Hard Defences Research Articles

Prioritising local sea level rise adaptation pathways in Shenzhen and Hong Kong using cost-benefit analysis

Local governments face urgent challenges from sea-level rise (SLR), impacting coastal urban areas significantly. Despite a shared commitment to adapting to climate change and SLR-induced hazards, strategies for SLR adaptation vary significantly between cities, reflecting a spectrum of political, socio-economic, and cultural contexts. This paper examines potential SLR adaptation strategies in Shenzhen and Hong Kong, cities with different political and socio-economic frameworks, to understand the effectiveness of varied local adaptation pathways to meet adaptation objectives. Through an analysis of shoreline adaptation infrastructures, including natural shelters and hard defense structures, alongside historical coastal reclamation data from 1985 to 2020, we identify the most cost-effective adaptation pathway. Specifically, our cost-benefit analysis reveals that Shenzhen's “Hybrid management” pathway offers superior economic efficiency, increasing benefits by up to 63% for only a 7%–16% rise in protection costs. Conversely, Hong Kong's “Relative-risk Reduction” pathway shows less timely adaptation actions, indicating a need for more dynamic approaches. The findings highlight the pitfalls of overly rigid SLR adaptation strategies and the necessity for flexible, transition-capable adaptation pathways to better manage future uncertainties. Lessons learned from this study will enable refinement of local SLR adaptation pathway approaches and could significantly improve decision-making under uncertainty in other coastal cities based on investment perspective.

Managing rising residual flood risk: A national survey of Aotearoa‐New Zealand

AbstractFlooding is one of the most frequent and costliest natural hazards around the world. Traditionally, flood risk management has relied on building protective structures such as levees and dams to protect assets based on historical data (e.g., 1% AEP flood), which encourages development on floodplains, provides a potentially false sense of security to communities, particularly in the context of climate change, and increases residual flood risk (the risk remaining after implementing risk reduction measures). This article aims to contribute to the management of residual risk by drawing on empirical findings from a survey carried out with flood risk practitioners from the public and private sector in Aotearoa New Zealand. Findings indicate fundamental concerns relating to how to best manage residual flood risk, despite its long profile and integration in current policy and practice. Other issues revolve around the use of outdated information to guide decisions and the lack of regulatory power to restrict developments in flood‐prone areas protected by hard defense structures. Identified barriers to improving current practice include the lack of national guidance and support, financial resources, public awareness, and some technical constraints such as uncertainties in flood modeling, staff expertise, and data availability.

Sediment and bottom water eDNA metabarcoding to support coastal management

Ocean sprawl and climate change exacerbate coastal erosion and flooding, resulting in habitat loss and decreasing biodiversity. To counteract these threats, different coastal defence tools have been developed, with an increasing emphasis on nature-based solutions. However, tracking the impacts of these interventions on marine benthic organisms requires appropriate sampling designs and timely investigation methods due to the dynamic nature of coastal environments. Environmental DNA metabarcoding is a promising, non-invasive, and quick technique to monitor community changes. Here, environmental DNA COI-based metabarcoding data from sediment and bottom water samples were used to characterize benthic communities at three sites along the Emilia-Romagna coast differing in the topology of coastal defence actions (from no defences to groynes and low-crested barriers) and to evaluate the effectiveness of the two sampling matrices in detecting local biodiversity. The findings revealed significant differences in the structure of the benthic communities depending on site, sample type (i.e., sediment versus bottom water), and their interaction. The three sites differ in abiotic characteristic affecting the community composition. Lido di Dante and Riccione showed higher species diversity due to the new type of substrata provided by the hard defence structure, while Foce del Bevano showed the presence of species typical of low impacted areas. Bottom water, hosting more traces of pelagic and nektonic species, showed significantly different species composition compared to sediment samples, suggesting the need to consider both matrices in coastal monitoring.

