North Stradbroke Island 3D Hydrology: Groundwater systems overview

North Stradbroke Island is a large sand mass that hosts a highly significant resource of fresh groundwater that is utilised for on-island supplies and piped to the mainland, plus is also used within sand mining operations. The regional groundwater body is recharged by local rainfall and also provides an important source of water to a range of ecosystems. A feature of note is that the regional watertable in some locations is up to 80m below the ground surface and in others intersects it and discharges as springs and seeps. The form, extent and variation of this water body have been difficult to define and represent using conventional graphical means. We utilise 3D visualisation of the island framework to display the spatial and temporal features of the water table, its relation to the surface water features and the character of the host sand aquifer. The visualisation model developed here does not incorporate the solid geometry of the sand mass but shows drillholes, their spatial distribution and the regional water table. Groundwater bore hydrographs are incorporated and clearly show that the main influence over groundwater levels is rainfall, and notably summer storms, and indicates a common lag of months (e.g. 4-6 months) of water level response. However, short term hydrograph records also display the effects of mining operations, which can be spatially variable. Trends over a 40 year period are generally of a water level decrease, although some recovery is apparent from 2008.