Murray-Darling Basin
Resources and Systems

The purpose of this note is to provide a consolidated report on the surface water store within the Murray–Darling Basin (MDB) region during the 2010–11 year. Information on all water flows to and from the surface water store are presented here, including between store flows (e.g. flows between surface water and groundwater stores) and transfers that are not presented in the water accounting statements.

A description of the MDB region's surface water resources is provided in the Surface water section of the Contextual information.

Table 1 shows that the total surface water store increased during the 2010–11 year in the MDB region.

 

Table 1. Surface water store volume at the start and end of the 2010–11 year for the MDB region

Description	30 June 2011 (ML)			30 June 2010 (ML)
	Northern Basin	Southern Basin	Whole region	Northern Basin	Southern Basin	Whole region
1 Surface water
1.1 Storages	3,333,324	15,831,830	19,165,154	788,363	6,658,886	7,447,249
1.2 Unregulated river	–	–	–	–	–	–
1.3 Regulated river	19,234	1,277,467	1,296,701	17,086	951,440	968,526
1.4 Lakes and wetlands	0	1,907,353	1,907,353	0	1,169,447	1,169,447
1.10 Other surface water assets	0	18,131	18,131	0	13,574	13,574
Total	3,352,558	19,034,781	22,387,339	805,449	8,793,347	9,598,796

Table 1 includes information only for five lakes: Lake Albert, Lake Alexandrina, Lake Burley Griffin, Lake Ginninderra and Lake Tuggeranong. Volume of water stored in other lakes and wetlands could not be quantified accurately due to a lack of available data.

The location of major storages within the MDB region, and the volume of water, including dead storage, in each storage as a percentage of total storage capacity (% full) at the end of the 2010–11 year, is shown in Figure 1.

 
 

Figure 1. Location map of major storages within the MDB region. The % full volume on 30 June 2011 for major storages is also shown

 

The water volume in majority of the storages within the MDB region at the end of the 2010–11 year was greater than that at the start (see line item 1.1 Storages). The large increase in surface water storage during the year is primarily attributed to the record high inflows into the storages during the 2010–11 year. This situation reflects the well above average rainfall conditions observed throughout the region in the 2010–11 year. Some areas, both in the Northern Basin and the Southern Basin, recorded their highest annual rainfall on record (see Rainfall in Climate overview 2010–11).

A schematic diagram representing all the inflows and outflows associated with the surface water store in the MDB region is provided in Figure 2. The inflow and outflow volumes for the surface water store during the 2010–11 year are given in Table 2. In addition to flows reported in the water accounting statements, Figure 2 and Table 2 also show flows between the surface water and groundwater stores within the region.

Figure 2. Schematic diagram of water inflows (blue arrows) and outflows (red arrows) for the surface water store within the MDB region during the 2010–11 year

Note: Solid arrows indicate water transfers; dotted arrows indicate natural water movement; waved arrows indicate leakage. Line item numbers are provided next to the flows.

 

Table 2. Volume of inflows and outflows for the surface water store within the MDB region during the 2010–11 year

Description		Volume (ML)
		Northern Basin	Southern Basin	Whole region
9 Surface water inflows
Line item number and name	9.1 Precipitation on surface water	226,858	1,792,762	2,019,620
	9.2 River inflow to region	0	1,840,333	0
	9.3 Groundwater discharge	4,541	8,670	13,211
	9.4 Runoff to surface water	31,009,785	43,201,180	74,210,965
	9.5 Point return from irrigation scheme	0	216,917	216,917
	9.6 Overbank flood return to river channel	–	–	–
	9.9 Discharge from urban water system	0	34,897	34,897
	9.10 Direct discharge by user	–	–	–
	9.11 Delivery of water under inter–region agreement	0	2,310,491	2,310,491
Total 9 Surface water inflows		31,241,184	49,405,250	78,806,101
17 Surface water outflows
Line item number and name	17.1 Evaporation from surface water	372,396	3,133,172	3,505,568
	17.2 River outflow from the region	1,840,333	12,849,073	12,849,073
	17.3 Leakage to groundwater	54,745	268,210	322,955
	17.4 Leakage to landscape	–	–	–
	17.5 Overbank flood spilling	652,699	0	652,699
	17.6 Diversions: other statutory rights	28,151	19,135	47,286
	17.7 Non-allocated diversions to users	1,451,542	565,240	2,016,782
	17.8 Non-allocated diversions – urban system	3,167	17,421	20,588
	17.10 River and floodplain leakage, evaporation and errors	23,767,902	18,546,512	42,314,414
	17.11 Surface water allocation diversion	507,631	3,513,176	4,020,807
	17.12 Surface water allocation diversion – urban system	15,509	251,875	267,384
Total 17 Surface water outflows		28,694,075	39,163,814	66,017,556
Balancing item – surface water store		0	2	2
Change in surface water storage		2,547,109	10,241,434	12,788,543
Opening surface water storage		805,449	8,793,347	9,598,796
Closing surface water storage		3,352,558	19,034,781	22,387,339

Note: Line items in italic indicate between-stores flows, which are not presented in the water accounting statements as they occur within the region. Volumes shown for the balancing item – surface water store are not equal to zero for the Southern Basin and the whole region due to rounding of the volumes for the line items to the nearest integer. Information on line items (presented in the table) and their values are available through the links provided.

Allocation diversions, non-allocated diversions, and water abstraction under other statutory rights are the main forms of surface water diversions within the MDB region.

