Murray–Darling Basin

Additional information

Private water store

Summary of information on off-channel private water stores

The off-channel private water store consists of all private reservoirs (farm dams, run-off dams, hill-side dams etc.) that are used to harvest run-off before reaching connected surface water store or filled by pumping from a watercourse or groundwater.

As discussed in Physical Information in the contextual statement, the off-channel private water store has been excluded from the Murray–Darling Basin (MDB) region for the purposes of the National Water Account 2010. Therefore off-channel private water store terms do not appear in the water accounting statement. However, the private water store terms are included in this note because they provide useful context for understanding the items in the water accounting statement.

Volumes held in the off-channel private water store at the beginning and end of 2009–10 are presented in the table below:

Item	Volume held at 1 July 2009 (ML)	Volume held at 30 Jun 2010 (ML)
Local catchment reservoirs¹	468,734	742,638
Off-channel storages – other lumped²	256,754	276,446
Total	725,488	1,019,084

Note:

All reservoirs above 600 metres Australian Height Datum (mAHD) were considered local catchment reservoirs. They are run-off dams filled by run-off (subject to the definition in following note) from their local catchment.
Reservoirs below 600 m AHD and within 50 m of a major or perennial channel, or located in areas receiving less than 400 mm annual rainfall are filled by pumping (considered under off-channel storages – other lumped).

Information on inflows to the off-channel private water store during 2009–10 is presented in the table below:

Item	Volume (ML)
Precipitation on off-channel store	1,174,028
Run-off harvesting into off-channel private water store	1,642,747
Surface water diversion into off-channel private water store	0¹
Groundwater extraction into off-channel private water store	Not available
Total for data available items	2,816,775

Note:

Any surface water diversion into off-channel private water store is included in the water accounting statements under Line Item 14.4 – Overbank flood spilling.

Information on outflows from the off-channel private water store during 2009–10 is presented in the table below:

Item	Volume (ML)
Evaporation from off-channel private store	2,341,844
Irrigation water application from off-channel private store	1,177,383
Stock and domestic use from off-channel private store	300,915
Total	3,820,142

The above three tables are not balancing together mainly because inflows received from groundwater extraction and other diversions have not been included. Details on information provided in the above tables follow.

Volume stored in local catchment reservoirs

Supporting information

The volumes of water stored in local catchment reservoirs at the beginning and end of 2009–10 are 468,734 ML and 742,638 ML respectively. A breakdown of the volumes is provided in the following table.

Region no.	Region name	State	Volume 1 July 2009 (ML)	Volume 30 June 2010 (ML)
1	Paroo	Qld/NSW	338	798
2	Warrego	Qld/NSW	17,351	27,799
3	Condamine–Balonne	Qld/NSW	55,107	99,654
4	Moonie	Qld/NSW	4,158	4,218
5	Border Rivers	Qld/NSW	40,514	41,832
6	Gwydir	NSW	26,988	19,085
7	Namoi	NSW	40,086	42,375
8	Macquarie–Castlereagh	NSW	95,763	135,869
9	Barwon–Darling	NSW	2,240	2,405
10	Lower Darling	NSW	0	0
11	Lachlan	NSW	40,256	99,443
12	Wimmera–Avoca	Vic	13,748	15,303
13	Ovens	Vic	13,522	18,817
14	Goulburn–Broken	Vic	31,249	61,021
15	Loddon	Vic	5,159	12,748
16	Campaspe	Vic	2,709	6,668
17	Murrumbidgee	NSW/ACT	53,919	113,706
18	Murray	NSW/Vic/SA	23,938	37,980
19	Eastern Mount Lofty Ranges	SA	1,688	2,916
Total			468,733	742,637

Quantification approach

Data source

Bureau of Meteorology: Geographical information system (GIS) layers, Australian Hydrological Geospatial Fabric (AHGF) waterbody feature class, daily rainfall grids, daily maximum temperature grids, daily minimum temperature grids and daily satellite observed solar radiation grids.

