Coastal Flooding Events Research Articles

Reflections on coastal inundation, climate change impact, and adaptation in built environment: progresses and constraints

Coastal inundation causes considerable impacts on communities and economies. Sea level rise due to climate change increases the occurrence of coastal flood events, creating more challenges to coastal societies. Here we intend to draw the understanding of coastal inundation from our early studies, and provide a silhouette of our approaches in assessing climate change impacts as well as developing risk-based climate adaptation. As a result, we impart a distinctive view of the adaption towards the integration of asset design, coastal planning and policy development, which reflect multiscale approaches crossing individual systems to regions and then nation. Having the approaches, we also discussed the constraints that would be faced in adaptation implementation. In this regard, we initially follow the risk approach by illustrating hazards, exposure and vulnerability in relation to coastal inundation, and manifest the impact and risk assessment by considering an urban environment pertinent to built, natural, and socioeconomic systems. We then extend the scope and recommend the general approaches in developing adaptation to coastal inundation under climate change towards ameliorating overall risks, practically, by the reduction in exposure and vulnerability in virtue of the integration of design, planning and polices. In more details, a resilience design is introduced, to effectively enhance the capacity of built assets to resist coastal inundation impact. We then emphasize on the cost-effective adaptation for coastal planning, which delineates the problem of under-adaptation that leaves some potential benefits unrealized or over-adaptation that potentially consumes an excessive amount of resources. Finally, we specifically explore the issues in planning and policies in mitigating climate change risks, and put forward some emerging constraints in adaptation implementation. It suggests further requirements of harmonizing while transforming national policies into the contents aligned with provincial and local governments, communities, and households.

Geological evidence of high-energy marine flooding events on the Tangier coastal plain, Morocco

The coastal sedimentary record is currently being studied to investigate evidence of past extreme coastal flooding events. Extreme marine inundations along Morocco's coasts are described in historical documents. In this work, evidence of high-energy marine flooding events on the Tangier coastal plain (the Ain Guemout area) was obtained by studying the size and mineralogy of quartz grains, performing exoscopy of the grains, and reconstructing their possible source sediments. In Ain Guemout, the inundation had run-up heights of more than 10 m and deposited distinct metric boulders, broken shells, sand, and lithic clasts 1 km inland. These unusual deposits typically underwent abrupt basal contact with a paleosoil. The deposits were found to thin and fine landward and present major structural and significant lateral variation. Textural analysis showed that clay and coarse sand are the most abundant grain populations in the sediments. The sand fraction is moderately or poorly sorted with a few well-sorted sandy deposits. In contrast to possible source sediments (coastal dune and beach sand), microtextural analysis indicated the recurrent presence of fresh surfaces and percussion marks. The deposits showed similarities to beach and coastal dune materials in their assemblages of heavy minerals, and presented a decreasing trend in such assemblages up-unit. The altitude reached by the sand layers, the increased boulder size inland, and the abundance of rip-up clasts in the sediments demonstrate the tsunamigenic origin of the Ain Guemout deposits. These results improve our understanding of marine floods, and should aid the development of strategies to protect coastal environments.

Physical model investigation of mid-scale mangrove effects on flow hydrodynamics and pressures and loads in the built environment

