Murray-Darling Basin
31.3 Water use

The volumetric value for the line item for the 2010–11 year was 1,043,431 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 storages in the MDB region for the 2010–11 year

Surface water resource plan area		State	Volume (ML)
Code	Name
SW 11–12 and SW17–19	Warrego – Paroo – Nebine, Condamine–Balonne, Moonie, NSW Intersecting Streams and Barwon–Darling watercourse	Qld and NSW	254,896
SW 15–16	Qld and NSW Border Rivers	Qld and NSW	74,467
SW14	Gwydir	NSW	35,690
SW13	Namoi	NSW	69,037
SW10	Macquarie–Castlereagh	NSW	132,416
Sub-total Northern Basin			566,505
SW9	Lachlan	NSW	113,637
SW 1 and 8	Murrumbidgee NSW and ACT	NSW and ACT	121,340
SW 2, 4, 5 and 7	NSW Murray and Lower Darling, Vic Murray, SA Murray and Wimmera–Mallee	NSW, Vic and SA	79,472
SW3	Northern Victoria	Vic	149,626
SW6	Eastern Mount Lofty Ranges	SA	12,851
Sub-total Southern Basin			476,926
Total for the region			1,043,431

 

(1) Bureau of Meteorology (the Bureau): National Climate Centre daily climate grids (rainfall, temperature and solar radiation), (2) Commonwealth Scientific and Industrial Research Organisation (CSIRO): WaterDyn and Australian water resource assessment – landscape (AWRA-L) model parameters, and monthly climatological average radiation grid data, and (3) Geoscience Australia: MDB human-made waterbody feature class and 9 arc-second digital elevation model (DEM).

The Bureau.

The tool for estimating dam impacts (STEDI) model (Sinclair Knight Merz 2011) was used to determine the volume of water abstracted from the off-channel water store. The model was provided inputs in the form of climate from gridded climate datasets, runoff from the AWRA-L v1.0.0 (Van Dijk 2010) model and dam 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 that:

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

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 STEDI model and the parameters used.

The spatial extent of water bodies subject to the assumptions and methods associated with the data provided by Geoscience Australia.

The uncertainty estimate was not quantified.

 

In the 2011 Account, the following changes were made that caused the 2009–10 year value to be restated:

• The scope of the line item was changed.

• The methodology used to quantify the line item was improved and resulted in a material change in volume.

The change in the values for 2009–10 was due to a combination of the exclusion of off-channel storages that are not filled by local catchment runoff and the use of AWRA-L model to estimate rainfall-runoff into local catchment storages. Modelling changes were made to provide more reliable estimates of runoff volumes. The difference of 830,663 ML represents a change of approximately 56% of the volume provided for the 2010 Account. The changes and their respective values are detailed in the following table.

 

Restatement of comparative year information made for the line item 31.3 Water use

Segment	Volume for the 2009–10 year reported in the 2010 Account (ML)	Difference due to change in the calculation method (ML)	Volume for the 2009–10 year reported in the 2011 Account (ML)
Northern Basin	787,355	–456,019	331,336
Southern Basin	690,943	–374,643	316,300
Whole region	1,478,298	–830,663	647,635