Case Study: An Integrated Approach to Determining Sustainable Abstraction Limits in Perth’s North West Urban Growth Corridor

Abstract

The North West urban growth corridor (NWGC) is an important area accommodating Perth’s expanding population which is expected to increase by 50% to 3.5 million by 2050. Groundwater from a shallow Quaternary aquifer is the preferred source for the reticulated water supply provided by the Water Corporation (WC). Due to rising demands, the Department of Water and Environmental Regulation (DWER) reviewed groundwater allocations in the area to provide increased security for environmental values related to wetlands and to manage the saltwater interface. Because of inadequacies in the regional numerical model in the NWGC area, DWER developed a spread sheet analytical model to calculate groundwater balances and discharge to the ocean. This assessment proposed lower allocations for users than derived by the model. After consultations with DWER, WC developed an analytical assessment using additional data and an alternative method. Instead of individual aquifer test results, the regional impacts of significant extraction from a wellfield over 15 years were used to develop a relationship between the aquifer’s response to pumping and transmissivity. This resulted in a larger estimate of throughflow which was more consistent with the original modelled estimates. These results were also confirmed by recently acquired drilling and aquifer testing data in the area.