Large (km-scale) mangrove forests can provide protection to shorelines and near-coast structures during extreme coastal flood events, including tsunamis and tropical cyclones. However, little is known about the effects of mangroves with a modest cross-shore thickness (~10–50 m), on flow hydrodynamics and resulting inland pressures and forces on near-coast structures. We constructed a 1:16 geometric-scale physical model of a Rhizophora mangle (red mangrove) fringe with modest cross-shore thickness to measure the effects of a mangrove forest's cross-shore thickness on wave attenuation and subsequent load reduction on near-coast structures, idealized during experiments with an array of cubes. Three configurations, one baseline with zero mangroves and two with mangrove cross-shore thicknesses corresponding to prototype-scale forest widths of 8.2 m and 19.0 m, were considered in front of an array of idealized slab-on-grade residential buildings. Transient wave conditions with varying incident parameters (wave amplitude, wave representative time scale, water level/mangrove emergence, and presence of a background current) were considered. Water surface elevations, water velocities, cross-shore forces, and pressures measured near and against the building array indicate that mangroves affected inland flow hydrodynamics and forces. The presence of mangroves was associated with elevated water levels and reduced peak velocities between the mangroves and inland structures. Increasing the mangrove cross-shore thickness reduced the cross-shore force on a structure by 11%–65% compared to the baseline case without mangroves. The force reduction by the mangrove configurations varied with incident wave representative time scale; waves with longer representative time scales required larger cross-shore thicknesses to provide similar force reductions to those observed for shorter waves. Further investigation into a wider range of mangrove cross-shore thicknesses, trunk densities, and wave conditions is needed to inform engineering performance of natural and nature-based features for resilient coastal design.

Coastal Flooding Process: Comparing Different Coastal Typologies Response to Extreme Hydrodynamic Conditions

Freire, P.; Oliveira, F. S. B. F. and Oliveira, J. N., 2020. Coastal flooding process: Comparing different coastal typologies response to extreme hydrodynamic conditions. In: Malvarez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 797–802. Coconut Creek (Florida), ISSN 0749-0208.To upgrade the response capability to coastal flood events, hazard predictions need to be improved through integrating the effect of the coastal morphological variability in the nearshore-foreshore-backshore hydromorphological processes induced by waves-tide-wind-atmospheric pressure. In order to evaluate the short-term morphological response of different coastal typologies to potential flood conditions (spring high tide level, storm surge, high wave height), field data acquired in 2019 in three sites in the West coast of Portugal with past flooding episodes are presented and discussed. The preliminary results point out that under the same forcing conditions the short-term response of the cross-shore beach profile that controls the flooding levels is dependent on the beach typology, namely: the nature of the lower and upper limits of the beach face, profile gradient and its alongshore context. This knowledge can be used to develop robust and validated flood prediction tools contributing to improve mitigation and adaptation management strategies.

Household level vulnerability in an Indian mangrove socio-ecological system

ABSTRACT The Sundarbans (West Bengal) is highly vulnerable to hydro-meteorological hazards such as coastal storm surges, flooding, cyclones and other climatic events. These events often lead to loss of productivity in ecosystem-based livelihoods, biodiversity, ecosystem goods and services. Communities directly dependent on socio-ecological systems for primary livelihood need to strengthen their resilience for early recovery and prepare for the impacts of future hazards. Current policies often assume that households are equally vulnerable to hazards. However, there is no robust empirical study available on the level and distribution of vulnerability amongst marginalised households. This study compared the levels of vulnerability amongst 500 households in five villages situated in the Mangrove ecosystem of the Indian Sundarban using the Livelihood Vulnerability Index (LVIs). The results uncover significant variations in levels and distribution of vulnerability between the villages. These findings could be used to tailor need-based bespoke adaptation and mitigation interventions to combat climate-induced variability or hazard events in the future. In order to optimise the benefits of policy or program for strengthening resilience of these households – this article recommends that policymakers consider micro-level differences in levels and distribution of vulnerability.

Coastal flood: a composite method for past events characterisation providing insights in past, present and future hazards—joining historical, statistical and modelling approaches

