Assessment of Coastal Compound Flooding in Tropical Catchment: Saltwater Creek Catchment in Australia

Compound flooding in coastal tropical cities is becoming increasingly prominent, driven by extreme rainfall events and sea level rise. Quantifying the impact of such events is often complex due to limited data, funding, and the need for advanced computational tools. This study employed an integrated hydrodynamic model to establish a coupled 1-dimensional (1D) and 2-dimensional (2D) model for the Saltwater Creek catchment in, tropical north Queensland, Australia. To test the impact of compounding effects, combinations of rainfall events, tides and sea level were included, with four combinations of events under current climate (CC) and four under representative concentration pathways (RCP) 8.5. The compound effects of flooding, using different combinations of flood drivers, resulted in 18% (scenario 1) of the area being inundated under CC conditions. Under the RCP 8.5 climate change scenario, the expansion of inundated areas ranges from 7% by 2090 compared to CC. In addition, the compound flooding scenarios resulted in an increase in inundation depth varying from 0 to 4.6 m with the CC scenario as the baseline. Under the RCP 8.5 climate change scenario, the observed water level increases range from 15% to 38% compared to baseline scenarios. Furthermore, the maximum velocity increase during the flooding period ranges from 0.3 to 4 m/s, with extreme velocities modelled at the upstream section of the catchment, prominently under climate change scenarios (RCP 8.5, 2090). In conclusion, the results show that this catchment is subject to two distinctive flood impacts: a low-lying area primarily impacted by inundation and the upper section of the catchment, which is characterised by higher velocity flows.