Sydney
41.1 Precipitation on storages

This line item refers to total precipitation on the major surface water storages used for urban water supply within the Sydney region.The total for this line item is 101,704 ML.

Total volume of rainfall on each storage during the 2010–11 year within the Sydney region is provided in the following table. Data from both the Bureau of Meteorology (the Bureau) and the Sydney Catchment Authority (SCA) has been provided in the following tables.

 

Precipitation volumes for the Sydney region using data provided by both the Bureau and the SCA

Storage reservoir	Precipitation (ML) – SCA
Cataract	7,918
Cordeaux	6,470
Avon	8,774
Nepean	3,763
Woronora	1,914
Lake Burragorang (Warragamba Dam)	43,733
Prospect	3,763
Wingecarribee	5,722
Fitzroy Falls	7,531
Lake Yarrunga (Tallowa Dam)	7,110
Blue Mountains1	544
Total	97,242

¹Blue Mountains storage reservoirs include Medlow Reservoir, Greaves Creek Reservoir, Upper Cascade Reservoir, Middle Cascade Reservoir and Lower Cascade Reservoir.

The following table uses data that was calculated by the Bureau.

Precipitation volumes for storages not managed by SCA

Storage reservoir1	Precipitation (ML)
Bamarang	701
Danjera	893
Flat Rock Creek	274
Pejar	1,477
Sooley	1,020
Farmers Creek No. 2	97
Total	4,462

¹Data for storage reservoirs not listed in the previous tables are not available.

Bureau of Meteorology: Australian Water Availability Project (AWAP) monthly precipitation grids; Australian Hydrological Geospatial Fabric (AHGF) waterbody feature class; Australian Water Resources Information System (AWRIS) water storage.

Bureau of Meteorology (the Bureau).

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

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 average monthly surface area of the major storages was calculated from daily storage levels and capacity tables.

The surface area of all the storages in the Sydney region was calculated using this dynamic method.

• The precipitation 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 capacity tables represent a monthly average and therefore will not capture changes that occur on a shorter temporal scale.

The uncertainty estimate was not quantified.

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.

SCA.

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.

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

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%.