Murray–Darling Basin
10.3 Recharge from landscape

The volumetric value for the line item for the 2012–13 year was 1,539,098 ML. The following table provides detailed volumetric information for the line item. 

 

Details of groundwater recharge from landscape in the MDB region during the 2012–13 year

Groundwater resource plan area	Groundwater sustainable diversion limit area		State	Type of recharge	Volume (ML) for the 2012–13 year	Data source
	Code	Name
GW21 Condamine–Balonne	GS64 and GS65	Upper Condamine Basalt, Upper Condmine Alluvium (Central Condamine Alluvium  and Tributaries)	Qld.	rainfall recharge	299,081	Bureau
GW15 Gwydir Alluvium	GS24	Lower Gwydir Alluvium	NSW	rainfall recharge	28,097	NSW models
				irrigation recharge	7,920	NSW models
GW14 Namoi Alluvium	GS29	Lower Namoi Alluvium	NSW	rainfall recharge	81,581	NSW models
	GS40	Peel Valley Alluvium	NSW	rainfall recharge	1,237	NSW models
				irrigation recharge	1,551	NSW models
	GS47	Upper Namoi Alluvium	NSW	rainfall recharge	73,436	NSW models
				irrigation recharge	13,698	NSW models
GW12 Macquarie–Castlereagh Alluvium	GS26	Lower Macquarie Alluvium	NSW	rainfall recharge and irrigation channel	20,185	NSW models
				irrigation recharge	19,318	NSW models
Sub-total Northern Basin					546,103
GW 10 Lachlan Alluvium	GS25	Lower Lachlan Alluvium	NSW	rainfall recharge	64,890	NSW models
				irrigation recharge	4,790	NSW models
	GS44	Upper Lachlan Alluvium	NSW	rainfall recharge	17,786	NSW models
				irrigation recharge	9,486	NSW models
GW 9 Murrumbidgee Alluvium	GS28	Lower Murrumbidgee Alluvium (shallow; Shepparton formation)	NSW	rainfall recharge	43,392	NSW models
				irrigation recharge	36,556	NSW models
	GS31	Mid-Murrumbidgee Alluvium	NSW	rainfall recharge	10,940	NSW models
				irrigation recharge	126	NSW models
GW8 Murray Alluvium	GS27	Lower Murray Alluvium, shallow; Shepparton formation	NSW	rainfall recharge	114,753	Bureau
	GS46	Upper Murray Alluvium	NSW	rainfall recharge	14,050	Bureau
GW2 Goulburn–Murray	GS8	Goulburn-Murray (Ovens–Kiewa sedimentary plain)	Vic.	rainfall recharge	92,814	Bureau
	GS8	Goulburn-Murray (Victorian Riverine sedimentary plain)	Vic.	rainfall recharge	237,387	Bureau
GW3 Wimmera–Mallee (groundwater)	GS9	Wimmera–Mallee (sedimentary plain)	Vic.	rainfall recharge	273,693	Bureau
GW5 Eastern Mount Lofty Ranges	GS01	Angas Bremer (Quaternary sediments and Murray Group limestone)	SA	rainfall recharge	10,918	Bureau
GW4 SA Murray Region	GS03	Mallee Murray Group limestone	SA	rainfall recharge	36,655	Bureau
	GS05	Peake–Roby–Sherlock (unconfined)	SA	rainfall recharge	24,759	Bureau
Sub-total Southern Basin					992,995
Total for the region					1,539,098

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 2013 Account.

(1) Bureau of Meteorology (the Bureau): National Climate Centre daily climate grids (rainfall, temperature, vapour pressure and solar radiation); (2) Australian soil resources information system: 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 water table was shallow. A shallow water table was assumed to be where the depth to the water table 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 water table 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.

A prior period error and a change made to the calculation method resulted in the restatement of the 2011–12 year volume. The respective volumes associated with the change are detailed in the following table.

Restatement of comparative year information made for the line item 10.3 Recharge from landscape 

Segment	2013 Account volume for the 2011–12 year (ML)	2012 Account volume for the 2011–12 year (ML)	Difference due to a prior period error and calculation method change (ML)
Northern Basin	254,547	254,547	0
Southern Basin	2,871,380	2,878,644	(7,264)
Whole region	3,125,927	3,133,191	(7,264)

The volume estimated for the comparison year for the 2013 Account is lower than the volume reported for the 2012 Account. This was due to the following reasons:

• There was a prior period error in the line item volume reported in the 2012 Account. The prior period error was a result of using solar radiation data with bias correction errors. Solar radiation is an input for line item volume calculation.
• The difference between the previously reported volume and the estimate produced for the comparison year can be partly attributed to the choice of different bore hole locations for measured groundwater levels (data from same set of bore holes used in the 2012 Account were not available for calculations).