17.1 Evaporation from surface water
The volumetric value for the line item at the end of the 2010–11 year was 3,505,568 ML.
The line item represents evaporation volumes from surface water assets within the Murray–Darling Basin (MDB) region. Evaporation from storages (included in line item 1.1); regulated river channels, locks and weirs (included in line item 1.3); lakes (included in line item 1.4); and other known water bodies within the region were taken into account in the line item. Information on evaporation from other surface water assets (mainly unregulated rivers and unknown water bodies) is not available.
Evaporation volumes from surface water assets on water resources plan (WRP) area basis are summarised in the following table. Specific details of evaporation from individual asset basis are included in the table thereafter. In the tables, volumes shown against a WRP or sustainable diversion limit (SDL) area are based on surface water assets geographically located within that area.
|Surface water resource plan area||
Volume (ML) for the 2010–11 year
|SW16||Qld Border Rivers||Qld||46,482|
|SW15||NSW Border Rivers||NSW||14,798|
|Sub-total Northern Basin||372,396|
|SW7||NSW Murray and Lower Darling||NSW||1,153,414|
|Sub-total Southern Basin||3,133,172|
|Total for the region||3,505,568|
|Water resource plan area||
Surface water asset
Volume (ML) for the 2010–11 year
|Cooby Creek Reservoir2||3,407|
|Jack Taylor Weir1||4,847|
|Neil Turner Weir2||175|
|Qld Border Rivers||SS24||Qld Border Rivers||Qld||Glenlyon Lake1||22,377|
|Storm King Dam2||1,281|
|NSW Border Rivers||SS23||NSW Border Rivers||NSW||Lake Inverell2||516|
|Split Rock Reservoir1||9,830|
|Spring Creek Reservoir2||969|
|Suma Park Reservoir2||1,955|
|Murrumbidgee NSW||SS15||Murrumbidgee||NSW||Berembed Weir1||1,445|
|NSW Murray and Lower Darling||SS18||Lower Darling||NSW||Lake Cawndilla1||176,014|
|Stephens Creek Reservoir2||10,644|
|SS14||NSW Murray||NSW||Lake Hume1||228,973|
|Upstream of Lock 7 (Rufus)2||6,334|
|Upstream of Lock 8 (Wangumma)2||9,141|
|Upstream of Lock 9 (Kulnine)2||14,583|
|Upstream of Lock 10 (Wentworth)2||13,087|
|Upstream of Lock 15 (Euston)2||81,946|
|Vic Murray||SS3||Kiewa||Vic||Lake Guy2||98|
|Rocky Valley Storage2||2,048|
|Northern Victoria||SS4||Ovens||Vic||Lake Buffalo1||2,929|
|Lake William Hovell1||1,461|
|SS6||Goulburn||Vic||Goulburn Weir 1||13,130|
|Upper Coliban Reservoir2||3,082|
|SS8||Loddon||Vic||Barkers Creek Reservoir2||632|
|Cairn Curran Reservoir1||18,908|
|Spring Gully Reservoir2||431|
|Vic Murray||SS2||Vic Murray||Vic||Kangaroo/Racecourse Lake2||14,432|
|Upstream of Lake Mulwala2||33,272|
|Upstream of Mildura Weir2||50,607|
|SA Murray||SS11||SA Murray||SA||Blanchetown Weir – Lock 11||17,010|
|Bookpurnong Weir – Lock 41||9,099|
|Overland Weir – Lock 31||16,784|
|Renmark Weir – Lock 51||10,905|
|Upstream of Lock 6 (Murtho)2||17,238|
|Upstream of Lake Alexandrina2||54,774|
|Waikerie Weir – Lock 21||14,267|
|Lake Burley Griffin2||7,241|
|Total for the region||3,505,568|
1 Dynamic surface area was used in calculations
2 Static surface area was used in calculations (based on boundaries defined for surface water bodies in Bureau of Meteorology's Australian Hydrological Geospatial Fabric)
The Priestly and Taylor method to estimate potential evaporation (as calculated by the WaterDyn model [Raupach 2008]) was used to estimate evaporation from the surface water assets. Monthly potential evaporation data produced by the Bureau were used, based on daily gridded climate data that is 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 data sets 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 data-sets are outlined in Jones et al. (2007).The evaporation at each waterbody was estimated from the proportionally weighted average of grid-pixels 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 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 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 do not capture changes that occur on a shorter time-scale.
This line item corresponds to line item 14.1 Evaporation from connected surface water, reported in the 2010 Account. In the 2011 Account, the following changes were made that caused the 2009–10 year value to be restated:
The scope of the line item was changed.
An error was committed in the values reported in the 2010 Account.
The methodology used to quantify the line item was improved and resulted in a material change in volume.
The changes and their respective values are detailed in the following table.
|2010 Account line items||
Volume for the 2009–10 year reported in the 2010 Account (ML)
Difference due to scope, prior period error correction and calculation method change (ML)
Volume for the 2009–10 year reported in the 2011 Account (ML)
|14.1 Evaporation from connected surface water||Northern Basin||261,749||–57,603||204,146|
Scope change was due to the following reasons:
Lake Mokoan, Lake Batyo Catyo, Pine Lake, Dock Lake and Green Lake (included in the 2010 Account) were excluded for the 2011 Account. Information for Lake Mokoan was not available. Qualification of other four storages as surface water asset was not verified at the data collection phase for the 2011 Account (they were considered as abandoned after the construction of Wimmera pipeline). For 2012 Account, these storages will be investigated for their inclusion.
Regulated river reaches upstream of Lock 10 and Lock 15 in the River Murray were included for the 2011 Account.
Prior period error correction was due to the following reason:
Barren Box Swamp was included in the 2010 Account. However, it is not a surface water asset for the 2011 Account because this storage is located in a water distribution system. Barren Box Swamp was excluded in the 2011 Account.
Calculation method change was due to the following reason:
Penman open water evaporation method was used for the 2010 Account. For the 2011 Account, Priestly and Taylor potential evaporation method was used. The change was made for better estimate of evaporation.