Identifying opportunities for living shorelines using a multi-criteria suitability analysis

The need to develop more sustainable solutions for coastal hazard risk reduction and to protect and restore degraded coastal habitats has led to an increased interest in living shorelines. A barrier to the wider implementation of living shorelines is a lack of guidance on where it is suitable to implement these solutions. We developed a shoreline suitability model to select areas of a representative coastline that would be either suitable for a soft (natural habitats only) or hybrid (natural habitats in combination with hard structures) approaches. We created species distribution models in MaxEnt to predict the potential distribution of 14 coastal species including four seagrasses, one mangrove, three saltmarsh, three shellfish and three dune species. These were combined in a multi-criteria analysis that also accounted for the accommodation (current space in the intertidal) and adaptation space (amount of space between the intertidal and nearest infrastructure) available to implement living shorelines at a 250 m resolution. This was done for the state of Victoria, Australia as a case study location where there is a high percentage of coastal infrastructure reaching the end of its design life. For the Victorian coastline 74% was suitable for hybrid approaches, while 65% was suitable for soft approaches and 4% of the coastline was not suitable for either approach. For the coastline already protected with hard defence structures, 67 and 69% would be suitable for at least one taxa, using a soft or hybrid approach, respectively. The percentage of coastline suitable for soft or hybrid approaches was similar in rural areas, however, suitability for hybrid was greater than soft approaches in urban and built-up areas, which could be due to a combination of habitat suitability and space available on the foreshore. This study has demonstrated how spatial multi-criteria analysis can be adapted to a complex coastal environment and inform more diverse coastal hazard mitigation actions to risk reduction and climate adaptation.

On simulating shoreline evolution using a hybrid 2D/one-line model

Hybrid 2D/one-line shoreline models are becoming increasingly applied over the mesoscale (10 1 –10 2 years; 10 1 –10 2 km) to inform coastal management. These models typically apply the one-line theory to simulate changes in shoreline morphology based on littoral drift gradients calculated from a 2DH coupled wave, flow, and sediment transport model. However, the key boundary conditions needed to effectively apply hybrid 2D/one-line models and their applicability beyond simple planform morphologies are uncertain, which can potentially comprise coastal management decisions. To address these uncertainties, an extensive numerical modelling campaign is carried out to both assess the sensitivity and calibrate an advanced hybrid 2D/one-line model (MIKE21) against six variables in three different sandy coastal system morphologies: (a) a simple planform morphology with a gentle sloping profile, (b) a simple planform morphology with a steep sloping profile, and (c) a complex planform morphology. The six variables considered include nearshore discretisation, bathymetry, bed friction, sand grain diameter, sand porosity, sediment grading, and the weir coefficient of hard defence structures. Five key conclusions are derived from the sensitivity testing and calibration results. First , the optimal boundary conditions for modelling shoreline evolution vary according to coastal geomorphology and processes. Second , specifying boundary conditions within physically realistic ranges does not guarantee reliable shoreline evolution predictions. Third , nearshore discretisation should be treated as a typical calibration parameter as (a) the finest discretisation does not guarantee the most accurate predictions, and (b) defining a discretisation based on process length scales also does not guarantee reliable predictions. Fourth , hybrid 2D/one-line models are not valid for application in complex planform morphologies plausibly because of the one-line theory assumption of a spatially invariable closure depth. Fifth , hybrid 2D/one-line models have limited applicability in simple planform morphologies where the active beach profile is subject to direct human modification, plausibly due to the one-line theory assumption of a constant time-averaged coastal profile form. These findings provide key theoretical insights into the drivers of shoreline evolution in sandy coastal systems, which have practical implications for refining the continued application of shoreline evolution models. • The hybrid 2D/one-line shoreline modelling approach is tested in three coastal morphologies. • Optimal boundary conditions correspond to observed coastal morphology. • The nearshore discretisation in shoreline models should be treated as a calibration parameter. • The hybrid 2D/one-line shoreline modelling approach is limited to simple planform morphologies.

Analysis of Hydraulic Characteristics According to the Cross-Section Changes in Submerged Rigid Vegetation

<i>Recently, not only Korea but also the world has been suffering from problems related to coastal erosion. The hard defense method has been primarily used as a countermeasure against erosion. However, this method is expensive and has environmental implications. Hence, interest in other alternative methods, such as the eco-friendly vegetation method, is increasing. In this study, we aim to analyze the hydraulic characteristic of submerged rigid vegetation according to the cross-sectional change through a hydraulic experiment and numerical simulation. From the hydraulic experiment, the reflection coefficient, transmission coefficient, and energy dissipation coefficient were analyzed according to the density, width, and multi-row arrangement of the vegetation zone. From numerical simulations, the flow field, vorticity distribution, turbulence distribution, and wave distribution around the vegetation zone were analyzed according to the crest depth, width, density, and multi-row arrangement distance of the vegetation zone. The hydraulic experiment results suggest that the transmission coefficient decreased as the density and width of the vegetation zone increased, and the multi-row arrangement condition did not affect the hydraulic characteristics significantly. Moreover, the numerical simulations showed that as the crest depth decreased, the width and density of vegetation increased along with vorticity and turbulence intensity, resulting in increased wave height attenuation performance. Additionally, there was no significant difference in vorticity, turbulence intensity, and wave height attenuation performance based on the multi-row arrangement distance. Overall, in the case of submerged rigid vegetation, the wave energy attenuation performance increased as the density and width of the vegetation zone increased and crest depth decreased. However, the multi-row arrangement condition did not affect the wave energy attenuation performance significantly.</i>

