@article {bnh-5203, title = {Developing better predictions for extreme water levels: Final data report}, year = {2018}, month = {12/2018}, institution = {Bushfire and Natural Hazards CRC}, address = {Melbourne}, abstract = {

The major hazard in coastal regions is inundation through extreme water levels generated in the ocean through different mechanisms such as storm surges and tsunamis or through a combination of effects such as a relatively small storm surge coinciding with high astronomical tides. With rising in sea level, given water levels will be exceeded more and more frequently as progressively less severe storm conditions are required to achieve that water level.\ Therefore, it is critical that the exceedance probabilities of extreme water levels are accurately evaluated to inform flood and erosion risk-based management and for future planning. To address this concern, this study estimated present day extreme sea level exceedance probabilities due to storm surges, tides and mean sea level around the whole coastline of Australia through the application of a numerical model.

The SCHISM hydrodynamic model, forced by TPXO tides and JRA55 atmospheric reanalysis (wind and air pressure), was successfully applied to produce a 59 year sealevel hindcast (1958-2016) for the entire Australian region.\ The outputs provide uninterrupted hourly sea level records at \<1 km resolution around the Australian coast. Improvements compared to the previous Haigh et al. [1] dataset included: extending the hindcast by six years including several\ record storm surge events, higher spatial resolution, improved meteorological\ forcing, and 3-D hydrodynamic model implementation. Other physical\ processes, missing from earlier studies, were also examined in detail including:\ effects of surface gravity waves, continental shelf waves, and meteorological\ tsunamis.\ 

Extreme value analysis has been applied to the sea level data to predict\ Average Recurrence Intervals (ARI) at ~1km spacing around the entire\ Australian coastline including islands. These statistics and relevant plots and\ time series data have been made available to the public via an interactive\ web tool (www.ozsealevelx.org), providing a consistent, accessible, up-todate\ dataset\ for\ use\ by\ coastal\ planners and emergency managers.

}, issn = {439}, author = {Charitha Pattiaratchi and Yasha Hetzel and Ivica Janekovic} } @article {bnh-5202, title = {Developing better predictions for extreme water levels: web user guide}, year = {2018}, month = {12/2018}, institution = {Bushfire and Natural Hazards CRC}, address = {Melbourne}, abstract = {

The major hazard in coastal regions is inundation through extreme water levels generated in the ocean through different mechanisms such as storm surges and tsunamis or through a combination of effects such as a relatively small storm surge coinciding with high astronomical tides. With rising in sea level, given water levels will be exceeded more and more frequently as progressively less severe storm conditions are required to achieve that water level.

Therefore, it is critical that the exceedance probabilities of extreme water levels\ are accurately evaluated to inform flood and erosion risk-based management\ and for future planning. To address this concern, this study estimated present\ day extreme sea level exceedance probabilities due to storm surges, tides and\ mean sea level around the whole coastline of Australia through the application\ of a numerical model.\ 

The SCHISM hydrodynamic model, forced by TPXO tides and JRA55\ atmospheric reanalysis (wind and air pressure), was successfully applied to\ produce a 59 year sealevel hindcast (1958-2016) for the entire Australian region.\ 

The outputs provide uninterrupted hourly sea level records at \<1 km resolution around the Australian coast. Improvements compared to the previous Haigh et al. [2014b] dataset included: extending the hindcast by six years including several record storm surge events, higher spatial resolution, improved meteorological forcing, and 3-D hydrodynamic model implementation. Other physical processes, missing from earlier studies, were also examined in detail including: effects of surface gravity waves, continental shelf waves, and meteorological tsunamis.

Extreme value analysis has been applied to the sea level data to predict Average Recurrence Intervals (ARI) at ~1km spacing around the entire Australian coastline including islands. These statistics and relevant plots and time series data have been made available to the public via an interactive web tool (www.ozsealevelx.org), providing a consistent, accessible, up-to-date dataset for use by coastal planners and emergency managers.

This report provides an overview of the website and describes of how to access and interpret the available extreme sea level data.

}, issn = {438}, author = {Charitha Pattiaratchi and Yasha Hetzel and Ivica Janekovic} } @conference {bnh-4788, title = {Improved predictions of extreme sea levels around Australia}, booktitle = {AFAC18}, year = {2018}, month = {09/2018}, publisher = {Bushfire and Natural Hazards CRC}, organization = {Bushfire and Natural Hazards CRC}, address = {Perth}, abstract = {

