Adelaide
18.3 Discharge to landscape

Supporting information

The volume reported (155,177 ML) included discharge through evapotranspiration from shallow groundwater and is summarised by groundwater management area in the following table

Groundwater discharge to landscape in the Adelaide region in the 2011–12 year
Region Groundwater discharge to landscape (ML) 
Adelaide Plains 7,724
McLaren Vale prescribed wells area
1,389
Western Mount Lofty Ranges (fractured rocks1) 146,064
 TOTAL 155,177

1 Recharge from the fractured rocks of the Myponga River catchment and Fleurieu Peninsula was not included as described in the quantification approach section.

Quantification approach

Data source

Bureau of Meteorology (the Bureau): National Climate Centre (NCC) – version 3 daily rainfall grids, daily maximum temperature grids, daily minimum temperature grids, daily satellite observed solar radiation grids, daily vapour pressure deficit grids; CSIRO: Australian Soil Resources Information System (ASRIS) soil information; Australian Bureau of Agricultural and Resource Economics – Bureau of Rural Sciences 2010: land use mapping; South Australian Department of Environment, Water and Natural Resources (DEWNR): bore locations and groundwater level data from online groundwater database (Department of Environment, Water and Natural Resources 2013).

Provided by

Bureau of Meteorology (the Bureau).

Method

Groundwater discharge to the landscape was estimated using the Water Atmosphere Vegetation Energy and Solutes (WAVES ) model (Zhang and Dawes 1998; Dawes et al. 1998). WAVES is a one-dimensional soil-vegetation-atmosphere-transfer model that integrates water, carbon and energy balances. Climate, depth to water table (only for the sedimentary areas), soil and vegetation data were used as inputs to the model. The climate data include rainfall, rainfall duration, maximum and minimum temperatures, vapour pressure deficit, and solar radiation.

The WAVES model has been used by the CSIRO in its sustainable yields projects (Crosbie et al. 2008) and the Bureau has built on this methodology. WAVES was run at selected points from across the Adelaide region for all combinations of soil type, vegetation type and depth to water table. The point estimates of the groundwater discharge (evapotranspiration from the water table) fraction for the 2011–12 year were interpolated to a 1-km grid based on soil type, vegetation type and depth to water table, and multiplied by a grid of annual rainfall for 2011–12.

The discharge to the landscape was determined by summing the spatially interpolated negative recharge estimates.

The following figure illustrates the net groundwater discharge (in red) and recharge (in grey) across the Adelaide region during the 2011–12 year using the WAVES model.

 

Map showing net groundwater recharge and discharge in the Adelaide region during the 2011–12 year
Map showing net groundwater recharge and discharge in the Adelaide region during the 2011–12 year

Assumptions, limitations, caveats and approximations

  • The assumptions made in developing the WAVES model as described in Dawes et al. (1998) were all applicable to the recharge estimations for the Adelaide region.
  • The national land-use grid (Australian Bureau of Agricultural and Resource Economics – Bureau of Rural Sciences 2010) was reclassified to three vegetation classes that include annuals, perennials and trees.  The major vegetation classes modelled were C3 annual pasture, C3 perennial pasture and Eucalypt trees with a grass understorey.
  • Annual net recharge and discharge was estimated for the whole of Adelaide region including both sedimentary and fractured rock areas. Recharge and discharge to the region was modelled given the effects of a shallow water table interpolated using kriging with an external drift 9" digital elevation model following the methodology presented in Peterson et al. (2011).
  • Only the fractured rocks area contributing to the flow in the confined sediments was considered (see fractured rock boundaries in figure) for calculation of the diffuse groundwater discharge to landscape. Discharge to the fractured rocks of the Fleurieu Peninsula and Myponga River catchment is not included in the balance.  This was done to maintain the groundwater balance.

Uncertainty information

The uncertainty estimate was not quantified.

Comparative year

Compared to the 2011 Account, an improved quantification method for groundwater discharge was applied in the 2012 Account:

  • A different bore data set was used for the 2012 Account corresponding to data available at the time of compiling the report.
  • The water table depth was interpolated using the methodology presented in Peterson et al. (2011). throughout the region, while in 2011 Account this method had not been used for the Adelaide Plains and McLlaren Vale regions.

As shown in the following table, the volume of groundwater discharge for the 2010–11 year of 99,677 ML published in the 2011 Account was restated to 54,866 ML in the 2012 Account as the difference was material (45%).

Restatement of comparative year information for line item 18.3 Discharge to landscape

Groundwater management area

2012 Account volume for the 2010–11 year (ML)

2011 Account volume for the 2010–11 year (ML)

Additional information

Adelaide Plains

3,321

79,357

Bore data and methodology change

McLaren Vale

1,399

4,714

Bore data and methodology change

Western Mount Lofty Ranges (fractured rocks)

50,146

15,606

Bore data change

Total

54,866

99,677