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.     

Multiple scenario analyses forecasting the confounding impacts of sea level rise and tides from storm induced coastal flooding in the city of Shanghai,China

Shanghai is physically and socio-economically vulnerable to accelerated sea level rise because of its low elevation, flat topography, highly developed economy and highly-dense population. In this paper, two scenarios of sea level rise and storm surge flooding along the Shanghai coast are presented by forecasting 24 (year 2030) and 44 (year 2050) years into the future and are applied to a digital elevation model to illustrate the extent to which coastal areas are susceptible to levee breach and overtopping using previously developed inflow calculating and flood routing models. Further, the socio-economic impacts are examined by combining the inundation areas with land use and land cover change simulated using GeoCA-Urban software package. This analysis shows that levee breach inundation mainly occurs in the coastal zones and minimally intrudes inland with the conservative protection of dike systems designed. However, storm surge flooding at the possible maximum tide level could cause nearly total inundation of the landscape, and put approximately 24 million people in Shanghai under direct risk resulting from consequences of flooding (e.g. contamination of potable water supplies, failure of septic systems, etc.).     

Coastal flooding: impacts of coupled wave–surge–tide models

Wind waves and elevated water levels together can cause flooding in low-lying coastal areas, where the water level may be a combination of mean sea level, tides and surges generated by storm events. In areas with a wide continental shelf a travelling external surge may combine with the locally generated surge and waves and there can be significant interaction between the propagation of the tide and surge. Wave height at the coast is controlled largely by water depth. So the effect of tides and surges on waves must also be considered, while waves contribute to the total water level by means of wave setup through radiation stress. These processes are well understood and accurately predicted by models, assuming good bathymetry and wind forcing is available. Other interactions between surges and waves include the processes of surface wind-stress and bottom friction as well as depth and current refraction of waves by surge water levels and currents, and some of the details of these processes are still not well understood. The recent coastal flooding in Myanmar (May 2008) in the Irrawaddy River Delta is an example of the severity of such events, with a surge of over 3 m exacerbated by heavy precipitation. Here, we review the existing capability for combined modelling of tides, surges and waves, their interactions and the development of coupled models.     

The impact of sea-level rise on the coast of Tianjin-Hebei,China

Bulletins of China’s National Sea Level show that the average rising rate of sea-levels in China is 3.3 mm/a over the past 40 years, with an obviously accelerated rising trend in the last decade. The rate of relative sea-level rise of the Yangtze River Delta reached >10 mm/a after considering the land subsidence, and Bohai Bay is even greater than 25 mm/a. The impact of the sea level rise to the coastal area will be greater in the coming years, so carrying out an assessment of this rising trend is urgent. This paper, taking the coastal area of Tianjin and Hebei as examples, comprehensively evaluates the impact of sea-level rise through multitemporal remote sensing shoreline interpretation, ground survey verification, elevation measurements for both seawall and coastal lowlands. The results show that the average elevation of the measured coastal areas of Tianjin and Hebei is about +4 m, and the total area of >100 km² is already below the present mean sea level. More than 270 km, ca. 31% of the total length of the seawall, cannot withstand a 1-in-100-year storm surge. Numerical simulations of the storm flooding on the west coast of Bohai Bay, for 1-in-50-years, 1-in-100-years, 1-in-200-years and 1-in-500-years, show that if there were no coastal dykes, the maximum flooding area would exceed 3000 km², 4000 km², 5300 km² and 7200 km², respectively. The rising sea has a direct and potential impact on the coastal lowlands of Tianjin and Hebei. Based on the latest development in international sea-level rise prediction research, this paper proposes 0.5 m, 1.0 m and 1.5 m as low, middle and high sea level rise scenarios by 2100 for the study area, and combines the land subsidence and other factors to the elevation of the existing seawall. Comprehensive evaluation results indicate that even in the case of a low scenario, the existing seawall will not be able to withstand a 1-in-100-years storm surge in 2030, and the potential flooding areas predicted by the model will become a reality in the near future. Therefore, the seawall design in the coastal areas of Tianjin and Hebei must consider the combined effects of land subsidence, sea level rise and the extreme storm surges caused by it.©2019 China Geology Editorial Office.     

