Perth

The volume of water within the water table aquifer cannot be quantified accurately. The Gnangara Mound is the largest and most important groundwater resource in the region. The Department of Water is currently working on a method to calculate the storage volume of water in the aquifer necessary to maintain and protect groundwater-dependent ecosystems (the ‘extractable limit’ water level). Preliminary results have shown that there are some areas of the Gnangara Mound where the aquifer levels are above this extractable limit and other areas where the aquifer levels are below this limit. Water above the extractable limit is considered to be a water asset. The gap between the water and the extractable limit is considered to be a water liability to the environment (i.e. water is owed back to the water table to raise it to the extractable limit). However, the volumes of water asset and water liability cannot yet be measured. This is the case for all other aquifers in the Perth region (including Stakehill and Rockingham Water table aquifers).

It should be noted that the extractable limit for the Jandakot Mound has already been prescribed to maintain and protect groundwater-dependent ecosystems. However, at the time of preparing this water accounting report the Department of Water has not commenced work to determine the volumes of water asset and water liability in the Jandakot Mound.