Murray–Darling Basin
30.3 Runoff harvesting into off-channel water store

Supporting information

The volumetric value for the line item for the 2011–12 year was 1,320,947 ML. The line item includes collection of runoff into off-channel water storages including local catchment runoff into off-channel water storages 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.


Runoff harvesting into off-channel water storages 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 268,185
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 100,793
SW15 NSW Border Rivers SS23 NSW Border Rivers  NSW
SW14 Gwydir SS22 Gwydir NSW 98,936
SW13 Namoi SS21 Namoi  NSW 89,669
SW10 Macquarie–Castlereagh SS20 Macquarie–Castlereagh  NSW 185,387
Northern Basin 742,969
SW9 Lachlan SS16 Lachlan  NSW 164,636
SW8 Murrumbidgee  SS15 Murrumbidgee  NSW NSW 158,636
SW1 ACT SS1 ACT ACT
SW7 NSW Murray and Lower Darling SS18 Lower Darling  NSW 83,005
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. 23,748
SS5 Broken  Vic. 79,334
SS6 Goulburn Vic.
SS7 Campaspe  Vic. 20,774
SS8 Loddon Vic. 34,351
SW6 Eastern Mount Lofty Ranges  SS13 Eastern Mount Lofty Ranges  SA 13,493
SS12 Marne Saunders  SA
Southern Basin 577,978
Whole MDB region 1,320,947

 

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

Rainfall runoff harvesting to off-channel water storages was estimated using the Australian water resources assessment system landscape (AWRA-L) version 2.0.0 model and a water balance tool based on a Fortran code.

Using climate grid data for the MDB region (including precipitation, temperature and solar radiation data), AWRA-L (Van Dijk 2010) was used to estimate the runoff depth at each grid-point within the region.

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 average runoff depth across the MDB sub-regions was determined as the weighted mean of runoff occurring from the relevant grid points within the region boundary. Points were weighted upon the area they represented within the MDB landscape to remove edge effects (where the area represented is not wholly within the MDB region) and the effect of changing area represented with changing latitude. The average runoff depth was converted to a volume by multiplying depth by the total area and was used as an input into the water balance tool based on the Fortran code.

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 the Geoscience Australia.
  • The use of a 9 arc-second DEM to determine catchment area may result in storages being assigned a catchment much larger or smaller than the true catchment. In some cases a storage may be assigned the catchment of a stream line hundreds of metres away.

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 30.3 Runoff harvesting into off-channel water store
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)
Northern Basin 773,931 778,663 -4,732
Southern Basin 741,628 727,822 13,806
Whole region 1,515,559 1,506,485 9,074


The volume estimated for the comparison year for the 2012 Account (1,515,559 ML) is higher than the volume reported for the 2011 Account (1,506,485 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 water balance tool. The AWRA-L v2.0.0 model is more reliable than previous models in estimating runoff. The difference of 9,074 ML represents a change of 6% of the previously reported value.