The characterisation of past coastal flood events is crucial for risk prevention. However, it is limited by the partial nature of historical information on flood events and the lack or limited quality of past hydro-meteorological data. In addition, coastal flood processes are complex, driven by many hydro-meteorological processes, making mechanisms and probability analysis challenging. Here, we tackle these issues by joining historical, statistical and modelling approaches. We focus on a macrotidal site (Gâvres, France) subject to overtopping and investigate the 1900–2010 period. We build a continuous hydro-meteorological database and a damage event database using archives, newspapers, maps and aerial photographs. Using together these historical information, hindcasts and hydrodynamic models, we identify nine flood events, among which five are significant flood events (four with high confidence: 1924, 1978, 2001, 2008; one with a lower confidence: 1904). These flood events are driven by the combination of sea-level rise, tide, atmospheric surge, offshore wave conditions and local wind. We further analyse the critical conditions leading to flood, including the effect of coastal defences, showing, for instance, that the present coastal defences would not have allowed to face the hydro-meteorological conditions of 09/02/1924, whose bi-variate return periods of exceedance $$T_\mathrm{R}$$ (still water level relative to the mean sea level and significant wave height) are larger than 1000 year. In the coming decades, $$T_\mathrm{R}$$ is expected to significantly decrease with sea-level rise, reaching values smaller than 1 year, for eight of the nine historical events, for a sea-level rise of 0.63 m, which is equal to the median sea-level rise projected by the 5th Assessment Report of the IPCC in this region for RCP8.5 in 2100.

Primary Valuation of Coastal Flood Impact to Fish Farming in Brebes, Central Java

High tide event has been recognized in most of coastal area especially in urban region. Meanwhile, there is still limited interest on tidal flood impact on non-urban area including fish farming in developing region. This study aims to identify coastal flood due to high tide event in Brebes, Central Java and its impact on fish farming area. Here we local information from in-depth interview to local group of fish farming and Geographic Information System (GIS) within inputs from national seamless Digital Elevation Model (DEM) data from \\ Geospatial Agency (BIG), and land use data from Google Earth. Additionally, this study also propose local context of coastal flood events on mapping the impact upon fish farming area. This research found that 3,309.53 ha of fish farming area has been flooded in the morning event of and 4,810.32 ha in the afternoon of mangsa peteruan. Meanwhile, in mangsa lanjar, the morning event has submerged around 4,521.72 ha, and 3,703.17 ha for afternoon event. This study depicts beneficial information for coastal zone planning as well as coastal disaster risk management in Indonesia.

Toward a User-Based, Robust and Fast Running Method for Coastal Flooding Forecast, Early Warning, and Risk Prevention

Idier, D.; Aurouet, A.; Bachoc, F.; Baills, A.; Betancourt, J.; Durand, J.; Mouche, R.; Rohmer, J.; Gamboa, F.; Klein T.; Lambert, J.; Le Cozannet, G.; Le Roy, S.; Louisor, J.; Pedreros, R., and Véron, A.L., 2020. Toward a user-based, robust and fast running method for coastal flooding forecast, early warning, and risk prevention. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 1111–1116. Coconut Creek (Florida), ISSN 0749-0208.Scientific progresses now allow properly modelling coastal flooding events. Such models are nevertheless very expensive in terms of computation time (>hours) which prevents any use for forecast and warning or even for estimating the coastal flood hazard return period together with uncertainties. In addition, there is a gap between model outputs and information actually needed by the decision makers. Within the RISCOPE project, we aim at developing a user-based method contributing to forecast, early-warning and prevention of coastal flooding risks. The method should be robust, fast and integrate the complexity of coastal flood processes. To build such coastal flooding models, the solution explored relies on meta-models, i.e. mathematical functions which estimate, with good precision and at a negligible computational cost (<minutes), the results obtained with the numerical model. The overall method is presented, as well as key results, meta-model skills to reproduce the complexity of the coastal flooding processes and products delivered by the Decision Support System prototype, on the study site of Gâvres (France).

Time‐Varying Emulator for Short and Long‐Term Analysis of Coastal Flood Hazard Potential

