Murray–Darling Basin
10.4 Recharge from surface water to groundwater

The volumetric value for the line item for the 2012–13 year was 680,878 ML. The following table provides detailed volumetric information for the line item.

Groundwater recharge from surface water in the MBD region during the 2012–13 year

Groundwater resource plan area	Groundwater sustainable diversion limit area		State	Volume for the 2012–13 year (ML)
	Code	Name
GW 14 Namoi Alluvium	GS29	Lower Namoi Alluvium	NSW	1,011
	GS47	Upper Namoi Alluvium	NSW	24,266
GW12 Macquarie–Castlereagh Alluvium	GS26	Lower Macquarie Alluvium	NSW	10,459
Sub-total Northern Basin				35,736
GW 10 Lachlan Alluvium	GS25	Lower Lachlan Alluvium	NSW	26,270
GW 9 Murrumbidgee Alluvium	GS28	Lower Murrumbidgee Alluvium (shallow; Shepparton formation and deep: Calivil formation and Renmark Group)	NSW	599,380
	GS31	Mid-Murrumbidgee Alluvium	NSW	19,492
Sub-total Southern Basin				645,142
Total for the region				680,878

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. Groundwater recharge from surface water in 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 2013 Account.

Inputs to the New South Wales groundwater models draw from knowledge of the hydrogeology and surface water processes to initialise parameters for river bed conductance and thickness.

NSW Office of Water.

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 (United States Geological Survey 2013) of the United States Geological Survey.

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 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.