3.2 Wastewater collection system
The volume reported included water held in the wastewater pipes system owned by SA Water, but did not include wastewater treatment lagoons. There was minimal new wastewater pipe construction in the 2010–11 year, hence opening and closing balances reported (95 ML) did not change. The volumes of water held in the wastewater collection system, itemised by gravity-fed and pumping pipes, are presented in the following table.
|Wastewater system||Storage volume at 30 June 2010 (ML)
||Storage volume at 30 June 2011 (ML)
|Wastewater pipes – gravity||63||63|
|Wastewater pipes – pumping||32||32|
The volumes of water held in pipes were estimated from pipe lengths and nominal diameters (stored in the Maximo system) using the following formula:
π x (D/2) x (D/2) x PL
D = Nominal diameter of the pipe
PL = Pipe length.
Assumptions, Limitations, Caveats and Approximations
- The volume in gravity and pumping wastewater pipes was assumed to be 20% and 100% of capacity, respectively.
- Pipes without recorded construction dates were assumed to have been constructed before the 2010–11 year.
- Nominal diameters of pipes were used for the calculation of volumes.
- Does not include volumes of water held within wastewater lagoons.
This line item corresponds to line item 5.2 Urban wastewater supply system reported in the 2010 Account. An error in the volume reported in the 2010 Account for pumping pipes and gravity pipes was identified due to data quality improvement processes. Although the changes to the volume reported were small, the volume was restated to correct this error and provide comparability between years.
These changes and their respective volumes are detailed in the following table. The restated comparative year volume for the opening and closing balance is 95 ML.
|2010 Account line item name
||Wastewater collection system
||Opening/closing volume at 30 June 2010 reported in 2010 Account (ML)||Value difference to volume reported due to prior period error correction (ML)||Opening/closing volume at 30 June 2010 reported in 2011 Account (ML)|
|5.2 Urban wastewater supply system||wastewater pipes – gravity||9||54||63|
|wastewater pipes – pumping||28||4||32|