Evaluation of coastal inundation hazard for present and future climates

Coastal inundation from hurricane storm surges causes catastrophic damage to lives and property, as evidenced by recent hurricanes including Katrina and Wilma in 2005 and Ike in 2008. Changes in hurricane activity and sea level due to a warming climate, together with growing coastal population, are expected to increase the potential for loss of property and lives. Current inundation hazard maps: Base Flood Elevation maps and Maximum of Maximums are computationally expensive to create in order to fully represent the hurricane climatology, and do not account for climate change. This paper evaluates the coastal inundation hazard in Southwest Florida for present and future climates, using a high resolution storm surge modeling system, CH3D-SSMS, and an optimal storm ensemble with multivariate interpolation, while accounting for climate change. Storm surges associated with the optimal storms are simulated with CH3D-SSMS and the results are used to obtain the response to any storm via interpolation, allowing accurate representation of the hurricane climatology and efficient generation of hazard maps. Incorporating the impact of anticipated climate change on hurricane and sea level, the inundation maps for future climate scenarios are made and affected people and property estimated. The future climate scenarios produce little change to coastal inundation, due likely to the reduction in hurricane frequency, except when extreme sea level rise is included. Calculated coastal inundation due to sea level rise without using a coastal surge model is also determined and shown to significantly overestimate the inundation due to neglect of land dissipation.     

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.     

Simulation of water levels and extent of coastal inundation due to a cyclonic storm along the east coast of India

The devastation due to storm surge flooding caused by extreme wind waves generated by the cyclones is a severe apprehension along the coastal regions of India. In order to coexist with nature’s destructive forces in any vulnerable coastal areas, numerical ocean models are considered today as an essential tool to predict the sea level rise and associated inland extent of flooding that could be generated by a cyclonic storm crossing any coastal stretch. For this purpose, the advanced 2D depth-integrated (ADCIRC-2DDI) circulation model based on finite-element formulation is configured for the simulation of surges and water levels along the east coast of India. The model is integrated using wind stress forcing, representative of 1989, 1996, and 2000 cyclones, which crossed different parts of the east coast of India. Using the long-term inventory of cyclone database, synthesized tracks are deduced for vulnerable coastal districts of Tamil Nadu. Return periods are also computed for the intensity and frequency of cyclones for each coastal district. Considering the importance of Kalpakkam region, extreme water levels are computed based on a 50-year return period data, for the generation of storm surges, induced water levels, and extent of inland inundation. Based on experimental evidence, it is advocated that this region could be inundated/affected by a storm with a threshold pressure drop of 66 hpa. Also it is noticed that the horizontal extent of inland inundation ranges between 1 and 1.5 km associated with the peak surge. Another severe cyclonic storm in Tamil Nadu (November 2000 cyclone), which made landfall approximately 20 km south of Cuddalore, has been chosen to simulate surges and water levels. Two severe cyclonic storms that hit Andhra coast during 1989 and 1996, which made landfall near Kavali and Kakinada, respectively, are also considered and computed run-up heights and associated water levels. The simulations exhibit a good agreement with available observations from the different sources on storm surges and associated inundation caused by these respective storms. It is believed that this study would help the coastal authorities to develop a short- and long-term disaster management, mitigation plan, and emergency response in the event of storm surge flooding.     

Modeling the impact of land reclamation on storm surges in Bohai Sea,China

A nested model for the simulation of tides and storm surges in the Bohai Sea, China, has been developed based on the three-dimensional finite-volume coastal ocean model. The larger domain covers the entire Yellow Sea and Bohai Sea with a horizontal resolution of ~10 km, and the smaller domain focuses on the Bohai Sea with a fine resolution up to ~300 m. For the four representative storm surges caused by extratropical storms and typhoons, the simulated surge heights are in good agreement with observations at coastal tide gauges. A series of sensitivity experiments are carried out to assess the influence of coastline change due to land reclamation in recent decades on water levels during storm surges. Simulation results suggest that changes in coastline cause changes in the amplitude and phase of the tidal elevation, and fluctuations of surge height after the peak stage of the storm surges. Hence, for the assessment of the influence of coastline changes on the total water level during storm surges, the amplitudes and phases of both the tidal and surge heights need to be taken into account. For the three major ports in the Bohai Bay, model results suggest that land reclamation has created a coastline structure that favors increasing the maximum water level by 0.1–0.2 m. Considering that during the storm surges the total water level is close to or even exceeds the warning level for these ports, further increasing the maximum water level by 0.1–0.2 m has the potential to cause severe damages and losses in these ports.

     

Understanding a coastal flood event: the 10th March 2008 storm surge event in the Solent, UK

Extreme sea-level events (e.g. caused by storm surges) can cause coastal flooding, and considerable disruption and damage. To understand the impacts or hazards expected by different sea levels, waves and defence failures, it is useful to monitor and analyse coastal flood events, including generating numerical simulations of floodplain inundation. Ideally, any such modelling should be calibrated and validated using information recorded during real events, which can also add plausibility to synthetic flood event simulations. However, such data are rarely compiled for coastal floods. This paper demonstrates the capture of such a flood event dataset, and its integration with defence and floodplain modelling to reconstruct, archive and better understand the regional impacts of the event. The case-study event comprised a significant storm surge, high tide and waves in the English Channel on 10 March 2008, which resulted in flooding in at least 37 distinct areas across the Solent, UK (mainly due to overflow and outflanking of defences). The land area flooded may have exceeded 7 km², with the breaching of a shingle barrier at Selsey contributing to up to 90 % of this area. Whilst sea floods are common in the Solent, this is the first regional dataset on flood extent. The compilation of data for the validation of coastal inundation modelling is discussed, and the implications for the analysis of future coastal flooding threats to population, business and infrastructure in the region.     

