A technique to evaluate the risk of storm tides (the combination of a storm surge and tide) under present and enhanced greenhouse conditions has been applied to Cairns on the north-eastern Australian coast. The technique combines a statistical model for cyclone occurrence with a state-of-the-art storm surge inundation model and involves the random generation of a large number of storm tide simulations. The set of simulations constitutes a synthetic record of extreme sea-level events that can be analysed to produce storm tide return periods. The use of a dynamic storm surge model with overland flooding capability means that the spatial extent of flooding is also implicitly modelled. The technique has the advantage that it can be readily be modified to include projected changes to cyclone behaviour due to the enhanced greenhouse effect. Sea-level heights in the current climate for return periods of 50, 100 , 500 and 1000 years have been determined to be 2.0m, 2.3m, 3.0m, and 3.4m respectively. In an enhanced greenhouse climate (around 2050), projected increases in cyclone intensity and mean sea-level see these heights increase to 2.4m, 2.8m, 3.8m, and 4.2m respectively. The average area inundated by events with a return period greater than a 100 years is found to more than double under enhanced greenhouse conditions.

McInnes, K. L., and Hubbert, G. D. (2003). A Numerical modelling study of storm surges in Bass Strait. Australian Meteorological Magazine. Volume 52, 143-156, No. 3. September 2003.

The relationship between severe weather events and storm surges in Bass Strait is investigated. The sustained westerly or southwesterly winds that accompany cold fronts along the south coast are found to be the most common cause of storm surges, although the intensification of low pressure systems in Bass Strait can also produce surges in this region. Two events, caused by cold fronts, are modelled using a high-resolution coastal ocean model. The storm surges produced by meteorological forcing show close agreement with observations at stations west of Bass Strait. In Bass Strait, measured sea-level residuals during strong westerly wind events exhibit a semi-diurnal oscillation resulting from an approximate 20 minute delay between the measured high tides and the predicted tides used to extract the sea level residuals. This delay can be reproduced by the model when run with atmospheric and tidal forcing and the tides subsequently removed, indicating that the enhanced westerly current during the surge event interacts with the tidal currents to produce a temporary phase delay in the tides in western Bass Strait, although the physical mechanism behind the response is not clear. The contribution to storm surge height due to atmospheric pressure is found to be only around 10 per cent of the inverse barometer effect indicating that wind stress is by far the dominant component of the storm surge height in this region. The role of remote and local wind forcing in Bass Strait is investigated by performing model simulations where the western boundary of the model domain is moved progressively eastwards. Exclusion of the narrow shelf region immediately to the west of Bass Strait by between 50 and 80 per cent in broad agreement with theoretical studies. An investigation of the effect of wind speed changes on storm surge height reveals that storm surge height responds linearly to changes in wind strength with a proportionality  coefficient of around two.

McInnes, K. L., Hubbert, G. D., Abbs, D. J., and Oliver, S. E. (2002). A Numerical Modelling Study of Coastal Flooding. In: Meteorol. Amos. Phys. 80, 217-233.

A coastal ocean model capable of modelling tides, storm surge and the overland flow of floodwaters has been further developed to include the flux of water from tributaries and the forcing from wave breaking that leads to wave setup in the nearshore zone. The model is setup over the Gold Coast Broadwater on the east coast of Australia. This complex region features a coastal lagoon into which five tributaries flow and is subject to flooding from extreme oceanic conditions such as storm surge and wave setup as well as terrestrial runoff. Weather conditions responsible for storm surge, waves and flooding include cyclones of both tropical and mid-latitude origin.

Two events are modelled. The first is an east coast low event that occurred in April 1989. This event verified well against available observations and analysis of the model simulations revealed that wave setup produced a greater contribution to the elevated water levels than the storm surge. The second case to be modelled was tropical cyclone Wanda, responsible for the 1974 floods. Modelled water levels in the Broadwater were reasonably well captured. Sensitivity experiments showed that storm surge and wave setup were only minor contributors to the elevated sea levels and their contribution was confined to the earlier stage of the event before the runoff reached its peak. The contribution due solely to runoff exhibited a tidal-like oscillation that was 180 degrees out-of-phase with the tide and this was attributed to the greater hydraulic resistance that occurs at high tide. A simulation of this event with present day bathymetry at the Seaway produced sea levels that were 0.3-0.4m lower than the simulation with 1974 bathymetry highlighting the effectiveness of deepened Seaway channel to reduce the impact of severe run-off evfents in the Broadwater.

Hubbert, G. D., and McInnes, K. L. (1999). A storm surge inundation model for coastal planning and impact studies. Journal of Coastal Research, 15 (1): 168-185.

A high resolution storm surge inundation model has been developed to model coastal flooding due to storm surges. The storm surge model, which features a nesting capability and inundation algorithm, is described. The flooding and draining rate is dependent on the modelled current in adjacent ‘wet’ grid cells which ensures realistic and smoothly varying results. Model simulations are carried out in two distinctly different geographic regions. The first of these is the town of Port Hedland on the northwest coast of Australia which was severely inundated by a tropical cyclone-induced storm surge in 1939. The model is shown to reproduce the peak flood levels and areas of inundation to a high degree of accuracy. Storm surge heights at the coast produced by a ‘fixed-coastline’ version of the model are compared with the inundation model results and indicate an overestimation of the storm surge heights by up to 17%. Simulations are conducted with varied horizontal resolution to investigate the robustness of the model. The flooding rates and areas of inundation are relatively unaffected by moderate variations in horizontal resolution. The second region studied is Port Phillip Bay, upon which the city of Melbourne is located. The model is used to simulate the storm surge and inundation produced by two separate cold fronts. The vulnerability of two locations within the Bay is investigated under altered sea level and storm strength conditions to demonstrate the potential impact of climate change. In a final simulation, levee banks on the tributaries draining into the bay are removed. The vastly increased inundation serves to illustrate the importance of maintaining and possibly increasing flood protection measures in this region in the future. 

