18.1 Groundwater outflow to outside region

Supporting information

a. Supporting Information

The volume reported in the water accounting statements (27,056 ML) represents the total volume of groundwater outflow to outside the Perth region boundary from aquifers within the Perth region during the 2012–13 year.

Lateral outflows from each groundwater store within the two model areas during the 2012–13 year are given in the following table.


Total outflow from each groundwater store during the 2012–13 year


Outflow (ML)

Groundwater store

Perth area

Peel–Harvey area

water table aquifer



underlying aquifer—Leederville



underlying aquifer—Yarragadee






b. Groundwater models

The Department of Water use the Perth Regional Aquifer Modelling System (PRAMS) version 3.4 and Peel–Harvey Regional Aquifer Modelling System (PHRAMS) to estimate the natural water movement to and from the groundwater store within the Perth region.

As shown in the following figure, PRAMS estimates groundwater movement for the area north of Mandurah. PHRAMS estimates groundwater movement for the Peel–Harvey area south of Mandurah. The volumes reported in this account refer to the natural water movement that occurs within each model area within the Perth region boundary.

Map of groundwater model areas relative to the Perth region boundary
Map of groundwater model areas relative to the Perth region boundary

Quantification approach

Data source

PRAMS version 3.4 and PHRAMS groundwater models.

Provided by

Department of Water.


Both groundwater models derive the lateral flux within the Perth region by defining the appropriate water balance zones and calculating the volume of water flowing across each boundary on an annual basis.

Assumptions, limitations, caveats and approximations

It is assumed that all groundwater flow to and from outside the region is via the north and south boundaries. There is no groundwater flow between the model areas and the Darling Range in the eastern part of the region due to the geology of that area.

Both models were initially developed for the purpose of estimating and assessing the impacts of changes in climatic conditions and varying extraction rates on the aquifers, not for the purposes of preparing water accounts. These models have since been modified to also provide data for water accounting.

Uncertainty information

The uncertainty estimate was not quantified.