The allocation diversions are associated with a water access entitlement. When an allocation is announced, an obligation (water liability) is created on the surface water to deliver water to the user. The entitlement holder (an individual or water supply organisation, where necessary) then orders the release or delivery of the allocated water and diverts it, which reduces the water liability. Allocation diversions, 4,288,191 ML, account for 67% of all diversions within the region for the 2010–11 year.

Non-allocated diversions are also associated with a water access entitlement, but are primarily unregulated diversions. Other statutory rights for surface water diversions are non-entitled water rights. They may be conferred by jurisdictional water acts or be written in water management plans and include land owner basic rights, riparian rights, indigenous rights and stock and domestic rights.

The entitlement, allocation announcement and forfeiture for water rights associated with surface water diversion during the 2010–11 year are provided in the Water rights, entitlements, allocations and restrictions note.

Figure 3 compares surface water diversions within the MDB region for the 2009–10 year and the 2010–11 year. Allocation diversions from storages during the 2010–11 year for urban supply have decreased but increased for all other categories compare to diversions made during the 2009–10 year.

 

Figure 3. Graph of surface water diversions from storages within the MDB region during the 2010–11 year and the 2009–10 year comparison

 

The volume of the balancing item represents the volume necessary to reconcile the opening and closing balances of the surface water store with the physical water inflows and outflows (Table 3). Inter-store flows between groundwater and surface water stores were included in calculating balancing volume for the surface water store (these flows were excluded in calculating unaccounted-for difference for the water accounting statements).

 

Table 3. Balancing item for the surface water store for the 2010–11 year

Description		Volume (ML)
		Northern Basin	Southern Basin	Whole region
	Opening balance (30 June 2010)	805,449	8,793,347	9,598,796
add	Total 9 Surface water inflows	31,241,184	49,405,250	78,806,101
less	Total 17 Surface water outflows	28,694,075	39,163,814	66,017,556
less	Closing balance (30 June 2011)	3,352,558	19,034,781	22,387,339
	Balancing item – surface water store	0	2	2

 

The volume of the balancing item for the MDB region should be zero (Value 2 ML is shown for the Southern Basin and the whole region due to rounding-off errors).  This is because line item 17.10 River and floodplain leakage, evaporation and errors was calculated applying a water balance approach. Therefore, any balancing volume for the region is included in that line item.

Information on 49 storages for which data were available is included in line item 1.1 Storages. Table 4 presents information on increases and decreases for the storages for which data were available.

All the volumes given in Table 4 relate to water flows into and out of the following surface water storages:

• Menindee Lake
• Hume Reservoir
• Dartmouth Reservoir
• Lake Victoria.

These flows are different from the flows reported in the water accounting statements or in Table 2, which refer to flows affecting the surface water store as a whole, including all storages recognised for the region, rivers and weirs.

 

Table 4. Volume of inflows and outflows for storages that are associated with surface water diversion in the MDB region during the 2010–11 year

Description		Volume (ML)
Opening storage		2,896,100
41 Storage inflows
Line item and name	41.1 Precipitation on storages	483,118
	41.2 Groundwater discharge into storages	–
	41.3 Runoff into storages	13,341,900
	41.4 Transfer of water into storages	–
Total 41 Storage inflows		13,825,018
42 Storage outflows
Line item and name	42.1 Evaporation from storages	679,513
	42.2 Groundwater recharge from storages	–
	42.3 Leakage from storages	–
	42.4 Spillage from storages	7,100,000
	42.5 Releases from storages	2,095,000
	42.6 Diversions from storages	320,000
Total 42 Storage outflows		10,194,513
Closing storage		6,526,605
Net change in volume		3,630,505

– = data not available during the data collection period for the 2011 Account.

The purpose of this note is to provide a consolidated report on the groundwater store within the Murray–Darling Basin (MDB) region during the 2010–11 year. Information on all water flows to and from the groundwater store are presented here, including between store flows and transfers that are not presented in the water accounting statements.

A description of the MDB region's groundwater resources are provided under Groundwater in the physical information section of the Contextual information.

Information on groundwater assets in the region is included in line item 2.5 Other groundwater assets. Long-term estimates of volumes for extraction (include volume of supplementary access licence that was available for use in New South Wales in the 2010–11 year) and basic landholder rights are defined as the groundwater assets considered for the region. These assets do not reflect temporal fluctuation of groundwater levels. Therefore, groundwater assets for the region are not responsive to groundwater storage changes resulting from water table fluctuations. As a result, groundwater assets are constant except for administrative changes to long-term estimates of volumes for extraction and landholder rights. Increases to administrative groundwater asset volumes may be the result of the commencement of a water resource plan for a groundwater source area within the basin. Decreases in administrative groundwater asset volume in New South Wales may be a result of the reduction of supplementary access licence volumes as outlined in the relevant water resource plans. Information for asset volumes separately on water table aquifers and underlying aquifers are not available for the region.

 

Table 5. Groundwater store volume at the start and end of the 2010–11 year

Description	30 June 2011 (ML)			30 June 2010 (ML)
	Northern Basin	Southern Basin	Whole region	Northern Basin	Southern Basin	Whole region
2 Groundwater
2.1 Water table aquifer	–	–	–	–	–	–
2.2 Underlying aquifers	–	–	–	–	–	–
2.5 Other groundwater assets	440,923	886,795	1,327,718	368,741	827,825	1,196,566
Total	440,923	886,795	1,327,718	368,741	827,825	1,196,566

– = Data not available

 

A schematic diagram representing all the inflows and outflows associated with the groundwater store in the MDB region is provided in Figure 4. The inflow and outflow volumes for the groundwater store during the 2010–11 year are given in Table 6. In addition to flows reported in the water accounting statements, Figure 4 and Table 6 also show flows between the surface water and groundwater stores.

