The Melbourne region’s Statement of Changes in Water Assets and Water Liabilities and Statement of Physical Water Flows show an unaccounted volume of 214,966 ML for the connected surface water store for 2009–10 (32% of the total water assets). This volume is the amount required to reconcile inflow volumes against the volume in the connected surface water store.
The most likely reason for this unaccounted volume is an underestimation of outflows to the sea.
In estimating outflows to sea, gauged data were used. However, only those streamflow stations not affected by tidal influences were included in the analysis. Therefore, a significant portion of the surface area of the Melbourne region did not contribute surface run-off.
The unaccounted-for difference is calculated according to the table below.
| Account | Volume (ML) | |
|---|---|---|
| Opening balance (01 July 2009) connected surface water store |
459,896 |
|
| add | Total 13 Connected surface water store inflows |
1,147,200 |
| minus | Total 14 Connected surface water store outflows |
853,423 |
| minus | Closing balance (30 June 2010) connected surface water store |
606,073 |
| Unaccounted-for difference |
214,966 |