Understanding perceived effectiveness of a novel coastal management project: The case of the Bacton-Walcott sandscaping scheme, UK

Adaptation at actively receding coastal areas requires swift and long-term solutions that build resilience for both people and the environment. Nature-based solutions are increasingly being promoted over hard defences, but there is a lack of empirical research on the effectiveness of novel approaches, including those deployed at different scales. Sandscaping, a one-off large-scale deposition of sand (1.8 M m3) on a beach frontage, was implemented for the first time in the UK at a section of beach between Bacton and Walcott villages, in North Norfolk, in 2019. The purpose of sandscaping in this location was primarily to protect the nationally important gas terminal, and neighbouring villages from coastal erosion and flooding. This study investigates the perceived effectiveness and impacts of sandscaping on coastal residents, by eliciting views of residents in the two closest villages to the scheme, and comparing findings to geomorphological observations (using LiDAR data). A survey of Bacton and Walcott residents was distributed in January 2022, with n=77 responses. Results reveal wide differences in perceptions, and notable levels of doubt, on the ‘effectiveness’ of sandscaping at present and in the future, alongside different lived experiences of the scheme and prevailing distrust by some residents about coastal management. Keeping residents updated on changes to sandscaping with environmental data and communicating the advantages of nature-based solutions appear relevant in this context, but the diversity and contrast of resident perceptions illustrates deeper challenges for future coastal management planning. There is a need to think through how future coastal change can be planned for, drawing upon multiple social perspectives. This paper also illustrates that ‘effectiveness’ of sandscaping should be more widely examined in relation to the experiences and perspectives of those impacted by the scheme, and beyond evaluations of geomorphological change.

Where land meets sea: Islands, erosion and the thing-power of hard coastal protection structures

In the last few decades, hard coastal protection structures, such as seawalls and groynes, have become increasingly commonplace around the world. Conventionally, the effects of such structures have been considered within a modernist framework that evaluates the degree of human control over the land–sea interface. However, this dominant viewpoint overlooks the central role that sea defences play in the ongoing production of coastal communities, particularly in small island states. This paper responds to these issues by revealing how coastal protection structures, as contingently performed material configurations, are devised and come into being and the social relations that these structures create and influence. Drawing on empirical research undertaken on a small island in the Maldives over a period of 6 years, the paper demonstrates not only the challenges that coastal communities face in attempting to exert control over the unruly sea but also the thing-power of the protection measures themselves that are made and unmade as part of this process. These findings suggest the need for sensitivity towards the social roles and effects of hard coastal protection structures when devising approaches and policies that might see the decommissioning of such structures in favour of softer, ‘nature-based’ responses to the vitality of the non-human world. As structures with their own unique material complexities, hard defence measures are deeply involved in the production of multinatural island futures.

An Empirical Study on the Setting and Evaluation Method of the Controlled Coastlines according to the Hard Defense of Coastal Improvement Project

In this study, the appropriateness of structure layout design was reviewed by conducting on empirical study on Namhangjin beach to which the hard defense was applied so that an efficient layout design could be made when the hard defense construction was applied in the future coastal improvement projects. As for the research method, the controlled coastlines was set for the target beach, the evaluation shoreline was calculated for the structure, and the accuracy was reviewed by comparing it with the shoreline survey data after the project. In the case of Namhangjin beach, the feasibility of the coastal improvement project was confirmed by this study, and improvements in the wave height transmission rate ERF calculation formula were confirmed.