AbstractRising seas coupled with ever increasing coastal populations present the potential for significant social and economic loss in the 21st century. Relatively short records of the full multidimensional space contributing to total water level coastal flooding events (astronomic tides, sea level anomalies, storm surges, wave run‐up, etc.) result in historical observations of only a small fraction of the possible range of conditions that could produce severe flooding. The Time‐varying Emulator for Short‐ and Long‐Term analysis of coastal flood hazard potential is presented here as a methodology capable of producing new iterations of the sea‐state parameters associated with the present‐day Pacific Ocean climate to simulate many synthetic extreme compound events. The emulator utilizes weather typing of fundamental climate drivers (sea surface temperatures, sea level pressures, etc.) to reduce complexity and produces new daily synoptic weather chronologies with an auto‐regressive logistic model accounting for conditional dependencies on the El Niño Southern Oscillation, the Madden‐Julian Oscillation, seasonality, and the prior two days of weather progression. Joint probabilities of sea‐state parameters unique to simulated weather patterns are used to create new time series of the hypothetical components contributing to synthetic total water levels (swells from multiple directions coupled with water levels due to wind setup, temperature anomalies, and tides). The Time‐varying Emulator for Short‐ and Long‐Term analysis of coastal flood hazard potential reveals the importance of considering the multivariate nature of extreme coastal flooding, while progressing the ability to incorporate large‐scale climate variability into site specific studies assessing hazards within the context of predicted climate change in the 21st century.

Recent coastal sea-level variations and flooding events in the Nigerian Transgressive Mud coast of Gulf of Guinea

Significant warming and sea-level rise that will greatly impact the coastal zone is expected to intensify the coastal flooding occurrence on low-lying coasts in the next few decades. This challenge necessitates improving understanding of the possible trends and contributions of different oceanic forcing to the local coastal sea-level change at different time-scales at different locations. The present study seeks to understand different processes responsible for sea-level variations and coastal flooding events along the low-lying Nigerian Transgressive Mahin Mud coast in the Gulf of Guinea. The contributions of astronomical tides, altimetry-derived sea level, meteorologically forced non-tide residuals and wave run-up to coastal sea-level variations were assessed over the period between 1993 and 2016. The results show a distinct seasonal cycle, with more occurrences during summer/wet season and fewer events in winter/dry season, typically connected to the annual cycles of swell-waves. The leading contributor to total sea-level variations along this mud coast, at daily, seasonal and inter-annual time-scales was wave run-up. However, the leading contributor to total sea-level variations at the monthly (sub-annual) time scale was astronomical tides. Results further show that while the altimetry-derived sea level was responsible for the trend in total sea-level variability, the wave run-up was the major forcing responsible for the extreme coastal flooding events. However, the interaction between wave run-up and astronomical tides further contributed to the extreme/coastal flooding events along the mud coast. It is concluded that the increase in the coastal flooding events in the last 12 years of the study may have rendered the study area vulnerable to chronic erosion and flood hazards, which may have triggered the accelerated rate of coastal degradation in the study area.

Employment accessibility and rising seas

Recent projections suggest worst-case scenarios of more than six ft (1.8 m) of global mean sea-level rise by end of century, progressively making coastal flood events more frequent and more severe. The impact on transportation systems along coastal regions is likely to be substantial. An analysis of impacts for Atlantic and Cape May counties in southern New Jersey is conducted. The impact on accessibility to employment is analyzed using a dataset of sea-level increases merged with road network (TIGER) data and Census data on population and employment. Using measures of accessibility, it is shown how access will be reduced at the block-group level. An additional analysis of low and high income quartiles suggest that lower-income block groups will have greater reductions in accessibility. The implication is that increasing sea levels will have large impacts on people and the economy, and large populations will have access to employment disrupted well before their own properties or places of employment may begin to flood (assuming no adaptation).