Figure 4. Schematic diagram of water inflows and outflows for the groundwater store within the MDB region during the 2010–11 year

Note: Dotted lines indicate natural flows while solid lines represent flows induced by human activities. Line item numbers are provided next to the flows.

 

Table 6. Volume of inflows and outflows for the groundwater store during the 2010–11 year

Description		Volume (ML)
		Northern Basin	Southern Basin	Whole region
10 Groundwater inflows
Line item number and name	10.1 Groundwater inflow from outside region	0	2,879	2,879
	10.2 Groundwater inflow from outside region at coast	0	62	62
	10.3  Recharge from landscape	5,417,751	4,366,668	9,784,419
	10.4 Recharge from surface water	54,745	268,210	322,955
	10.5 Leakage from off-channel water storage	–	–	–
	10.6 Leakage from urban system	–	–	–
	10.7 Leakage from irrigation scheme	–	–	–
	10.8 Managed aquifer recharge – private user	0	4,158	4,158
	10.13 Other groundwater increases	80,562	65,215	145,777
Total 10 Groundwater inflows		5,553,058	4,707,192	10,260,250
17 Surface water outflows
Line item number and name	18.1 Groundwater outflow to outside region	0	3	3
	18.2 Groundwater outflow to outside region at coast	0	1,663	1,663
	18.3 Discharge to landscape	36,992	271,136	308,128
	18.4 Discharge to surface water	4,541	8,670	13,211
	18.7 Extraction: other statutory rights	12,858	10,825	23,683
	18.11 Groundwater allocation extraction	125,032	208,880	333,912
	18.12 Groundwater allocation extraction – urban water system	9,047	1,339	10,386
	18.18 Other groundwater decreases	8,380	6,245	14,625
Total 18 Groundwater outflows		196,850	508,761	705,611
Balancing item – groundwater store1		5,284,026	4,139,461	9,423,487
Change in groundwater storage		72,182	58,970	131,152
Opening groundwater storage		368,741	827,825	1,196,566
Closing groundwater storage		440,923	886,795	1,327,718

 ¹ See Supporting information of line item 25.1 Unaccounted–for difference for details.

Line items in italic indicate between-store flows. These flows are not presented in the water accounting statements as they occur within the region.

 

 Allocation extraction and water abstraction under other statutory rights are the main forms of groundwater extractions within the MDB region. The allocation extractions are associated with a water access entitlement.

Figure 5 compares groundwater extractions within the MDB region for 2009–10 and 2010–11 years. Allocation extractions reported in line item 18.11 (primarily for non-urban purposes), of 333,912 ML, account for 91% of all extractions within the region for the 2010–11 year. These extractions during the 2010–11 year were decreased by 59% compared to 2009–10 extractions. No major change in extractions was observed for other water use categories.

 

 

Figure 5. Graph of extractions from aquifers within the MDB region during the 2010–11 year and 2009–10 comparison

 

 

The entitlement, allocation announcement and forfeiture for water rights associated with groundwater extraction during the 2010–11 year are provided in the Water rights, entitlements, allocations and restrictions note.

Balancing item – groundwater store

Information on balancing item – groundwater store is available under Supporting information of line item 25.1

Unaccounted–for difference.

Changes in the groundwater store volume of the water table aquifers during the 2010–11 year were evaluated using aquifer characteristics and groundwater level measurements (see quantification methods given below).

Changes in store volumes are not reported in the water accounting statements for the MDB region because asset volumes were based on long term estimates of volumes for extraction and landholder rights.

Table 7 reports on changes in the groundwater store volume of the watertable aquifers for the sustainable diversion limit (SDL) areas within region for which data were available.

 

Table 7. Volumetric values of changes in groundwater storage in the MDB region for the 2010–11 year

Groundwater resource plan area	Groundwater SDL area		State	Change in groundwater storage in the 2010–11 year (ML)1	Method used to quantify change in groundwater storage	Groundwater asset volume (ML)	Change in groundwater storage relative to groundwater asset (%)
	Code	Name
Gwydir Alluvium	GS29	Lower Gwydir Alluvium	NSW	–19,147	The Bureau method	43,139	–44%
Namoi Alluvium	GS34	Lower Namoi Alluvium	NSW	425,160	The Bureau method	99,741	426%
	GS51	Upper Namoi Alluvium	NSW	31,752	NSW model zone 2-12	142,209	22%
Macquarie–Castlereagh Alluvium	GS31	Lower Macquarie Alluvium	NSW	62,034	NSW model zone 1 to 6	72,223	86%
Sub-total Northern Basin				499,799		–	–
Lachlan Alluvium	GS30	Lower Lachlan Alluvium	NSW	114,050	NSW model	126,876	90%
Murrumbidgee Alluvium	GS33	Lower Murrumbidgee Alluvium, shallow: Shepparton Formation	NSW	467,400	NSW model	–	–
Murray Alluvium	GS32	Lower Murray Alluvium, shallow: Shepparton Formation	NSW	1,142,477	The Bureau method	–	–
Goulburn–Murray	GS8e	Goulburn–Murray: Ovens–Kiewa Sedimentary Plain	Vic	205,677	The Bureau method	–	–
	GS8f	Goulburn-Murray: Victorian Riverine Sedimentary Plain, shallow: Shepparton Formation	Vic	2,548,063	The Bureau method	–	–
Wimmera–Mallee (groundwater)	GS9a	Wimmera–Mallee: West Wimmera, Loxton Parilla Sands	Vic	255,732	The Bureau method, unconfined aquifer	–	–
		Wimmera-Mallee: West Wimmera, Murray Group Limestone	Vic
	GS9c	Wimmera-Mallee: Wimmera–Mallee Border Zone, Loxton Parilla Sands	Vic
		Wimmera-Mallee: Wimmera–Mallee Border Zone, Murray Group Limestone	Vic
South Australian Murray	GS3	Mallee, Pliocene Sands	SA
		Mallee Murray, Group Limestone	SA
	GS5	Peake – Roby – Sherlock, unconfined	SA
Sub-total Southern Basin				4,733,399		–	–
Total for the region				5,233,198		–	–

