10.4 Recharge from surface water
The volumetric value for the line item for the 2011–12 year was 349,794 ML. The following table provides detailed volumetric information for the line item.
|Groundwater resource plan area||
Groundwater sustainable diversion limit area
Volume (ML) for the 2011–12 year
|GW14 Namoi Alluvium||GS29||Lower Namoi Alluvium||NSW||
|GS47||Upper Namoi Alluvium||NSW||
|GW12 Macquarie–Castlereagh Alluvium||GS26||Lower Macquarie Alluvium||NSW||
|Sub-total Northern Basin||
|GW10 Lachlan Alluvium||GS25||Lower Lachlan Alluvium||NSW||
|GW9 Murrumbidgee Alluvium||GS28||Lower Murrumbidgee Alluvium (shallow; Shepparton formation and deep; Calivil formation and Renmark Group)||NSW||
|Sub-total Southern Basin||
|Total for the region||
Groundwater recharge from surface water was only calculated for those New South Wales sustainable diversion limit (SDL) areas for which there was a groundwater model and groundwater recharge from a river was considered to be an important component of the groundwater balance. SDL areas other than those included in the table exist and may be relevant to the line item; however, relevant information was not available for the 2012 Account.
Groundwater interaction with surface water can be represented in MODFLOW models in several ways. Options that have been used in the New South Wales groundwater models are the MODFLOW river package and the MODFLOW drain package.
For more details about MODFLOW calculations; see documentation at MODFLOW website (USGS 2013) of the United States Geological Survey (USGS).
Assumptions, limitations, caveats and approximations
Groundwater models make numerous assumptions and approximations to represent water balance (refer to the MODFLOW website for more details).
Estimates of water level in rivers that are input to groundwater models are usually taken to be monthly average levels, and the levels would usually have a high level of uncertainty unless a river gauge is located within the groundwater model cell.
The uncertainty estimate was not quantified. It is currently not feasible to estimate the uncertainty of modelled groundwater recharge from surface water from outputs of a MODFLOW groundwater model.
A scope change resulted in the restatement of the 2010–11 year volume. The scope change was due to inclusion of the volume for Lower Namoi Alluvium (not included in the 2011 Account) within the Northern Basin in the 2012 Account. Resulting volume increase was 67,550 ML for the 2010–11 year.