Developments in storm tide modelling and risk assessment in the Australian region

An overview is provided of some of the significant storm tide modelling and risk assessment studies undertaken over the past few years within Australia and the nearby oceanic regions for government and industry. Emphasis is placed on the need for integrated planning and forecasting approaches for storm tide risk assessment. The importance of the meteorological forcing and the appropriate modelling of each of the storm tide components, namely, astronomical tide, storm surge, breaking wave setup and coastal inundation is discussed. The critical role of tropical cyclone “best track” datasets for risk assessment studies and the potential impacts on design criteria and risk assessment studies is highlighted, together with the challenge of developing credible enhanced-greenhouse climate change scenarios. It is concluded that storm tide modelling needs to be undertaken in a holistic framework that considers the relative uncertainties in each of the various elements—atmospheric, hydrodynamic and data, as well as addressing operational forecasting, design and planning needs.     

Assessing future risk: quantifying the effects of sea level rise on storm surge risk for the southern shores of Long Island, New York

Sea level rise threatens to increase the impacts of future storms and hurricanes on coastal communities. However, many coastal hazard mitigation plans do not consider sea level rise when assessing storm surge risk. Here we apply a GIS-based approach to quantify potential changes in storm surge risk due to sea level rise on Long Island, New York. We demonstrate a method for combining hazard exposure and community vulnerability to spatially characterize risk for both present and future sea level conditions using commonly available national data sets. Our results show that sea level rise will likely increase risk in many coastal areas and will potentially create risk where it was not before. We find that even modest and probable sea level rise (.5 m by 2080) vastly increases the numbers of people (47% increase) and property loss (73% increase) impacted by storm surge. In addition, the resulting maps of hazard exposure and community vulnerability provide a clear and useful example of the visual representation of the spatial distribution of the components of risk that can be helpful for developing targeted hazard mitigation and climate change adaptation strategies. Our results suggest that coastal agencies tasked with managing storm surge risk must consider the effects of sea level rise if they are to ensure safe and sustainable coastal communities in the future.     

A modelling approach for estimating the frequency of sea level extremes and the impact of climate change in southeast Australia

An efficient approach for evaluating storm tide return levels along the southeastern coastline of Australia under present and future climate conditions is described. Storm surge height probabilities for the present climate are estimated using hydrodynamic model simulations of surges identified in recent tide gauge records. Tides are then accounted for using a joint probability method. Storm tide height return levels obtained in this way are similar to those obtained from the direct analysis of tide gauge records. The impact of climate change on extreme sea levels is explored by adding a variety of estimates of mean sea level rise and by forcing the model with modified wind data. It is shown that climate change has the potential to reduce average recurrence intervals of present climate 1 in 100 year storm tide levels along much of the northern Bass Strait coast to between 1 and 2 years by the year 2070.     

钱塘江河口杭州湾风暴潮溢流计算方法研究

建立钱塘江河口杭州湾风暴潮模型,探讨风暴潮出现溢流的计算方法。将可能出现溢流的沿海堤防以及海水侵入的陆地均依照高程概化为计算区域,采用糙率控制潮水的溢流流量,以模型的堤顶单宽流量和根据计算潮位采用宽顶堰公式换算流量的一致性来率定糙率值。在此基础上模拟了风暴潮漫溢堤防的过程,结果表明风暴潮出现溢流后,钱塘江河口杭州湾之间两岸大片的陆地存在淹没风险,沿程潮位由于溢流出现不同程度的降低响应。     

Designing a long-term flood risk management plan for the Scheldt estuary using a risk-based approach

