Adelaide
10.1 Groundwater inflow from outside region

Supporting information

The volume reported (38 ML) represents regional groundwater inflow to the Adelaide region in the 2011–12 year at the northern boundary, through the major sedimentary aquifers in the Adelaide Plains (T1 and T2 aquifers). This represents the only groundwater inflow from outside the region, except that occurring at the coast (reported at line item 10.2 Groundwater inflow from outside region at coast).

Regional groundwater flow also occurs between the fractured rock aquifers and the sedimentary aquifers of the Adelaide Plains and McLaren Vale Prescribed Wells Area (PWA). However, this flow is within the Adelaide reporting region and therefore is not included in this item. The Adelaide region boundary along the Mount Lofty Ranges is considered a groundwater divide with no groundwater flow across this divide. In general, groundwater flows from the fractured rock aquifers of the Mount Lofty Ranges west towards the Adelaide Plains and St Vincent Basin (Ellis and Fox 2004).


Regional groundwater inflow broken down by aquifer to the Adelaide region in the 2011–12 year
Groundwater management area Aquifer Groundwater inflow (ML)
Adelaide Plains
T1 27
T2 11
Total 38

Quantification approach

Data source

South Australian Department of Environment, Water and Natural Resources (DEWNR): Drillhole Enquiry System; groundwater level data from online groundwater database; Aquaterra 2011.

Provided by

Bureau of Meteorology.

Method

Regional groundwater flow into the Adelaide region was calculated using a simple GIS approach based on Darcy's Law (Bureau of Meteorology 2010). Groundwater levels measured at monitoring bores were interpolated to a groundwater-level grid for each season during the 2011–12 year using the ArcGIS Topo-to-Raster tool. Seasonal groundwater-flow grids were then derived from these groundwater-level grids along with aquifer thickness and hydraulic conductivity data using a modification of the ArcGIS Darcy velocity tool. Groundwater inflow was subsequently calculated across selected regional groundwater boundaries in the Adelaide Plains using a simple Geographic Information System analysis. Seasonal inflow volumes were summed to determine the total volume for the 2011–12 year.

The following two maps are presented to aid interpretation of the methodology used to quantify this item. The first map illustrates the location and concentration of bores used in the quantification approach. 

Map showing the location and concentration of bores used in the quantification approach
Map showing the location and concentration of bores used in the quantification approach


The second map identifies the lateral groundwater flow boundaries used in the quantification approach. The purple line at the north of the Adelaide region illustrates the area across which groundwater inflow from outside the region was calculated.

Map of the lateral groundwater flow boundaries in the Adelaide region
Map of the lateral groundwater flow boundaries in the Adelaide region

Assumptions, limitations, caveats and approximations

  • Flow across the remaining unit boundaries was assumed to be small on an annual basis, either due to limited flow (e.g. in fractured rock) or because limitations of the method prevented its application.

  • Regional groundwater inflow was estimated for the confined and semi-confined aquifers only (T1, T2). These productive aquifers are considered to be the most hydraulically conductive units and flow in other units is assumed to be insignificant.

Uncertainty information

The uncertainty estimate is not quantified.

Comparative year

A different bore data set was used for the 2012 Account corresponding to data available at the time of compiling the report. Using that same bore data set to quantify the volume for the 2010–11 year resulted in a material difference (62%) with the volume quantified for the 2011 Account. Consequently, the 2010–11 year volume has been restated from 22 ML in the 2011 Account to 36 ML in the 2012 Account as shown in the following table.


Restatement of comparative year information for line item 10.1 Groundwater inflow from outside region
Groundwater management area

Aquifer

2012 Account volume for the 2010–11 year (ML)

2011 Account volume for the 2010–11 year (ML)

Additional information

Adelaide Plains

T1

                                  25

                                9

new bore data set

T2

                                  11

                               13

new bore data set

Total

36

22