2.1 Water table aquifer
Due to a lack of available data, the volume of water within the water table aquifer cannot be quantified accurately and thus is not presented in the Statement of water assets and water liabilities.
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 determine the water level surface in the unconfined aquifer necessary to maintain and protect groundwater-dependent ecosystems and the saltwater interface (the 'extractable limit' water level surface). 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. In areas where the water table is below the extractable limit, the gap between the water table 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).
The Department of Water is working on a similar method for the confined aquifers in the Gnangara Mound area, but it will be some time before these methods can be applied to the other groundwater aquifers in the Perth region (including Stakehill and Rockingham water table aquifers).
It should be noted that Jandakot Mound groundwater levels have 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.