The Scheldt is a tidal river that originates in France and flows through Belgium and the Netherlands. The tides create significant flood risks in both the Flemish region in Belgium and the Netherlands. Due to sea level rise and economic development, flood risks will increase during this century. This is the main reason for the Flemish government to update its flood risk management plan. For this purpose, the Flemish government requested a cost-benefit analysis of flood protection measures, considering long-term developments. Measures evaluated include a storm surge barrier, dyke heightening and additional floodplains with or without the development of wetlands. Some of these measures affect the flood risk in both countries. As policies concerning the limitation of flood risk differ significantly between the Netherlands and Flanders, distinctive methodologies were used to estimate the impacts of measures on flood risk. A risk-based approach was applied for Flanders by calculating the impacts of flood damage at different levels of recurrence, for the base year (2000) and in case of a sea level rise of 60 cm by 2100. Policy within the Netherlands stipulates a required minimal protection level along the Scheldt against storms with a recurrence period of 1 in 4,000 years. It was estimated how flood protection measures would delay further dyke heightening, which is foreseen as protection levels are presently decreasing due to rising sea levels. Impacts of measures (safety benefits) consist of delays in further dyke heightening. The results illustrate the importance of sea level rise. Flood risks increased fivefolds when a sea level rise of 60 cm was applied. Although more drastic measures such as a storm surge barrier near Antwerp offer more protection for very extreme storms, a combination of dykes and floodplains can offer higher benefits at lower costs.     

Risk assessment on storm surges in the coastal area of Guangdong Province

The coastal area of Guangdong Province is one of the most developed regions in China. It is also often under severe risk of storm surges, as one of the few regions in China which are seriously threatened by storm surges. Based on the data of storm surges in the study area in the past 30 years, the return periods of 18 tide stations for storm surge are calculated separately. Using the spatial analysis technology of ArcGIS, combined with the topography data of the study area, the submerged scope for storm surge in the coastal area of Guangdong Province is determined, and the hazard assessment is carried out. According to the view of systematic point, this article quotes the result of vulnerability assessment which was done by the author in the previous research. Based on the hazard evaluation and vulnerability evaluation, risk assessment of storm surges in the study region is done, and the risk zoning map is drawn. According to the assessment, Zhuhai, Panyu and Taishan are classified as the highest risk to storm surges in Guangdong Province; Yangdong, Yangjiang and Haifeng are in higher risk to storm surges; Dongguan, Jiangmen, Baoan and Huidong are in middle risk to storm surges; Zhongshan, Enping, Shanwei, Huiyang, Longgang and Shenzhen are in lower risk of storm surges; Guangzhou, Shunde and Kaiping are in the lowest risk to storm surges. This study builds a complete process for risk assessment of storm surges. It reveals the risk of storm surges in the coastal cities, and it would guide the land use of coastal cities in the future and provide scientific advices to the government for the prevention and mitigation of storm surge disaster. It has important theoretical and practical significance.     

A modeling study of coastal inundation induced by storm surge,sea-level rise,and subsidence in the Gulf of Mexico

The northern coasts of the Gulf of Mexico (GoM) are highly vulnerable to the direct threats of climate change, such as hurricane-induced storm surge, and such risks are exacerbated by land subsidence and global sea-level rise. This paper presents an application of a coastal storm surge model to study the coastal inundation process induced by tide and storm surge, and its response to the effects of land subsidence and sea-level rise in the northern Gulf coast. The unstructured-grid finite-volume coastal ocean model was used to simulate tides and hurricane-induced storm surges in the GoM. Simulated distributions of co-amplitude and co-phase lines for semi-diurnal and diurnal tides are in good agreement with previous modeling studies. The storm surges induced by four historical hurricanes (Rita, Katrina, Ivan, and Dolly) were simulated and compared to observed water levels at National Oceanic and Atmospheric Administration tide stations. Effects of coastal subsidence and future global sea-level rise on coastal inundation in the Louisiana coast were evaluated using a “change of inundation depth” parameter through sensitivity simulations that were based on a projected future subsidence scenario and 1-m global sea-level rise by the end of the century. Model results suggested that hurricane-induced storm surge height and coastal inundation could be exacerbated by future global sea-level rise and subsidence, and that responses of storm surge and coastal inundation to the effects of sea-level rise and subsidence are highly nonlinear and vary on temporal and spatial scales.     

A new typhoon bogussing scheme to obtain the possible maximum typhoon and its application for assessment of impacts of the possible maximum storm surges in Ise and Tokyo Bays in Japan

We developed the new typhoon bogussing scheme to obtain the possible maximum typhoon approaching any region under any climatic conditions by using a potential vorticity inversion method. Numerical simulations with the new typhoon bogussing scheme are conducted for assessment of storm surges by possible maximum typhoons under the present-day and global warming climatic conditions in Ise and Tokyo Bays in Japan. The results suggest that the storm tide higher than the maximum storm tide in recorded history can occur in Ise and Tokyo Bays even for the present-day climate and the storm tide higher than the design sea level can cause severe damage to Nagoya and Tokyo megacities, in particular, airport facilities in Ise Bay for the global warming climate. These results suggest that the new typhoon bogussing scheme we developed is useful for assessment of impacts of storm surge by the possible maximum typhoons.     

