Sydney
17.2 River outflow from the region
- Supporting Information
-
Quantification Approach
- Downstream diversions from flow leading to sea
- Natural streamflows in gauged streams
- Quantification approach for natural streamflows in ungauged streams
- Rule-based environmental flow releases
- Treated water releases from wastewater treatment plants
- Unspecified releases and spills from reservoirs and weirs to downstream rivers
- Comparative year
Supporting Information
Outflow from the Sydney region is the streamflow reaching the sea. The estimated volume for the line item is 3,039,529 ML.
This item includes streamflows resulting from:
- rule-based environmental flows, other unspecified releases and spills from most downstream storages, and weirs to rivers
- natural runoff from the catchment of rivers downstream of storages and weirs, and streams leading to the sea (less downstream diversions)
- treated water releases from wastewater treatment plants.
Banked environmental flow releases have been separately accounted for in line item 17.16. The following table provides a summary of outflow from the Sydney region to the sea.
Description |
Volume during 2010–11 (ML) |
Rule-based environmental flow releases from storages |
293,094 |
Unspecified releases from storages |
19,950 |
Spills from most downstream storages and weirs |
576,421 |
Natural runoff from the catchment of rivers downstream of storages and weirs, and unregulated streams leading to the sea |
2,142,348 |
Treated water releases from wastewater treatment plants |
74,554 |
Less downstream diversions |
(66,838) |
Outflow to the sea |
3,039,529 |
Authority responsible for environmental flow releases |
Storage reservoir/weir from which the release was made |
Environmental flow release during 2010–11 (ML) |
Sydney Catchment Authority
|
Woronora |
7,126 |
Lake Burragorang (Warragamba Dam) |
3,197 |
|
Prospect |
Not applicable1 |
|
Lake Yarrunga (Tallowa Dam) |
219,245 |
|
Blue Mountains2 |
Not applicable1 |
|
Pheasants Nest Weir |
38,877 |
|
Broughton Pass Weir |
24,649 |
|
Total |
293,094 |
1Environmental flows have not been specified from these storage reservoirs.
2Blue Mountains storage reservoirs include Medlow Reservoir, Greaves Creek Reservoir, Upper Cascade Reservoir, Middle Cascade Reservoir and Lower Cascade Reservoir.
The previous table shows net environmental flow reaching the sea because the released flows were not diverted to downstream storages/weirs and not used for other purposes. Details of released environmental flows including volumes reached at downstream storages/weirs are available in Water for environmental benefit under Water access.
Storage/weir |
Other releases during 2010–11 (ML)1 |
Spills during 2010–11 (ML) |
Total during 2010–11 (ML) |
Lake Burragorang (Warragamba Dam) |
2,907 |
0 |
2,907 |
Lake Yarrunga (Tallowa Dam) |
16,4192 |
538,645 |
555,064 |
Blue Mountains |
224 |
180 |
404 |
Pheasants Nest Weir |
0 |
6,462 |
6,462 |
Broughton Pass Weir |
0 |
7,601 |
7,601 |
Danjera2 |
0 |
23,533 |
23,533 |
Total |
19,950 |
576,421 |
595,971 |
1Other releases were made to facilitate scheduled deliveries (e.g. to meet minimum discharge required to operate a gate — also known as 'conveyance water'). Fitzroy Falls storage release of 736 ML is not accounted in the table because the flow was received at Lake Yarrunga (Tallowa Dam).
2When the spill rate is above the required environmental release no additional release is required. However, for operational reasons, the release from the outlet is maintained through the period of spill.
Gauged flows are not available to cover all river reaches downstream of storages and weirs, and streams leading to the sea. Many of the gauges are tidal and only river height data are available for some of them. Gauged flow data are not available for:
- the Hawkesbury River and the lower Nepean River (except the tributaries shown in the following table)
- northern Sydney rivers
- southern Sydney rivers, except for the Woronora River (at Gauge No. 213211)
- the Illawarra rivers
- downstream river reaches below the gauges shown in the following table.
Natural runoff was therefore estimated from available gauged flows for the rivers listed in the following table, and estimated runoff for other streams.
Total natural runoff is 2,142,348 ML for 2010–11, made up of 740,134 ML of gauged flows and 1,402,214 ML of flows below these gauges, as well as in ungauged and tidal streams. This is detailed in the following two tables.
River |
Gauge No.1 |
Flow volume for 2010–11 (ML) |
Comments |
Macdonald River at St Albans |
212228 |
100,910 |
|
Colo River at Upper Colo |
212290 |
352,476 |
|
Gross River at Burralow |
212291 |
89,804 |
|
South Creek at Richmond Road |
212297 |
7,876 |
Excludes 3,662 ML of treated wastewater released from St Marys Water Recycling Plant, this has been accounted for separately |
Woronora River at Needles North Engadine |
213211 |
24,150 |
Excludes 7,126 ML environmental flow release, which was accounted for separately |
Shoalhaven River at Grassy Gully No. 2 |
215216 |
164,918 |
Excludes (from the gauged flow):
Excluded items were accounted for separately |
Total gauged flow |
740,134 |
|
1The Sydney Catchment Authority manages the gauging stations.
