Sydney

The following tables provide a summary and breakdown of evaporation from connected surface water in the Sydney region.

Evaporation from connected surface water—summary

Breakdown of evaporation from storage reservoirs managed by the Sydney Catchment Authority

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

Breakdown of evaporation from storage reservoirs not managed by the Sydney Catchment Authority

* Data were calculated by the Bureau of Meteorology. Data for storage reservoirs not listed in this disclosure note are not available. Evaporation for those reservoirs has been considered with evaporation in the landscape.

Breakdown of evaporation from river sections

* Data were calculated by the Bureau of Meteorology. Only the river sections for which river volumes have been calculated are included. Evaporation for all the other river reaches has been considered with evaporation in the landscape.

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

Note a: The Bureau of Meteorology

Data source

• Bureau of Meteorology (the Bureau): data from the National Climatic Centre (NCC) rainfall, temperature and solar radiation grids; geographical information system (GIS) layers; Australian Hydrological Geospatial Fabric (AHGF) waterbody feature class; and Australian Water Resources Information System.
• NSW Office of Water: river channel cross-section and flow data from Hydstra and Computer Aided Improvements to River Operations (CAIRO) databases.
• Sydney Catchment Authority (SCA): spatial outline of SCA area of operations.

Data provider

The Bureau provided evaporation data for the following storage reservoirs, which are not managed by SCA:

• Bamarang Reservoir
• Danjera Reservoir
• Flat Rock Creek Reservoir
• Pejar Reservoir
• Sooley Reservoir.

The Bureau provided evaporation data from the river sections in:

• Capertee River
• Coxs River
• Macdonald River
• Shoalhaven River
• Wollondilly River.

Method

General

Evaporation from the connected surface water store was estimated using monthly open water evaporation data produced by the Bureau, in conjunction with the Commonwealth Scientific and Industrial Research Organisation (CSIRO), as part of the Australian Water Availability Project (AWAP). It is a Penman evaporation estimate based on daily gridded climate data and is available on a 0.05 degree (5 km) national grid. The daily gridded climate data-sets are generated by the Bureau, and include precipitation, downward solar irradiance, and maximum and minimum air temperature. The methods used to generate these gridded data-sets are outlined in Jones, Wang and Fawcett (2007a).

The evaporation from each waterbody was estimated from the average of evaporation estimates in 5 x 5 km grid-cells that intersected the water feature. The volume was then estimated using the surface area of each waterbody.

Specific to the Sydney region

In the Sydney region, the evaporation from the connected surface water store was calculated for:

• Flat Rock Creek, and Bamarang, Danjera, Sooley and Pejar reservoirs
• the sections of the Shoalhaven, Coxs, Wollondilly, Capertee and Macdonald rivers considered within the Sydney Connected Surface water store.

The surface area of the reservoirs was estimated using the static default AHGF waterbody feature class. The surface area of the river sections was estimated using cross-section and gauge data from the upper sections of the river reaches.

Uncertainty

The volume was estimated from measured data. Uncertainty is ungraded.

Approximations, assumptions, caveats/limitations

• The Penman evaporation estimates are subject to approximations associated with interpolating the observation point data to a national grid detailed in Jones, Wang and Fawcett (2007a).
• 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 waterbody feature class surface area was an approximation only.
• The cross-section and gauge data used to define the width of the river sections was from locations in the upper reaches of the river sections. This is likely to have resulted in an underestimation of the river width and, therefore, the area in the lower reaches of the river. This would lead to an underestimation of the evaporation from the connected surface water store.
• Separate data for Farmers Creek No. 2, Bundanoon and Medway storage reservoirs are not available.
• Only the river sections for which river volumes have been calculated for this subaccount are included. Evaporation for all the other river reaches, and Farmers Creek No. 2, Bundanoon and Medway storage reservoirs have been considered as evaporation in the landscape.

Note b: The Sydney Catchment Authority

Data source

Daily Return System (DRS) database.

Data provider

Evaporation from following storage reservoirs is 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.

Method

Measured pan evaporations were adjusted by a pan factor.

Uncertainty

The evaporation volume is based on measured data. Estimated uncertainty based on measurement accuracy, professional judgment on the calculation method and organisational practice is +/–10%.

Approximations, assumptions, caveats/limitations

Nil.