McInnes, K. L., and Hubbert, G. D. (2001). The impact of eastern Australian cut-off lows on coastal sea level. Meteorological Applications, 8 (2): 229-244.

Cut-off lows that develop off the east coast of Australia are a major cause of elevated coastal sea levels it in this region. Their duration often exceeds a day and the combination of elevated sea levels with the high rainfall that commonly accompanies these events means that coastal flooding can be a major hazards The processes contributing to higher-than-normal sea levels are a combination of storm surge and breaking wave setup. Three events are modelled using an atmospheric model, storm surge model and wave setup model. The storm surges resulting from the depressions are found to explain between one-third and one-half of the measured sea-level residuals at the coast and are shown to develop in a regime of coast-parallel winds that produce onshore Ekman transport. The timing of the storm surges are well captured in two of the events in which the atmospheric depressions are of broad spatial scale and well simulated by the atmospheric model. However, a poor simulation by the atmospheric model of the location of the third low, which is of smaller spatial scale, results in an inaccurate timing of the onset of the surge. The wave setup model produces sea levels at the coast that are around 11 % of the incident rms wave heights. The total modelled sea-level residual, obtained by adding the modelled wave setup to the storm surge, is qualitatively similar to the measured sea-level residual However, the modelled values are higher, especially at Sydney where the tide gauge is situated in a sheltered harbour location. in such sheltered locations, it is expected that some attenuation of the wave setup would occur and suggests that sea levels on the open coast could be considerably higher during such events.

McInnes, K. L., Hubbert, G. D., and Oliver, S.  (2002). Evaluating the storm surge threat for Pacific Island countries. In: Abstract volume 9^th National AMOS Conference, University of Melbourne (AMOS Publication,  18) . [Melbourne?]: AMOS. p. 57 .

The threat of rising sea levels due to the enhanced greenhouse effect and the risk of severe inundation of low-lying Pacific Island Countries prompted the initiation of the South Pacific Sea Level and Climate Monitoring Project funded by AusAID. The earlier stages of the project saw the deployment of a network of sea level/meteorological monitoring stations by the National Tidal Facility at eleven sites including Papua New Guinea, Solomon Islands, Vanuatu, Nauru, Kiribati, Tuvalu, Marshall Islands, Fiji, Samoa, Tonga and Cook Islands.

Phase III of the project, while continuing sea level monitoring in the South Pacific is also required to carry out more research and assist in the building of capacity within the region in the areas of environmental planning and assessing the risk of inundation. To this end, CSIRO Atmospheric Research in conjunction with Global Environmental Modelling Systems (GEMS) has commenced a project to evaluate the risk of cyclone-induced storm surge and inundation for several locations within the South Pacific using the GEMS coastal inundation model. One aim of the project is to provide a user-friendly Windows-based coastal ocean model capable of modelling tides and storm surges on a desktop PC for the locations of interest. It is envisaged that the system can be used for real-time prediction of tides and storm surge in the region. A second aim of the project is to evaluate the risk of storm surge for the chosen locations by calculating the return periods of extreme sea level based on historical cyclone behaviour and Monte-Carlo simulations using the coastal inundation model. The data generated in this part of the project will be incorporated into a PC data-base so that the information can be easily accessed for risk assessment and coastal planning applications. The evaluation of the current risk of severe sea level events is a critical first step to evaluating the impact of climate change either through sea level rise or changing characteristics of tropical cyclones. In this talk, progress toward these goals will be described and the operation of the system will be demonstrated.

McInnes, K. L., and Hubbert, G. D. (2001). Impact of Sea Level Rise & Storm Surges on a Coastal Community. 

A technique to evaluate the risk of storm tides (the combination of a storm surge and tide) under present and enhanced greenhouse conditions has been applied to Cairns on the northeastern Australian coast. The technique combines a statistical model for cyclone occurrence with a state-of-the-art storm surge inundation model and involves the random generation of a large number of storm tide simulations. The set of simulations constitutes a synthetic record of extreme sea level events that can be analysed to produce storm tide return periods. The use of a dynamical storm surge model with overland flooding capability means that the spatial extent of flooding is also implicitly modelled. The technique has the advantage that it can readily be modified to include projected changes to cyclone behaviour due to the enhanced greenhouse effect. Sea level heights in the current climate for return periods of 50, 100, 500 and 1000 years have been determined to be 2.0 m, 2.3 m, 3.0 m and 3.4 m respectively. In an enhanced greenhouse climate (around 2050), projected increases in cyclone intensity and mean sea level see these heights increase to 2.4 m, 2.8 m, 3.8 m and 4.2 m respectively. The average area inundated by events with a return period greater than 100 years is found to more than double under enhanced greenhouse conditions.