Select a Different Region

Select a Water Region Adelaide Canberra Daly Melbourne Ord Perth South East Queensland Sydney

Sydney
Quantification approaches

• Summary of quantification approaches
• Detail of quantification approaches

Summary of quantification approaches

Table 1 outlines the quantification approaches used to derive the line item volumes for the Sydney region. For a more detailed description of the quantification approach, click on the relevant item name in the table.

 

Table 1  Quantification approaches used to derive line item volumes

Approach or data used	Item	Source
Water storage product data	Storages	Energy Australia, Goulburn Mulwaree Council, Lithgow City Council, Shoalhaven City Council, Sydney Catchment Authority and Wingecarribee Shire Council
	Unregulated river	NSW Office of Water
Climate grid data	Precipitation on surface water	Bureau of Meteorology and Sydney Catchment Authority
	Runoff to surface water
	Evaporation from surface water
Stream monitoring data	River outflow from the region	Bureau of Meteorology, NSW Office of Water, Sydney Catchment Authority and Sydney Water Corporation
Water resourcing licence database / annual reports / Water Sharing Plan for the Greater Metropolitan Unregulated River Water Sources	Surface water diversions:Other statutory rights	NSW Office of Water, Goulburn Mulwaree Council, Lithgow City Council, Shoalhaven City Council, Wingecarribee Shire Council and Energy Australia
	Surface water and groundwater allocation announcements
	Entitled abstraction of allocated water to individual users
	Adjustment and forfeiture of water allocation
Database / meter readings / Supervisory control and data acquisition (SCADA) system and data spreadsheets	Entitled diversion of allocated surface water to urban water system	Goulburn Mulwaree Council, Lithgow City Council, Palerang Council, Sydney Catchment Authority and Wingecarribee Shire Council
	Direct discharge by user	Energy Australia
	Delivery of water under inter-region agreement	Energy Australia and Sydney Catchment Authority
	Inter-region claims on water
	Increase of inter-region surface water claims / urban water claims on water
Metered and estimated data provided by water authorities via Bureau's urban water template	Wastwater collected	Goulburn Mulwaree Council, Lithgow City Council, Shoalhaven City Council Sydney Water Corporation and Wingecarribee Shire Council
	Delivery of water from outside region to urban water system
	Delivery of water by inter-region agreement to urban water system
	Evaporation from urban water system
	Leakage to groundwater
	Delivery to urban water system users
	Discharge to surface water from urban water sytem
	Wastewater discharge outside of region
	Transfer of water outside of region
	Other urban water system decreases
Not quantified	Regulated rivers
	Lakes and wetlands
	Water table aquifer
	Stored asset: Urban water supply system
	Stored asset: Wastewater system
	Stored asset: Recycled water system
	Groundwater discharge to surface water
	Groundwater flow from/to outside region
	Groundwater recharge
	Groundwater extractions: other statutory rights

 

Detail of quantification approaches

Water storage product data

Storages

Storage volume at the start and end of the year was calculated using water level data (metres above Australian Height Datum) collected at each storage. Rating tables established for each storage were used to convert the height measurement to a volume. The volume of individual storages was aggregated to present the total volume for the line item as detailed in the supporting information table. The uncertainty estimate for these volumes is +/–5%.

The assumptions made in calculating the volumes were as follows:

• Storage–volume curves represent specifically surveyed parts of the storage and may not reflect the storage–volume relationship across the entire storage.
• Storages are subject to sedimentation and other physical changes over time, which in turn affect the accuracy of the storage–volume curves.

 

Unregulated river

The volume of water is an estimate of static volume held in the river reaches. The river sections for which data was available were taken for calculation as given below.

• Capertee River: from Glen Davis to Upper Colo
• Coxs River: from Lithgow to Kelpie Point
• Shoalhaven River: from Kadoona to Fossickers Flat
• Wollondillt River: from Jooriland to Golden Vally

The volume at each river section was estimated multiplying the average daily flow at the upstream and downstream river gauges by estimated travel time between the two sections.

The limitations associated with this approach are:

• travel times are estimated to the nearest day
• daily flow change between gauging sites is assumed to be linear.

The volumes for the following unregulated river channels  were not estimated due to non-availability of reliable data.

