Coastal Seminar Series 2016 – Dr Yasha Hetzel

Yasha Hetzel (University of Western Australia) will give a guest talk as part of the coastal seminar series at University of Southampton, entitled:

Assessing the ability of storm surge models to include wave setup and coastal trapped waves around Australia


Yasha Hetzel1,2, Ivica Janekovic1,2,  Charitha Pattiaratchi 1,2, E.M.S. Wijeratne1,2, Aron Roland3
1 School of Civil, Environmental, and Mining Engineering / UWA Oceans Institute, The University of Western Australia, Crawley, Australia;
2 Bushfire and Natural Hazards Cooperative Research Centre, Melbourne, Australia
3BGS IT&E GmbH, D-64297 Darmstadt, Germany

Some of the most costly natural disasters arise from tropical and extratropical cyclones making landfall, with much of the damage caused by coastal flooding due to extreme sea levels. Extreme sea levels result from the combined effects of a range of factors including astronomical tides, coastal trapped waves (CTWs), long term sea level variability, storm surges due to pressure and wind, and wave breaking processes that include wave setup and run up. In this talk I will introduce how two of these processes—wave-breaking and remotely forced CTWs—influence extreme sea levels around the Australian coast, and will discuss successes and challenges in simulating these processes in numerical models. We investigated storm surge dynamics, including the effects of waves, using a new unstructured fully coupled numerical modeling system. The 3D SCHISM sigma-z hydrodynamic model was fully 2-way coupled with the WWM-III wave model to simulate waves and storm surges around Australia. Despite the large domain, the finite element model grid was capable of resolving coastal regions at order of 100 m (Figure 1). Model simulations for the whole of Australia have been conducted and validated with observations. In this presentation, the focus is on two major destructive Australian tropical cyclones:  Alby (1978) in Western Australia and Yasi (2011) in Queensland, both which resulted in significant damage to coastal infrastructure due to extreme water levels and waves. We highlight the improvements gained when 2-way coupled waves are included. Results indicated that including the effects of waves in the model can often account for between 15-35% of simulated storm surge heights during an extreme event. Coastally trapped waves (CTW) are longer period (~days) sea level fluctuations caused by tropical cyclones and winter cold fronts that are commonly observed to propagate anti-clockwise for thousands of kilometres along the western and southern coasts of Australia. These CTWs can be both forced and free waves and can cause important current and water level oscillations in the region, particularly when elevated water levels from a CTW coincide with local storms and high tides. I will present results from a series of SCHISM and ROMS sensitivity studies that highlight requirements for simulating CTWs, the extent to which events are forced or free waves, and the influence of bathymetry and density stratification on propagation.