¹ Change in groundwater storage is the estimated difference between all inflows to the store and outflows from the store for the 2010–11 year (see Method in quantification approaches for more details).

NSW = New South Wales, VIic = Victoria, SA = South Australia, The Bureau = Bureau of Meteorology

Table 7 also indicates what method was used to quantify the change in groundwater storage in each SDL area: either the Bureau method based on measured groundwater levels or the New South Wales groundwater model results (NSW models).

With time, trends in the yearly changes in groundwater storages will provide more useful information about the adequacy of the extraction limits set in the groundwater management plans. For instance, a long-term trend of negative changes in groundwater storage may indicate that groundwater in an area may be over allocated.

Quantification approaches for the estimation of changes in groundwater stored in aquifers

Data source: The Bureau method

Bore locations and groundwater level data in South Australia were sourced from the Drill-hole Enquiry System (Department for Water 2011c).

Bore locations and groundwater level data in Victoria were sourced from the Department of Sustainability and Environment (DSE) and Victorian Department of Primary Industries (DPI) through a database developed by the University of Melbourne.

Bore locations and groundwater level data in New South Wales were sourced from NSW Office of Water.

Bore locations and groundwater level data in Queensland were sourced from Department of Environment and Resource Management (DERM).

The geographic information system (GIS) data relating to the boundaries of the aquifers and SDL regions were extracted from the Interim Groundwater Geodatabase developed for the Bureau by Sinclair Knight Merz (Bureau of Meterology 2011b).

Data source: NSW Office of Water method

The outputs of the New South Wales groundwater models available within selected SDL areas were used.

Data provider

The Bureau and NSW Office of Water (groundwater models).

Method: The Bureau method

Change in extractable storage is estimated using a simple GIS approach based on measured groundwater levels and aquifer properties. Firstly, groundwater levels at the start (1 July 2010) and the end (30 June 2011) of the 2010–11 year were estimated. This was achieved by considering all groundwater level measurements between March 2010 to October 2010 and March 2011 to October 2011, respectively, and using the measurements closest in time to interpolate the start and end levels. The estimated groundwater levels on the start and end dates were then spatially interpolated to grids using the ArcGIS Topo-to-Raster tool. The change in volume within the sedimentary area was calculated using these interpolated groundwater level surfaces. By comparison the change was also calculated using only the interpolation of the change in level within each bore.

These volumes were multiplied by appropriate specific yield values (Commonwealth Scientific and Industrial Research Organisation and Sinclair Knight Merz 2010a and 2010b) to convert the volume to a change in groundwater storage. Finally, change in storage was only considered within a 10 km mask of each groundwater observation bore to ensure an appropriate influence from the change in each bore.

The two estimates were compared for consistency and the average of these volumes was reported for the unconfined aquifers only. 
 

Figure 6. SDL areas used to estimate changes in groundwater storage

 

Method: NSW Office of Water method

NSW groundwater (see list of applicable SDL areas in Table 7) model outputs were used to evaluate the changes in groundwater storage. The change in groundwater storage derived from the groundwater models in New South Wales included all the groundwater model layers (not just the water table aquifer layer).

Uncertainty: The Bureau method

Uncertainty estimate was not quantified.

The uncertainty in the field-measured data (e. g. groundwater levels, specific yield) was not specified and hence the impacts of such uncertainty on the change in storage were not estimated.

The change in storage estimations were calculated from the interpolated groundwater level grids produced using ArcGIS Topo-to-Raster tool. Use of other interpolation methods may impact the values of the groundwater level grids and hence the estimated values for change in groundwater storage.

Uncertainty: NSW Office of Water method

The uncertainty estimate was not quantified.

It is currently not feasible to estimate the uncertainty of modelled change in extractable storage from outputs of a MODFLOW groundwater model.

Approximations, assumptions, caveats and limitations

The Bureau method:

• Change in groundwater storage was not calculated for confined aquifers. Under normal circumstance, the annual change in storage is considered to be negligible for confined aquifers due to their very low storage coefficient, which is much lower than the specific yield of unconfined aquifers (Freeze and Cherry 1979, Johnson 1967). As long as confined aquifers remain saturated, changes in piezometric levels (i. e. aquifer pressure) usually cause small changes in water volumes stored in the aquifers; the changes are equivalent to the volumetric expansion/contraction of the water and the pore space.

• The specific yield values used in each watertable aquifer are presented in the following table.

NSW groundwater models (see list of applicable SDL areas concerned in Table 7):

• Details on the limitations of groundwater models used by NSW Office of Water can be accessed through its webpage on Water accounting.