地面沉降对渤海湾风暴潮灾害防治的影响研究

渤海湾沿海地区地面沉降严重、风暴潮灾害频发。本文以天津作为典型区域,对风暴潮潮位测定、风暴潮灾害和防风暴潮预案措施等方面开展研究,认为地面沉降对上述3方面均有的不同程度的影响,在风暴潮灾害防治中必须考虑地面沉降问题。     

Vulnerability of Hampton Roads,Virginia to Storm-Surge Flooding and Sea-Level Rise

Sea-level rise will increase the area covered by hurricane storm surges in coastal zones. This research assesses how patterns of vulnerability to storm-surge flooding could change in Hampton Roads, Virginia as a result of sea-level rise. Physical exposure to storm-surge flooding is mapped for all categories of hurricane, both for present sea level and for future sea-level rise. The locations of vulnerable sub-populations are determined through an analysis and mapping of socioeconomic characteristics commonly associated with vulnerability to environmental hazards and are compared to the flood-risk exposure zones. Scenarios are also developed that address uncertainties regarding future population growth and distribution. The results show that hurricane storm surge presents a significant hazard to Hampton Roads today, especially to the most vulnerable inhabitants of the region. In addition, future sea-level rise, population growth, and poorly planned development will increase the risk of storm-surge flooding, especially for vulnerable people, thus suggesting that planning should steer development away from low-lying coastal and near-coastal zones.     

Coastal erosion hazard and vulnerability assessment for southern coastal Tamil Nadu of India by using remote sensing and GIS

The measurement and recording of the height and spatial extent reached by coastal storm surges is fundamental to scientific progress in understanding these phenomena. Such information is required for better prediction and for risk assessment. Model-based evaluation of increasing delta vulnerability, for example, cannot be tested without long-term, consistent, and sustained observation of actual events. Also, storm surges occur within the temporal context of tidal variation, which must first be characterized through observation. Present standard approaches for measuring storm surges are not optimum. Thus, tidal gauges provide information at one point, whereas the heights reached by surges vary spatially. Also, post-surge ground surveys are expensive, laborious, and commonly lack comparison to similar data obtained for previous surges or for high tides. The advent of moderate spatial resolution, high temporal resolution remote sensing initiated by the launch of the two NASA MODIS sensors greatly reduces these constraints. For over a decade, daily coverage of most coastal land areas, though restricted by cloud cover, has systematically captured the maximum extents reached by both high tides and by storm surges. Automated water classification algorithms are now transforming the incoming image data into GIS water boundary files, again at daily or near-daily time steps. This paper provides a retrospective view of sample storm surges as mapped via these sensors and describes: (a) the present, MODIS-based surface water surveillance system, (b) the mapping enhancement to be provided by frequent-repeat, wide-swath satellite radar imaging, and (c) the emerging prospects for routine global surveillance of storm surge events. Such will be necessary if long-term trends are to be recognized, characterized, and understood, along coastal zones now being affected by both increasing subsidence and rising sea level.     

Impact of cyclonic wind field on interaction of surge–wave computations using finite-element and finite-difference models

Both finite-element and finite-difference numerical models are applied to simulate storm surges and associated currents generated by tropical cyclones that struck the coast of Andhra Pradesh, located on the east coast of India. During a cyclone, the total water level at any location on the coast is made up of the storm surge, surge–wind wave interaction and the tide. The advanced circulation two-dimensional depth-integrated (ADCIRC-2DDI) model based on finite-element formulation and the two-dimensional finite-difference model of storm surges developed at IIT Delhi, hereafter referred as IITD storm surge model, are used. These models are driven by astronomical tides at the open ocean boundary and cyclonic asymmetric winds over the surface of the computational domain. Comparison of model simulated sea-surface elevations with coarse and finer spatial resolutions suggests that the grid resolution near the coast is very crucial for accurate determination of the surges in addition to the local bathymetry. The model underpredicts surges, and the peak surge location shifts more to the right of the landfall as the spatial resolution of the model becomes coarser. The numerical experiments also demonstrate that the ADCIRC model is robust over the IITD storm surge model for surge computations as the coastline is better represented in the former.     

