Adelaide
18.3 Discharge to landscape

Supporting information

The volume reported (108,290 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 2012–13 year

Region

Groundwater discharge to landscape (ML) 

Adelaide Plains

10,760

McLaren Vale

3,020

Western Mount Lofty Ranges (fractured rocks1)

94,510

Total

108,290

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: 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: land use mapping 2010; South Australian Department of Environment, Water and Natural Resources (DEWNR): bore locations and groundwater level data from online groundwater database (DEWNR 2013).

Provided by

Bureau of Meteorology.

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 of Meteorology 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 2012–13 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 2012–13.

The following figure illustrates the net groundwater discharge (in red) and recharge (in grey) across the Adelaide region during the 2012–13 year using the WAVES model.

Map showing net groundwater recharge and discharge in the Adelaide region during the 2012–13 year
Map showing net groundwater recharge and discharge in the Adelaide region during the 2012–13 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 and the 9" digital elevation model as an external driver 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

The comparative year volume for line item '19.3 Discharge to landscape' was restated in the water accounting statements from the 2012 Account due to an error identified in the method used to calculate this volume. Please refer to Restatement of comparative year information in the 'Water accounting policies' for more information.