Murray–Darling Basin
10.3 Recharge from landscape

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.

(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.

The Bureau and NSW Office of Water.

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.

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.

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.

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.