Simulation of the Hurricane Dennis storm surge and considerations for vertical resolution

A high-resolution storm surge model of Apalachee Bay in the northeastern Gulf of Mexico is developed using an unstructured grid finite-volume coastal ocean model (FVCOM). The model is applied to the case of Hurricane Dennis (July 2005). This storm caused underpredicted severe flooding of the Apalachee Bay coastal area and upriver inland communities. Accurate resolution of complicated geometry of the coastal region and waterways in the model reveals processes responsible for the unanticipated high storm tide in the area. Model results are validated with available observations of the storm tide. Model experiments suggest that during Dennis, excessive flooding in the coastal zone and the town of St. Marks, located up the St. Marks River, was caused by additive effects of coincident high tides (~10–15% of the total sea-level rise) and a propagating shelf wave (~30%) that added to the locally wind-generated surge. Wave setup, the biggest uncertainty, is estimated on the basis of empirical and analytical relations. The Dennis case is then used to test the sensitivity of the model solution to vertical discretization. A suite of model experiments is performed with varying numbers of vertical sigma (σ) levels, with different distribution of σ-levels within the water column and a varying bottom drag coefficient. The major finding is that the storm surge solution is more sensitive to resolution within the velocity shear zone at mid-depths compared to resolution of the upper and bottom layer or values of the bottom drag coefficient.     

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.     

渤海湾西部风暴潮漫滩数值模拟

基于ROMS海洋模式,结合近年的地质实测资料,建立了渤海湾西部地区风暴潮漫滩的数值模型。对模型进行验证后,对渤海湾西部区域重现期为50a、100a、200a及500a的风暴潮漫滩进行了数值模拟,分析了不同重现期风暴潮漫滩发展的动态过程及最大漫滩淹水范围。结果表明,数值模型基本能反映风暴潮的增水趋势,能够模拟风暴潮漫滩发生发展的动态过程。随着风暴潮强度的增加,渤海湾西部地区淹水范围具有从东海岸向西部内陆区域扩展的趋势。通过曲线拟合发现,风暴潮最大漫滩面积比值与高水位之间基本呈线性关系。     

An experimental study of mitigating coastal sand dune erosion by microbial- and enzymatic-induced carbonate precipitation

Acta Geotechnica - Due to more extreme weather events and accelerating sea-level rise, coastal sand dunes are subjected to more frequent storm wave inundation and surge impacts, which contribute to...     

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.     

Review: Advances in delta-subsidence research using satellite methods

Most of the world’s major river deltas are sinking relative to local sea level. The effects of subsidence can include aquifer salinization, infrastructure damage, increased vulnerability to flooding and storm surges, and permanent inundation of low-lying land. Consequently, determining the relative importance of natural vs. anthropogenic pressures in driving delta subsidence is a topic of ongoing research. This article presents a review of knowledge with respect to delta surface-elevation loss. The field is rapidly advancing due to applications of space-based techniques: InSAR (interferometric synthetic aperture radar), GPS (global positioning system), and satellite ocean altimetry. These techniques have shed new light on a variety of subsidence processes, including tectonics, isostatic adjustment, and the spatial and temporal variability of sediment compaction. They also confirm that subsidence associated with fluid extraction can outpace sea-level rise by up to two orders of magnitude, resulting in effective sea-level rise that is one-hundred times faster than the global average rate. In coming years, space-based and airborne instruments will be critical in providing near-real-time monitoring to facilitate management decisions in sinking deltas. However, ground-based observations continue to be necessary for generating complete measurements of surface-elevation change. Numerical modeling should seek to simulate couplings between subsidence processes for greater predictive power.     

Sea-level rise and shoreline retreat of the Nile Delta promontories, Egypt

Studies of the Nile Delta coast have indicated wide values of local subsidence, ranging from 0.4 to 5 mm/yr. Trend analysis of sea-level rise and shoreline retreat at two Nile Delta promontories have been studied. Records from tide gauges at Alexandria (1944–1989) and Port Said (1926–1987), north of the Nile delta coast, indicate a submergence of the land and/or a rise of the sea-level of 2 and 2.4 mm/yr, respectively.Dramatic erosion has occurred on some beaches of the Nile Delta. This is greatest at the tips of the Rosetta and Damietta promontories, with shoreline retreat up to 58 m/yr. Relationship between the shoreline retreat and sea level trends in terms of correlation analysis and application of the Bruun Rule indicates that the sea level rise has, by itself, a relatively minor effect on coastal erosion. The sea-level trend at the Nile delta coast is found to be only one of several effects on shoreline retreat. Major recent effects include a combination of cut-off of sediment supply to the coast by damming the River Nile and local hydrodynamic forces of waves and currents. Estimates of local future sea-level rise by the year 2100 at Alexandria and Port Said, respectively, is expected to be 37.9 and 44.2 cm. These expectations, combined with other factors, could accelerate coastal erosion, inundate wetlands and lowlands, and increase the salinity of lakes and aquifers.