2.1 Water table aquifer
The volume presented in the water accounting statements (22,054 ML) represents the sum of the permissible consumptive volume for each water table aquifer in groundwater management unit in the Melbourne region.
Permissible consumptive volumes were originally announced in 2006 and represent the maximum annual volume that can be extracted from each groundwater management unit. All previous permissible consumptive volumes were amalgamated into a single order in July 2011.
The following table shows the permissible consumptive volume for each water table aquifer in groundwater management units within the Melbourne region in the reporting year. The slight increase from 21,873 ML in 2011–12 year to 22,054 ML in 2012–13 year was due to increase of volume of existing lincence. The increases were 97 ML in Nepean groundwater management area (GMA) and 84 ML in the Wandin Yallock water supply protection area (WSPA) Groundwater managment units.
|Groundwater management unit||Permissible consumptive volume (ML)|
|Deutgam WSPA — groundwater
|Wandin Yallock WSPA—groundwater||3,008|
Kinglake GMA is located on the boundary of the Melbourne region. The majority of this GMA lies outside of the boundary and is therefore not considered part of the total groundwater asset for the Melbourne region. The permissible consumptive volume of Kinglake is 2,015 ML.
The volume presented does not include groundwater in unincorporated areas outside of groundwater management units. Unincorporated areas have not been evaluated from a groundwater resource perspective and do not have established permissible consumptive volume. The allocation limit for unincorporated areas in the southern half of Victoria was 71,385 ML. The Melbourne region is only a small part of this area.
For a map of groundwater management units in the Melbourne refer to Physical information > Groundwater in the 'Contextual information'.
The Victorian Department of Environment and Primary Industries determined the volume of underlying aquifers in groundwater management units to set a permissible consumptive volume for each aquifer.
Permissible consumptive volumes for the water table aquifers of groundwater management units were determined as follows:
- Moorabbin GMA, Nepean GMA, Wandin Yallock WSPA, and Deutgam WSPA: Permissible consumptive volumes are based on the total volumes of existing licenses issued for these groundwater management units.
- Frankston GMA: permissible consumptive volume was determined using rainfall recharge, hydrograph fluctuation, through-flow and aquifer storage.
- Lancefield GMA: permissible consumptive volume was determined on the rainfall recharge method.
- Merrimu GMA: permissible consumptive volume was derived from a rounded calculation of rainfall recharge.
Assumptions, limitations, caveats and approximations
- Permissible consumptive volumes represent the groundwater asset within groundwater management units in the Melbourne region. An estimate of the size of the groundwater asset in the unincorporated areas outside groundwater management units has not been made, making it difficult to estimate the total groundwater resource for the Melbourne region.
- Frankston, Moorabbin, Nepean, Wandin Yallock, and Lancefield groundwater management units include all geological formations.
- Merrimu and Deutgam groundwater management units include all geological formations from 0m–30m below the surface.
- Frankston GMA: permissible consumptive volume has a low confidence rating due to uncertainty in the derivation of the infiltration factor, hydrograph, and through-flow calculations and the extent of the recharge area.
- Lancefield GMA: permissible consumptive volume has a low confidence rating due to uncertainty in rainfall infiltration data, recharge processes, and distribution.
- Merrimu GMA: permissible consumptive volume has a low confidence rating due to uncertainty in rainfall infiltration data, recharge processes, and distribution.
- Frankston GMA and Lancefield GMA: permissible consumptive volume estimation assumed rainfall infiltration factors of 5%.
- Merrimu GMA: permissible consumptive volume assumed rainfall infiltration factors of 10% in the north, 7.5% in the central area, and 5% in the south.