 

Table 8. Specific yield values used in calculating the change in groundwater storage with the Bureau method

SDL area		Specific Yield
Code	Name
Northern Basin
GS29	Lower Gwydir Alluvium	0.20
GS34	Lower Namoi Alluvium	0.10
Southern Basin
GS32	Lower Murray Alluvium, shallow: Shepparton Formation	0.10
GS8e	Goulburn–Murray: Ovens–Kiewa Sedimentary Plain	0.15
GS8f	Goulburn–Murray: Victorian Riverine Sedimentary Plain, shallow: Shepparton Formation	0.10
GS3	Mallee, Pliocene Sands	0.115, Unconfined aquifer
	Mallee Murray, Group Limestone
GS5	Peake – Roby – Sherlock, unconfined
GS9a	Wimmera–Mallee: West Wimmera, Loxton Parilla Sands
	Wimmera–Mallee: West Wimmera, Murray Group Limestone
GS9c	Wimmera–Mallee: Wimmera–Mallee Border Zone, Loxton Parilla Sands
	Wimmera–Mallee: Wimmera–Mallee Border Zone, Murray Group Limestone

 

Groundwater inflow from other SDL areas within a segment has been calculated for selected SDL areas. Tables 9 and 10 provide details for the Northern Basin and the Southern Basin.

 

Table 9. Details of groundwater inflow to a SDL area from other SDL areas within the Northern Basin

SDL area		Volume (ML) for the 2009–10 year	Volume (ML) for the 2010–11 year
Code	Name
GS29	Lower Gwydir Alluvium	284	279
GS34	Lower Namoi Alluvium	655	667

Table 10. Details of groundwater inflow to a SDL area from other SDL areas within the Southern Basin

SDL area		Other details	Volume (ML) for the 2009–10 year	Volume (ML) for the 2010–11 year
Code	Name
GS3	Mallee, Pliocene Sands	Unconfined aquifer	16,160	15,831
	Mallee Murray, Group Limestone
GS5	Peake–Roby–Sherlock, unconfined
GS9a	Wimmera–Mallee: West Wimmera, Loxton Parilla Sands
	Wimmera–Mallee: West Wimmera, Murray Group Limestone
GS9c	Wimmera–Mallee: Wimmera–Mallee Border Zone, Loxton Parilla Sands
	Wimmera–Mallee: Wimmera–Mallee Border Zone, Murray Group Limestone
GS3	Mallee, Renmark Group	Confined aquifer	9686	7652
GS5	Peake–Roby–Sherlock, confined
GS9a	Wimmera–Mallee: West Wimmera, Tertiary Confined Sands
GS9c	Wimmera–Mallee: Wimmera–Mallee Border Zone, Tertiary Confined Sand Aquifer
GS8e	Goulburn–Murray: Ovens–Kiewa Sedimentary Plain		1	4
	Goulburn–Murray: Ovens–Kiewa Confined		192	212
GS8f	Goulburn–Murray: Victorian Riverine Sedimentary Plain, deep: Calivil and Renmark Formations		59,437	61,413
	Goulburn–Murray: Victorian Riverine Sedimentary Plain, shallow: Shepparton Formation		6,546	6,280
GS30	Lower Lachlan Alluvium		220	370
GS32	Lower Murray Alluvium, deep: Renmark Group and Calivil Formation		324,336	276,448
	Lower Murray Alluvium, shallow: Shepparton Formation		16,880	17,034
GS33	Lower Murrumbidgee Alluvium, deep: Calivil Formation and Renmark Group		10,850	9,330
	Lower Murrumbidgee Alluvium, shallow: Shepparton Formation		470	1,030

Quantification approaches for the estimation of inflow to a SDL area from other SDL areas within a segment – Northern Basin

Two estimation methods, the Bureau method and NSW Office of Water method were applied in calculations (see line Item 10.1 Groundwater inflow from outside region for more details on the methods).

Data source

The Bureau method:

• Bore locations and groundwater level data in New South Wales were sourced from NSW Office of Water.

• Bore locations and groundwater level data in Queensland were sourced from Department of Environment and Resource Management.

• The GIS data relating to the boundaries of the SDL regions were provided by the Murray–Darling Basin Authority.

NSW Office of Water method:

• The outputs of the New South Wales groundwater models available within selected SDL areas were used.

 Data Provider

The Bureau and NSW Office of Water.

 Method: The Bureau method

The regional groundwater flow across selected SDL areas within the Northern Basin was considered. The selected SDL areas represent major groundwater resources for the Northern Basin. The boundaries through which groundwater flow was estimated are shown in Figure 7. Groundwater flow was estimated for the unconfined and selected confined aquifers that underlie these boundaries.

Groundwater flow was calculated using a simple GIS approach based on Darcy's Law. Groundwater levels were interpolated for seasons using the ArcGIS Topo-to-Raster tool from reduced groundwater levels measured at monitoring bores. Seasonal groundwater flow-grids were derived from groundwater level grids, aquifer thickness and hydraulic conductivity using a modification of the ArcGIS Darcy Velocity tool. Groundwater flow across selected flow boundaries was then calculated using a simple GIS analysis and seasonal values were aggregated to the 2010–11 year.

 

 

Figure 7. Through flow boundaries considered for inflow calculations

 

Method: NSW Office of Water method

The outputs of the New South Wales groundwater models available within selected SDL areas were used.

Uncertainty information: The Bureau method

The uncertainty estimate was not quantified.

