Sydney
17.1 Evaporation from surface water

Supporting information

The reported volume for evaporation from surface water is 141,766 ML.


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

(ML)

Storages managed by the Sydney Catchment Authority

117,385

Storages not managed by the Sydney Catchment Authority

10,818

river sections

13,563

Total

141,766


 

Evaporation from each storage managed by the Sydney Catchment Authority during the 2012–13 year

Storage

Evaporation

(ML)

Avon 8,118
Blue Mountains1 315
Cataract 5,998
Cordeaux 5,267
Fitzroy Falls 5,868
Lake Burragorang (Warragamba Dam) 62,027
Lake Yarrunga (Tallowa Dam) 10,556
Nepean 3,383
Prospect 6,341
Wingecarribee 6,406
Woronora 3,107

Total

117,385

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


Evaporation from each storage not managed by the Sydney Catchment Authority during the 2012–13 year

Storage1

Managing authority

Evaporation

(ML)

Bamarang

Shoalhaven City Council

818

Bundanoon Wingecarribee Shire Council 263

Danjera

Shoalhaven City Council

1,048

Farmers Creek No. 2 Lithgow City Council 92

Flat Rock Creek

Shoalhaven City Council

257

Lake Lyell Delta Electricity 2,191
Lake Wallace Delta Electricity 1,362
Medway Wingecarribee Shire Council 230

Pejar

Goulburn Mulwaree Council

1,545

Sooley

Goulburn Mulwaree Council

1,229

Thomsons Creek Dam

Delta Electricity

1,783

Total

10,818

1 Data were calculated by the Bureau of Meteorology. Data for storages not listed in this disclosure note are not available. Where required, static surface area was used.

 

Evaporation from river sections during the 2012–13 year
River1 From To Evaporation (ML)
Capertee Glen Davis Upper Colo

1,512

Coxs Lithgow Kelpie Point

2,014

Macdonald Howes Valley St Albans

208

Shoalhaven Kadoona Fossickers Flat

4,247

Wollondilly Pomeroy Golden Valley

5,582

Total

13,563

 

1 Data were calculated by the Bureau. Only the river sections for which river volumes have been calculated are included. Where required, static surface area was used.


Quantification approach

Bureau of Meteorology

Data source

The Bureau of Meteorology: National Climate Centre daily climate grids (rainfall), Australian Hydrological Geospatial Fabric waterbody feature class; Australian Water Resources Information System.

Provided by

The Bureau of Meteorology provided evaporation data for the river sections and the storages which are not managed by the Sydney Catchment Authority.

Method

The potential evaporation estimate produced by the Australian Water Resources Assessment system Landscape model (AWRA-L) version 3.0 (Van Dijk 2010) was used to calculate evaporation from the surface water store. The AWRA-L model uses a modified version of the Penman-Monteith method to produce the potential evaporation. Daily AWRA-L potential evaporation grids were produced based on daily gridded climate data that were available on a 0.05 degree (approximately 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-cells 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 average monthly surface area was calculated from daily storage levels and capacity tables. Where this data was not available a static surface area was produced from the AHGF. The surface area of the rivers was estimated using cross-section and long term average river level data and remains static in these calculations.

 

Assumptions, limitations, caveats and approximations

  •  The AWRA-L 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. (2007)
  • 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, weirs, and river sections listed in the supporting information.

Uncertainty information

Uncertainty was not quantified.

Sydney Catchment Authority

Data source

DRS database.

Provided by

The Sydney Catchment Authority provided data for the storages under their management.

Method

Measured pan evaporations were adjusted by a pan factor.

Assumptions, limitations, caveats and approximations

Nil.

Uncertainty information

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