Sand dynamics in Darwin Harbour
: a tool for coastal management

  • Silvia Gabrina Tonyes

    Student thesis: Doctor of Philosophy (PhD) - CDU


    Coastal management has evolved from being mainly concerned with a coastal engineering approach to deal with coastal erosion, to a wider range of coastal morphodynamics assessments to aid in understanding the processes occurring in a coastal environment. Sandy beaches are particularly susceptible to erosion due to natural and human-induced activities and Darwin Harbour, a tropical, macro-tidal environment in northern Australia, is not an exception.

    This study investigates sand-sized sediment sources and pathways in Darwin Harbour using a multidisciplinary approach, combining numerical modelling and geochemical analysis. Sand transport pathways were inferred using a 2D hydrodynamic model (RMA-2) coupled with a sand transport model (RMA-11) from Resource Modelling Associates. Simulations were also carried out on the hypothetical dredging of a sandbar that was once partially dredged to supply sand for a development project. The calcium carbonate and trace element content were used to complement the simulation results, inferring the sources and depositional area of sand independently of the modelling.

    The sand-sized sediment in Darwin Harbour displays a mix of marine and terrigenous sources with the offshore derived sand-sized sediment deposited in the Harbour significantly greater than the fluvially derived sediment. The primary source of sand-sized sediment in the Outer Harbour and the eastern beaches originates from the continental shelf and the reworking of Harbour sediment while the fluvial sediment shows the best correlation with the Inner Harbour and the western beaches. Factors influencing the sand transport pathways are the low catchment to estuary ratio, the dumbbell shape of the Harbour/embayment and high tidal current velocities. The modelling simulations on the hypothetical sandbar dredging resulted in up to 30% decrease of deposition in the adjacent beach and intertidal area.

    This study suggests that any development in the Harbour requires a thorough study of the changes in sediment movement patterns that could affect the dynamics of nearshore – beach – dune systems and the erosion – deposition rates on the beaches. Future studies should be directed to coastal compartment determination, providing an analysis of coastal resilience and coastal setback as the precautions against coastal erosion and storm-induced flooding.
    Date of Award2018
    Original languageEnglish
    SupervisorRobert Wasson (Supervisor), Ken Evans (Supervisor) & Niels Munksgaard (Supervisor)

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