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Bribie Island at 34 kilometres long and 8 kilometres at its widest, is the smallest and most northerly of the three major sand islands sheltering the northern part of Moreton Bay, in south-east Queensland. The others are Moreton Island and North Stradbroke Island. Much of Bribie Island is a national park and Pumicestone Passage is in a marine park conservation zone as well as being a listed Ramsar Wetlands Site. Northern Bribie Island has a long history of coastal erosion, with monitoring by the Queensland Department of Environment and Science (DES) since 1995, showing recession of the eastern shoreline of between 1m to 2m per year. On 2 January 2022, large waves caused by ex-Tropical Cyclone Seth over-washed the dunes on northern Bribie Island and cut a tidal channel through the island, creating a new entrance to Pumicestone Passage from Moreton Bay. Since January 2022, the breakthrough of the island has widened to about 1km and has become the dominant entrance. The Caloundra bar (which is the original entrance to the north) is infilling with sand and closing over and a huge sand bar is now blocking the main north-south channel of the passage. This paper will provide a description of the geomorphic processes at northern Bribie Island and in the Pumicestone Passage and present a satellite photo time series of the dynamic changes that have occurred since the breakthrough occurred in early 2022. The paper will also present the initial results of the hydrodynamic and sediment transport modelling commissioned by Maritime Safety Queensland (MSQ) to investigate various scenarios (eg do nothing, or intervention via an excavator or dredging) and discuss the viability of potential management options to improve navigational access in the environmentally sensitive Pumicestone Passage. [ABSTRACT FROM AUTHOR]

Existing numerical modelling of storm tide using tide plus surge only approaches within Moreton Bay has underestimated observed peak tidal residuals by over 40%. Scientific debate regarding the source of this "missing" contribution hypothesises it to result from one, or a combination of: storm tide enhancement due to wave breaking and wave-current interaction; limitations of our current wind surface stress parameterisation for surge generation in extreme conditions; and/or the disturbance of existing offshore geostrophic currents by extreme weather events and their 3D interaction with the continental shelf and nearshore bathymetry. This study investigates the wave breaking and wave-current interaction hypothesis by undertaking integrated hydrodynamic and spectral wave modelling hindcast experiments supported by high quality gridded wind, observed water level and wave data at sites throughout Moreton Bay and the Southeast Queensland coast. The case studies for these experiments are the observed regional surge responses occurring during the passages of Ex. Tropical Cyclone Oswald and Tropical Cyclones Dinah, Daisy, Roger, and Oma. For all simulated case study events, the shape and magnitude of modelled residuals resulting from experiments with breaking-wave influences activated provide a 20-30% better match to observations than did experiments with tide plus surge only. Findings also support the theory of offshore geostrophic effects, particularly for remote approach systems TC Roger and TC Oma. Experiments with an allowance for both breaking-wave influences and regional geostrophic mean sea level variations provide a 30 to 95% improvement over experiments with tide plus surge only. The implication of these findings is that each key surge-generating physical process (wind and pressure, waves, and regional offshore ocean weather) requires careful representation in order to reproduce observed storm surges in sub-tropical, semi-open coastal embayments such as Moreton Bay. [ABSTRACT FROM AUTHOR]