Murray-Darling Basin
10.3 Recharge from landscape

The volumetric value for the line item for the 2010–11 year was 9,784,419 ML. The following tables provide detailed volumetric information for the line item. 

 

Summary of groundwater recharge from landscape in the Murray–Darling Basin (MDB) region in the 2010–11 year

Groundwater resource plan area		State	Volume (ML) for the 2010–11 year
Code	Name
GW23	Warrego – Paroo – Nebine	Qld	–
GW22	Condamine–Balonne	Qld	–
GW21	Moonie	Qld	–
GW20	Qld Border Rivers	Qld	–
GW19	NSW Border Rivers Alluvium	NSW	–
GW18	New England Fractured Rock and Northern Basalts	NSW	–
GW17	Eastern Porous Rock	NSW	–
GW16	Gwydir Alluvium	NSW	63,256
GW15	Namoi Alluvium	NSW	5,303,311
GW14	NSW Alluvium above GAB	NSW	–
GW13	NSW Sediments above GAB	NSW	–
GW12	Macquarie–Castlereagh Alluvium	NSW	51,184
GW11	Lachlan and South Western Fractured Rock	NSW	–
GW7	Darling Alluvium	NSW	–
Sub-total Northern Basin			5,417,751
GW11	Lachlan and South Western Fractured Rock	NSW	–
GW7	Darling Alluvium	NSW	–
GW10	Lachlan Alluvium	NSW	175,290
GW9	Murrumbidgee Alluvium	NSW	432,950
GW8	Murray Alluvium	NSW	927,976
GW6	Western Porous Rock	NSW	–
GW2	Goulburn-Murray	Vic	2,174,256
GW3	Wimmera–Mallee (groundwater)	Vic	467,768
GW5	Eastern Mount Lofty Ranges	SA	–
GW4	SA Murray	SA	400,248
GW1	ACT (groundwater)	ACT	–
Sub-total Southern Basin			4,366,668
Total for the region			9,784,419

– = Data not available

 

Details of groundwater recharge from landscape in the MDB region in the 2010–11 year

Groundwater resource plan area	Groundwater sustainable diversion limit area		State	Type of recharge	Volume (ML) for the 2010–11 year	Data source1
	Code	Name
GW11 Gwydir Alluvium	GS29	Lower Gwydir Alluvium	NSW	Rainfall recharge	63,256	Bureau
GW 15 Namoi Alluvium	GS34	Lower Namoi Alluvium	NSW	Rainfall recharge	5,212,583	Bureau
	GS51	Upper Namoi Alluvium	NSW	Rainfall recharge	77,030	NSW models
				Irrigation recharge	13,698	NSW models
GW12 Macquarie–Castlereagh Alluvium	GS31	Lower Macquarie Alluvium	NSW	Rainfall recharge and irrigation channel	31,864	NSW models
				Irrigation recharge	19,320	NSW models
Sub-total Northern Basin					5,417,751
GW 10 Lachlan Alluvium	GS30	Lower Lachlan Alluvium	NSW	Rainfall recharge	170,500	NSW models
				Irrigation recharge	4,790	NSW models
GW 9 Murrumbidgee Alluvium	GS33	Lower Murrumbidgee Alluvium, shallow; Shepparton Formation	NSW	Rainfall recharge	211,820	NSW models
				Irrigation recharge	221,130	NSW models
GW8 Murray Alluvium	GS32	Lower Murray Alluvium, shallow; Shepparton Formation	NSW	Rainfall recharge	927,976	Bureau
GW2 Goulburn–Murray	GS8e	Ovens–Kiewa Sedimentary Plain	Vic	Rainfall recharge	393,675	Bureau
	GS8f	Victorian Riverine Sedimentary Plain, shallow: Shepparton Formation	Vic	Rainfall recharge	1,780,581	Bureau
GW3 Wimmera–Mallee (groundwater)	GS9a	West Wimmera, Murray Group Limestone	Vic	Rainfall recharge	286,179	Bureau
	GS9c	Wimmera–Mallee Border Zone, Murray group Limestone	Vic	Rainfall recharge	181,589	Bureau
GW4 SA Murray	GS03	Mallee Murray Group Limestone	SA	Rainfall recharge	340,661	Bureau
	GS05	Peake – Roby – Sherlock (unconfined)	SA	Rainfall recharge	59,587	Bureau
Sub-total Southern Basin					4,366,668
Total for the region					9,784,419

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 2011 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) inputs to the New South Wales groundwater models draw from knowledge of the hydrogeology and surface water processes and outputs from same models received from NSW Office of Water.

The Bureau and NSW Office of Water.

For the SDL areas for which 'Data source' is shown as Bureau in the tables provided under Supporting information 

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 watertable was considered for all regions where the depth to watertable was shallow. A shallow watertable was assumed to be where the depth to the watertable was 4 m or less below the ground surface. 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 tables provided under Supporting information

Recharge volumes were calculated for selected SDL areas applying New South Wales groundwater models based on MODFLOW (United States Geological Survey 2011) 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 watertable 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 2011).

• 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.

This line item corresponds to line item 15.2.1 Diffuse groundwater recharge from landscape water, reported in the 2010 Account. In the 2011 Account, the following changes were made that caused the 2009–10 year value to be restated:

• The scope of the line item was changed.

• The presentation of the line items has changed since the 2010 Account.

• The methodology used to quantify the line item was improved and resulted in a material change in volume.

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

 

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

2010 Account line items	Segment	Volume for the 2009–10 year reported in the 2010 Account (ML)	Difference due to scope change  (ML)	Difference due presentation and calculation methodology change  (ML)	Volume for the 2009–10 year reported in the 2011 Account (ML)
15.2.1 Diffuse groundwater recharge from landscape water	Northern Basin	123,215	4,147,725	1,284	4,272,224
	Southern Basin	1,630,496	–166,336	69,321	1,533,481
	Whole region	1,753,711	3,981,389	70,605	5,805,705

 

The scope change was due to the following reasons:

• Northern Basin – expansion of Lower Namoi Alluvium (4,147,725 ML) to cover whole area instead of a part of the area (for which groundwater models were available) considered in the 2010 Account

• Southern Basin – inclusion of Ovens–Kiewa Sedimentary Plain (change: 182,059 ML)

• Southern Basin – exclusion of Upper Lachlan Alluvium (339,527 ML) and Upper Murray Alluvium (8,868 ML) to maintain consistency with the asset information provided in line item 2.5.

The presentation change was due to the following reason:

• The restated value for the 2011 Account was an estimate of recharge only while the values reported for the 2010 Account was estimated as the net recharge, which is the difference between the recharge and discharge.