Geoscience Australia: GIS layers.

Commonwealth Scientific and Industrial Research Organisation (CSIRO): raster spatial data, WaterDyn model parameters, and radiation data.

Data provider

Bureau of Meteorology.

Method

Storages (local catchment reservoirs) in the off-channel private water store were defined from the Geoscience Australia GIS information for the Murray–Darling Basin region.

All named waterbodies and those identified as being for pondage, evaporation or aquaculture were removed as they were unlikely to be local catchment reservoirs. The following filtering process was used to separate local catchment reservoirs:

All reservoirs above 600 m were considered local catchment reservoirs.
Reservoirs below 600 m and within 50 m of a major or perennial channel are filled by pumping (considered under off-channel storages – other lumped).
Reservoirs in areas that receive less than 400 mm of rainfall on average for the World Meteorological Organization (WMO) standard years 1961–1990 are not considered to be local catchment reservoirs (considered under off-channel storages – other lumped).

The capacity volume for individual local catchment reservoirs was calculated by the surface area to volume relationship:

V = 0.000145 SA ^1.314

where V is the volume of a local catchment reservoir in megalitres and SA is the surface area in square metres

(Lowe et al. 2005).

The contributing area (catchment) for each farm was determined from the flow direction GIS data.

The change in storage was estimated using the Spatial Tool for Estimating Dam Impact (STEDI) model (SKM 2010b).

Inflows of run-off were calculated from the volume of run-off from the total landscape associated with each

STEDI model run.

Precipitation was provided to the STEDI model in the form of an average depth across the extent of the model

per time step.

The STEDI model calculates a volumetric evaporation value for each local catchment reservoir by multiplying the depth of evaporation by the surface area of the local catchment reservoir.

Water use patterns were determined by the size of the reservoir:

reservoirs greater than 5 ML were considered to be used for irrigation
reservoirs equal to or less than 5 ML were considered to be used for stock and domestic purposes.

Stock and domestic monthly demand patterns were determined from the average maximum daily temperatures

during 2009–10.

Uncertainty

Uncertainty estimate is ungraded.

Approximation, assumptions, caveats/limitation

The application of the same surface area across all local catchment reservoirs mapped as points (320.5 m²) is an assumption that was unavoidable for the calculation of the National Water Account 2010 terms for the Murray–Darling Basin account.
The surface area to volume relationship used is a simplification that is likely to vary across regions and topography.

Volume in off-channel storages – other lumped

Supporting information

The volumes of water stored in off-channel storages – other lumped at the beginning and end of 2009–10 are 256,754 and 276,446 ML respectively. A breakdown of the volumes is provided in the following table.

Region no.	Region name	State	Volume 1 July 2009 (ML)	Volume 30 June 2010 (ML)
1	Paroo	Qld/NSW	2,371	2,533
2	Warrego	Qld/NSW	71,745	80,756
3	Condamine–Balonne	Qld/NSW	9,012	9,888
4	Moonie	Qld/NSW	690	693
5	Border Rivers	Qld/NSW	18,351	19,051
6	Gwydir	NSW	9,774	10,051
7	Namoi	NSW	1,660	1,753
8	Macquarie–Castlereagh	NSW	9,701	9,997
9	Barwon–Darling	NSW	15,162	15,841
10	Lower Darling	NSW	5,423	5,584
11	Lachlan	NSW	5,939	5,600
12	Wimmera–Avoca	Vic	10,164	9,219
13	Ovens	Vic	69	78
14	Goulburn–Broken	Vic	171	209
15	Loddon	Vic	2,369	2,503
16	Campaspe	Vic	144	164
17	Murrumbidgee	NSW/ACT	64,504	69,556
18	Murray	NSW/Vic/SA	29,091	32,255
19	Eastern Mount Lofty Ranges	SA	411	715
Total			256,751	276,446

Quantification approach

See ‘Volume stored in local catchment reservoirs’.