Storm extreme levels and coastal flood hazards: A parametric approach on the French coast of Languedoc (district of Leucate)

Coastal flooding is a significant risk on the shores of Languedoc-Roussillon. The storms that periodically hit the coast can generate strong swells and storm surges. Most beach resorts, built on a low elevation dune ridge, are periodically flooded during major storms. Although risks zoning regulations take into consideration coastal flood hazards, the delineation of vulnerable areas is still insufficient and the commonly accepted threshold is regularly exceeded during most severe storms. This paper presents a method to improve the assessment of extreme storm-related water levels. It relies on fieldwork carried out in the Leucate commune (Aude), which is particularly exposed to the risk of sea level rise. It considers both storm surges and wave phenomena that occur within the surf zone (set-up and swash), calculated from the Simulating WAves Nearshore (SWAN^®) numerical wave model and the Stockdon formula. Water levels reached during several recent storm events have been reconstructed and simulations of submerged areas were carried out by numerical modelling.     

Potential impacts of extreme storm surges on a low-lying densely populated coastline: the case of Dunkirk area, Northern France

Along the southern coast of the North Sea, a large proportion of the Flemish coastal plain consists of densely populated reclaimed land, much of which lying below mean high tide level. This is particularly the case along the northern coast of France, from Dunkirk to the Belgium border, where the shoreline consists of coastal dunes that protect low-lying reclaimed lands from marine flooding. This area is vulnerable and subject to several risks. Extreme weather conditions could induce strong surges that could cause (1) a shoreline retreat, (2) marine submersion and (3) land and/or urban flooding due to drainage problems of the polders. Highly energetic events such as the November 2007 storm could have had much more severe consequences especially if they occurred at high tide and/or during a spring tide. In the current context of global change and projected sea-level rise, it is then important for the local authorities to take into account the potential impacts and return periods of such events, in order to implement coastal risk policies prevention and management, to reinforce sea defense, increase pumping station efficiency and plan warning systems against marine submersion and polder flooding, which is not the case yet in Northern France.     

Prioritization of disaster risk in a community using GIS

Prioritization of disaster risk was carried out for a community in Toronto, Canada. Geographic information systems (GIS) were used for spatial analysis, including spatial overlays and clipping for extracting spatial and attribute information related to people’s vulnerability, critical infrastructure and landuse. In order to determine disaster risk, the overall community vulnerability was evaluated by combining social, economic, physical and environmental vulnerabilities. This paper uses the propane explosion incident as the case in point to demonstrate the methodology and procedure used to evaluate risk using GIS techniques. City of Toronto spatial data have been integrated with the study area to gather landuse information, identify risk zones based on the propane storage facility location and evaluate risks. Statistics Canada 2006 census data have been used for area demographics and people’s social and economic status. Vulnerability indicators were determined based on the GIS-derived spatial and attribute data for the hazard and evacuation zones followed by a quantitative spatial risk estimation and ranking. The methodology of this study, based on the risk evaluation and prioritization conducted, can be applied to future decision making in effective landuse planning and the development of risk management strategies.     

Impact of Sea-level Rise and 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 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 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.     

Flood Hazard Assessment for a Hyper-Tidal Estuary as a Function of Tide-Surge-Morphology Interaction

Astronomical high tides and meteorological storm surges present a combined flood hazard to communities and infrastructure. There is a need to incorporate the impact of tide-surge interaction and the spatial and temporal variability of the combined flood hazard in flood risk assessments, especially in hyper-tidal estuaries where the consequences of tide and storm surge concurrence can be catastrophic. Delft3D-FLOW is used to assess up-estuary variability in extreme water levels for a range of historical events of different severity within the Severn Estuary, southwest England as an example. The influence of the following on flood hazard is investigated: (i) event severity, (ii) timing of the peak of a storm surge relative to tidal high water and (iii) the temporal distribution of the storm surge component (here in termed the surge skewness). Results show when modelling a local area event severity is most important control on flood hazard. Tide-surge concurrence increases flood hazard throughout the estuary. Positive surge skewness can result in a greater variability of extreme water levels and residual surge component, the effects of which are magnified up-estuary by estuarine geometry to exacerbate flood hazard. The concepts and methodology shown here can be applied to other estuaries worldwide.     

