Murray–Darling Basin
9.4 Runoff to surface water

Supporting information

The volumetric value for the line item for the 2011–12 year was 63,583,187 ML.

The line item represents runoff volumes to surface water within the Murray–Darling Basin (MDB) region.  River losses have not been included in this line item.  They are included in line item 17.10 River and floodplain leakage, evaporation and errors.

Rainfall runoff volumes to surface water within the MDB region are summarised in the following table.

 Details of rainfall runoff to surface water 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

19,936,956

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

2,158,207

SW15 NSW Border Rivers SS23 NSW Border Rivers  NSW
SW14 Gwydir SS22 Gwydir NSW

3,327,553

SW13 Namoi SS21 Namoi  NSW

2,672,373

SW10 Macquarie–Castlereagh SS20 Macquarie–Castlereagh  NSW

4,397,348

Northern Basin

32,492,437

SW9 Lachlan SS16 Lachlan  NSW

4,567,034

SW8 Murrumbidgee  SS15 Murrumbidgee  NSW NSW

7,082,066

SW1 ACT SS1 ACT ACT
SW7 NSW Murray and Lower Darling SS18 Lower Darling  NSW

11,685,453

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.

2,867,386

SS5 Broken  Vic.

4,068,328

SS6 Goulburn Vic.
SS7 Campaspe  Vic.

290,149

SS8 Loddon Vic.

401,395

SW6 Eastern Mount Lofty Ranges  SS13 Eastern Mount Lofty Ranges  SA

128,938

SS12 Marne Saunders  SA
Southern Basin

31,090,750

Whole MDB region

63,583,187

 

Rainfall runoff volumes were based on hydrological boundaries of river catchments within the region.  These volumes were not available individually for some of water resources planning areas. Therefore, the volumes were provided in the above table individually for some of the water resource plan areas and as clusters for the others.

Quantification approach

Data source

(1) Bureau of Meteorology (the Bureau): (a) National Climate Centre (NCC) daily climate grids (rainfall, temperature and solar radiation) and (b) Australian Hydrological Geospatial Fabric (AHGF) waterbody feature class; (2) Commonwealth Scientific and Industrial Research Organisation (CSIRO): (a) Australian water resources assessment system landscape model (AWRA-L) model parameters and (b) CSIRO monthly climatological average radiation grids data; and (3) Geoscience Australia: MDB human-made waterbody feature class.

Provided by

The Bureau.

Method

Rainfall runoff to surface water was estimated based on the AWRA-L version 2.0.0 (Van Dijk 2010) model outputs.

  • Using climate grid data for the MDB region (including precipitation, temperature and solar radiation data), AWRA-L was used to estimate the runoff depth at each grid point within the region. Only runoff from the landscape is considered; therefore, the surface areas of the major storages, local catchment storages and other mapped waterbodies were excluded from the analysis.

Runoff from the landscape is divided into two components: runoff into the surface water store (major storages, rivers and drains) and runoff into local catchment storages. Only runoff into the surface water store is considered here.

The average runoff depth from the landscape into the surface water was determined as the weighted mean of the relevant grid-points within the MDB region boundary. Points were weighted based upon the area they represented within the region 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.  Mean runoff depth was converted to a runoff volume by multiplying runoff depth by the total area of the region (excluding storages). 

Assumptions, limitations, caveats and approximations

  • The estimated runoff was compared against historical flows at unimpaired catchments within the MDB region for the 2011–12 year and provided a suitable representation of the runoff for this year.
  • The runoff estimates were subject to the assumptions of the AWRA-L model detailed in Van Dijk (2010).
  • The estimated runoff corresponds to the runoff expected from an unimpaired catchment. The impairment on runoff from local catchment storages is estimated using a local catchment storage water balance model. Where this is applied, the runoff estimates inherit the approximations, assumptions and caveats of the local catchment storage water balance model and the parameters used.

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


Restatement of comparative year information made for the line item 9.4 Runoff to surface water
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 33,913,170 31,009,785 2,903,385
Southern Basin 49,069,283 43,201,180 5,868,103
Whole region 82,982,453 74,210,965 8,771,488


The volume of runoff estimated for the comparison year for the 2012 Account (82,982,453 ML) is higher than the volume reported for the 2011 Account (74,210,965 ML). This was due to a change in modelling methods. The difference between the previously reported estimate of runoff 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. The AWRA-L v2.0.0 model is more reliable than previous models in estimating runoff. The difference of 8,771,488 ML represents a change of approximately 12% of the previously reported value.