A 90-year Morphodynamic Analysis in Southern Queensland (Australia)

Silva, A.P.; Woortmann, L.G.; Vieira da Silva, G., Murray, T.; Strauss, D., and Tomlinson, R., 2020. A 90-year Morphodynamic Analysis in Southern Queensland (Australia). In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 438-442. Coconut Creek (Florida), ISSN 0749-0208. This paper investigates the beach morphology changes in response to coastal structures and wave conditions on the Southern Gold Coast region (Letitia Spit, NSW to Kirra Beach, QLD). To do so, 137 individual days – spanning approximately 90 years (1930 – 2017) - were analysed using remote-sensing. Images were rectified and mapped in ArcGIS 10.3, identifying sandbars, spit formations, shoreline indicator and the river delta. The analysis showed long-term trends in response to the major coastal interventions (training walls and artificial bypassing). In general, the beach equilibrium was reestablished in ∼10 years after the interventions, even though this condition could mean a complete upper beach depletion. Both the river and headland bypassing systems presented changes as results of the anthropogenic structures and to natural stressors. For instance, to have a natural recovery of Point Danger bypassing, the river delta would need to rebuild, and a continuous increased longshore transport would be necessary. These conditions were observed during strong El Nino years. In addition, the bypassing systems within Coolangatta Bay showed that sediment deposits location and seasonal wave variability control the type and occurrence of the bypassing. Overall, the study proved the complex interconnection between coastal compartments that is essential to understand for having an effective coastal management. The knowledge of long-term morphodynamic processes gained with this approach can support coastal cities to maintain healthy and resilient beach systems.