Process regime change on a Silurian siliciclastic shelf: controlling influences on deposition of the Gray Sandstone Formation,Pembrokeshire, UK

Shallow marine deposits comprising the Silurian Gray Sandstone Formation (GSF) exhibit pronounced process regime changes through time. The formation was deposited on the southern shelf of the Lower Palaeozoic Welsh Basin (UK), and conformably overlies the Coralliferous Formation. The basal Lithofacies Assemblage A (of Sheinwoodian age) is dominated by a storm‐dominated process regime, comprising shoreface and offshore shelf facies associations. The overlying Lithofacies Assemblage B records a mixed process regime, with units being deposited under both storm‐ and tide‐influenced conditions. Tidal‐influence prevailed during deposition of the overlying Lithofacies Assemblage C, with proximal to distal facies variations across a significant tide‐influenced river delta being observed. A return to storm‐dominated shoreface conditions is seen in the succeeding Lithofacies Assemblage D. Lithofacies Assemblage E (Homerian age) records the return of a tide‐influenced river delta to the area, prior to the conformable transition into the overlying Old Red Sandstone (ORS) Red Cliff Formation (of Ludlow age). Northward thickening of the formation across southern Pembrokeshire into the Musselwick Fault indicates a tectonic control on sedimentation, the formation infilling accommodation space developed in an intra‐shelf half‐graben. Recurring changes in process regime from storm‐ to tide‐influenced sedimentation may be related to the onset and subsequent cessation of tidal resonance in sub‐basins across the shelf area which itself was probably controlled by episodic tectonism. It is proposed that the Coralliferous and Gray Sandstone formations comprise the newly erected Marloes Group. Copyright © 2009 John Wiley & Sons, Ltd.     

Simultaneous meteorological tsunamis and storm surges at Buenos Aires coast,southeastern South America

Meteorological tsunamis are frequently observed in different tide stations at the southeastern coast of South America. They are associated with the occurrence of atmospheric gravity waves during the passages of cold fronts over the Buenos Aires Province continental shelf. On the other hand, storm surges are also frequent in the region, and they are associated with strong and persistent southerlies, which are also frequent during cold front passages. The impact of meteorological tsunamis in coastal erosion and in the statistics of storm surge trends is discussed in this paper. For this study, fifteen meteorological tsunamis (with maximum wave heights higher than 0.20 m), seven of them simultaneous to the occurrence of storm surge events (with extreme levels higher than |±0.60 m|), are selected from April 2010 to January 2013. The impact of meteorological tsunamis in the storm erosion potential index (SEPI) is evaluated. Not significant differences are obtained between SEPI calculated with and without filtering the meteorological tsunami signal from the storm surge data series. Moreover, several experiments are carried out computing SEPI from synthetic sea level data series, but very low changes (lower than 4 %) are also obtained. It is concluded that the presence of moderate meteorological tsunamis on sea level records would not enhance this index at the Buenos Aires Province coast. On the other hand, taking into account that meteorological tsunamis can reach up the 20–30 % of the storm surge height, it was concluded that the statistics of storm surge trends (and their uncertainties) should be revised for Mar del Plata data series.     

Dynamic issues in the SE South America storm surge modeling

The ability of the SMARA storm surge numerical prediction system to reproduce local effects in estuarine and coastal winds was recently improved by considering one-way coupling of the air–sea momentum exchange through the wave stress, and best forecasting practices for downscaling. The inclusion of long period atmospheric pressure forcing in tide and tide/surge calculations corrected a systematic error in the surge, produced by the South Atlantic Ocean quasi-stationary pressure patterns. The maximum forecast range for the storm surge at Buenos Aires provided by the real-time use of water level observations is approximately 12 h. The best available water level prediction is the 6-h forecast (nowcast) based on the closest water level observations. The 24-h forecast from the numerical models slightly improves this nowcast. Although the numerical forecast accuracy degrades after the first 48 h, the improvement to the full range observation-based prediction is maintained at the inner Río de la Plata area and extends to the first 3 days at the intermediate navigation channels.     

