Bribie Island Breakthrough - A Dynamic Coastal System.

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]