The uncertainty in the field-measured data (e.g. groundwater levels, hydraulic conductivity) was not specified and unknown and hence the impacts of such uncertainty on the calculated groundwater flow were not estimated.

The regional flow estimations were based on the interpolated groundwater level grids produced using ArcGIS Topo-to-Raster tool. Use of different interpolation methods may impact on the values of the groundwater level grids and hence the estimated regional flow.  However, a comparison of this methodology was carried out using a simple groundwater flow model developed on MODFLOW model (United States Geological Survey 2011). The results from the two methodologies indicated a 6% to 7% difference.

Groundwater flow was estimated for a simplified boundary constructed from a series of line segments. Groundwater flow across this boundary was calculated using the method described above. The uncertainty surrounding this simplification was not analysed.

Uncertainty Information: NSW Office of Water method

The uncertainty estimate was not quantified.

It is currently not feasible to estimate the uncertainty of modelled regional flow from outputs of a MODFLOW groundwater model.

Assumptions, limitations, caveats and approximations

The Bureau method:

• Regional flow estimations are provided for the SDL areas indicated in Table 9 only. Due to the fact that not all the hydrological processes within the Northern Basin have been taken into consideration, the total regional inflows to the Northern Basin are not comparable with that provided in Table 9.

• Constant aquifer thicknesses were assumed for the Lower Gwydir SDL region. The thicknesses were consistent with those reported in the RAAM report (Commonwealth Scientific and Industrial Research Organisation and Sinclair Knight Merz 2010a and 2010b) and Lower Gwydir Valley Groundwater Model (Huseyin 2002). Aquifer conductivity values were also used from the Lower Gwydir Valley Groundwater Model (Huseyin 2002). Transmissivity values are calculated by multiplying the aquifer thickness with the relevant hydraulic conductivity.

• For the Lower Namoi SDL region, spatially distributed aquifer transmissivity values were provided by the NSW Office of Water.

NSW Office of Water method:

• Details on the limitations of groundwater models used by NSW Office of Water are available in General Purpose Water Accounting Reports - Groundwater methodologies.

Quantification approaches for the estimation of inflow to a SDL area from other SDL areas within a segment – Southern Basin

Two estimation methods, the Bureau method and NSW Office of Water method, were applied in calculations (see line Item 10.1 Groundwater inflow from outside region for more details on the methods).

Data source

The Bureau method:

• Bore locations and groundwater level data in South Australia were sourced from the Drillhole Enquiry System (Department for Water 2011c).

• Bore locations and groundwater level data in Victoria were sourced from the Department of Sustainability and Environment (DSE) and Victorian Department of Primary Industries (DPI) through a database developed by the University of Melbourne

• Bore locations and groundwater level data in New South Wales were sourced from NSW Office of Water.

NSW Office of Water method:

• The NSW Office of Water has developed a series of groundwater models for selected areas using the groundwater flow simulation computer program MODFLOW. The outputs of the New South Wales groundwater models available within selected SDL areas were used.

Data Provider

The Bureau and NSW Office of Water.

Method: The Bureau method

The regional groundwater flow across selected SDL areas within the Southern Basin was considered.  The boundaries through which groundwater flow was estimated are shown in Figure 7. Groundwater flow was estimated for the unconfined and selected confined aquifers that underlie these boundaries.

Groundwater flow was calculated using a simple GIS approach based on Darcy's Law. Groundwater levels were interpolated for seasons using the ArcGIS Topo-to-Raster tool from reduced groundwater levels measured at monitoring bores. Seasonal groundwater flow-grids were derived from groundwater level grids, aquifer thickness and hydraulic conductivity using a modification of the ArcGIS Darcy Velocity tool. Groundwater flow across selected flow boundaries was then calculated using a simple GIS analysis and seasonal values were aggregated to the 2010–11 year.

Method: NSW Office of Water method

The outputs of the New South Wales groundwater models available within selected SDL areas were used.

Uncertainty information: The Bureau method

The uncertainty estimate was not quantified.

The uncertainty in the field-measured data (e.g. groundwater levels, hydraulic conductivity) was not specified and unknown and hence the impacts of such uncertainty on the calculated groundwater flow were not estimated.

The regional flow estimations were based on the interpolated groundwater level grids produced using ArcGIS Topo-to-Raster tool. Use of different interpolation methods may impact on the values of the groundwater level grids and hence the estimated regional flow.  However, a comparison of this methodology was carried out using a simple groundwater flow model developed on MODFLOW model (United States Geological Survey 2011). The results from the two methodologies indicated a 6% to 7% difference.

Groundwater flow was estimated for a simplified boundary constructed from a series of line segments. Groundwater flow across this boundary was calculated using the method described above. The uncertainty surrounding this simplification was not analysed.

Uncertainty information: NSW Office of Water method

The uncertainty estimate was not quantified.

It is currently not feasible to estimate the uncertainty of modelled regional flow from outputs of a MODFLOW groundwater model.

Assumptions, limitations, caveats and approximations

The Bureau method:

• Regional flow estimations were provided for the aquifers indicated in Table 10 only and also due to the fact that not all the hydrological processes within the Southern Basin have been taken into consideration, the total regional inflows to the Southern Basin are not comparable with that provided in Table 10.