An integrated study of wave attenuation by vegetation

Coastal protection is an important issue. For many years, protection of coastal areas has been approached from an engineering perspective, creating hard defences to withstand wave forces. However, ‘soft engineering’ alternatives that blend in with the natural environment. Vegetation such as seagrass can dissipate wave energy, acting as a natural barrier. In contrast to hard defences, there are currently limited design guidelines for designing soft defences based on vegetation. Here, we present a mathematical model of wave attenuation by vegetation. Of interest is whether a relatively simple wave model is capable of capturing the attenuation of wave energy by vegetation. Specifically, whether the attenuation of short and long waves can be mimicked through the introduction of a linear drag or diffusion term in the momentum equation. The model is based on the shallow water equations. To accommodate the dispersive effect that appears in short waves, we modified the model further to include the hydrodynamic pressure. The equations are solved numerically using a free-damping-error method. Analytical solutions derived for the case where the seabed is flat are used to verify the computational solutions. In addition, results of laboratory experiments of wave attenuation by artificial seagrass provide additional testing of the computational model. Extremely good agreement between computations and analytical solutions was found. In comparisons with the laboratory experiments, the best results with the computational model were found using diffusion for long waves and using a simple drag term for short waves. Wave attenuation was also found to depend strongly on the dimension of the vegetated area.

Canada’s and Russia’s Security and Defence Strategies in the Arctic: A Comparative Analysis

This comparative article reveals how the general focus of Canadian and Russian threat perceptions in the Arctic have shifted from a Cold War fixation on hard defence to accommodate soft security issues over the last three decades. Both countries now pay greater attention to threats and challenges stemming from climate change, security, and safety risks associated with resource development and increasingly accessible sea routes. Although concern about military conflict arising from Arctic disputes continues to frame some media discussions in both countries, most strategic analysts and academics have moved away from this line of argument. Instead, military functions now include assertion of Canadian and Russian sovereignty over their respective internal waters, as well as protection of resources in their exclusive economic zones and on and in extended continental shelves; protection of economic interests in the North, including mineral and bio-resources; prevention of potential terrorist attacks against critical industrial and state infrastructure; and dual-use functions, such as search and rescue operations, surveillance of air and maritime spaces, support to safe navigation, and mitigation of natural and human-made catastrophes. The authors argue that analysts should parse two forms of military modernization in the Arctic: one of capability development related to the global strategic balance, where the Arctic serves as a bastion or a thoroughfare; and a second intended to address emerging non-traditional security challenges. They contend that these modernization programs do not inherently upset the Arctic military balance and need not provoke a regional arms race.

Cuticular Hydrocarbon Profile of Parasitic Beetles, Aethina tumida (Coleoptera: Nitidulidae).

Simple SummarySocial insects use cuticular hydrocarbons for chemical recognition and communication. Cuticular hydrocarbons can also be exploited by parasites to their advantage for undermining host recognition systems. The small hive beetle (SHB) is a parasite of honey bee colonies but can also infest nests of other bee species. However, its chemical profile is still not known. For the first time, the present study investigated the SHB chemical profile and compared it with that of its honey bee host. The results show that the SHB has a low chemical profile that is similar to its honey bee host’s. However, while honey bees had a clear colony-specific chemical profile, SHBs did not. The generic chemical profile of the SHB is most likely linked to its free-flying behaviour in the field as these parasites are known to switch between host colonies, possibly limiting the acquisition of a colony specific chemical profile. Our findings also suggest that SHBs do not exploit any finely tuned chemical strategy to conceal their presence inside host colonies and probably rely on behavioural adaptations.Cuticular hydrocarbons (CHCs) cover insects’ bodies and play important roles in chemical communication, including nestmate recognition, for social insects. To enter colonies of a social host species, parasites may acquire host-specific CHCs or covertly maintain their own CHC profile by lowering its quantity. However, the chemical profile of small hive beetles (SHBs), Aethina tumida, which are parasites of honey bee, Apis mellifera, colonies, and other bee nests, is currently unknown. Here, adults of SHB and honey bee host workers were collected from the same field colonies and their CHC profiles were analysed using GC-MS. The chemical profiles of field-sampled SHBs were also compared with those of host-naive beetles reared in the laboratory. Laboratory-reared SHBs differed in their CHC profiles from field-sampled ones, which showed a more similar, but ten-fold lower, generic host CHC profile compared to host workers. While the data confirm colony-specific CHCs of honey bee workers, the profile of field-collected SHBs was not colony-specific. Adult SHBs often commute between different host colonies, thereby possibly preventing the acquisition of a colony-specific CHC profiles. An ester was exclusive to both groups of SHBs and might constitute an intraspecific recognition cue. Our data suggest that SHBs do not use any finely tuned chemical strategy to conceal their presence inside host colonies and instead probably rely on their hard exoskeleton and defence behaviours.

