Sydney

The following tables provide a summary and breakdown of rainfall-run-off to connected surface water assets from landscape in the Sydney region.

Run-off to connected surface water—summary

Breakdown of run-off to storage reservoirs managed by the Sydney Catchment Authority

* Blue Mountains storage reservoirs include Medlow Reservoir, Greaves Creek Reservoir and Upper Cascade Reservoir, Middle Cascade Reservoir and Lower Cascade Reservoir.

** Pheasants Nest and Broughton Pass weirs divert water to water treatment plants and Prospect Reservoir.

Breakdown of run-off to storage reservoirs not managed by the Sydney Catchment Authority

¹ Flat Rock Creek is a small reservoir. Run-off volume for 2009–10 is not available.
² The value represents retained inflow because outflow from the most downstream reservoir, Lake Lyell, is counted as run-off to Lake Burragorang (Warragamba Dam).
³ The values represent net inflows to the reservoirs after accounting for precipitation, evaporation and other reservoir losses. Precipitation and evaporation for these reservoirs are not separately presented. They have been included in relevant landscape items. The value for Farmers Creek No. 2 also includes 492 ML received from the Clarence Water Transfer Scheme.

Run-off to rivers below the reservoirs 

This line item comprises three different data-sets. The method for each data-set is shown below.

Note a: The Bureau of Meteorology

Data source

Landscape water drain to Farmers Creek No. 2 Reservoir

Mass balance calculations were carried out using measured storage volumes and diversions from the reservoir recorded in Lithgow City Council’s data spreadsheets to calculate inflow.

Landscape water drain to Bundanoon and Medway reservoirs

Wingecarribee Shire Council provided following data for the mass balance calculations to produce inflow by the Bureau:

• measured storage volumes sourced from level monitoring at the reservoirs with Vega-type hydrometric sensors linking to council’s radio telemetry system and data spreadsheets
• measured diversions made from the reservoirs sourced from ABB magflow meters based at raw-water pump stations, council’s supervisory control and data acquisition (SCADA) system and data spreadsheets.

River reaches not within the SCA operational area, and the Bamarang, Danjera, Flat Rock Creek, Pejar and Sooley reservoirs

The Bureau modelled the landscape water balance to estimate inflows using following data sources:

• the Bureau: climate data and geographic information system (GIS) layers.
• Commonwealth Scientific and Industrial Research Organisation (CSIRO): raster spatial data, WaterDyn and AWRA-L model parameters, and radiation data.
• NSW Office of Water: GIS data on waterbody and river channel sections.
• SCA: GIS data on its operation area.
• Geoscience Australia: built-up areas and other GIS layers.
  

Data provider

The Bureau provided run-off to:

• storage reservoirs, excluding those managed by SCA and Delta Electricity
• rivers downstream of the reservoirs and not within the SCA operational area.

Method

Farmers Creek No. 2, Bundanoon and Medway reservoirs

Run-off to reservoirs was estimated from mass balance calculations using storage volumes and known diversions. Run-off also includes 492 ML received from the Clarence Water Transfer Scheme. Precipitation, evaporation and other losses from the reservoirs were accounted for and, therefore, the estimates produced are net inflows.

River reaches not within SCA operational area and the Bamarang, Danjera, Flat Rock Creek, Pejar and Sooley reservoirs

General

Run-off was calculated as the average of ‘discharge’ from the WaterDyn model and ‘streamflow’ from the AWRA-L model. These two estimates were averaged because studies suggested that an ensemble of these two model outputs generally provide a better estimate of run-off than that given by either model individually (Bacon et al. 2010, Viney 2010).

The WaterDyn and AWRA-L models were run for the Australian continent using meteorological inputs from the Bureau’s National Climate Centre (NCC) and parameters from CSIRO.

Volumetric run-off was determined by multiplying the depth of the average run-off by relevant catchment areas. The catchment areas were determined from the landscape layers of the reporting region. The average run-off across an area was determined as the unweighted arithmetic mean of all grid-points that fell within that area.

Information specific to the Sydney region

The Sydney region landscape feature was derived from the Bureau’s Sydney feature within the National Water Account’s 2010 region subaccount boundary polygon.

The spatial extent of each storage on the agreed list of storages was removed from the landscape feature.

Sections of the Shoalhaven, Coxs, Wollondilly, Capertee and Macdonald rivers considered within the connected surface water store (Line item 1.2) were removed from the Sydney subaccount landscape.

Storages (local catchment reservoirs) in the off-channel private water store were also removed from the estimated volume. Water bodies that were considered unlikely to be local catchment reservoirs were also removed. Lithgow City Council received 492 ML from the Clarence Water Transfer Scheme, and this was deducted from the estimated volume.

Estimating the reduction in run-off due to interception by the off-channel private water store

The depth of run-off was multiplied by the area of the landscape to provide an estimate of total run-off from the landscape. The estimate of total run-off from the landscape store was divided into what flowed into the connected surface water store and what was intercepted by the off-channel private water store.

Uncertainty

Farmers Creek No. 2, Bundanoon and Medway reservoirs

The volume was estimated. Uncertainty is ungraded.

