Sydney
17.1 Evaporation from surface water

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

Evaporation from surface water – summary

Connected surface water asset	Evaporation from the asset during 2010–11 (ML)
Storages managed by the Sydney Catchment Authority	95,911
Storages not managed by the Sydney Catchment Authority	5,568
River sections	13,415
Total	114,894

 

Breakdown of evaporation from storages managed by the Sydney Catchment Authority

Storage reservoir	Evaporation during 2010–11 (ML)
Cataract	6,274
Cordeaux	4,598
Avon	7,087
Nepean	5,340
Woronora	1,496
Lake Burragorang (Warragamba Dam)	46,196
Prospect	5,340
Wingecarribee	5,759
Fitzroy Falls	5,492
Lake Yarrunga (Tallowa Dam)	8,050
Blue Mountains1	279
Total	95,911

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

Breakdown of evaporation from storages not managed by the Sydney Catchment Authority

Storage reservoir1	Managing authority	Evaporation during 2010–11 (ML)
Bamarang	Shoalhaven City Council	765
Danjera	Shoalhaven City Council	938
Flat Rock Creek	Shoalhaven City Council	259
Pejar	Goulburn Mulwaree Council	1,768
Sooley	Goulburn Mulwaree Council	1,344
Farmers Creek No. 2	Lithgow City Council	77
Medway	Wingecarribee Shire Council	216
Bundanoon	Wingecarribee Shire Council	201
Total		5,568

¹Data were calculated by the Bureau of Meteorology. Data for storage reservoirs not listed in this disclosure note are not available.

Breakdown of evaporation from river sections

River1	From	To	Evaporation during 2010–11 (ML)
Capertee	Glen Davis	Upper Colo	1,275
Coxs	Lithgow	Kelpie Point	1,788
Macdonald	Howes Valley	St Albans	195
Shoalhaven	Kadoona	Fossickers Flat	4,203
Wollondilly	Pomeroy	Golden Valley	5,954
Total			13,415

¹Data were calculated by the Bureau of Meteorology. Only the river sections for which river volumes have been calculated are included.

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.

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 and Wollondilly River.

The Priestly and Taylor method (Raupach 2008) to estimate potential evaporation (as calculated by the WaterDyn model) was used to estimate evaporation from the surface water store. Monthly potential water evaporation data produced by the Bureau of Meteorology were used, based on daily gridded climate data that are available on a 0.05 degree (5 km) national grid.

Potential evaporation is an estimate of the evaporative demand of the environment. The daily gridded climate datasets used to produce this estimate are generated by the Bureau and include downward solar irradiance, and maximum and minimum air temperature. The methods used to generate these gridded datasets are outlined in Jones et al. (2007).

The evaporation at each waterbody was estimated from the proportionally weighted average of grid-pixels that intersected each water feature. The volume was then estimated using the monthly average surface area of each waterbody. The surface area varied dynamically with changing reservoir storage level for storages where the relationship between storage level and surface area had been derived.

 

• The Priestly and Taylor method for potential evaporation estimates are subject to approximations associated with interpolating the observation point input data to a national grid as described in Jones et al.

• 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 timescale.

• The total surface area of the surface water store within the Sydney region included only the storages, urban storages and weirs listed in the supporting information.

Uncertainty was not quantified.

Daily Return System (DRS) database.

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 and Lower Cascade Reservoir.

Measured pan evaporations were adjusted by a pan factor.

Nil.

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%.

The following table compares the value at 30 June 2010 reported in this account with the corresponding value reported in the 2010 Account.

 

Comparative information from the 2010 Account for line item 17.1

2011 Account line item	2010 Account line item	Value reported in the 2010 Account (ML)	Value reported in the 2011 Account (ML)	Additional information
17.1 Evaporation from surface water	14.1 Evaporation from connected surface water	130,565	130,565	Change in line item name and number