Sydney
17.2 River outflow from the region

Outflow from the Sydney region is the streamflow that reaches the sea. The estimated volume for the line item is  4,232,133 ML.

As the Sydney region's river and storage system is complex there are a number of flows that contribute to this line item.

This line item excludes releases and spills which have been captured downstream, but itemises streamflows which have reached the sea. These streamflows include:

• 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.

Volume of total outflow from the Sydney region to the sea during the 2012–13 year

	Description	Volume (ML)
	rule-based environmental flow releases from storages	308,484
add	unspecified releases from storages	10,384
add	spills from most downstream storages and weirs	1,097,045
add	natural runoff from the catchment of rivers downstream of storages and weirs, and unregulated streams leading to the sea	2,774,031
add	treated water releases from wastewater treatment plants	67,359
less	downstream diversions	25,170
	Outflow to the sea	4,232,133

 

Volume of rule-based environmental flow releases from storage that reached the sea from storages during the 2012–13 year

Authority responsible for environmental flow releases	Storage from which the release was made	Environmental flow release (ML)
Sydney Catchment Authority	Woronora	5,787
	Lake Burragorang (Warragamba)	0
	Prospect	0
	Lake Yarrunga (Tallowa)	251,341
	Blue Mountains1	0
	Pheasants Nest Weir	34,722
	Broughton Pass Weir	16,634
Total		308,484

¹ Blue 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 and use.

Volume of unspecified releases and spills from storages during the 2012–13 year

Storage	Other releases (ML)1	Spills (ML)	Total (ML)
Lake Burragorang (Warragamba)	10,384	451,649	462,033
Lake Yarrunga (Tallowa)	02	562,146	562,146
Blue Mountains	0	1,250	1,250
Pheasants Nest Weir	0	59,000	59,000
Broughton Pass Weir	0	23,000	23,000
Total	10,384	1,097,045	1,107,429

¹ Other 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 1,275 ML is not accounted in the table because the flow was received at Wingecarribee. Similarly, Wingecarribee storage release of 550 ML is not accounted in the table because the unregulated flow was recieved at Warragamba storage.

² Release of 14,824 ML released was provided to Shoalhaven City Council for urban supply. This is provided in line item 17.12 Surface water allocation diversion – urban water system.

Gauged flows are not available to cover all river reaches downstream of storages 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 1,327,862 ML for the 2012–13 year, made up of  ML of gauged flows and  ML of flows below these gauges, as well as in ungauged and tidal streams. This is detailed in the following two tables.

Volume of gauged flows for streams leading to the sea during the 2012–13 year

River	Gauge no.1	Flow volume for 2012–13 (ML)	Comments
Macdonald River at St Albans	212228	206,715	Some data missing which contributes to approximately 61% of entire record.
Colo River at Upper Colo	212290	483,080	Some data missing which contributes to approximately 86% of entire record.
Gross River at Burralow	212291	97,718	Some data missing which contributes to approximately 29% of entire record.
South Creek at Richmond Road	212297	2,638	Some data missing which contributes to approximately 83% of entire record. Excludes 15,142 ML of treated wastewater released from St Marys Water Recycling Plant; this has been accounted for separately.
Woronora River at Needles North Engadine	213211	19,623	Excludes 5,787 ML environmental flow release, which was accounted for separately
Shoalhaven River at Grassy Gully No. 2	215216	518,088	Excludes (from the gauged flow): 14,824 ML diverted by the Sydney Catchment Authority to Shoalhaven City Council pumping at Burrier. 251,341 ML environmental flow release and  562,146 ML dam spilling from Lake Yarrunga. Excluded items were accounted for separately.
Total gauged flow		1,327,862

¹ The Sydney Catchment Authority manages the gauging stations. Volume stated is based on available data only.

Volume of natural streamflow in the river reaches in ungauged and tidal streams during the 2012–13 year

Description	Volume (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)	1,446,169	based on the Bureau of Meteorology calculation of line item 9.4 Runoff to surface water

 

Volume of treated water releases from wastewater treatment plants during the 2012–13 year

Description	Volume (ML)
Treated effluent releases to the rivers from the area managed by Sydney Water Corporation (see 19.5 Urban water discharge to surface water)	64,691
Treated effluent releases to the Shoalhaven River below Gauge no. 215216, from the area managed by Shoalhaven City Council	2,668
Total	67,359

 

Volume of deductions from natural river flows for downstream diversions during the 2012–13 year

Description	Volume (ML)	Comments
riparian right releases	18,535	based on total estimated riparian use provided by the New South Wales Office of Water
stock and domestic, and other lumped access licence releases in the respective river reaches	240	as estimated by the New South Wales Office of Water based on entitlement information available in Water Sharing Plan for the Greater Metropolitan Region Unregulated River Water Sources
Sydney Water Corporation diversion from the Hawkesbury River for North Richmond	6,395	based on the value provided by Sydney Water Corporation
Total	25,170

 

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.

See line items 17.6 Diversions – other statutory rights and 17.11 Surface water allocation diversion.

See line items 17.6 Diversions – other statutory rights and 17.11 Surface water allocation diversion.

See line items 17.6 Diversions – other statutory rights and 17.11 Surface water allocation diversion.

See line items 17.6 Diversions – other statutory rights and 17.11 Surface water allocation diversion.

See line items 17.6 Diversions – other statutory rights and 17.11 Surface water allocation diversion.

Stream gauge data from the Hydstra system.

Sydney Catchment Authority.

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 Sydney Catchment Authority's radio telemetry system so that gauging data are readily available. For the other sites, data are downloaded to the authority's Hydstra system in regular intervals from logged data at the site.

Nil.

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.

The Bureau of Meteorology: National Climate Centre daily climate grids (rainfall, temperature and solar radiation), Australian Hydrological Geospatial Fabric waterbody feature class; New South Wales Office of Water: GIS data on waterbody and river channel sections; Sydney Catchment Authority: GIS data on its operation area; Geoscience Australia: built-up areas and other GIS layers.

The Bureau of Meteorology; New South Wales Office of Water; Sydney Catchment Authority; Geosciences Australia.

The natural river flow was estimated based on the AWRA-L version 3.0 (Van Dijk 2010) streamflow model outputs (see the method described in line item 9.4 Runoff to surface water).

The Bureau of Meteorology calculated natural streamflow for the ungauged and tidal rivers.

See line item 9.4 Runoff to surface water in the 'Rivers below the reservoirs' section.

 

The volume is based on modelled and estimated data. Uncertainty is ungraded.

Daily Return System database.

Sydney Catchment Authority.

Known release rates from flow meters, orifice plates, valves with rating tables or measured outlets were used to derive the volume.

Nil.

The volume is based on measured data. Estimated uncertainty based on meter accuracy, and professional judgement on rating tables and site configuration issues is +/– 10%.

See line item 9.9 Discharge from urban water system.

Sydney Water Corporation and Shoalhaven City Council.

See line item 9.9 Discharge from urban water system.

See line item 9.9 Discharge from urban water system.

See line item 9.9 Discharge from urban water system.