Precipitation on off-channel store

Supporting information

The volumetric value for the line item for 2009–10 is 1,174,028 ML. The following table provides the breakdown

of the volume.

Region no.	Region name	State	Volume 2009-10 (ML)
1	Paroo	Qld/NSW	4,186
2	Warrego	Qld/NSW	32,820
3	Condamine–Balonne	Qld/NSW	237,342
4	Moonie	Qld/NSW	23,210
5	Border Rivers	Qld/NSW	99,680
6	Gwydir	NSW	96,578
7	Namoi	NSW	82,677
8	Macquarie–Castlereagh	NSW	144,580
9	Barwon–Darling	NSW	7,980
10	Lower Darling	NSW	6,519
11	Lachlan	NSW	87,335
12	Wimmera–Avoca	Vic	38,141
13	Ovens	Vic	21,999
14	Goulburn–Broken	Vic	66,505
15	Loddon	Vic	27,466
16	Campaspe	Vic	15,754
17	Murrumbidgee	NSW/ACT	108,426
18	Murray	NSW/Vic/SA	64,445
19	Eastern Mount Lofty Ranges	SA	8,384
Total			1,174,027

Quantification approach

Data source

Bureau of Meteorology: Geographical information system (GIS) layers and version 3 daily rainfall grids.

Geoscience Australia: GIS layers.

Data provider

Bureau of Meteorology.

Method

See the method for ‘Volume stored in local catchment reservoirs’.

Uncertainty

Estimated uncertainty is ungraded.

Approximation, assumptions, caveats/limitation

This method of calculating precipitation assumed average precipitation depth across the spatial extent of the STEDI model. This may have caused some issues in areas that have a strong rainfall gradient.
The STEDI model assumed that the surface area of each reservoir remains constant even if the reservoir is empty.
The precipitation estimates are subject to approximations associated with interpolating the observation point data to a national grid detailed in Jones et al. (2007).
Precipitation on the surface water features that were not considered explicitly in the account (e.g. some wetlands and lakes) is captured in the landscape precipitation.

Run-off harvesting into off-channel private water store

Supporting information

The volumetric value for the line item for 2009–10 is 1,642,747 ML (see the following table for the breakdown

of the volume).

Region no.	Region name	State	Volume 2009–10 (ML)
1	Paroo	Qld/NSW	1,334
2	Warrego	Qld/NSW	55,711
3	Condamine–Balonne	Qld/NSW	193,400
4	Moonie	Qld/NSW	18,850
5	Border Rivers	Qld/NSW	104,980
6	Gwydir	NSW	49,312
7	Namoi	NSW	104,440
8	Macquarie–Castlereagh	NSW	292,337
9	Barwon–Darling	NSW	4,984
10	Lower Darling	NSW	Not available
11	Lachlan	NSW	229,476
12	Wimmera–Avoca	Vic	44,653
13	Ovens	Vic	39,824
14	Goulburn–Broken	Vic	123,310
15	Loddon	Vic	38,449
16	Campaspe	Vic	20,311
17	Murrumbidgee	NSW/ACT	224,687
18	Murray	NSW/Vic/SA	81,528
19	Eastern Mount Lofty Ranges	SA	15,161
Total for data available regions			1,642,747

Quantification approach

Data source

Geoscience Australia: GIS layers.

Commonwealth Scientific and Industrial Research Organisation (CSIRO): raster spatial data, WaterDyn and AWRA-L model parameters, and radiation data.

Data provider

Bureau of Meteorology.

Method

Run-off was estimated by averaging discharge volumes from WaterDyn and AWRA-L rainfall-run-off computer

modelling softwares.

Volumetric run-off was determined by multiplying the depth of the averaged run-off by the area of the reporting regions. The reporting region area was determined from the reporting region landscape layers. The average run-off across an area was determined as the simple average of all grid points that fell within that area.

Uncertainty

Estimated uncertainty is ungraded.

