South East Queensland
3.1 Urban water supply system
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 considered under this line item included LinkWater, 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.
|Organisation||30 June 2011||30 June 2010|
|Allconnex Water|| –
|Queensland Urban Utilities||332||652||984||332||652||984|
- Where data were not available this has been represented with a dash (–).
The volume of water within LinkWater pipes increased from 465 to 467 ML. This was due to the construction of additional pipes within their network. The urban retailer volumes are the same at the start and end of the 2010–11 year as only one dataset was available and this was used for both the 30 June 2010 and 2011 volumes.
Although data were not available for various components, some additional information was provided on these water assets:
Allconnex Water manages 103 tanks, 95 of which are located within the SEQ region
The total length of potable water supply pipes (including bulk suppliers and retailers) in the SEQ region is approximately 14,837 km.
The volume of water within each pipe diameter class was calculated based on the diameter 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 pipes.
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 Unity Water. Data were not available for Allconnex Water. Due to lack of availability of actual storage volumes on 30 June 2010 and 2011, the entire capacity for each tank was included for this line item as the volume.
Assumptions, Limitations, Caveats and Approximations
It was assumed that the actual storage volume within each tank was 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 Allconnex Water. 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 2011 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) but the internal diameter may vary, depending on the pipe material and pressure rating – 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. It is expected that this is of the order of 5% for individual pipe segments.
Due to the live nature of GIS, the storage volume of urban retailer pipes was only able to be calculated at the time of request, resulting in identical volume estimates for the start and end of the 2010–11 year. 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.
This line item corresponds to line item 5.1 Urban potable water supply system reported in the 2010 Account. Data were not available from urban retailers for pipe and tank volumes at the time of 2010 Account publication. Data are now available to estimate this volume for a number of urban retailers. Given the minor change in volume that occurs from year to year within potable pipe networks, the 2010 Account closing balance volumes were amended with these new data.
The following table compares the value at 30 June 2010 reported in the 2011 Account with the corresponding value reported in the 2010 Account.
|2011 Account line item||2010 Account line item||Component||Volume reported in the 2010 Account
|Prior period error correction
|Volume difference due to scope change
|Restated volume reported in the 2011 Account
|3.1 Urban water supply system||5.1 Urban potable water supply system||Pipes||465||0||332||797||Data now available for some urban retailer pipes|
|Tanks||0||0||1,257||1,257||Data now available for some urban retailer tanks|