3-Dimensional density dependent model of seawater intrusion for Pine Rivers Shire, North Brisbane, Queensland G A Tularam and R. Singh a.tularam@griffith.edu.au Lecturer, Faculty of Environmental Sciences Griffith University Queensland, Australia roshan.singh@student.griffith.edu.au Postgraduate student, Environmental Engineering Griffith University Queensland, Australia Abstract: The coastal fringe of Australia, in particular the eastern seaboard of Queensland is undergoing rapid urban and agricultural development. With a population of more than 75000 and being one of the fastest developing regions of Australia, the water resources of Pine Rivers Shire coastal aquifer will be under strain in future. Seawater intrusion due to extraction of groundwater is an important issue for Pine Rivers Shire coastal aquifer. A 3D model is developed to study the situation and solved using the GMS-FEMWATER finite element solver that simulates density dependent flow and transport in variably saturated media. A conceptual model of the Pine Rivers Shire aquifer is developed but the seaward boundary condition is treated differently to consider the effects of aquifer recharge due to infiltration of waves and tides. The results are presented showing seawater intrusion in the form of concentration contours on the vertical cross section of the 3-D model and also on the 3-D model itself. Time series plots of concentration at a considerable distance from the seawater boundary are also demonstrated showing the gradual increase in the concentration due to seawater intrusion into the aquifer. Keywords: Seawater intrusion, FEMWATER, Coastal aquifer, Freshwater, Saltwater.