Approximation, assumptions, caveats/limitation

The run-off estimates were subject to the assumptions of the WaterDyn model detailed in Raupach et al. (2008) and the AWRA-L model detailed in van Dijk (2010).
The run-off estimates were modelled only and were not verified by real-time analysis of streamflow records. The reported value is an estimate of water that is likely to enter the connected water store from the landscape.
All approximations, assumptions and caveats/limitations associated with the calculation of ‘Volume stored in local catchment reservoirs’ are applicable to this item.

Evaporation from off-channel private store

Supporting Information

The volumetric value for the line item for 2009–10 is 2,341,844 ML (see the following table for the breakdown of

the volume).

Region no.	Region name	State	Volume 2009-10 (ML)
1	Paroo	Qld/NSW	17,477
2	Warrego	Qld/NSW	96,256
3	Condamine–Balonne	Qld/NSW	377,930
4	Moonie	Qld/NSW	39,040
5	Border Rivers	Qld/NSW	179,343
6	Gwydir	NSW	146,206
7	Namoi	NSW	143,494
8	Macquarie–Castlereagh	NSW	293,080
9	Barwon–Darling	NSW	28,076
10	Lower Darling	NSW	35,498
11	Lachlan	NSW	207,524
12	Wimmera–Avoca	Vic	115,180
13	Ovens	Vic	31,895
14	Goulburn–Broken	Vic	105,055
15	Loddon	Vic	50,119
16	Campaspe	Vic	24,460
17	Murrumbidgee	NSW/ACT	272,965
18	Murray	NSW/Vic/SA	161,881
19	Eastern Mount Lofty Ranges	SA	16,365
Total			2,341,844

Quantification approach

Data source

Geoscience Australia: GIS layers.

Commonwealth Scientific and Industrial Research Organisation (CSIRO): raster spatial data, WaterDyn model parameters, and radiation data.

Data provider

Bureau of Meteorology.

Method

Evaporation from the off-channel private water store was estimated using monthly open water evaporation data produced by the Bureau of Meteorology in conjunction with CSIRO as part of the Australian Water Availability Project (AWAP). It is a Penman evaporation estimate based on daily gridded climate data and is available on a 0.05 degree (5 km) national grid.

As a potential evaporation dataset, it is an estimate of the evaporative demand of the atmosphere and is based entirely on the AWAP climate input gridded datasets rather than the output from WaterDyn.

Penman open water potential evaporation was averaged across the spatial extent of each STEDI model run. The averaged values were then entered into the STEDI model. The STEDI model then assumes that each individual reservoir will evaporate from the entire surface area unless the reservoir is empty, at which point evaporation ceased.

Uncertainty

Estimated uncertainty is ungraded.

Approximation, assumptions, caveats/limitation

The Penman evaporation estimates were subject to approximations associated with interpolating the observation point data to a national grid detailed in Jones et al. (2007).
This method of calculating evaporation assumed average evaporation depth across the spatial extent of the STEDI model. This may cause some issues in areas that have a strong potential evaporation gradient.
The STEDI model does not adjust for a change in surface area as the volume of water impounded in an individual local catchment reservoir is reduced. This simplification may lead to an overestimation of evaporation under certain circumstances, but is also likely negated in part by a reduction in potential evaporation as the open water surface becomes increasingly shielded from wind and sun as the water level drops further below the height of the banks.
This method is reliant on reliable estimates of the volume stored in the off-channel private water store and is therefore subject to the relevant approximation, assumptions and caveats/limitations associated with ‘Volume stored in local catchment reservoirs’ and ‘Volumes in off-channel private storages – other lumped’.

Irrigation water application from off-channel private store

Supporting information

The volumetric value for the line item for 2009–10 is 1,177,383 ML (see the following table for the breakdown

of the volume).

