We provide a methodology and an example of how to incorporate monitoring trends into a groundwater allocation plan. The Gnangara groundwater system is a vital source of groundwater for Perth, Western Australia and about 350 GL of groundwater is abstracted annually. The Gnangara system maintains groundwater dependent ecosystems (GDEs), mostly wetlands and native vegetation. Declining groundwater levels across the system have led to undesired impacts on a number of GDEs.
Western Australia’s Department of Water recently prepared a Water Management Plan for the Gnangara system. To assist in reviewing allocation limits, an adaptive methodology, based on the groundwater system response (monitored data) was developed and implemented. The methodology may be used as a corrective tool for the short- and medium-term, to assist in achieving long-term sustainability of groundwater management in the context of changing climate and declining groundwater levels. The methodology will direct water allocations towards “more sustainable levels” on the basis of measured trends and can also identify potential problem areas where the principles or calculations used for long-term sustainable groundwater allocation would need to be reviewed.
Changes in groundwater storage represent an aquifer’s response to stressors, including climate, groundwater abstraction and land use. Trends for groundwater levels were analysed for more than 500 monitoring wells and, through the use of GIS modelling, used to estimate volumetric storage changes to management units known as groundwater sub-areas. The storage changes were considered, in addition to modelling results and other assessment techniques, as a basis for corrective adjustments to the existing allocation limits in a recent review of the Gnangara System.
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