Murray–Darling Basin
17.10 River and floodplain leakage, evaporation and errors

Supporting information

The volumetric value for the line item for the 2011–12 year was 42,957,139 ML. The line item represents river and floodplain losses including evaporation and seepage, and gauging errors in river inflow and outflow measurements in the Murray–Darling Basin (MDB) region. A breakdown of line item volume is provided in the following table.


River and floodplain leakage, evaporation and errors in the MDB region for the 2011–12 year
Water resource plan (WRP) area Sustainable diversion limit (SDL) area State/Territory  Volume (ML) for the 2011–12 year   Volume (ML) reported for the 2010–11 year 

Code

Name

SW19 Warrego–Paroo–Nebine SS29 Paroo  Qld 17,649,763 18,448,591
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 965,961 905,437
SW15 NSW Border Rivers SS23 NSW Border Rivers  NSW
SW14 Gwydir SS22 Gwydir NSW 1,811,336 315,729
SW13 Namoi SS21 Namoi  NSW 974,052 2,027,855
SW10 Macquarie–Castlereagh SS20 Macquarie–Castlereagh  NSW 3,247,055 2,070,290
Northern Basin 24,648,167 23,767,902
SW9 Lachlan SS16 Lachlan  NSW 3,927,170 2,507,684
SW8 Murrumbidgee  SS15 Murrumbidgee  NSW NSW 3,441,863 5,208,573
SW1 ACT SS1 ACT ACT
SW7 NSW Murray and Lower Darling SS18 Lower Darling  NSW 8,199,338 8,090,191
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
SW6 Eastern Mount Lofty Ranges  SS13 Eastern Mount Lofty Ranges  SA
SS12 Marne Saunders  SA
SW3 Northern Victoria SS4 Ovens  Vic. 2,740,601 2,740,064
SS5 Broken  Vic.
SS6 Goulburn Vic.
SS7 Campaspe  Vic.
SS8 Loddon Vic.
Southern Basin 18,308,972 18,546,512
Whole MDB region 42,957,139 42,314,414

 

Volumes for the line item 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 previous table individually for some of the water resource plan areas and as clusters for the others.

Quantification approach

Data source

There was no separate data source for the line item. Values of other line items for the MDB region water account were used as the inputs for the calculations.

Provided by

Bureau of Meteorology (the Bureau).

Method

A water balance approach was adopted in calculating the volumes for the line item. The calculations were based on hydrological boundaries of river catchments within the region. Total inflows less total outflows and changes in surface water storage for surface water in a reporting unit (a water resource plan area) was considered as the river loss (river and floodplain leakage, evaporation and errors) for the same unit. Details of the calculation method applied in the water balance approach are as follows.

The line item value for the water resource plan area (stated in the table provided under 'Supporting information') for which necessary details are available, is equal to:

 

I– O – ΔS

where:

I is total inflow to the water resource plan area

O is total outflow from the water resource plan area

ΔS is change in total surface water storage during the 2011–12 year in the water resource plan area.

 

Total inflow to the water resource plan area was calculated using the following equation:

 

I =  R1+R2 + P +Qi

where:

R1 is rainfall runoff to surface water (line item 9.4)

R2 is return flows (line items 9.3, 9.5, 9.9 and 9.11)

P is precipitation on surface water (line item 9.1)

Qi is inflow from upstream water resource plan areas (estimated using relevant streamflow gauge data, not applicable to all water resource plan areas).

 

Total outflow (O) was calculated using the following equation:


O =  D+E +Qo

where:

D is diversions from surface water (line items 17.3, 17.5 to 17.8, 17.11 and 17.12)

E is evaporation from surface water (line item 17.1)

Qo is outflow to downstream water resource plan areas or sea (estimated using relevant streamflow gauge data, not applicable to all water resource plan areas).

 

Change in surface water storage (ΔS) in the water resource plan area is the difference between total storage volumes at the end and beginning of the 2011–12 year.  Storage information is available in line items 1.1, 1.3, 1.4 and 1.10.

Assumptions, limitations, caveats and approximations

Assumptions made for the line items (see the above Method for input variables) from which values were used as input variables may affect accuracy of the calculations.

A water balance approach was adopted in calculations (total inflows less total outflows and changes in surface water storage was considered as the volumes for the line item).

At present, attempts to calculate the line item value on small spatial units are limited by the resolution of available data particularly diversion and return data at present. The Bureau is looking to implement the AWRA-R model over the next 2–3 years, which will be able to better attribute some of the inputs for the calculation and attribute these inputs to individual river reaches.

Uncertainty information

The uncertainty estimate was not quantified.

Comparative year

Restatements made for the 2010–11 year in a number of line items, which are inputs to this line item, resulted in the restatement of the 2010–11 year volume. 

The same water balance approach applied for the 2011–12 year was used to calculate the 2010–11 year value for the 2012 Account. Therefore restatements associated with all line items (related to inflows, outflows and storage volumes that are inputs in the water balance calculation) contributed to the difference between the  2010–11 year value calculated for the 2012 Account and reported for the 2011 Account. The major contributor for this difference was the change made to reported (for the 2011 Account) and recalculated value for line item 9.4 'Runoff to surface water' for the 2010–11 year. The change for that line item was 8,771,489 ML (12% increase) due to the choice of the AWRA-L v2.0.0 model instead of the previously used AWRA-L v1.0.0 for the calculations.

The line item shows an increase of the recalculated volume by 9,320,333 ML (22% change) for the 2010–11 year. The respective volumes associated with the change are detailed in the following table.

 

Restatement of comparative year information made for the line item 17.10 River and floodplain leakage, evaporation and errors
Segment 2012 Account volume for the 2010–11 year (ML) 2011 Account volume for the 2010–11 year (ML) Difference due to updated information (ML)
Northern Basin 26,656,458 23,767,902 2,888,556
Southern Basin 24,978,289 18,546,512 6,431,777
Whole region 51,634,747 42,314,414 9,320,333