• The Geofabric version 2 (Bureau of Meteorology 2011a), and Southern Riverine Plains Groundwater Model (Goode and Barnett 2008) were used to estimate aquifer thicknesses. The hydraulic conductivity values were sourced from Mallee Prescribed Wells Area – Murrayville Water Supply Protection Area Groundwater Model (Barnett and Osei-bonsu 2006), Southern Riverine Plains Groundwater Model (Goode and Barnett 2008) and the report on Sustainable Extraction Limits Derived from the Recharge Risk Assessment Method – New South Wales (Commonwealth Scientific and Industrial Research Organisation and Sinclair Knight Merz 2010a and 2010b). The transmissivity values were calculated by multiplying the aquifer thickness with the relevant hydraulic conductivity.

•  It is possible that small differences occur between the University of Melbourne database and the DSE groundwater database (from which bore locations and groundwater level data in Victoria were sourced).

Groundwater outflow to other SDL areas within a segment has been calculated for selected SDL areas. Tables 11 and 12 provide details for the Northern Basin and the Southern Basin.

  

Table 11. Details of groundwater outflow from a SDL area to other SDL areas within the Northern Basin

SDL area		Volume (ML) for 2009–10	Volume (ML) for the 2010–11 year
Code	Name
GS29	Lower Gwydir Alluvium	1,129	1,109
GS34	Lower Namoi Alluvium	251	260

 

Table 12. Details of groundwater outflow from a SDL area to other SDL areas within the Southern Basin

SDL area		Other details	Volume (ML) for 2009–10	Volume (ML) for the 2010–11 year
Code	Name
GS3	Mallee, Pliocene Sands	Unconfined aquifer	16,505	16,576
	Mallee Murray, Group Limestone
GS5	Peake–Roby–Sherlock, unconfined
GS9a	Wimmera–Mallee: West Wimmera, Loxton Parilla Sands
	Wimmera–Mallee: West Wimmera, Murray Group Limestone
GS9c	Wimmera–Mallee: Wimmera–Mallee Border Zone, Loxton Parilla Sands
	Wimmera–Mallee: Wimmera–Mallee Border Zone, Murray Group Limestone
GS3	Mallee, Renmark Group	Confined aquifer	11,661	12,199
GS5	Peake–Roby–Sherlock, confined
GS9a	Wimmera–Mallee: West Wimmera, Tertiary Confined Sands
GS9c	Wimmera–Mallee: Wimmera–Mallee Border Zone, Tertiary Confined Sand Aquifer
GS8e	Goulburn–Murray: Ovens–Kiewa Sedimentary Plain		1,560	1,729
	Goulburn–Murray: Ovens–Kiewa Confined		8,903	7,751
GS8f	Goulburn–Murray: Victorian Riverine Sedimentary Plain, deep: Calivil and Renmark Formations		127,578	117,410
	Goulburn–Murray: Victorian Riverine Sedimentary Plain, shallow: Shepparton Formation		10,334	10,133
GS30	Lower Lachlan Alluvium		24,640	24,750
GS32	Lower Murray Alluvium, deep: Renmark Group and Calivil Formation		164,922	184,377
	Lower Murray Alluvium, shallow: Shepparton Formation		9,129	8,702
GS33	Lower Murrumbidgee Alluvium, deep: Calivil Formation and Renmark Group		104,290	118,190
	Lower Murrumbidgee Alluvium, shallow: Shepparton Formation		2,340	4,260

 

Quantification approaches for the estimation of outflow from a SDL area to other SDL areas within a segment

Two estimation methods, the Bureau method and NSW Office of Water method, were applied in calculations (see line Item 10.1 Groundwater inflow from outside region for more details on the methods).

Data source

The Bureau method:

• Bore locations and groundwater level data in New South Wales were sourced from NSW Office of Water.

• Bore locations and groundwater level data in Queensland were sourced from Department of Environment and Resource Management.

NSW Office of Water method:

•  The outputs of the New South Wales groundwater models available within selected SDL areas were used.

Data provider

The Bureau and NSW Office of Water.

Method: The Bureau method

The regional groundwater flow across selected SDL areas within a segment was considered. The selected SDL areas represent major groundwater resources for the segment. The boundaries through which groundwater flow was estimated are shown in Figure 7. Groundwater flow was estimated for the unconfined and selected confined aquifers that underlie these boundaries.

Groundwater flow was calculated using a simple GIS approach based on Darcy's Law. Groundwater levels were interpolated for seasons using the ArcGIS Topo-to-Raster tool from reduced groundwater levels measured at monitoring bores. Seasonal groundwater flow-grids were derived from groundwater level grids, aquifer thickness and hydraulic conductivity using a modification of the ArcGIS Darcy Velocity tool. Groundwater flow across selected flow boundaries was then calculated using a simple GIS analysis and seasonal values were aggregated to the 2010–11 year.

Method: NSW Office of Water method

The outputs of the New South Wales groundwater models available within selected SDL areas were used.

Uncertainty information: The Bureau method

The uncertainty estimate was not quantified.

The uncertainty in the field-measured data (e.g. groundwater levels, hydraulic conductivity) was not specified and unknown and hence the impacts of such uncertainty on the calculated groundwater flow were not estimated.

The regional flow estimations were based on the interpolated groundwater level grids produced using ArcGIS Topo-to-Raster tool. Use of different interpolation methods may impact on the values of the groundwater level grids and hence the estimated regional flow.  However, a comparison of this methodology was carried out using a simple groundwater flow model developed on MODFLOW model (United States Geological Survey 2011). The results from the two methodologies indicated a 6% to 7% difference.

Groundwater flow was estimated for a simplified boundary constructed from a series of line segments. Groundwater flow across this boundary was calculated using the method described above. The uncertainty surrounding this simplification was not analysed.

