Murray–Darling Basin
27.1 Off-channel water storages

Supporting information

The volumetric value for the line item for the 2011–12 year was 1,152,737 ML. The line item represents the volume of water held in constructed storages that are not connected either seasonally or perennially to rivers, filled predominantly by local catchment runoff within the Murray–Darling Basin (MDB) region. The following table presents breakdown information for the volumetric value on a surface water resource plan area basis.


Details of volume of water stored in off-channel water storages in the MDB region at the start and end of the 2011–12 year
Water resource plan area Sustainable diversion limit area State/Territory  Volume on 30 June 2012 (ML) Volume on 30 June 2011 (ML)
Code Name
SW19 Warrego–Paroo–Nebine SS29 Paroo  Qld 191,684 206,181
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 57,253 56,857
SW15 NSW Border Rivers SS23 NSW Border Rivers  NSW
SW14 Gwydir SS22 Gwydir NSW 52,677 34,992
SW13 Namoi SS21 Namoi  NSW 64,007 57,108
SW10 Macquarie–Castlereagh SS20 Macquarie–Castlereagh  NSW 168,615 158,212
Northern Basin 534,236 513,351
SW9 Lachlan SS16 Lachlan  NSW 168,115 149,845
SW8 Murrumbidgee  SS15 Murrumbidgee  NSW NSW 168,527 158,443
SW1 ACT SS1 ACT ACT
SW7 NSW Murray and Lower Darling SS18 Lower Darling  NSW 87,496 100,354
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. 32,570 33,315
SS5 Broken  Vic. 96,181 99,205
SS6 Goulburn Vic.
SS7 Campaspe  Vic. 20,990 24,906
SS8 Loddon Vic. 32,743 41,215
SW6 Eastern Mount Lofty Ranges  SS13 Eastern Mount Lofty Ranges  SA 11,879 11,304
SS12 Marne Saunders  SA
Southern Basin 618,502 618,587
Whole MDB region 1,152,737 1,131,938

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: mapping of man-made waterbodies in the MDB spatial dataset, and 9 arc-second digital elevation model (DEM).

Provided by

The Bureau.

Method

A Fortran code water balance routine was used to determine the volume of water stored in off-channel water storages. The calculation routine 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 was divided into 105 regions 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 calculation routine performs a water balance on each individual storage at each time step using runoff and precipitation as inflows and spills, evaporation and usage as outflows. The volume of water held in storage is an output of this water balance.

 

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 estimated volume available in storage for evaporation is subject to the assumptions associated with the Fortran code and the parameters used.
  • The spatial extent of water bodies are subject to the assumptions and methods associated with the data provided by the 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 27.1 Off-channel water storages
Segment 2012 Account volume at 30 June 2011 (ML) 2011 Account volume at 30 June 2011 (ML) Difference due to calculation method change (ML)
Northern Basin 513,351 456,528 56,823
Southern Basin 618,587 580,559 38,028
Whole region 1,131,938 1,037,087 94,851


The volume estimated for the comparison year for the 2012 Account (1,131,938 ML) is higher than the volume reported for the 2011 Account (1,037,087 ML). This was due to a change in modelling methods. 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 calculation routine. The AWRA-L v2.0.0 model is more reliable than previous models in estimating runoff. The difference of 94,851 ML represents a change of 9% of the previously reported value.