Inlet migration and flood-tidal delta morphodynamic evolution: Case study of Noosa - QLD, Australia

This paper investigates the natural patterns of variability of the Noosa inlet estabilished after decades of adaptation to the new configuration of the river system resulted from man-made structures installed in the 1970-80's. Features such as the Northern Spit, Southern Spit, flood-tidal deltas, river channel and surrounding shorelines were mapped, measured and compared based on aerial images from recent years (2010-2018) in a Geographic Information System (GIS). The analysis revealed that Noosa River has currently fluctuated between two dominant patterns of inlet migration integrated with the Northern and Southern Spits development and meandering variability. With a fully-developed flood-tidal delta, Noosa River presents ~ 400,000 m2 of stable sand deposits, including some vegetated areas, towards the northern river bank. These formations and the Northern Spit have constrained the Northern Channel that became essentially inactive. In this configuration, Middle and Southern Channel have dominated the river's morhodynamics. Under a Middle Channel Dominance a quasi shore-parallel migration of the Northern Spit occurs, with the inlet throat migrating towards the training wall. This pattern presents relations to positive rainfall anomalies, mostly during strong La Nina years. The Southern Channel Dominance occurs when wave-dominated conditions favour the longshore sediment transport that builds up the Southern Spit and, consequently, pushes the inlet towards a northward orientation. As a response, the river meandering intensifies the currents that Erode Noosa Woods beach. This scenario was observed after a sequence of strong El Nino years. A broad understanding of the flood-tidal delta morphodynamics facing anthropogenic interventions and climate drivers was proven to be a fundamental tool for the management of the Noosa River and adjacent area.