Murray–Darling Basin
10.4 Recharge from surface water

Supporting information

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 recharge from surface water in the Murray–Darling Basin region in the 2011–12 year
Groundwater resource plan area

Groundwater sustainable diversion limit area

State

 Volume (ML) for the 2011–12 year 

Code

Name

GW14 Namoi Alluvium GS29 Lower Namoi Alluvium NSW

51,742

GS47 Upper Namoi Alluvium NSW

30,368

GW12 Macquarie–Castlereagh Alluvium GS26 Lower Macquarie Alluvium NSW

22,867

Sub-total Northern Basin

104,977

GW10 Lachlan Alluvium GS25 Lower Lachlan Alluvium NSW

28,350

GW9 Murrumbidgee Alluvium GS28 Lower Murrumbidgee Alluvium (shallow; Shepparton formation and deep; Calivil formation and Renmark Group) NSW

193,067

GS31 Mid-Murrumbidgee Alluvium NSW

23,400

Sub-total Southern Basin

244,817

Total for the region

349,794


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.

Quantification approach

Data source

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.

Provided by

NSW Office of Water.

Method

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.

Uncertainty information

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.

Comparative year

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.