Dramatic increase in mud distribution across a large sub-tropical embayment, Moreton Bay, Australia

Major flood events can dramatically alter the coastal sediment environment. This study established the current sediment distribution in a large sub-tropical embayment, Moreton Bay, Australia, and examined the effect of three recent floods on modifying this distribution. In 2015, surface sediment samples were collected from 223 sites across the study area and analysed for particle size distribution with the resultant sediment distribution mapped. In addition, sampling of flood waters during two major events in 2011 and 2013 was undertaken and particle size distribution of suspended sediment was determined. Data was compared to the result of an earlier large-scale survey completed in 1970, with three large flood events occurring between the two surveys. The sediment environment has undergone a dramatic change with muddy sediments now covering an estimated area of over 860km2, more the double the area found in 1970. Mud is now the dominant sediment type within Moreton Bay. •Dramatic expansion in mud distribution across large, developed, subtropical embayment.•Sediments containing >50% mud occupy a surface area of over 860km2 compared with 400km2 in 1970.•Comparison between common sites demonstrates average mud content has increased from 50% in 2015.•Mud is characterised by fine silt and clay, similar to the PSD found in suspended sediment during large flood events.