Coastal Flooding and Inundation and Inland Flooding due to Downstream Blocking

Extreme atmospheric wind and precipitation events have created extensive multiscale coastal, inland, and upland flooding in United States (U.S.) coastal states over recent decades, some of which takes days to hours to develop, while others can take only several tens of minutes and inundate a large area within a short period of time, thus being laterally explosive. However, their existence has not yet been fully recognized, and the fluid dynamics and the wide spectrum of spatial and temporal scales of these types of events are not yet well understood nor have they been mathematically modeled. If present-day outlooks of more frequent and intense precipitation events in the future are accurate, these coastal, inland and upland flood events, such as those due to Hurricanes Joaquin (2015), Matthew (2016), Harvey (2017) and Irma (2017), will continue to increase in the future. However, the question arises as to whether there has been a well-documented example of this kind of coastal, inland and upland flooding in the past? In addition, if so, are any lessons learned for the future? The short answer is “no”. Fortunately, there are data from a pair of events, several decades ago—Hurricanes Dennis and Floyd in 1999—that we can turn to for guidance in how the nonlinear, multiscale fluid physics of these types of compound hazard events manifested in the past and what they portend for the future. It is of note that fifty-six lives were lost in coastal North Carolina alone from this pair of storms. In this study, the 1999 rapid coastal and inland flooding event attributed to those two consecutive hurricanes is documented and the series of physical processes and their mechanisms are analyzed. A diagnostic assessment using data and numerical models reveals the physical mechanisms of downstream blocking that occurred.

Assessment of climatic variability risks with application of livelihood vulnerability indices

The study applies vulnerability index models to appraise livelihood vulnerability to climate change of human communities living in coastal fronts of some selected mouzas of Namkhana Block part of the Indian Sundarbans. Primary household surveys (528 households in seven mouzas) are carried out to procure data on indicators of socio-demographic profile, livelihood strategies, health, food, water, social networks, natural disaster and climatic fluctuations. The data then have been processed by indices like livelihood vulnerability index (LVI) and livelihood vulnerability index-intergovernmental panel on climate change (LVI-IPCC) to evaluate and compare vulnerabilities of mouzas currently suffering from physical processes like coastal erosion, embankment breaching and flood events. The research outcome implies that Baliara and Iswaripur mouzas are highly vulnerable (LVI score > 0.600 and LVI-IPCC score > 0.170); Narayanpur, Mousuni, Kusumtala mouzas are moderately vulnerable (LVI score 0.540–0.600 and LVI-IPCC score 0.060–0.170); and Bagdanga, Patibania mouzas are least vulnerable (LVI score > 0.540 and LVI-IPCC score < 0.060) to changing climate phenomena. The foremost reasons behind higher vulnerability are greater exposure to climatic fluctuation, natural hazards and higher sensitivity to improper access to food, health, water and finally lower adaptive capacity in terms of poor socio-demographic profile and livelihood security. Findings of the study provide a deeper understanding of people’s perception, adaptation and their ever-increasing vulnerability to changing climate. This approach based on indicators emphasizes sectors that necessitate particular intercession to design management plans for threatened communities. Such type of pragmatic approach of study formulates reliable methodology to quantify vulnerability and develop disaster management strategies to increase the resilience of vulnerable coastal people to climate change.

Habitat selection can reduce effects of extreme climatic events in a long-lived shorebird.

Changes in the frequency of extreme climatic events (ECEs) can have profound impacts on individual fitness by degrading habitat quality. Organisms may respond to such changes through habitat selection, favouring those areas less affected by ECEs; however, documenting habitat selection in response to ECEs is difficult in the wild due to the rarity of such events and the long-term biological data required. Sea level rise and changing weather patterns over the past decades have led to an increase in the frequency of coastal flooding events, with serious consequences for ground nesting shorebirds. Shorebirds therefore present a useful natural study system to understand habitat selection as a response to ECEs. We used a 32-year study of the Eurasian oystercatcher (Haematopus ostralegus) to investigate whether habitat selection can lead to an increase in nest elevation and minimize the impacts of coastal flooding. The mean nest elevation of H. ostralegus has increased during the last three decades. We hypothesized that this change has been driven by changes in H. ostralegus territory settlement patterns over time. We compared various possible habitat selection cues to understand what information H. ostralegus might use to inform territory settlement. There was a clear relationship between elevation and territory settlement in H. ostralegus. In early years, settlements were more likely at low elevations but in more recent years the likelihood of settlement was similar between high and low elevation areas. Territory settlement was associated with conspecific fledgling output and conspecific density. Settlement was more likely in areas of high density and areas with high fledgling output. This study shows that habitat selection can minimize the effects of increasingly frequent ECEs. However, it seems unlikely that the changes we observe will fully alleviate the consequences of anthropogenic climate change. Rates of nest elevation increase were insufficient to track current increases in maximum high tide (0.5 vs. 0.8cm/year). Furthermore, habitat selection cues that rely on information from previous breeding seasons (e.g. conspecific fledgling output) may become ineffective as ECEs become more frequent and environmental predictability is diminished.