Description |
Volume for 2010–11 (ML) |
Comment |
Natural streamflow in the river reaches downstream of the gauges, and in ungauged and tidal streams (before any addition and diversions at further downstream reaches) |
1,402,214 |
Based on the Bureau of Meteorology calculation of line item 9.4 Runoff to surface water |
Description |
Volume for 2010–11 (ML) |
Wastewater releases to the rivers from the area managed by Sydney Water Corporation |
55,648 |
Recycled water releases to Boundary Creek (a tributary of the Nepean River) by Sydney Water Corporation |
15,989 |
Wastewater releases to the Shoalhaven River below Gauge No. 215216, from the area managed by Shoalhaven City Council |
2,917 |
Total |
74,554 |
Description |
Volume for 2010–11 (ML) |
Comments |
Riparian right releases |
22,718 |
Based on total estimated riparian use provided by the NSW Office of Water (9,837 ML released from Lake Burragorang was deducted from the total use) |
Stock and domestic, and other lumped access licence releases in the respective river reaches |
38,531 |
As estimated by the NSW Office of Water based on entitlement information available in Draft Water Sharing Plan for the Greater Metropolitan Region Unregulated River Water Sources (2012a) |
Sydney Water Corporation diversion from the Hawkesbury River for North Richmond |
5,589 |
Based on the value provided by Sydney Water Corporation
|
Total |
66,838 |
|
Quantification approaches are provided separately for the following inputs used to calculate outflow to the sea:
- rule-based environmental flow releases
- unspecified releases and spills from storages and weirs to downstream rivers
- natural streamflows in gauged streams
- natural streamflows in ungauged streams
- treated water releases from wastewater treatment plants
- downstream diversions from flow leading to sea.
Quantification Approach
Downstream diversions from flow leading to sea
Data Source
Provided by
Method
See the following:
Assumptions, Limitations, Caveats and Approximations
See the following:
Uncertainty Information
See the following:
Natural streamflows in gauged streams
Data Source
Provided by
Method
River levels are gauged and converted to a flow rate using a rating table. Rating tables are updated by manual stream gauging.
Some of the gauging sites have been linked to the SCA's radio telemetry system so that gauging data are readily available. For the other sites, data are downloaded to SCA's Hydstra system in regular intervals from logged data at the site.
Assumptions, Limitations, Caveats and Approximations
Uncertainty Information
The volume is based on measured data. Estimated uncertainty based on measurement accuracy and professional judgment on rating tables is +/– 10% to 50%, depending on the site characteristics and flow rate.
Quantification approach for natural streamflows in ungauged streams
Data Source
Provided by
Method
The Bureau calculated natural streamflow for the following ungauged and tidal rivers:
- the Hawkesbury River and the lower Nepean River, except catchment areas upstream of
- Warragamba River at Lake Burragorang (Warragamba Dam) (Gauge No. 212243)
- Pheasants Nest Weir (Gauge No. 212203)
- Broughtons Pass Weir (Gauge No. 212233)
- Macdonald River at St Albans (Gauge No. 212228)
- Colo River at Upper Colo (Gauge No. 212290)
- Gross River at Burralow (Gauge No. 212291)
- South Creek at Richmond Road (Gauge No. 212297)
- northern Sydney rivers
- southern Sydney rivers, except the catchment area upstream of the Woronora River at Needles North Engadine (Gauge No. 213211)
- the Illawarra river
- the Shoalhaven River, except the catchment area upstream of Grassy Gully No. 2 (Gauge No. 215216).
Natural river flow in the river reaches is based on landscape water draining into the rivers modelled by the Bureau (see the method described in line item 9.4 Runoff to surface water).
Assumptions, Limitations, Caveats and Approximations
See line item 9.4 Runoff to surface water - rivers below the reservoirs.
Uncertainty Information
The volume is based on modelled and estimated data. Uncertainty is ungraded.
Rule-based environmental flow releases
Data Source
Provided by
Method
Assumptions, Limitations, Caveats and Approximations
Uncertainty Information
Treated water releases from wastewater treatment plants
Data Source
Provided by
Method
Assumptions, Limitations, Caveats and Approximations
Uncertainty Information
Unspecified releases and spills from reservoirs and weirs to downstream rivers
Data Source
Provided by
Method
Agency |
Method |
Bureau of Meteorology |
Storage mass balance calculations using measured storage volumes, estimated precipitation and evaporation, and modelled runoff |
Sydney Catchment Authority |
Spill volumes derived from water levels and rating tables for spillways |
Assumptions, Limitations, Caveats and Approximations
Agency |
Approximations, assumptions, caveats/limitations |
Bureau of Meteorology |
Based on data provided by Shoalhaven City Council, water was not supplied from Danjera Reservoir during 2010–11. Storage losses other than spills have been assumed as negligible. For other approximations and assumptions, see the following line items: |
Sydney Catchment Authority |
Nil |
Uncertainty Information
Agency |
Uncertainty |
Bureau of Meteorology |
The volume was estimated from measured and modelled data. Estimated uncertainties for some of the inputs used for the calculation of spilling volume from Danjera Reservoir are not quantified. These inputs are precipitation, evaporation and modelled run-off. Therefore, uncertainty for the spilling volume from Danjera Reservoir is ungraded. Estimated uncertainty for storage volume, which was the remaining input for the calculation, is +/– 5% |
Sydney Catchment Authority |
The volume is based on measured data. Estimated uncertainty based on meter accuracy, and professional judgment on rating tables, site configuration issues and local issues at the time of spilling at each site is +/– 5% to 10% |
Comparative year
2011 Account line item |
2010 Account line item |
Value reported in the 2010 Account (ML) |
Value reported in the 2011 Account (ML) |
Additional information |
17.2 River outflow from the region |
14.2 Streamflow to downstream entity |
1,196,052 |
1,196,052 |
Change in line item name and number |