Sydney

The following tables provide a summary and breakdown of precipitation on connected surface water assets in the Sydney region.

Precipitation on connected surface water—summary

Breakdown of precipitation on 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 precipitation on storage reservoirs not managed by the Sydney Catchment Authority

* Data for storage reservoirs not listed in the above tables are not available. Precipitation for those reservoirs has been considered with precipitation in the landscape.

Breakdown of precipitation on river sections

* Only the river sections for which river volumes have been calculated are included. Precipitation for all the other river reaches has been considered with precipitation 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): Australian Water Availability Project (AWAP), 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.
• NSW Office of Water: GIS layers.
• NSW Office of Water: GIS database, river channel sections included in the Sydney Connected Surface water store.
• NSW Office of Water: New South Wales waterbody polygon ArcSDE feature class.

Data provider

The Bureau provided precipitation data for following storage reservoirs not managed by the Sydney Catchment Authority:

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

Precipitation for the river sections in:

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

Method

Monthly precipitation data were produced by the Bureau. Monthly data were based on daily data from approximately 6,500 rain gauge stations and interpolated to a 0.05 degree (5 km) national grid (Jones, Wang & Fawcett, 2007b).

The precipitation at each waterbody was estimated from the average of the grid-points within a 5 km radius of each water feature. The volume was then estimated using the surface area of each waterbody.

The surface area of the storage 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 precipitation volume was estimated from measured data. The uncertainty estimate is ungraded.

Approximations, assumptions, caveats/limitations

• The precipitation estimates were subject to approximations associated with interpolating the observation point data to a national grid detailed in Jones, Wang and Fawcett (2007a).
• The use of the static default AHGF waterbody feature class surface area is 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 area, in the lower reaches of the river and therefore an underestimation of the precipitation on the Sydney Connected Surface water store.
• Separate data for Farmers Creek No. 2, Bundanoon and Medway storage reservoirs were not available.
• Only the river sections for which river volumes have been calculated for the National Water Account 2010 are included. Precipitation for all the other river reaches, and Farmers Creek No. 2, Bundanoon and Medway storage reservoirs have been considered with precipitation on landscape.

Note b: The Sydney Catchment Authority

Data source

The source for rainfall data is SCA’s Daily Return Systems (DRS) Database. Some stations from which DRS database receives data are managed by the Bureau. Data are also held in the Hydstra system.

Data provider

Precipitation for 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.

Method

Rainfall received over the entire catchment area was calculated by interpolating rainfall values from point gauges (primarily tipping-bucket rain gauges). Rainfall volumes over reservoirs were calculated by multiplying relevant surface areas and interpolated rainfall values.

Uncertainty

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

Approximations, assumptions, caveats/limitations

Catchment average rain assumed to fall on the surface of a lake.