Murray–Darling Basin
31.3 Off-channel water abstraction

Supporting information

The volumetric value for the line item for the 2011–12 year was 973,602 ML. The line item includes volume of water abstracted from off-channel water storages within the Murray–Darling Basin (MDB) region. The following table presents breakdown information for the line item on a surface water resource plan area basis.

 

Abstraction from off-channel water stirages in the MDB region for the 2011–12 year
Water resource plan area Sustainable diversion limit area State/Territory   Volume (ML) for the 2011–12 year 
Code Name
SW19 Warrego–Paroo–Nebine SS29 Paroo  Qld 203,639
SS28 Warrego  Qld
SS27 Nebine  Qld
SW18 Condamine–Balonne SS26 Condamine–Balonne  Qld
SW17 Moonie SS25 Moonie  Qld
SW11 Barwon–Darling Watercourse SS19 Barwon–Darling Watercourse  NSW
SW12 NSW Intersecting Streams SS17 NSW Intersecting Streams NSW
SW16 Qld Border Rivers SS24 Qld Border Rivers  Qld 68,639
SW15 NSW Border Rivers SS23 NSW Border Rivers  NSW
SW14 Gwydir SS22 Gwydir NSW 75,981
SW13 Namoi SS21 Namoi  NSW 61,952
SW10 Macquarie–Castlereagh SS20 Macquarie–Castlereagh  NSW 121,223
Northern Basin 531,432
SW9 Lachlan SS16 Lachlan  NSW 108,945
SW8 Murrumbidgee  SS15 Murrumbidgee  NSW NSW 111,748
SW1 ACT SS1 ACT ACT
SW7 NSW Murray and Lower Darling SS18 Lower Darling  NSW 68,347
SS14 NSW Murray NSW
SW2 Vic. Murray SS3 Kiewa Vic.
SS2 Vic. Murray  Vic.
SW4 Wimmera–Mallee  SS9 Wimmera–Mallee  Vic.
SW5 SA Murray SS11 SA Murray SA
SS10 SA Non-prescribed areas  SA
SW3 Northern Victoria SS4 Ovens  Vic. 27,283
SS5 Broken  Vic. 70,878
SS6 Goulburn Vic.
SS7 Campaspe  Vic. 18,069
SS8 Loddon Vic. 28,235
SW6 Eastern Mount Lofty Ranges  SS13 Eastern Mount Lofty Ranges  SA 8,665
SS12 Marne Saunders  SA
Southern Basin 442,169
Whole MDB region 973,602

Quantification approach

Data source

(1) Bureau of Meteorology (the Bureau): National Climate Centre daily climate grids (rainfall, temperature and solar radiation) and (2) Geoscience Australia: MDB human-made waterbody feature class and 9 arc-second digital elevation model (DEM).

Provided by

The Bureau.

Method

A water balance tool based on a Fortran code was used to determine the volume of water abstracted from the off-channel water store. The tool was provided inputs: climate data from gridded climate datasets, runoff from the Australian water resources assessment system landscape (AWRA-L) model version 2.0.0 (Van Dijk 2010) and storage details derived from spatial data.

The MDB region was divided into 105 units for the purpose of modelling the off-channel water store. The off-channel water store consisted of storages filled primarily by local catchment runoff. These were determined from waterbody mapping conducted by Geoscience Australia as those which:

  • are not named storages (assuming that any storage with a name is unlikely to be a off-channel water storage)
  • are above 600 m in elevation
  • are below 600 m in elevation 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. The catchment of each individual storage was determined via analysis of the 9 arc-second DEM.

The water balance tool determines the water stored in each off-channel water storage at each time step and determines the volume required for use from the storage. The tool assumes that water will be abstracted from the storage at the rate required unless storage empties, at which time, abstraction will cease.

Assumptions, limitations, caveats and approximations

  • The gridded climate input data are subject to approximations associated with interpolating observation point data to a national grid detailed in Jones et al. (2007).
  • The spatial extent of water bodies subject to the assumptions and methods associated with the data provided by Geoscience Australia.

Uncertainty information

The uncertainty estimate was not quantified.

 

Comparative year

A change made to the calculation method resulted in the restatement of the 2010–11 year volume. The method used to quantify the line item was improved and resulted in a material change in volume.

The respective volumes associated with the change are detailed in the following table.


 

Restatement of comparative year information made for the line item 31.3 Off-channel water abstraction
2011 Account line item Segment 2012 Account volume for the 2010–11 year (ML) 2011 Account volume for the 2010–11 year (ML) Difference due to calculation method change (ML)
Line item 31.3 Water use Northern Basin 596,566 566,505 30,061
Southern Basin 509,945 476,926 33,019
Whole region 1,106,511 1,043,431
63,079


The volume estimated for the comparison year for the 2012 Account (1,106,511 ML) is higher than the volume reported for the 2011 Account (1,043,431 ML). 

The difference between the previously reported volume and the estimate produced for the comparison year can be attributed to the choice of the AWRA-L v2.0.0 model (instead of the previously used AWRA-L v1.0.0) to provide inputs to the water balance tool. The AWRA-L v2.0.0 model is more reliable than previous models in estimating runoff.

The difference of 63,079 ML represents a change of 6% of the previously reported volume.