Application of the hybrid ABV procedure for assessing community risk to hurricanes spatially

In 2011, the National Oceanic and Atmospheric Administration (NOAA) reported that the coastal population of the US that lives within 50 miles of the shoreline exceeded 50 % for the first time in history in spite of a high level of exposure to hurricanes and related flooding. Hurricane Andrew (1992), Mitch (1998), Ivan (2004), Katrina (2005), and Sandy (2012) are recent reminders of both the financial and human toll that result from hurricanes. Generally, hurricanes bring with them torrential rains and storm surges which enable destructive flooding inland and at the coastal (land–sea) interface and cause extensive and severe damages to residential structures and fatalities. An improved understanding of hurricanes and its interactive effects on the built environment will significantly reduce structural and non-structural damage and loss of life. This paper presents the method and results of a study that focused on application of a hybrid loss model which combines structural and non-structural damage vulnerabilities to quantify the damage and subsequent loss as a result of hurricanes, but particularly the extension to the community level. The methodology presented in this paper will help enable designers and/or planners to assess the change in anticipated losses at the community level as a result of one or more mitigation strategies as well as provide insight into land use planning.     

On the accuracy of atmospheric forcing for extra-tropical storm surge prediction

The ability of the SMARA storm surge numerical prediction system to reproduce local effects in estuarine and coastal winds was recently improved by considering one-way coupling of the air–sea momentum exchange through the wave stress, and best forecasting practices for downscaling. The inclusion of long period atmospheric pressure forcing in tide and tide/surge calculations corrected a systematic error in the surge, produced by the South Atlantic Ocean quasi-stationary pressure patterns. The maximum forecast range for the storm surge at Buenos Aires provided by the real-time use of water level observations is approximately 12 h. The best available water level prediction is the 6-h forecast (nowcast) based on the closest water level observations. The 24-h forecast from the numerical models slightly improves this nowcast. Although the numerical forecast accuracy degrades after the first 48 h, the improvement to the full range observation-based prediction is maintained at the inner Río de la Plata area and extends to the first 3 days at the intermediate navigation channels.     

21世纪中叶天津沿海地区极端高水位趋势预测

据统计,天津沿海地区50年一遇的风暴潮极端增水水位为 4.092m,开展控沉工作后的地面下沉速率约为15mm/a,目前沿岸海挡顶面高程一般为 4.332m.参考孟加拉湾、伦敦、汉堡等沿海地区在2050年海平面上升(取较今高约0.2m的推测值)背景下的极端增水趋势预测(增加0.5m),推测天津沿海地区2050年的极端高水位将增加到 4.792m(4.092m 0.2m 0.5m),现有海挡顶面高程将下沉至 3.687m(以2007年为起算年份).2050年极端高水位将比届时的海挡顶面高1.105m,由此将加重风暴潮水漫溢致灾的危险.如果再考虑波浪叠加、河口效应、极端海面上升等不确定因素的影响,危险将更加严重.     

Records of palaeo‐sea level and eruption duration in a coastal tuff ring,Jeju Island,Korea

Phreatomagmatic volcanoes and their sedimentary products can preserve high‐resolution records of earth surface processes because of their high deposition rate. Songaksan, Jeju Island, Korea, is a phreatomagmatic volcano, which erupted c. 3.7 ka BP in a coastal setting. Its tuff ring preserves a record of intertidal to supratidal facies transition in the basal part, which reveals the position of palaeo‐high‐tide level for at least 13 high‐tide events, and a record of a storm‐surge event in the middle part of the tuff ring, which lasted approximately three tidal cycles. Based on these features, the phreatomagmatic eruption of Songaksan is estimated to have taken place over a month. The sea level at the time was almost identical to that at present. This study shows that coastal phreatomagmatic volcanoes can preserve high‐resolution records of eruption duration and palaeo‐sea level, and can provide accurately levelled and dated data points to the Quaternary sea‐level curve.