The major hazard in coastal regions is inundation through extreme water levels generated in the ocean through different mechanisms such as storm surges and tsunamis or through a combination of effects such as a relatively small storm surge coinciding with high astronomical tides. With rising in sea level, given water levels will be exceeded more and more frequently as progressively less severe storm conditions are required to achieve that water level. Therefore, it is critical that the exceedance probabilities of extreme water levels are accurately evaluated to inform flood and erosion risk-based management and for future planning. To address this concern, this study estimated present day extreme sea level exceedance probabilities due to storm surges, tides and mean sea level around the whole coastline of Australia through the application of a numerical model. The SCHISM hydrodynamic model, forced by TPXO tides and JRA55 atmospheric reanalysis (wind and air pressure), was successfully applied to produce a 59 year sealevel hindcast (1958-2016) for the entire Australian region. The outputs provide uninterrupted hourly sea level records at \<1 km resolution around the Australian coast. Improvements compared to the previous Haigh et al. [1] dataset included: extending the hindcast by six years including several record storm surge events, higher spatial resolution, improved meteorological forcing, and 3-D hydrodynamic model implementation. Other physical processes, missing from earlier studies, were also examined in detail including: effects of surface gravity waves, continental shelf waves, and meteorological tsunamis. Extreme value analysis was applied to the sea level data to predict Average Recurrence Intervals (ARI) at ~2km spacing around the entire Australian coastline including islands. These statistics and relevant plots and time series data have been made available to the public via an interactive web tool, providing a consistent, accessible, up-to-date dataset for use by coastal planners and emergency managers.\ 

}, author = {Charitha Pattiaratchi and Yasha Hetzel and Ivica Janekovic} } @conference {bnh-2948, title = {Improved predictions of Australian extreme sea levels through a coupled wave-surge model}, booktitle = {AFAC16}, year = {2016}, month = {08/2016}, publisher = {Bushfire and Natural Hazards CRC}, organization = {Bushfire and Natural Hazards CRC}, address = {Brisbane}, abstract = {

In order to protect life and property coastal planners and emergency managers require accurate estimates of flood risk. Providing reliable predictions of extreme sea levels for this purpose represents a significant challenge due to the range of complex processes that vary from beach to beach, town to town, and state to state around the entire Australian continent. As a result, a reliable comprehensive dataset of extreme sea levels for the entire coastline does not yet exist. Recent technological advances have allowed us to develop a high-resolution numerical model capable of analysing ocean dynamics to better understand how storms will impact local beaches on an Australia-wide scale. The advanced, high-resolution (in the coastal zone ~100m) 3D finite element hydrodynamic model (SCHISM) coupled with the state-of-the art WWMIII wave model included the effects of wave breaking on top of storm surges caused by wind and pressure. Simulations of multiple extreme sea level events, ranging from Southern Ocean winter storms to destructive tropical cyclones revealed that including waves in the simulations raised surge levels between 10{\textendash}50 per cent, depending on local water depths and coastline orientation. To illustrate the robustness of the coupled wave-surge model we present results from Cyclone Yasi (2011), the largest and most intense storm to impact Queensland since 1913. The cyclone caused extensive damage to property and infrastructure costing $800 million over more than 500 km of coastline. A storm surge of 5.5 m was simulated in Cardwell with waves exceeding 12 m offshore and 6 m near the coast. Wave effects raised water levels by up to 35 per cent, highlighting the benefits of a coupled wave-surge model that includes wave setup effects.

}, author = {Yasha Hetzel and Ivica Janekovic and Charitha Pattiaratchi} } @article {bnh-2587, title = {Predicting continental shelf waves in Australia}, number = {160}, year = {2016}, month = {02/2016}, institution = {Bushfire and Natural Hazards CRC}, address = {Melbourne}, abstract = {

A range of processes can cause extreme water levels that endanger human life and cause property damage. Storm surges caused by tropical cyclones are well known to pose a risk for coastal inhabitants.\  However, a lesser-known effect of landfalling cyclones is the generation of coastally trapped waves that can propagate along the coast and influence water levels thousands of kilometres away. Examples of such waves include continental shelf waves (CSWs) that travel to the left along the coastline in the southern hemisphere and are common along the Australian coastline (Church et al., 1986; Eliot and Pattiaratchi, 2010).

This study investigated the generation and propagation characteristics of continental shelf waves (CSWs) in Western Australia, a hotspot of continental shelf wave activity in Australia, utilising the Regional Ocean Modelling System (ROMS).\  An idealised model of the North West Shelf (NWS) with ~ 4 km spatial resolution and 30 vertical sigma layers was forced by simulated tropical cyclones that varied in speed, direction (parallel, perpendicular or at 45{\textdegree} to the coastline) and category.\  Realistic cyclone simulations were performed for Tropical Cyclone Bianca in 2011 using an Australia-wide model and comparisons made to observations.

