Adelaide
18.2 Groundwater outflow to outside region at coast

The regional groundwater outflow at the coastline of the Adelaide region (842 ML) was the sum of flow out of the region at the coast through the major sedimentary aquifers in the McLaren Vale prescribed wells area (PWA) (Maslin Sands and Port Willunga aquifers) and Adelaide Plains (T1 and T2 aquifers).

South Australian Department of Environment, Water and Natural Resources (DEWNR): Drillhole Enquiry System; Aquaterra 2011.

Coastal groundwater inflow to 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 2012–13 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 coastal boundaries in the McLaren Vale PWA and the Adelaide Plains using a simple GIS analysis. Seasonal inflow volumes were summed to determine the total volume for the 2012–13 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

The second map identifies the lateral groundwater flow boundaries used in the quantification approach. The blue line at the coast illustrates the area across which groundwater outflow to outside region at coast was calculated.

Map of lateral groundwater flow boundaries in the Adelaide region

• Flow across boundaries not included in the estimates for this line item was assumed to be negligible on an annual basis either due to limited flow (e.g., in fractured rock) or could not be estimated because limitations of the method prevented its application.
• Regional groundwater outflow was estimated for the confined and semi-confined aquifers only (T1, T2, Maslin Sands and Port Willunga Formation). These productive aquifers are considered to be the most hydraulically conductive units and flow in other units was assumed to be insignificant.