Sand transport pathways in Darwin Harbour, Northern Territory, Australia, are being investigated to assist with coastal management. Coastal erosion, which threatens public and private infrastructure, is one of the major problems along the harbour beaches. A study of sediment transport is essential to identify the challenges encountered by the stakeholders in coastal management. Darwin Harbour, located in the tropical, cyclone prone area of Australia, was, until recently, considered a near pristine estuary. A semi-diurnal macro-tidal embayment, the tidal variation in the harbour reaches up to 8 m with a mean tidal range of 3.7 m. The beach morphology consists of sandy pocket beaches between coastal cliffs, sandbars, rocky shore platforms, tidal flats and mangrove fringes. A two-dimensional depth averaged finite-element hydrodynamic model (RMA-2), coupled with a sediment transport model (RMA-11) from Resource Modelling Associates, has been used to infer the sources and the depositional areas of sand in the harbour. Grain size distributions and geochemical analysis are also used to characterize the sand and its source(s). Initial results show that the beach sand is mostly of offshore origin with small sand input from the rivers. Potential supplementary sand sources are the eroded materials from the shore platforms and the rocky cliffs. Due to the rapid development in Darwin Harbour, this study is fundamental in understanding coastal processes to support decision making in coastal management, particularly in a macro-tidal, tropical estuary.