Uncertainty information: NSW Office of Water method

The uncertainty estimate was not quantified.

It is currently not feasible to estimate the uncertainty of modelled regional flow from outputs of a MODFLOW groundwater model.

Assumptions, limitations, caveats and approximations

The Bureau of Meteorology method:

• Regional flow estimations were provided for the SDL areas shown in tables 11 and 12 only. Due to the fact that not all the hydrological processes within the segments have been taken into consideration, the total regional outflow are not comparable with that provided in tables 11 and 12.

NSW Office of Water method:

Details on the limitations of groundwater models used by the NSW Office of Water are available in General Purpose Water Accounting Reports - Groundwater methodologies.

The purpose of this note is to provide a consolidated report on the off-channel water storages within the Murray–Darling Basin (MDB) region during the 2010–11 year. Information on storage volumes, inflows and outflows for the off-channel water storages is provided in this note.

The off-channel water storages consists of all private reservoirs that are used to harvest runoff before reaching the surface water store or that are filled by pumping from a watercourse or groundwater.

The store includes constructed storages that are not connected either seasonally or perennially to rivers, filled predominantly by local catchment runoff. They include off-channel farm dams, run-off dams, hill-side dams, industrial, commercial and mining water storages. They exclude on-channel farm dams and other storages.

The off-channel water storages for the 2011 Account were determined from waterbody mapping conducted by Geoscience Australia as those that are:

• not named storages (assuming that any storage with a name is unlikely to be a off-channel storage)

• above 600 m in elevation or are in areas that receive greater than 400 mm per annum in precipitation and are not within 50 m of a major or perennial stream.

The above rules attempt to divide storages into those that are likely to be filled primarily by local catchment runoff and those which are filled by abstraction from surface water, groundwater or floodplain harvesting.

As discussed in General description in Physical information section in the Contextual information, the off-channel water store has been excluded from the scope of the MDB region for the purposes of the 2011 Account, because it is constituted of water already abstracted from the shared pool of water resources. Therefore off-channel water store reporting line items do not appear in the water accounting statements. Off-channel water storages influence water assets and water liabilities recognised in the water accounting statements though, as they harvest water from the landscape and thus reduce groundwater recharge and runoff into surface water.

Table 13 shows that the total off-channel water store increased during the 2010–11 year in the MDB region.

 

Table 13. Off-channel water storage volume at the start and end of the 2010–11 year for the MDB region

Description	30 June 2011 (ML)			30 June 2010 (ML)
	Northern Basin	Southern Basin	Whole region	Northern Basin	Southern Basin	Whole region
27.1 Off-channel water storages	456,528	580,559	1,037,087	427,567	405,289	832,856
27.2 Rainwater tanks	–	–	–	–	–	–
Total	456,528	580,559	1,037,087	427,567	405,289	832,856

 –  = Data not available

 

The water volume held in off-channel water storages within the MDB region at the end of the 2010–11 year was more than that at the start (1 July 2010). This was primarily attributed to the record high rainfalls and inflows in the region during the 2010–11 year. Some areas, both in the Northern Basin and the Southern Basin, recorded their highest annual rainfall on record (see Rainfall in Climate overview 2010–11 section in the Contextual information).

The inflow and outflow volumes for the off-channel water store during the 2010–11 year are given in Table 14.

 

Table 14. Volume of inflows and outflows for the off-channel water store during the 2010–11 year

Description	Volume (ML)
	Northern Basin	Southern Basin	Whole region
Off-channel water inflows
30.1 Precipitation on off-channel water store	857,566	579,923	1,437,489
30.2 Groundwater discharge into off-channel water store	–	–	­–
30.3 Runoff harvesting into off-channel water store	778,663	727,822	1,506,485
30.4 Surface water diversion into off-channel water store	–	–	­–
30.5 Groundwater extraction into off-channel water store	–	–	­–
Total Off-channel water inflows	1,636,229	1,307,745	2,943,974
Off-channel water outflows
31.1 Evaporation from off-channel water storages	1,040,673	655,482	1,696,154
31.2 Leakages from off-channel water storages	–	–	­–
31.3 Water use	566,505	476,926	1,043,431
Total Off-channel water outflows	1,607,178	1,132,407	2,739,585
Balancing item – off-channel water	90	68	158
Change in off-channel water storage	28,961	175,270	204,231
Opening off-channel water storage	427,567	405,289	832,856
Closing off-channel water storage	456,528	580,559	1,037,087

– = data not available

 

Precipitation on off-channel water store and runoff harvesting into them increased by 47% and 8% respectively for the 2010–11 year compared to the 2009–10 year. Most likely due to that reason, water use from off-channel storages increased by 61% in the 2010–11 year compared to the previous years' use.

This volume represents the volume necessary to reconcile the opening and closing balances of the off-channel water storage with the physical water inflows and outflows. The difference was calculated according to Table 15.

 

Table 15. Balancing item – off-channel water 2010–11 year

	Account	Volume (ML)
	Opening balance (30 June 2010)	832,856
add	Total 30 Off-channel water inflows	2,943,974
less	Total 31 Off-channel water outflows	2,739,585
less	Closing balance (30 June 2011)	1,037,087
	Balancing item – off-channel water store	158

 

The calculation of the water balance on the off-channel water store yielded a balance of 158 ML. This is negligible compared to the opening and closing balances. Despite this, one should note that the values presented for off-channel storages remain broad estimates based on numerous assumptions and simplifications (see quantification approaches of the various line items linked from the tables).