Results from the idealised numerical model showed that a cyclone{\textquoteright}s path, speed and category affect continental shelf wave generation and propagation.\  Greater cyclone category resulted in higher amplitude continental shelf waves.\  Cyclones that travelled parallel to the coastline generated continental shelf waves that were faster than the cyclone forward speed and produced higher amplitude waves than those generated by different trajectories.\  Increased parallel cyclone forward speed corresponded to an increase in the continental shelf wave height. If the parallel cyclone forward speed was too fast (i.e. greater than 14 ms-1), the continental shelf wave height decreased.\  Parallel moving cyclones travelling near to the continental shelf break with a forward speed of ~ 7.5 ms-1 generated the highest amplitude waves. If the cyclone discontinued travelling parallel, the continental shelf wave gained similar properties to continental shelf waves generated by perpendicular or 45{\textdegree} travelling cyclones.\  These type of cyclones generated continental shelf waves that had a lower wave height, which were even lower for faster moving cyclones.\  The propagation speed of these waves scaled to the Coriolis parameter and characteristic length scale of the continental shelf.\  The lower wave height of these waves can be explained by the continental shelf wave travelling as a "free wave".

Propagation characteristics of continental shelf waves generated by Cyclone Bianca and Carlos from realistic cyclone simulations showed cyclone path and continental shelf bathymetry had an influence on CSW height and propagation speed. The calculated approximate travel speed from lag correlation analysis was 5.8 ms-1 for both continental shelf waves.\  Tropical Cyclone Bianca travelled parallel to the Western Australian coastline which reinforced the continental shelf wave height. Tropical Cyclone Carlos continued offshore from Exmouth so the continental shelf wave had little energy to propagate around the curved coastline in the Capes Region.\  Both continental shelf waves decreased in propagation speed between Exmouth and Carnarvon where the continental shelf width decreased rapidly.\  The continental shelf wave generated by Tropical Cyclone Bianca rapidly decreased at Albany which may be explained by the curvature of the coastline which resulted in wave scattering.\ \ \ 

Results from this study demonstrate how particular cyclone properties influence the generation of continental shelf waves and through this improves our ability to predict the influence of CSWs on extreme water levels along the Australian coast. .\  It is recommended that design criteria, modelling studies and inundation risk assessments for coastal regions in Western Australia need to consider the effects of continental shelf waves.\ \ 

}, issn = {160}, author = {Charitha Pattiaratchi and E.M.S Wijeratne and Yasha Hetzel and Ivica Janekovic} } @article {bnh-2405, title = {Developing better predictions for extreme water levels}, year = {2015}, author = {Charitha Pattiaratchi and Ivica Janekovic and Yasha Hetzel} } @conference {bnh-2088, title = {Improved modeling of extreme storm surges and waves along the Australian coast - non peer reviewed extended abstract}, booktitle = {Adelaide Conference 2015}, year = {2015}, address = {Adelaide, Australia}, abstract = {

Research proceedings from the Bushfire and Natural Hazards CRC \& AFAC Conference in Adelaide, 1-3 September 2015.\ 

}, author = {Ivica Janekovic and Yasha Hetzel and Charitha Pattiaratchi} } @conference {bnh-2389, title = {Storm surge risk from transitioning tropical cyclones in Australia}, booktitle = {Australasian Coasts \& Ports Conference 2015}, year = {2015}, month = {11/2015}, publisher = {ResearchGate}, organization = {ResearchGate}, address = {Auckland, NZ}, abstract = {

When tropical cyclones come ashore strong winds can set up storm surges that devastate coastal communities through erosion and inundation of low lying areas. In Australia, storm surge risk from tropical cyclones is generally restricted to warmer northern regions whilst in the southern regions damaging storm surges tend to arise from extratropical low pressure systems. Often, tropical cyclones weaken as they move into higher latitudes passing over cooler waters and experiencing higher wind shear. However, in some cases tropical cyclones can interact with mid-latitude weather systems causing the storms to lose tropical characteristics and become extratropical in nature, often intensifying and accelerating{\textendash} this is known as Extratropical Transition (ET). Storms that undergo ET pose a serious threat to life and property by extending tropical cyclone-like conditions over a larger area in latitudes that do not normally experience such events. Here we aim to describe the storm surge risk from tropical cyclones transitioning into the higher latitudes around Australia using observations, atmospheric reanalyses, and a coupled storm surge-wave model. We highlight modelling challenges and examine two contrasting case studies: (1) the worst case scenario of Cyclone Alby (1978) that underwent ET causing large waves, flooding, erosion and $50 million in damage in southwest Australia; and, (2) a {\textquoteleft}near miss{\textquoteright} event from Cyclone Bianca (2011) that weakened just before making landfall in the same region. The simulated surge from Alby peaked at 1.1 m in Busselton, with approximately 10\% of the height resulting from wave effects included in the model. Predicted wave heights exceeded 10 m offshore. Cyclone Bianca weakened dramatically before landfall and major damage did not occur. We propose that tropical cyclones moving into higher latitudes need to be given special consideration due to their unpredictable nature and the potential for damaging storm surges.

}, author = {Yasha Hetzel and Ivica Janekovic and Charitha Pattiaratchi and E.M.S Wijeratne} }