Murray-Darling Basin
18.3 Discharge to landscape

The volumetric value for the line item for the 2010–11 year was 308,128 ML. The line item represents discharge from aquifers to landscape that includes soil, unconnected lakes and wetlands. The following tables provide detailed volumetric information for the line Item.

 

Summary of groundwater discharge to landscape in the Murray–Darling Basin region in the 2010–11 year

Groundwater resource plan area		State	Volume (ML)
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	–
GW15	Namoi Alluvium	NSW	36,992
GW14	NSW Alluvium above GAB	NSW	–
GW13	NSW Sediments above GAB	NSW	–
GW12	Macquarie–Castlereagh Alluvium	NSW	–
GW11	Lachlan and South Western Fractured Rock	NSW	–
GW7	Darling Alluvium	NSW	–
Sub-total Northern Basin			36,992
GW11	Lachlan and South Western Fractured Rock	NSW	–
GW7	Darling Alluvium	NSW	–
GW10	Lachlan Alluvium	NSW	5,550
GW9	Murrumbidgee Alluvium	NSW	14,750
GW8	Murray Alluvium	NSW	790
GW6	Western Porous Rock	NSW	–
GW2	Goulburn–Murray	Vic	250,046
GW3	Wimmera–Mallee (groundwater)	Vic	–
GW5	Eastern Mount Lofty Ranges	SA	–
GW4	SA Murray	SA	–
GW1	ACT (groundwater)	ACT	–
Sub-total Southern Basin			271,136
Total for the region			308,128

– = Data not available

 

Details of groundwater discharge to landscape in the MDB region in the 2010–11 year

Groundwater resource plan area	Groundwater sustainable diversion limit area		State	Volume (ML)
	Code	Name
GW 15 Namoi Alluvium	GS51	Upper Namoi Alluvium	NSW	36,992
Sub-total Northern Basin				36,992
GW 10 Lachlan Alluvium	GS30	Lower Lachlan Alluvium		5,550
GW 9 Murrumbidgee Alluvium	GS33	Lower Murrumbidgee Alluvium, shallow: Shepparton Formation	NSW	14,750
GW8 Murray Alluvium	GS32	Lower Murray Alluvium, shallow: Shepparton Formation	NSW	790
GW2 Goulburn–Murray	GS8e	Ovens–Kiewa Sedimentary Plain	Vic	989
	GS8f	Victorian Riverine Sedimentary Plain, shallow: Shepparton Formation	Vic	249,057
Sub-total Southern Basin				271,136
Total for the region				308,128

 

Sustainable diversion limit (SDL) areas other than those included in the detail table exist and may be relevant to the line item, however, relevant information was not available for the 2011 Account.

For SDL areas Lower Lachlan Alluvium, Lower Murrumbidgee Alluviums and Upper Namoi Alluvium: 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. For the other SDL areas: (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, and (3) Australian Bureau of Agricultural and Resource Economics and Sciences: Land-use data.

The Bureau and NSW Office of Water.

The Bureau method (For SDL areas other than Lower Lachlan Alluvium, Lower Murrumbidgee Alluvium and Upper Namoi Alluvium)

Groundwater discharge was estimated along with diffuse groundwater recharge 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 watertable was 4 m or less below the ground surface. Where the watertable was not shallow, free drainage conditions were assumed. For SDL areas with a shallow watertable, the model may produce a net discharge from groundwater over the calculation period.

New South Wales groundwater models method (For SDL areas Lower Lachlan Alluvium, Lower Murrumbidgee Alluvium and Upper Namoi Alluvium)

Discharge was calculated for selected SDL areas by applying New South Wales groundwater models where the MODFLOW (United States Geological Survey 2011) evapotranspiration routines were activated to represent groundwater discharge.

The Bureau method:

• The assumptions made in developing the WAVES model as described in Dawes et al. (1998) were all applicable to the discharge estimations carried out for this line item.

• 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 discharge 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 (refer to the United States Geological Survey website for more details).

The uncertainty estimate was not quantified.

For the Bureau method, the uncertainty in the input parameters and the corresponding impacts on the modelled discharge values were not studied and the uncertainty of the estimated discharge resulting from different interpolation methods was not estimated.

For New South Wales groundwater models, uncertainty of a discharge estimate was not evaluated for the groundwater models.

This line item corresponds to line item 16.3.1 Groundwater discharge to landscape, 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 presentation of the line items has changed since the 2010 Account; the restated value was an estimate of discharge only, while the values reported for the 2010 Account were estimated as the net recharge which is the difference between the recharge and discharge.

• The scope of the line item was changed; Goulburn-Murray SDL area was included in the 2011 Account (no value was provided in the 2010 Account). Mid-Murrumbidgee Alluvium was excluded in the 2011 Account to maintain consistency with the information provided in other groundwater line items.

• The methodology used to quantify the line item was improved and resulted in a material change in volume; the 2009–10 year modelled volumes for Lower Murrumbidgee SDL areas were updated.

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

 

Restatement of comparative year information made for the line item 18.3 Discharge to landscape

2010 Account line items	Segment	Volume for the 2009–10 year reported in the 2010 Account (ML)	Difference due to presentation, scope and calculation methodology change (ML)	Volume for the 2009–10 year reported in the 2011 Account (ML)
16.3.1 Groundwater discharge to landscape	Northern Basin	0	0	0
	Southern Basin	28,130	220,099	248,229
	Whole region	28,130	220,099	248,229