Adelaide

The volume reported in the water accounting statement (1841 ML) represents regional groundwater flow into the Adelaide region through the major sedimentary aquifers in the McLaren Vale Prescribed Wells Area (PWA; Maslin Sands and Port Willunga aquifers) and Northern Adelaide Plains PWA (T1 and T2 aquifers) at the coastline and northern boundary. The dominant direction of groundwater flow in the Adelaide region is from the recharge area in the fractured rock aquifers of the Mount Lofty Ranges towards the St Vincent Basin in the west (Ellis and Fox 2004). The St Vincent Basin, including the major sedimentary aquifers, extends under the sea with only the shallow unconfined aquifers interacting with the sea at the coastline (Hodgkin 2004).

The regional groundwater inflow to the Adelaide region is provided by the aquifers and management areas in the table below.

Data source

South Australian Department for Water: bore locations and groundwater-level data from Water Regulations.

Hydraulic conductivity and aquifer thickness data (Zulfic et al. 2008).

Data provider

Bureau of Meteorology.

Method

Groundwater flow into and out of the Adelaide region was calculated using a simple Geographic Information System (GIS) approach based on Darcy’s Law (BoM 2010). Groundwater levels measured at monitoring bores (refer to figure below) were interpolated to a groundwater-level grid for each season during 2009–10 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 and outflow were subsequently calculated across selected boundaries in the Northern Adelaide Plains and McLaren Vale Prescribed Wells Areas (refer to figure below) using a simple GIS analysis. Seasonal inflow and outflow volumes were summed to determine the total volume for 2009–10.

Map of hydrogeology within the Adelaide region and section of region boundary for which lateral groundwater flow was calculated

Uncertainty

Ungraded.

Assumptions, approximations and caveats/limitations

• The location of bores and the flow boundary considered in the estimations are indicated in the figure above. Flow across the remaining boundaries 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 flow was estimated for the confined and semi-confined aquifers only (i.e. 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 is assumed to be insignificant.