This line item comprises three different data-sets. The method for each data-set is shown below.
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.
Wingecarribee Shire Council provided following data for the mass balance calculations to produce inflow by the Bureau:
The Bureau modelled the landscape water balance to estimate inflows using following data sources:
The Bureau provided run-off to:
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.
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.
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.
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.
The volume was estimated. Uncertainty is ungraded.
The volume was modelled. Uncertainty is ungraded.
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.
Data spreadsheets.
Delta Electricity provided run-off to Lake Lyell, Lake Wallace and Thomsons Creek Reservoir.
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.
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.
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.
Run-off to the following storage reservoirs are managed by SCA:
Inflows to Fitzroy Falls and Wingecarribee reservoirs were calculated as follows:
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).
The volume is based on measured data. Estimated uncertainty based on meter accuracy, professional judgment on calculation methods and organisation practice is +/–10%.
Nil.