South East Queensland
3.1 Urban water supply system

The volumetric value for the line item at the end of the 2011–12 year was 2,842 ML.

This line item represents the volume of water held within potable water supply pipes and tanks (balancing reservoirs) by urban utilities within the South East Queensland (SEQ) region. Urban utilities included under this line item are: LinkWater (Seqwater), Queensland Urban Utilities, Allconnex Water and Unity Water.

The potable water supply system consists of large diameter bulk transmission mains that transport potable water from the water treatment plant to key water tanks and distribution points within the urban potable water supply system. Smaller distribution mains distribute water to end users from these tanks and distribution points. LinkWater manages large diameter bulk transmission mains and the three urban retailers manage distribution mains.

The volume of water within pipes and tanks can be seen in the following table.

•  Where data were not available this has been represented with a en dash (–).

The volume of water within LinkWater pipes increased from 467–512 ML. This was due to completion of the next stage of the Northern Pipeline Interconnector. The urban retailer volumes are the same at the start and end of the 2011–12 year as only one dataset was available; this was used for both the 30 June 2011 and 30 June 2012 volumes.

Although data were not available for various components, some additional information was provided on these water assets:

• The total length of potable water supply pipes (including bulk suppliers and retailers) in the SEQ region is approximately 14,837 km.

LinkWater (Seqwater) geographic information system (GIS) database (LinkWater pipe volume); Qldwater Statewide Water Information Management (SWIM) system indicator AS41 and AS42 (tank volume for individual urban utilities); Queensland Urban Utilities GIS database (Queensland Urban Utilities pipe volume).

SEQ Water Grid Manager (currently Seqwater), Queensland Urban Utilities, Gold Coast City Council, Logan City Council, Redland City Council, Unitywater.

Pipe volume

The volume of water within each pipe diameter class was calculated based on the cross section of each pipe multiplied by the total length of pipe of this diameter. The volumes of all pipes of various diameters were then summed to give the total volume within each pipe class.

Tank volume

The total storage capacity of each tank was obtained from Qldwater statewide water information management (SWIM) indicator AS41 and AS42 for Queensland Urban Utilities and Unitywater. Due to lack of availability of actual storage volumes on 30 June 2011 and 30 June 2012, the entire capacity for each tank was included for this line item as the volume.

It is assumed that the actual storage volume within each tank is equal to the total storage capacity of each tank. The volume reported for this line item is an overestimate, but this overestimate would be less than the underestimate that would occur by not including any volume for the tanks at all.

Pipe volume was not available for Unitywater and Logan City Council. The volume reported for this line item will include an underestimate for distribution pipes.

The pipe volume could only be calculated for the potable bulk water pipelines for the SEQ Water Grid. This system extends outside the 2012 Account SEQ region in the north and includes part of the Mary Water Resource Plan (WRP) area (Sunshine Coast). The volume reported for this line item for bulk transmission pipes is overestimated.  

The diameter code rounds off the diameter of the pipe to provide an even number to work with, rather than using the exact internal diameter. For example, a diameter 250 has a 250 mm nominal diameter (DN). For example, polyethylene DN250 may have an internal diameter of around 230 mm, and a ductile iron DN250 may have an internal diameter of around 270 mm. The use of nominal diameter rather than internal diameter to determine volume results in some inaccuracies in the estimate.

Due to the live nature of Geographic Information System (GIS), the storage volume of urban retailer pipes was  calculated at the time of request corresponding to the start and end of the 2011–12 year, resulting in identical volume estimates. It is expected that only a minor change in volume occurred between these dates as limited additional infrastructure was commissioned during the year.

The uncertainty estimate was not quantified.

The following table compares the value at 30 June 2011 reported in the 2012 Account with the corresponding value reported in the 2011 Account.