Region no.	Region name	State	Volume 2009-10 (ML)
1	Paroo	Qld/NSW	10,004
2	Warrego	Qld/NSW	233,547
3	Condamine–Balonne	Qld/NSW	89,180
4	Moonie	Qld/NSW	1,640
5	Border Rivers	Qld/NSW	95,784
6	Gwydir	NSW	47,564
7	Namoi	NSW	34,969
8	Macquarie–Castlereagh	NSW	105,115
9	Barwon–Darling	NSW	56,334
10	Lower Darling	NSW	18,987
11	Lachlan	NSW	47,116
12	Wimmera–Avoca	Vic	33,918
13	Ovens	Vic	12,188
14	Goulburn–Broken	Vic	17,600
15	Loddon	Vic	15,551
16	Campaspe	Vic	2,902
17	Murrumbidgee	NSW/ACT	219,966
18	Murray	NSW/Vic/SA	129,168
19	Eastern Mount Lofty Ranges	SA	5,851
Total			1,177,384

Quantification approach

Data source

Geoscience Australia: GIS layers.

Commonwealth Scientific and Industrial Research Organisation (CSIRO): raster spatial data, WaterDyn model parameters, and radiation data.

ABS water Murray–Darling Basin usage data (Pink 2008).

Data provider

Bureau of Meteorology.

Method

The STEDI model was used to determine the volume of water taken from the off-channel private water store for irrigation.

Reservoirs with a capacity of 5 ML or less were considered to be primarily used for stock and domestic purposes. Reservoirs of greater than 5 ML were considered to be primarily used for irrigation purposes. This threshold has been used previously for studies conducted in the Victoria (Lowe et al. 2005), Murray–Darling Basin (Jordan & Wiesenfeld 2007) and southwest Western Australia (Ritson 2007).

The volume of water applied for irrigation purposes from the off-channel private water stores was calculated as a function of water demand and availability.

The maximum water available for irrigation from the off-channel private water store is set by the maximum capacity of reservoirs used for irrigation in a particular region. This is done by separating local catchment reservoirs used for irrigation from local catchment reservoirs used for stock and domestic purposes as detailed above. The STEDI model estimated the volume of water available for irrigation by performing a water balance at each time step.

Irrigation demands were broken up based upon the five broad regions. The regions were based upon state and climatic/agronomic boundaries. The regions were:

Queensland
NSW North
NSW South and ACT
Victoria
South Australia.

State boundaries were used because water use data existed for individual irrigation practices within each State. NSW was divided into two regions due to the significant differences between the agronomic practices applied in the different regions.

Demands were calculated by determining the proportion of water used by each individual crop based on Pink (2008). A likely pattern of monthly demands was then applied to each crop type. The proportional water use and pattern of each crop type were then combined to give to total monthly demand patterns for each STEDI model run in the Murray–Darling Basin.

Water use patterns were determined by the size of the reservoir:

reservoirs greater than 5 ML were considered to be used for irrigation
reservoirs equal to or less than 5 ML were considered to be used for stock and domestic purposes.

Irrigation monthly demand patterns for individual crops and the proportion of total water used by those crops were based upon irrigation water estimates made by the Australian Bureau of Statistics (Pink 2008). Estimates of irrigation water taken were provided lumped for each State within the Murray–Darling Basin.

Uncertainty

Estimated uncertainty is ungraded.

Approximation, assumptions, caveats/limitation

Irrigation demand patterns remained identical during the length of the model run (July 2005 until June 2010). It is likely that the demands did change throughout those years, however, given that the 2009–10 water year was the reporting year and the previous years were only used to ‘warm up’ the STEDI model, demand patterns likely for 2009–10 were considered appropriate.
The approximations, assumptions and caveats/limitations associated with the estimates of water available for consumption from the off-channel private water store are discussed further in the Notes for ‘Volume stored in local catchment reservoirs’ and ‘Volumes in off-channel private storages – other lumped’.

Stock and domestic use from off-channel private store

Supporting information

The volumetric value for the line item for 2009–10 is 300,915 ML (see the following table for the breakdown

of the volume).

