5.6 Other surface water liability

Supporting Information

The volume for this line item is 5,363 ML.

The Sydney Catchment Authority (SCA) manages banked environmental flow in the Sydney region.

Between 1 June 2005 and 3 March 2008, environmental flow releases into the Hawkesbury–Nepean River required under SCA's water management licence were halved as directed by the minister responsible for water in New South Wales due to the continuing drought. A condition of halving the flows was that the SCA would maintain a rolling 12-month bank in storage reservoirs and release the banked water as directed by the minister. The total banked water was 9,795 ML at the beginning of the 2010–11 year.

During the 2010–11 year, a total of 3,100 ML was added to the banked environmental flow after a period of construction at Pheasant's Nest Dam that disrupted environmental flows.

SCA released a volume of 28 ML/day from the banked environmental flow from Warragamba Dam from 5 October 2010 to 30 June 2011. This event used 7,532 ML (see line item 17.16), leaving a balance of 5,363 ML as applicable at end of the 2010–11 year.

Reconciliation of this line item is shown in the following table.

Calculation of other surface water liability for the 2010–11 year
Line item
Volume (ML)


Opening balance (as at 1 July 2010)



21.6 Other surface water liability increase



17.16 Other delivery of allocated surface water



13.6 Other surface water liability



Closing balance (as at 30 June 2011)


Quantification Approach

Data Source

SCA and NSW Office of Water agreement, SCA database of daily requirements and releases, SCA compliance reporting to the NSW Office of Water.

Provided by



For 2010–11, the released banked environmental flow volume was derived from orifice-rating tables and stream gauging downstream of environmental flow release from Warragamba Reservoir. The banked environmental flow was reduced by the released volume.

Assumptions, Limitations, Caveats and Approximations


Uncertainty Information

The reduction in the banked volume is based on measured data. Estimated uncertainty based on accuracy of stream gauging is +/– 10%.

Comparative year

The following table compares the value at 30 June 2010 reported in this account with the corresponding value reported in the 2010 Account.


Comparative information from the 2010 Account for line item 5.6

2011 Account line item

2010 Account line item

Value reported in the 2010 Account (ML)

Value reported in the 2011 Account (ML)

Additional information

5.6 Other surface water liability Allocation on regulated flows remaining – other lumped holders



Change in line item name