• Hawkesbury and Nepean rivers (except the river sections given above)
• Shoalhaven River, except the reach from Kadoona to Fossiker's Flat
• northern Sydney rivers
• southern Sydney rivers
• rivers of the Illawarra.

 

Climate grid data

Precipitation on and evaporation from surface water

Data source: Bureau of Meteorology

Monthly precipitation grids for the region were produced using daily data from approximately 6,500 rain gauge stations and interpolated to a 0.05 degree (5 km) national grid (Jones et al. 2007).

Potential evaporation across the region was estimated using the Australian Water Resources Assessment system Landscape model (AWRA-L) version 3.0 (Van Dijk 2010). The AWRA-L model uses a modified version of the Penman–Monteith method to produce the potential evaporation. Daily AWRA-L potential evaporation grids for the region were produced based on daily gridded climate data (including precipitation, solar radiance and temperature) that were available on a 0.05 degree (5 km) national grid (Jones et al. 2007).

The precipitation and evaporation at each waterbody were estimated from the proportionally weighted average of grid cells that intersected each water feature. The volume was then estimated by multiplying by the surface area of each waterbody. The average monthly surface area of the major storages was calculated from daily storage levels and capacity tables. In the Sydney region, the surface area of the four storages was calculated dynamically and the surface area of the three urban lakes was a static value produced from the Australian Hydrological Geospatial Fabric (AHGF).

The limitations associated with this approach are:

• The precipitation and AWRA-L potential evaporation estimates were subject to approximations associated with interpolating the observation point data to a national grid as detailed in Jones et al. (2007).
• The dynamic storage surface areas calculated from the levels and storage rating tables represent a monthly average and therefore will not capture changes that occur on a shorter temporal scale.
• The use of the static default AHGF surface area is an approximation only. It represents the storages at capacity and therefore likely results in an over-estimation of precipitation and evaporation on the storages.

Data source: Sydney Catchment Authority

Sydney Catchment Authority provided precipitation date for the following storages: Avon Reservoir, Blue Mountains reservoirs, Cataract Reservoir, Cordeaux Reservoir, Fitzroy Falls Reservoir, Lake Burragorang (Warragamba Dam), Lake Yarrunga (Tallowa Dam), Nepean Reservoir, Prospect Reservoir, Wingecarribee Reservoir and Woronora Reservoir.

Rainfall received over the entire catchment area was calculated by interpolating rainfall values from point gauges (primarily tipping-bucket rain gauges). Rainfall volumes over storages were calculated by multiplying relevant surface areas and interpolated rainfall values. It was assumed that catchment average rain falls on the surface of a lake.

The Sydney Catchment Authority provided evaporation data for the storages listed above. Measured pan evaporations were adjusted by a pan factor.

The precipitation and evaporation volumes are based on measured data. Estimated uncertainty based on accuracy of rain gauges, limitations in the calculation method and organisational practice is +/– 10%.

 

Runoff to surface water

Runoff to surface water in the Sydney region was estimated seperately for:

• storages managed by the Sydney Catchment Authority
• storages not managed by the Sydney Catchment Authority
• river sections.

Data source: Bureau of Meteorology

The runoff volume related to the storages not managed by the Sydney Catchment Authority and river sections was estimated by the Bureau of Meteorlogy. The Bureau  calculated the streamflow estimates from the AWRA-L model outputs. Using climate grid data for the Sydney region (including precipitation, temperature and solar radiation data), AWRA-L was used to estimate the runoff depth at each grid point within the region. Only runoff from the landscape was considered; therefore, the surface areas of the major storages were excluded from the analysis.

The runoff from the catchment contributing to major storages and the remaining runoff within the region were separately calculated.

The average runoff depth from the landscape into the connected surface water store was determined as the weighted mean of the relevant grid points within the region boundary. Points were weighted based upon the area they represented within the reporting region to remove edge effects (where the area represented is not wholly within the reporting region) and the effect of changing area represented with changing latitude. Runoff depth was converted to a runoff volume by multiplying runoff depth by the total area of the region (excluding storages).

The limitations associated with the calculation of runoff volumes are:

• The runoff estimates were subject to the assumptions of the AWRA-L model detailed by Van Dijk (2010).
• The estimated runoff was compared against historical flows at unimpaired catchments within the Sydney region and provided a suitable representation of the runoff for this year.

