Murray–Darling Basin

The volumetric value for the line item is 1,753,711ML. The following table provides a breakdown of the volume.

Volumes of net diffuse groundwater recharge from landscape water in the Murray–Darling Basin (MDB) for 2009–10

No.	Groundwater management unit (GMU)	State	Volume 2009–10 (ML)	Quantification method1
1	Lower Gwydir Alluvium	NSW	14,040	BoM method
2	Lower Lachlan Alluvium	NSW	116,000	NSW models
3	Upper Lachlan Alluvium	NSW	339,527	BoM method
4	Lower Macquarie Alluvium	NSW	46,052	NSW models
5	Lower Murray Alluvium	NSW	98,914	BoM method
Lower Murrumbidgee – sum composed of GMUs 6 & 7			330,000	NSW models
6	Lower Murrumbidgee Deep Groundwater source	NSW
7	Lower Murrumbidgee Shallow Groundwater source	NSW
8	Mid Murrumbidgee Alluvium	NSW	8,868	NSW models
9	Lower Namoi Alluvium	NSW	21,200	NSW models
10	Upper Namoi Alluvium	NSW	41,923	NSW models
Katunga-Campaspe – sum composed of GMUs 11–13			274,141	BoM method
11	Campaspe Deep Lead Water Supply Protection Area	Vic
12	Katunga Water Supply Protection Area	Vic
13	Shepparton Irrigation Water Supply Protection Area	Vic
14	Mid Loddon Water Supply Protection Area	Vic	32,870	BoM method
Lower Murray–Darling Basin GMUs – sum composed of GMUs 15–27			430,176	BoM method
15	Balrootan (Nhill) Groundwater Management Area	Vic
16	Goroke Groundwater Management Area	Vic
17	Kaniva TCSA Groundwater Management Area	Vic
18	Murrayville Water Supply Protection Area	Vic
19	Nhill Groundwater Management Area	Vic
20	Telopea Downs Water Supply Protection Area	Vic
21	Angas–Bremer Prescribed Wells Area	SA
22	Coorong	SA
23	Ferries–McDonald	SA
24	Mallee Prescribed Wells Area	SA
25	Murraylands	SA
26	Peake, Roby and Sherlock Prescribed Wells Area	SA
27	River Murray Prescribed Water Course	SA
	Total Basin		1,753,711

1 See ‘Quantification approach’, below, for explanations of the methods used

 

Data source

Bureau of Meteorology method (see list of GMUs concerned in the table under supporting information)

Bureau of Meteorology, National Climate Centre (NCC):

• version 3 daily rainfall grids as at 10 August 2010 for July 2009 – December 2009 and as at 23 August 2010 for January 2010 – June 2010
  
  
• version 3, annual rainfall grids derived from daily rainfall grids as at 10 August 2010 for July 2009 – December 2009 and as at 23 August 2010 for January 2010 – June 2011
  
  
• daily maximum temperature grids as at 10 August 2010 for July 2009 – December 2009 and as at 23 August 2010 for January 2010 – June 2010
  
  
• daily minimum temperature grids as at 10 August /2010 for July 2009 – December 2009 and as at 23 August 2010 for January 2010 – June 2010
  
  
• daily satellite observed solar radiation grids as at 10 August 2010 for July 2009 – December 2009 and as at 23 August 2010 for January 2010 – June 2010
  
  
• daily vapour pressure deficit grids as at 10 August 2010 for July 2009 – December 2009 and as at 23 August 2010 for January 2010 – June 2010
  

Soil data from Australian Soil Resources Information System (ASRIS).

Land-use data from Australian Bureau of Rural Sciences Water (2010).

Data used in areas with New South Wales groundwater models (see list of GMUs concerned in the table under supporting information)

Recharge is a calibrated input to, and output from, groundwater models.

Data provider

Bureau of Meteorology and NSW Office of Water.