River reaches not within SCA operational area and the Bamarang, Danjera, Flat Rock Creek, Pejar and Sooley reservoirs

The volume was modelled. Uncertainty is ungraded.

Approximations, assumptions, caveats/limitations

Farmers Creek No. 2, Bundanoon and Medway reservoirs

Values are net inflows to the reservoirs. The Farmers Creek No. 2 value also includes supplementary flow received from the Clarence Water Transfer Scheme. Precipitation, evaporation and other reservoir losses were taken into account. Precipitation and evaporation for these storage reservoirs were separately available.

River reaches not within SCA operational area and the Bamarang, Danjera, Flat Rock Creek, Pejar and Sooley reservoirs

• Only the run-off estimates were modelled, and were not verified by real-time analysis of streamflow records. The reported value was an estimate of water that was likely to have entered the connected water store from the landscape.
• The run-off estimates were subject to the assumptions of the WaterDyn model detailed in Raupach et al. (2008) and the AWRA-L model detailed in van Dijk (2010).
• Where the volume of water intercepted by the off-channel private water store has been calculated, the run-off estimates inherit the approximations, assumptions and caveats of the local catchment reservoir model (i.e. STEDI) and the parameters used.
• The calculation of the landscape run-off assigned each grid-point an equal contribution despite less than 100% of some grid-cells having a portion within or outside the reporting region boundaries. This had a limited influence because the average is then multiplied by the catchment area, which is not calculated based on the spatial dimensions of the model grid-cells.

Note b: Delta Electricity

Data source

Data spreadsheets.

Data provider

Delta Electricity provided run-off to Lake Lyell, Lake Wallace and Thomsons Creek Reservoir.

Method

River water level was converted to a volume using a rating table in a spreadsheet. Gauging stations for the water level measurement are located at the Farmers Creek (Gauge No. 212042), the Coxs River upstream of Lake Lyell (Gauge No. 212058) and Wallerawang (Gauge No. 212054). Water levels have been measured at a weir in the Coxs River upstream of Lake Lyell. For the other two stations, water levels have been measured at a well-defined cross-section of the streams.

Uncertainty

The volume is based on measured data. Estimated uncertainty based on meter accuracy is +/–5%.

The NSW Office of Water conducts an annual verification review on Delta Electricity’s water data.

Approximations, assumptions, caveats/limitations

The provided value is the combined retained inflow to Thomsons Creek Reservoir, Lake Wallace and Lake Lyell, minus the outflows from Lake Lyell (which is the most downstream reservoir). The retained inflow value includes all sources of water from the catchment excluding return flows (e.g. discharges from power stations), upstream reservoir diversions and any spilling.

Note c: The Sydney Catchment Authority

Data source

• Mass balance calculations provided in the SCA Water Balance 2009–10 for the Independent Pricing and Regulatory Tribunal (IPART). Note that inflow values in the SCA Water Balance 2009–10 include both precipitation on reservoirs (Line item 13.1) and inflow to reservoirs (this line item).
• Databases and Calculated Monthly Catchment Run-off (CMCR) and annual spreadsheet calculations.
• Customer invoices.

Data provider

Run-off to the following storage reservoirs are managed by SCA:

• Cataract Reservoir
• Cordeaux Reservoir
• Avon Reservoir
• Nepean Reservoir
• Woronora Reservoir
• Lake Burragorang (Warragamba Dam)
• Prospect Reservoir
• Wingecarribee Reservoir
• Fitzroy Falls Reservoir
• Lake Yarrunga (Tallowa Dam)
• Blue Mountains reservoirs
• • Medlow Reservoir
  • Greaves Creek Reservoir
  • Upper Cascade Reservoir
  • Middle Cascade Reservoir
  • Lower Cascade Reservoir
• Pheasants Nest Weir
• Broughtons Pass Weir.

Method

Inflows to Fitzroy Falls and Wingecarribee reservoirs were calculated as follows:

• Fitzroy Falls Reservoir: inflow was estimated as 4.4 times the gauged flow at Wildes Meadow (Gauge No. 215233), based on the extent of catchment area at the reservoir and the gauge.
• Wingecarribee Reservoir: inflow was estimated as 2.5 times the gauged flow at Maugers in Caalang Creek (Gauge No. 212274), based on the extent of catchment area at the reservoir and the gauge.

The level sensors at the two gauging sites have been linked to SCA’s radio telemetry system. Previously, developed rating tables have been used to convert water levels to a volume.

For all other reservoirs, mass balance calculation was used to estimate inflow to each reservoir. In the calculation, inflow, reservoir diversions, precipitation, evaporation and other known losses, and beginning and end storage volumes for each reservoir were balanced for 2009–10. Reservoir diversions, precipitation, evaporation, and beginning and end storage volumes were either measured data or calculated data (interpolations, application of rating tables) from measured data. SCA Water Balance 2009–10 provides the results of the mass balance calculation. Note that inflow values in the SCA Water Balance 2009–10 include both precipitation on reservoirs (Line item 13.1) and inflow to reservoirs (this line item).

Uncertainty

The volume is based on measured data. Estimated uncertainty based on meter accuracy, professional judgment on calculation methods and organisation practice is +/–10%.

Approximations, assumptions, caveats/limitations

Nil.