages are involved: Stage 1: Correlating isotope depletion and the total monthly rainfall Analysis of the GNIP data from continental stations shows a widespread trend towards increasing stable isotope depletion with increasing monthly average rainfall. Stage 2: Matching stable isotope levels in groundwater with those in rainfall with monthly totals exceeding a threshold value The stable isotope levels in groundwater is generally depleted relative to that in mean average rainfall at recharge. The groundwater levels match those in rainfall provided the monthly intensity reaches a threshold value. This value, which may be expressed as a percentile of all monthly data for the GNIP station, is interpreted as the threshold value for effective recharge. The difference between the stable isotope ratios in groundwater and in the mean rainfall is called the 'groundwater depletion'. Stage 3: Correlating the 'groundwater depletion' with aridity. It will be shown with reference to data from Australian aquifers that the 'groundwater depletion' correlates with a defined 'aridity index'. Stage 4: Development of the predictive tool: The above mentioned correlation is the basis of a tool which may be applied to a) assessing groundwater sustainability, b) predicting soil moisture in the root zone and thus contribute to agricultural sustainability and c) evaluating climate change models. a) Groundwater sustainability: Climate change leads to variations in the 'aridity index' and hence to variations in the threshold intensity for effective recharge (Stage 3 above). Climate changes may be modelled numerically, assessed through correlations with sub-global parameters such as ENSO (El Nino Southern Oscillation) Index or simply postulated as scenarios. Reliable knowledge of predicted changes to effective recharge, would provide decision makers with additional time to adjust the groundwater exploitation rate consistent with the long term sustainability of the resource. b) Sustainability of the agricultural and pastoral industries: Variations in soil productivity depend on a number of factors including moisture levels in the root zone. Predictions of the soil moisture levels will depend on the temporal variation of the effective recharge (above), the water balance and the residence time distribution of the water. The use of isotopes to establish a water balance at a site in the Darling basin has been demonstrated. c) Evaluation of climate models: The use of isotopes to evaluate climate change models has been demonstrated in the Amazon basin. The principles will be extended to arid and semi arid areas using isotopic data in age dated groundwater as a probe for variations in effective recharge and therefore in the aridity index. The concept will be illustrated with data from the Great Artesian Basin and the Mereenie Sandstone aquifer in Central Australia. On-going project work will be focussed on ANSTO's contribution to the Murray-Darling Water Basin Study through the GEWEX (Global Energy and Water Cycle Experiment) Hydrometeorological Panel and the IAEA Coordinated Research Program Isotope Tracing of Hydrological Processes in Large River Basins, 2002-2004. The Organisation is also contributing to the Integrated Climate System Study (ICSYS) initiative of the IAEA/WCRP (World Climate Research Programme). © The authors.
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    Temporal analysis of stable water isotopic characteristics in the Murray Darling Basin
    (International Atomic Energy Agency, 2004-10-24) Henderson-Sellers, A; Airey, PL; Stone, DJM; Bradd, J; McGuffie, K
    “Water shortages, especially in tropical countries, are the climate challenge for this century” [1]. The isotopic composition of water and carbon in e.g. ice cores, ground water and biomass has been recognized as relevant to hydro-climates on timescales from glacial [2] to extreme weather [3]. We present Australian stable water isotope (SWI) research capability and exploit it in novel ways in order to establish objective validation of and improvement in existing water resource models ultimately reducing uncertainty in predictions. The use of stable water isotopes in hydro-climate modelling is refined on three timescales for the Murray Darling Basin. Isotopes demonstrate that in semi-arid regions, groundwater recharge occurs when the rainfall intensities exceed a threshold suggesting improvement of aquifer predictions over tens to thousands of years using isotopic threshold estimates. A range of atmospheric global circulation models ’ simulations of key hydrological parameters over years to decades reveals poor results for the majority (13 in 20) and underlines the value of isotopic constraints on basin hydrology. Modelling minute to monthly isotope fluxes using land surface schemes and a steady state (phenomenological) model of river hydrology allows comparison of the partitions of precipitation between transpiration, run-off and ‘lake’ evaporation with isotope observations from June 2002 to January 2003. These results will have the greatest importance if combined to improve the dynamics of simulations of regional water cycles [4]. Three timescales have been used here to explore the role of stable water isotopes in refining climate and hydrological models of the Murray Darling Basin. Firstly, over tens to thousands of years, we have examined the processes leading to the effective recharge of groundwater. The isotope data clearly indicate that in the warm arid/semi-arid regions, in contrast to the behaviour in cool temperate zones, effective recharge only occurs when the rainfall intensities exceed a threshold value. Isotopic estimates of this recharge threshold rainfall intensity could be applied to predictions of future groundwater resources. Secondly, over years to decades, we have assessed the success of a range of atmospheric global circulation models in simulating key hydrological parameters over the AMIP II period including El Niño and La Niña forcing. The results are rather poor for the majority (13 out of 20) GCMs suggesting that further constraints on the basin’s hydrology, such as from isotopes, may be valuable. In our third approach, we have modelled minute to monthly isotope fluxes using (a) land surface schemes (LSSs) at particular grid points within the Murray Darling Basin and (b) a steady state (phenomenological) model of river hydrology. Model conservation, climatic variations and ‘plausibility’, all pre-requisites for good simulations, have been investigated here for the Murray Darling. Models’ partitions of precipitation between transpiration, run-off and ‘lake’ evaporation are compared with isotope observations from the Darling River between June 2002 and January 2003. We find that: (i) more work is needed on gross water fluxes first; (ii) simple isotopic models generate plausible values but more complex ones, as yet, do not; and (iii) isotopes have potential for evaluation of whether LSSs are (in)correctly recharging and accessing groundwater reservoirs and for evaluation of the partitioning of water into runoff cf. re-evaporation. Tests based around these concepts offer a novel addition to the traditional methods of validating climate models and their sub-components.