Method

Bureau of Meteorology method (see list of GMUs concerned in the table under supporting information)

Diffuse groundwater recharge was estimated using the Water Atmosphere Vegetation Energy and Solutes (WAVES) model (Zhang and Dawes 1998; Dawes et al. 1998). In the recharge calculations, free drainage conditions at the base of the soil profile was assumed in the WAVES model – no discharge occurs when free drainage conditions exist. Free drainage conditions are expected to exist in most areas of the MDB and the data required to estimate groundwater discharge (depth to water table data) were not available for all areas.

WAVES is a one-dimensional soil-vegetation-atmosphere-transfer model that integrates water, carbon, and energy balances with a consistent level of process detail. The input data-sets required for WAVES include climate, soil and vegetation data. The climate data used at selected points include rainfall, rainfall duration, maximum and minimum temperatures, vapour pressure deficit, and solar radiation. The relevant vegetation parameters required for modelling were selected from the WAVES User Manual (Dawes et al. 1998). WAVES uses the soil hydraulic model of Broadbridge and White (1998) with saturated hydraulic conductivity, saturated moisture content, residual moisture content, inverse capillary length scale and an empirical constant as input parameters calculated from soil properties accessed in the ASRIS database (Johnston et al. 2003).

The WAVES model has been used by the Commonwealth Scientific and Industrial Research Organisation (CSIRO) in its Sustainable Yields projects (Crosbie et al. 2008) and the Bureau of Meteorology built on this methodology. WAVES was run for all combinations of soil, vegetation, and depth to water table at a number of discrete points within the GMU areas. Groundwater recharge was then estimated for each 5 km × 5 km grid-square across the MDB region by interpolating between the discrete points using the annual rainfall, and the dominant soil and vegetation present in the pixel. The net recharge within the MDB region was estimated by summing the recharge estimates for each pixel within the region.

New South Wales groundwater models method (see list of GMUs concerned in the table under supporting information)

Groundwater recharge is both an input to and, an output from, a groundwater model. There is no single method for estimating recharge used in the New South Wales groundwater models; however, several models estimate recharge as a percentage of rainfall. The magnitude of recharge (as a percentage of rainfall) can be adjusted during the calibration of a groundwater model so that the observed groundwater levels are reproduced in model outputs as accurately as possible, typically for a period of around 20 years if data are available.

In contrast to the Bureau of Meteorology method, the MODFLOW groundwater model can output volumes of both groundwater recharge and discharge where these fluxes are modelled. Discharge is only calculated in some MDB models where the MODFLOW evapotranspiration routines are activated to represent this flux – see Line item16.3.1.

Uncertainty

Uncertainty is ungraded.

For Bureau of Meteorology method:

• The uncertainty in the input parameters and the corresponding impacts on the modelled recharge values were not studied.
  
  The uncertainty of the estimated recharge resulting from different recharge interpolation methods was not estimated.
  

For New South Wales groundwater models:

• Uncertainty of a recharge estimate is not evaluated for the groundwater models.
  

Approximations, assumptions, caveats/limitations

Bureau of Meteorology method:

• The values reported are recharge estimates calculated assuming free drainage at the base of an unsaturated soil profile (i.e. no shallow water table).
  
  
• The assumptions made in developing the WAVES model as described in Dawes et al. (1998) were all applicable to the recharge estimations carried out for the MDB region.
  
  
• The Bureau of Rural Sciences land-use map of Murray–Darling Basin Water Reporting region is reclassified to three vegetation classes that include annuals, perennials, and trees. The major vegetation classes modelled were C3 and C4 annual pasture, C3 and C4 perennial pasture and Eucalypt trees with a grass understorey.

New South Wales groundwater models:

• Groundwater models make a lot of assumptions and approximations to represent water balance (refer to the United States Geological Survey website for more details).
  
  
• As stated above, several of the New South Wales groundwater models assume that recharge can be estimated as a percentage of rainfall.