Region no.	Region name	State	Volume 2009-10 (ML)
1	Paroo	Qld/NSW	334
2	Warrego	Qld/NSW	1,939
3	Condamine–Balonne	Qld/NSW	16,371
4	Moonie	Qld/NSW	2,563
5	Border Rivers	Qld/NSW	13,961
6	Gwydir	NSW	9,844
7	Namoi	NSW	16,716
8	Macquarie–Castlereagh	NSW	50,243
9	Barwon–Darling	NSW	1,247
10	Lower Darling	NSW	1,115
11	Lachlan	NSW	42,109
12	Wimmera–Avoca	Vic	19,678
13	Ovens	Vic	6,226
14	Goulburn–Broken	Vic	24,334
15	Loddon	Vic	8,350
16	Campaspe	Vic	4,000
17	Murrumbidgee	NSW/ACT	57,565
18	Murray	NSW/Vic/SA	21,157
19	Eastern Mount Lofty Ranges	SA	3,162
Total			300,914

Quantification approach

Data source

Bureau of Meteorology: Geographical information system (GIS) layers and monthly temperature grids.

Geoscience Australia: GIS layers.

Data provider

Bureau of Meteorology.

Method

The STEDI model was used to determine the volume of water taken from the off-channel private water store for stock and domestic purposes.

Reservoirs with a capacity of 5 ML or less were considered to be primarily used for stock and domestic purposes. Reservoirs of greater than 5 ML were considered to be primarily used for irrigation purposes. This threshold has been used previously for studies conducted in Victoria (Lowe et al. 2005), Murray–Darling Basin (Jordan & Wiesenfeld 2007) and southwest Western Australia (Ritson 2007).

The volume of water taken for stock and domestic purposes from the off-channel private water stores was calculated as a function of water demand and availability.

The maximum water available for stock and domestic take from the off-channel private water store is set by the maximum capacity of reservoirs used for irrigation in a particular region. This is done by separating local catchment reservoirs used for irrigation from local catchment reservoirs used for stock and domestic purposes as detailed above. The STEDI model estimated the volume of water available for stock and domestic take by performing a water balance at each time step.

The monthly patterns of demands were based on the average maximum daily temperature for each month during 2009–10.

The following formula was used to determine the daily water requirements of a single Dry Sheep Equivalent (DSE):

DR = 0.191183 T - 2.88245 (Luke 1987)

DR = Drinking rate (L/day)

T = Average daily maximum temperature (ºC)

The minimum daily value was set to 0.01 L/day to prevent zero or negative values. The results of the above formula were used to provide the monthly pattern of water use.

Uncertainty

Estimated uncertainty is ungraded.

Approximation, assumptions, caveats/limitation

The temperature estimates were subject to approximations associated with interpolating the observation point data to a national grid detailed in Jones et al. (2007). Additionally, averaging daily maximum temperatures across the spatial extent of STEDI runs may cause issues where temperature fluctuations are greater in parts of the spatial extent.
Stock and domestic demand patterns remained identical during the length of the model run (July 2005 until June 2010). It is likely that the demands did change throughout those years, however, given that the 2009–10 water year was the reporting year and the previous years were only used to ‘warm up’ the STEDI model, climate data from the 2009–10 water year were used to estimate stock and domestic demand patterns.
The estimates of stock and domestic demand factors for the Murray–Darling Basin were subject to the assumptions of Lowe et al. (2005). The demand factors for these accounts are based on a survey of private storage operators across Victoria. These demand factors may not be relevant to other areas. The estimates of monthly demand patterns were subject to the assumptions of Luke (1987) and have only been used to provide an estimate of the likely pattern of usage.
The approximations, assumptions and caveats/limitations associated with the estimates of water available for consumption from the off-channel private water store are applicable and are discussed further in the Notes for ‘Volume stored in local catchment reservoirs’ and ‘Volumes in off-channel private storages – other lumped’.

National Water Account 2010