Murray–Darling Basin
10.3 Recharge from landscape

Supporting information

The volumetric value for the line item for the 2011–12 year was 3,133,191 ML. The following table provides detailed volumetric information for the line item. 

 

Details of groundwater recharge from landscape in the MDB region in the 2011–12 year
Groundwater resource plan area

Groundwater sustainable diversion limit area

State

Type of recharge

 Volume (ML) for the 2011–12 year 

Code

Name

GW15 Gwydir Alluvium GS24 Lower Gwydir Alluvium  NSW Rainfall recharge

40,261

GW14 Namoi Alluvium GS29 Lower Namoi Alluvium NSW Rainfall recharge

64,238

GS47 Upper Namoi Alluvium NSW Rainfall recharge

87,980

Irrigation recharge

13,698

GW12 Macquarie–Castlereagh Alluvium GS26 Lower Macquarie Alluvium NSW Rainfall recharge and irrigation channel 

29,050

Irrigation recharge

19,320

Sub-total Northern Basin

254,547

GW 10 Lachlan Alluvium GS25 Lower Lachlan Alluvium  NSW Rainfall recharge

142,170

Irrigation recharge

4,790

GW 9 Murrumbidgee Alluvium GS28 Lower Murrumbidgee Alluvium (shallow; Shepparton formation) NSW Rainfall recharge

139,104

Irrigation recharge

227,574

GS31 Mid-Murrumbidgee Alluvium NSW Rainfall recharge

23,550

Irrigation recharge

232

GW8 Murray Alluvium GS27 Lower Murray Alluvium, shallow; Shepparton formation  NSW Rainfall recharge

462,044

GS46 Upper Murray Alluvium NSW Rainfall recharge

17,406

GW2 Goulburn–Murray GS8 Goulburn-Murray (Ovens–Kiewa sedimentary plain)  Vic Rainfall recharge

249,264

GS8 Goulburn-Murray (Victorian Riverine sedimentary plain) Vic Rainfall recharge

650,466

GW3 Wimmera–Mallee (groundwater) GS9 Wimmera–Mallee (sedimentary plain)  Vic Rainfall recharge

848,316

GW5 Eastern Mount Lofty Ranges GS01 Angas Bremer (Quaternary sediments and Murray Group limestone) SA Rainfall recharge

8,083

GW4 SA Murray GS03 Mallee Murray Group limestone SA Rainfall recharge

95,445

GS05 Peake–Roby–Sherlock (unconfined) SA Rainfall recharge

10,200

Sub-total Southern Basin

2,878,644

Total for the region

3,133,191


1
 Bureau = Bureau of Meteorology, NSW models = New South Wales models

Sustainable diversion limit (SDL) areas other than those included in the table exist and may be relevant to the line item; however, relevant information was not available for the 2012 Account.

Quantification approach

Data source

(1) Bureau of Meteorology (the Bureau): National Climate Centre (NCC) daily climate grids (rainfall, temperature, vapour pressure and solar radiation); (2) Australian soil resources information system (ASRIS): soil data; (3) Australian Bureau of Agricultural and Resource Economics and Sciences: land-use data; and (4) NSW Office of Water: inputs to the New South Wales groundwater models draw from knowledge of the hydrogeology and surface water processes and outputs from same models.

Provided by

The Bureau and NSW Office of Water.

Method

For the SDL areas for which 'Data source' is shown as  the Bureau in the table

The Bureau estimated the diffuse groundwater recharge volumes using the water atmosphere vegetation energy and solutes (WAVES) model (Zhang and Dawes 1998; Dawes et al. 1998). In the recharge calculations, depth to water table was considered for all regions where the depth to watertable was shallow. A shallow water table was assumed to be where the depth to the watertable was 4 m or less below the ground surface. The shallow water table was interpolated using kriging with external drift and the 9" Digital Elevation Model as a physical constraint following the methodology presented in Peterson et al. (2011). Where the watertable was not shallow, free drainage conditions were assumed. The recharge within the MDB region was determined by summing the spatially interpolated positive recharge estimates.

For the SDL areas for which 'Data source' is shown as New South Wales models in the table

Recharge volumes were calculated for selected SDL areas applying New South Wales groundwater models based on MODFLOW (United States Geological Survey 2013) modelling process.

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.

Assumptions, limitations, caveats and approximations

The Bureau:

  • 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 national land use grid (Australian Bureau of Agricultural and Resource Economics and 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 for SDL areas to the south of 31 oS and C4 annual pasture, C4 perennial pasture and eucalypt trees with a grass understorey for the SDL areas to the north of 31 oS.

  • Annual recharge was estimated using a shallow water table surface estimated by interpolating measured groundwater levels.

New South Wales groundwater models:

  • Groundwater models make many assumptions and approximations to represent water balance (United States Geological Survey 2013).

  • Several of the New South Wales groundwater models assume estimation of recharge volume as a percentage of rainfall.

Uncertainty information

The uncertainty estimate was not quantified.

For the Bureau 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.

Comparative year

The following changes resulted in the restatement of the 2010–11 year volume:

  • changes made to the calculation method
  • scope change.

The changes and their respective values are detailed in the following table.

 

Restatement of the comparative year information made for the line item 10.3 Recharge from landscape
Segment 2012 Account volume for the 2010–11 year (ML) 2011 Account volume for the 2010–11 year (ML) Difference due to changes in scope and calculation method (ML)
Northern Basin 260,133 5,417,751 -5,157,618
Southern Basin 10,012,996 4,366,668 5,646,328
Whole region 10,273,129 9,784,419 488,710


The scope change was due to the following reasons:

  • Southern Basin: inclusion of Upper Murray Alluvium (45,435 ML) and  Angas Bremer (12,821 ML)
  • Southern Basin: inclusion of  rainfall recharge volume for Lower Murrumbidgee Alluvium (211,820 ML)
  • Southern Basin: extension of the area used in the 2011 Account for Wimmera Mallee sedimentary plains.

The change of methodology was due to the following reason:

  • The depth to water table was interpolated using the methodology presented in Peterson et al. (2011).
  • New set of bores was used based on the data availability.
  • Northern Basin: Application of New South Wales groundwater models instead of the Bureau method to estimate the recharge volume for Lower Namoi Alluvium.