Data source: Sydney Catchment Authority

For the storages managed by Sydney Catchment Authority, the level sensors at the gauging sites have been linked to Sydney Catchment Authority's radio telemetry system. Rating tables are used to convert water levels to a volume.
For all storages, mass balance calculation was used to estimate inflow to each storage. In the calculation, inflow, storage diversions, precipitation, evaporation, and other known losses, and beginning and end storage volumes for each storage were balanced for the year. These volumes were either measured data or calculated data (interpolations, application of rating tables) from measured data.

Estimated uncertainty based on meter accuracy, professional judgement on calculation methods and organisation practice is +/– 10%.

 

River outflow from the region

The river outflow from the region represents the volume of water that flows out of the Sydney region. It compises:

• rule-based environmental flows, other unspecified releases and spills from most downstream storages and weirs to rivers
• natural runoff from river catchments downstream from storages and weirs, and from streams leading to the sea (less downstream diversions)
• treated water releases from wastewater treatment plants.

For rule-based environmental flows, the water level in each river was monitored at these sites and converted to a flow volume using a rating table. The daily flows from these sites during reporting year were used to calculate the annual streamflow.

Natural runoff was estimated using available gauged flows. Runoff was estimated when gauges were not available.

Treated water releases from wastewater treatment plants were measured using meters.

The limitations associated with the calculations are:

• The level of uncertainty of these gauging stations is estimated at +/– 20 % during low to medium flows and the uncertainty during high flows is ungraded. This is based on four manual physical flow gaugings performed per year. At these sites, the water surface level is measured constantly by on-site equipment. This water level is used to estimate a flow rate, based on a rating curve produced by physical flow gauging in as many flow conditions as possible.

• There is some uncertainty in the flow rates. The river flows have not been gauged under all flow conditions, and the river channel can change from time to time, due to deposition and movement of river sediments, which impacts the cross-sectional area of the channel and changes the velocity of the water.

 

Water resourcing licence database / annual reports / Water Sharing Plan for the Greater Metropolitan Unregulated River Water Sources

Surface water diversions: other statutory rights

The estimated annual water abstraction under riparian right for stock and domestic purposes and for cultural purposes was extracted from Water Sharing Plan for the Greater Metropolitan Region Unregulated River Water Sources and the Water Sharing Plan for the Kangaroo River Water Source. 

No cultural basic rights are estimated to occur in areas other than the Kangaroo River system.

 

Surface water and groundwater allocation announcements / abstractions / adjustment and forfeitures

The surface water and groundwater allocation remaining corresponds to the volume of water allocation that can be carried over between water years. The Water Sharing Plan for the Greater Metropolitan Unregulated River Water Sources details the rules for access licences. Diversion data was obtained from the relevant authorities. According to these rules, carry-over of unused allocation is allowed. For each water management licence, the licensed water management year is from 1 July–30 June. At the end of the water management year, any unused allocation is forfeited. Therefore, for the purposes of the National Water Account, the closing balance for the water allocation remaining is zero.

The water allocation remaining at 30 June 2014 is calculated as shown in Table 2.

 

Table 2  Calculation of remaining water allocation

	Account
	Opening balance (at 1 July 2013)
add	Water liability increase (allocation announcement)
less	Entitled abstraction of allocated water
less	Water liability decrease (forfeiture)
	Closing balance (at 30 June 2014)

 

Database / meter readings / supervisory control and data acquisition (SCADA) system and data spreadsheets

Entitled diversion of allocated surface water to urban water system

The allocation diversion of surface water to urban system comprises of two components:

• Sydney Catchment Authority diversion and supply to urban holders: Goulburn Mulwaree Council, Sydney Water Corporation, Shoalhaven City Council, Wingecarribee Shire Council and raw and unfiltered water supplied by Sydney Catchment Authority to retail customers
• diversion by urban entitlement holders: Goulburn Mulwaree Council, Lithgow City Council, Palerang Council and Wingecarribee Shire Council.

The calculation is based on metered raw water diversion from surface water and inflow to water treatment plants. Raw water supplied directly as untreated (nonpotable water) is the metered diverted volume from the water source.

For sources managed through Sydney Catchment Authority entitlements, the surface water diversion volumes are reported by them, which have some slight differences to the reported inflow to water treatment plants by the respective water authorities.

The uncertainty is estimated to be +/– 2% to +/– 20%.