1.2 Unregulated river
The volume reported for the opening (437 ML) and closing (460 ML) balance for unregulated river represents the sum of individual storage volumes for surface water weirs (including dead storage) operated by SA Water at 30 June 2010 and 30 June 2011 respectively. This volume includes surface water weirs that contribute to the operation of the urban water supply system through diversion to urban water storages, and for which appropriate storage height data was available to estimate total storage volume.
For more information on surface water weirs refer to the Surface water section of the Contextual information.
The surface water weir storage volume, total storage capacity and dead storage are provided in the following table.
|Surface water weir||Total storage capacity (ML)||Dead storage capacity (ML)||Storage volume at 30 June 2010 (ML)||Storage volume at 30 June 2011 (ML)|
The volume reported here did not include
- the volume of water stored in unregulated river channels
- the volume of water stored in private on-channel storages
These volumes could not be quantified in a way that is complete, neutral and free from material error, therefore they were not reported in the water accounting statements.
Unregulated rivers include all rivers and tributaries within the major catchments in the Adelaide region and private on-channel storages, which are common throughout the region. For more information refer to the Surface water section of the Contextual information. These rivers support a range of environmental, recreational and commercial activities. In particular, water from unregulated rivers is diverted for agricultural and industrial purposes as authorised by water licences and sections of the Natural Resource Management Act 2004 (South Australia). The volume of water held in unregulated rivers is an important water asset for the region. Therefore the omission of this information is highly relevant to the users of this report.
The volume of water held within unregulated rivers is considered to be substantial and will have a material impact on the volume reported for the surface water store, however its omission is not expected to have a material impact on the surface water balance. While private on-channel storages are known to be common throughout the region, accurate information on the number and storage capacity is currently not available and it is difficult to quantify their impact on the surface water store.
Storage volume was measured using gauged water level height(s) in metres with respect to the Australian Height Datum for individual storages. The height measurement was converted to a volume using the storage-volume relationship(s) provided by SA Water. The storage volume of individual surface water storages was aggregated to present the total volume for the line item.
Assumptions, Limitations, Caveats and Approximations
Storage-volume relationships were derived from surveys of specific parts of the individual storage (weir), and may not reflect the storage-volume relationship across the entire storage.
Water storages are subject to sedimentation and other physical changes over time, which in turn may affect the accuracy of the storage-volume relationships.
This line item corresponds to line item 1.2 Unregulated channel reported in the 2010 Account. In the 2011 Account, the Bureau changed the classification of some storages and weirs reported in the 2010 Account in order to provide the users with clearer information. The Bureau of Meteorology reclassified surface water weirs to line item 1.2 Unregulated river because weirs have a different purpose than the surface water storages. The purpose of weirs is to control river flow to assist with water delivery to the urban water system, whereas surface water storages provide medium to long term water storage for water supply.
These changes and their respective volumes are detailed in the following table. The restated comparative year opening balance is 578 ML and the closing balance is 437 ML.
|2010 Account line item name||Storage||Volume at 30 June 2010 reported in 2010 Account (ML)||Value difference to volume reported due to reclassification (ML)||Volume at 30 June 2010 reported in 2011 Account (ML)|
|Opening balance||Closing balance||Opening balance||Closing balance||Opening balance||Closing balance|
|1.2 Unregulated channel||Barossa Weir||91||93||91||93|