Digital mapping of coastal boulders – high‐resolution data acquisition to infer past and recent transport dynamics

AbstractCoastal boulder fields provide clues to long‐term frequency‐magnitude patterns of coastal flooding events and have the potential to play an important role in coastal hazard assessment. Mapping boulders in the field is time and labour‐intensive, and work on intertidal reef platforms, as in the present study, is physically challenging. By addressing coastal scientists who are not specialists in remote sensing, this contribution reports on the possibilities and limitations of digital applications in boulder mapping in Eastern Samar, Philippines, where recent supertyphoons Haiyan and Hagupit induced high waves, coastal flooding and boulder transport. It is demonstrated how satellite imagery of sub‐metre resolution (from Pléiades and WorldView‐3 imagery) enables efficient analysis of transport vectors and distances of larger boulders, reflecting variation in latitudes of both typhoon tracks and approaching angles of typhoon‐generated waves. During the investigated events, boulders with a‐axes of up to 8 m were clearly identified to have been shifted for up to 32 m, mostly along the seaward margin of the boulder field. It is, however, hard to keep track of smaller boulders, and the length of a‐axes and b‐axes including their orientation is often impossible to map with sufficient accuracy. Orthophotographs and digital surface models created through the application of an unmanned aerial vehicle and the ‘Structure from Motion’ technique provide ultra‐high‐resolution data, and have the potential to not only improve the results of satellite image analysis, but also those from field mapping and may significantly reduce overall time in the field. Orthophotographs permit unequivocal mapping of a‐axes and b‐axes including their orientation, while precise values for c‐axes can be derived from the respective digital surface models. Volume of boulders is best inferred from boulder‐specific Structure from Motion‐based three‐dimensional models. Battery power, flight speed and altitude determine the limits of the area covered, while patches shielded by the boulders are difficult to resolve. For some tasks, field mapping remains mandatory and cannot be replaced by currently available remote sensing tools: for example, sampling for rock type, density and age dating, recording of lithological separation of boulders from the underlying geological unit and of geomorphic features on a millimetre to decimetre‐scale, or documentation of fine‐grained sediment transport in between the boulders in supratidal settings. In terms of future events, the digital products presented here will provide a valuable reference to track boulder transport on a centimetre to decimetre‐scale and to better understand the hydrodynamics of extreme‐wave events on a fringing reef coastline.

New York City Panel on Climate Change 2019 Report Chapter 5: Mapping Climate Risk

New York City Panel on Climate Change 2019 Report Chapter 5: Mapping Climate Risk

A simplified hindcast method for the estimation of extreme storm surge events in semi-enclosed basins

Human presence, coastal erosion, and tourism activities are increasing the attention to coastal flooding risk. To perform risk assessments, long time series of observed or hindcast wave parameters and tide levels are then necessary. In some cases, only a few years of observation are available, so that observed extreme data are not always representative and reliable. A hindcast system aimed to reconstruct long time series of total tide levels may be of great help to perform robust extreme events analysis and then to protect human life, activities as well as to counteract coastal erosion by means of risk assessments. This work aims to propose a simplified method to hindcast storm surge levels time series in semi-enclosed basins with low computational costs. The method is an extension of a previous work of some of the authors and consists of a mixed approach in which the estimation of storm surge obtained by using the theory of linear dynamic system is corrected by using a statistical method. Both steps are characterized by low computational costs. Nevertheless, the results may be considered reliable enough also in view of the simplicity of the approach. The proposed method has been applied to the Manfredonia case study, a small village located in the Southern Adriatic Italian coast and often prone to coastal flooding events. The comparison of extreme events estimated on the basis of hindcast levels time series is satisfactorily similar to those estimated on the basis of observed tide series.

