Modelling sediment transport during extreme weather events

Mr Michael Thomson1, Mr Daniel Rodger1

1JBPacific, Brisbane, Australia


Coastal sediment transport is a natural phenomenon that is driven by wind, waves, and tidal currents. Understanding and managing sediment transport is a challenging problem for coastal asset managers and engineers, particularly around coastal structures where seasonal transport can cause sediment accumulation or erosion, such as beach access ways and storm water outfalls. Failure to account for this natural process can mean higher maintenance costs for Councils, and the potential for reduced performance of the coastal structure. To aid the structure design process, numerical modelling can be used as a tool for mapping sediment transport pathways, prior to construction.

This project focuses on a study area in Moreton Bay, north of Brisbane, where a coastal stormwater outfall is experiencing regular sand build-up from longshore sediment transport. The build-up of sand at the outfall, if not mechanically cleared, can cause burial of the outlet valves, restriction of outflow and potential flooding upstream.

The numerical model XBeach was used to study the movement of sand along the Moreton Bay coastline and compare a range of approaches for mitigating sediment build-up and maintenance of the outfall. Four key questions are addressed: 1) How does severe weather effect sediment flow in the area? 2) How much sand build-up can be expected from a given storm event? 3) Will this build-up cause flooding upstream? 4) How will this effect be exacerbated by future sea level rise?


Michael is a graduate coastal and civil engineer currently working in statistical analysis and coastal processes to model coastal geomorphologic and hydrologic design conditions. Michael’s current area of interest is developing nature-based engineering strategies for coastal protection.