17.1 Evaporation from surface water
The volumetric value for the line item at the end of the 2011–12 year was 3,258,419 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||State/Territory||Volume (ML)|
|SW16||Qld Border Rivers||Qld||42,609|
|SW15||NSW Border Rivers||NSW||13,483|
|SW12||NSW Intersecting Streams||NSW||–|
|Sub-total Northern Basin||366,255|
|SW7||NSW Murray and Lower Darling||NSW||993,975|
|SW6||Eastern Mount Lofty Ranges||SA||–|
|Sub-total Southern Basin||2,892,164|
|Total for the region||3,258,419|
|Water resource plan area||
Sustainable diversion limit (SDL) area
Surface water asset
Volume (ML) for the 2011–12 year
|SW18 Condamine–Balonne||SS26||Condamine–Balonne||Qld||Buckinbah Weir1||2,782|
|Cooby Creek Reservoir2||3,289|
|Jack Taylor Weir1||4,043|
|Neil Turner Weir2||149|
|SW16 Qld Border Rivers||SS24||Qld Border Rivers||Qld||Glenlyon Lake1||22,307|
|Storm King Reservoir2||1,213|
|SW15 NSW Border Rivers||SS23||NSW Border Rivers||NSW||Lake Inverell2||470|
|Tenterfield Creek Reservoir2||296|
|SW14 Gwydir||SS22||Gwydir||NSW||Lake Copeton1||49,262|
|SW13 Namoi||SS21||Namoi||NSW||Chaffey Reservoir1||6,216|
|Split Rock Reservoir1||16,893|
|SW8 Macquarie–Castlereagh||SS20||Macquarie–Castlereagh||NSW||Chifley Reservoir2||3,116|
|Spring Creek Reservoir2||938|
|Suma Park Reservoir2||1,870|
|SW9 Lachlan||SS16||Lachlan||NSW||Carcoar Lake1||3,979|
|SW8 Murrumbidgee NSW||SS15||Murrumbidgee NSW||NSW||Berembed Weir1||1,178|
|SW7 NSW Murray and Lower Darling||SS18||Lower Darling||NSW||Lake Cawndilla1||146,993|
|Stephens Creek Reservoir2||8,930|
|SS14||NSW Murray||NSW||Lake Hume1||198,930|
|Upstream of Lock 7 (Rufus)2||5,358|
|Upstream of Lock 8 (Wangumma)2||7,753|
|Upstream of Lock 9 (Kulnine)2||12,436|
|Upstream of Lock 10 (Wentworth)2||11,853|
|Upstream of Lock 15 (Euston)2||76,407|
|SW2 Vic. Murray||SS3||Kiewa||Vic.||Lake Guy2||82|
|Rocky Valley Storage2||1,846|
|SW3 Northern Victoria||SS4||Ovens||Vic.||Lake Buffalo1||1,826|
|Lake William Hovell1||1,302|
|McCall Say Reservoir1||114|
|SS6||Goulburn||Vic.||Goulburn Weir 1||12,170|
|Upper Coliban Reservoir2||3,094|
|SS8||Loddon||Vic.||Barkers Creek Reservoir2||615|
|Cairn Curran Reservoir1||19,034|
|Laanecoorie Reservoir 1||4,953|
|Newlyn Reservoir 1||659|
|Spring Gully Reservoir2||403|
|SW2 Vic. Murray||SS2||Vic. Murray||Vic.||Kangaroo/Racecourse Lake2||12,767|
|Upstream of Lake Mulwala2||30,518|
|Upstream of Mildura Weir2||45,072|
|SW4 Wimmera–Mallee||SS9||Wimmera–Mallee||Vic.||Dock Lake1||5,950|
|Lake Batyo Catyo1||1,523|
|SW5 SA Murray||SS11||SA Murray||SA||Blanchetown Weir – Lock 11||14,030|
|Bookpurnong Weir – Lock 41||7,949|
|Overland Weir – Lock 31||13,703|
|Renmark Weir – Lock 51||9,445|
|Upstream of Lock 6 (Murtho)2||14,451|
|Upstream of Lake Alexandrina2||50,509|
|Waikerie Weir – Lock 21||13,082|
|SW1 ACT||SS1||ACT||ACT||Bendora Reservoir1||667|
|Lake Burley Griffin 2||6,330|
|Whole MDB region||
2 Static surface area used (based on boundaries defined for surface water bodies in Bureau of Meteorology's [the Bureau's] Australian hydrological geospatial fabric [AHGF])
The potential evaporation estimate produced by the Australian Water Resources Assessment system landscape model (AWRA-L) version 2.0.0 (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 0.050 (approximately 5 km) national grid.
Potential evaporation was an estimate of the evaporative demand of the environment. The daily gridded climate data sets used to produce this estimate were generated by the Bureau and included downward solar irradiance, and maximum and minimum air temperature. The methods used to generate these gridded data-sets have been 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, where this relationship was not available the static AHGF surface area was used.
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 do not capture changes that occur on a shorter time-scale.
- The use of the static default AHGF surface area is an approximation only. It represents the waterbody at capacity and therefore likely results in an overestimation of precipitation on those features.
The following changes resulted in the restatement of the 2010–11 year volume:
- a change made to the calculation method
- scope change.
The changes and their respective values are detailed in the following table.
|Segment||2012 Account volume for the 2010–11 year (ML)||2011 Account volume for the 2010–11 year (ML)||Difference due to calculation method and scope change (ML)|
Scope change was due to inclusion of McCall Say Reservoir, Lake Batyo Catyo, Pine Lake, Dock Lake and Green Lake (not included in the 2011 Account) in the 2012 Account. Resulting volume change due to the scope for the 2010–11 year is not available.
Calculation method change was due to selecting AWRA-L method in the 2012 Account instead of Priestly and Taylor potential evaporation method used for the 2011 Account. The change was made for better estimate of evaporation. Resulting volume change due to the calculation method change for the 2010–11 year was decrease of the volume by 491,847 ML which represents a change of 14% of the previously reported value.