Characterization of Coastal Flood Damage States for Residential Buildings

AbstractRisk management programs and catastrophe models use fragility and vulnerability curves extensively. For the case of coastal flood events, the independent variable for these damage functions...

EROSION AND BREACHING OF COASTAL BARRIERS IN A CHANGING CLIMATE: ASSOCIATED PROCESSES AND IMPLICATION FOR CONTAMINATION OF COASTAL AQUIFERS

Europe and many other countries all over the world are often surrounded by coastal defence systems (e.g. protective dunes and dykes) in order to protect coastal areas from threats of wave attack, storm surges and subsequent coastal floods. During moderate sea conditions, wave attack and coastal erosion is limited to nearshore areas and may only cause shore erosion. Under the same conditions, fresh groundwater, which is hydraulically interconnected with seawater, is in equilibrium with the laterally intruding seawaters. Such equilibrium prevails as long as the moderate sea level (MSL) and the hydrogeological conditions at the sea/land boundary are stationary. However, during extreme storm surges, the higher water levels may temporally threaten the coastal defence systems. In fact, shortwaves riding on the temporally rising sea level during storm surge events may directly runup, rundown and/or impact on barriers, possibly causing seaward erosion followed by lowering of barrier’s crest and hence wave overtopping or overflow through combined surge and waves. As a result, barriers may breach, inducing coastal inundation and subsequent vertical saltwater intrusion (VSWI) behind the breached barriers due to the vertical infiltration of inundating seawater into the fresh groundwater. In this study, a new integral physically based methodology is developed to reliably assess the possible implications of extreme storm surges on the safety of coastal barriers and the implications of possible breaching for contamination of coastal aquifers. The integral model is therefore capable to successively simulate breaching/overtopping of coastal barriers forced by storm surges as a hydraulic load, induced flood propagation in the hinterland and subsequent VSWI into coastal aquifers while considering the complexity of these processes and mutual interaction among them. The modelling methodology consists of an improved XBeach code (Roelvink et al., 2009) for hydro-morphodynamics unidirectionally coupled with the SEAWAT code (Langevin et al., 2008) for groundwater flow. The model is applied to a case study in northern Germany, showing that marine floods represent a serious threat to usability of coastal aquifers which are extremely important water resources. Outcomes of model application showed that a coastal flood event of a few hours may contaminate coastal aquifers for many decades, thus reducing the agricultural yield and hindering the sustainable development in coastal areas prone to coastal floods. This study represents, to the knowledge of the author, the first systematic research study that addresses the safety of natural coastal sandy barriers under extreme storm surge conditions together with the consequences of possible barrier breaching and overwash on subsequent flooding and saltwater intrusion into fresh groundwater. Moreover, it is probably the foremost study that attempts to mitigate storm-driven saltwater intrusion through the use and modelling of a subsurface drainage network. Besides improving the agricultural yield in coastal areas, the use of subsurface drainage network significantly reduces the natural remediation interval required for aquifers recovery after a coastal flood event. Moreover, it limits the vertical extent of the salt intrusion. The multiple flow domains and aspects discussed in this research make it a multi-disciplinary study that is quite relevant for the coastal engineering community, for flood risk managers, for coastal hydrologists, for groundwater suppliers as well as for sustainable development planners.

RISK ANALYSIS FOR COASTAL FLOODING UNDER CLIMATE CHANGE

Climate change and increases in population density in coastal areas might increase the difficulty of coastal management decision-making. Although recent research has proposed several flood risk assessment methods in response to climate change, few approaches have addressed all significant effects. Therefore, this study aims to establish a thorough method to evaluate the risks of future coastal flooding events, including all climate change effects. The study proposes an advanced risk analysis scheme that covers all annual flood events during a target term. To confirm the effectiveness of the proposed model, this study applies the model to actual risk analysis in the North Somerset coast in the UK under 10 different cases.