Perth
18.3 Discharge to landscape

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

The volume reported in the water accounting statements (422,257 ML) represents the total volume of groundwater discharged to the landscape within the Perth region during the 2011–12 year.

Groundwater discharge to the landscape from the saturated zone of each aquifer for the two model areas during the 2011–12 year are given in the following table.

Groundwater discharge to the landscape was estimated using PRAMS and PHRAMS. Both models calculate evapotranspiration from the saturated zone of the aquifers, which is considered to be equal to the groundwater discharge to landscape. Note that this should not be confused with evapotranspiration from the unsaturated zone, which is rainfall water that has entered the ground in the unsaturated zone but is removed before it reaches the water table at the top of the saturated zone.

Both models use the MODFLOW evaporation module to calculate evapotranspiration from the saturated zone open water wetland surfaces and near surface water table areas.

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.