Sydney
17.1 Evaporation from surface water

Supporting Information

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.

Quantification Approach

Bureau of Meteorology

Data Source

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.

Provided by

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.

Method

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.

 

Assumptions, Limitations, Caveats and Approximations

  • 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 Information

Uncertainty was not quantified.

Sydney Catchment Authority

Data Source

Daily Return System (DRS) database.

Provided by

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.

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 judgment on the calculation method and organisational practice is +/– 10%.

Comparative year

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