Coastal erosion on the north coast of Java: adaptation strategies and coastal management

Coastal erosion remains a problem for the socio-economic development of the coastal zone in the north coast of Java. This study aims to determine the coastal characteristics, shoreline changes, and adaptation strategies of the north coast of Java through satellite study and on-ground observations. The analysis covers two decadal periods of satellite data starting from 1998 to 2018. The coastal characteristic of the north coast of Java is typified by sandy, muddy, and gravelly coast. At particular coasts have been extensively modified becoming coastal structure buildings. The shoreline changes are characterized by sectors alternating between erosion and accretion, although in general indicating the erosion processses. The conversion of mangrove ecosystems into fish ponds along with an increase of coastal constructions such as groins, jetties, and seawalls may have strong influences on the coastal erosion at the particular coastal environments. Since traditional hard defense methods used so far have had more damaging than protective effects, there is a need now for the use of soft prevention alternatives and for providing new guidelines for coastal management. A set of permeable breakwater measures, in conjunction with sediment managing schemes, are proposed for the sustainable development of the coastal zone.

Anthropogenic Impact on Beach Heterogeneity within a Littoral Cell (Northern Tuscany, Italy)

In this paper the evolution of the Northern Tuscany littoral cell is documented through a detailed analysis of the increasing anthropogenic pressure since the beginning of the 20th century. This sector of the Tuscany coast has been experiencing strong erosion effects that resulted in the loss of large volumes of sandy beaches. The anthropogenic impact on natural processes have been intensified by the construction of two ports in the early decades of the 20th century. Competent authorities reacted by building hard protection structures that tried to fix the position of the shoreline but offset the erosion drive downdrift. Therefore, in the last 20 years a regional Plan was undertaken to gradually replace the hard defense schemes with a softer approach, which involved a massive use of sediment redistribution activities. Many nourishments have been done ever since, using both sand and gravel. All these hard and soft protection operations have been archived in a geodatabase, and visualized in maps that clearly show the progressive change from hard to soft defense. This database may improve the approach to any future analysis of the littoral cell both in terms of research and management, while providing a practical example that may be easily replicated elsewhere.

A Layout Design System of Hard Defense and Soft Defense Methods for Coastal Erosion Mitigation

A Layout Design System of Hard Defense and Soft Defense Methods for Coastal Erosion Mitigation

Coastal Morphology and Human Intervention in Golfo Nuevo, Patagonia Argentina

Bunicontro, M.P.; Marcomini, S.C., and Lopez, R.A., 2020. Coastal morphology and human intervention in Golfo Nuevo, Patagonia Argentina. Journal of Coastal Research, 36(4), 780–794. Coconut Creek (Florida), ISSN 0749-0208.The Patagonian coastal zone is a complex and dynamic macrotidal environment that is sparsely urbanized, except locally where large cities are located. This human occupation has affected the natural beach dynamics and induced drastic coastal changes in the past 40 years that demand a redirection of initiatives to provide a basis for management efforts. This study analyzes the coastal morphology and beach characteristics of Golfo Nuevo (Chubut, Argentina) for modelling coastal behaviour through field measurements along 17 beach profiles. Beaches were classified into four types according to their sediment grain size, morphology, and morphometric parameters (beach width and gradient). Also, the coast was divided into five categories according to the coastline morphologies and environmental quality: (1) littoral pediments, (2) cliff-top dunes and aeolian ramps, (3) active cliffs, (4) beach ridge terraces, and (5) dunes. Additionally, different human interventions were analyzed to determine how they have affected the natural coastal equilibrium. The coast was divided into low, moderate, and high levels of intervention according to the status of the landscape modification. The most shocking activities were identified as mining (gravel and sand extraction), coastal armouring with hard defences, and urban building. Indeed, the most affected and vulnerable coastal areas have been beach ridge terraces and coastal dunes. It was determined that the coastal extension affected by these human activities reaches at least 37% of the study zone, increasing beach and coastal erosion susceptibility. The coastal classification and the evaluation of human intervention were combined and used to perform an accurate zoning map of the coastal environment. This map represents an essential tool for decision makers of Puerto Madryn city, showing clearly the most vulnerable places where coastal planning strategies urgently need to be applied for a sustainable use of resources.

Influence of hard defence structures on shoreline erosion along Molise coast (southern Italy): a preliminary investigation

The 36 km long coastline of Molise region is part of the Central Adriatic coast and consists of two nearly independent physiographic sub-units separated by the rocky promontory of Termoli. The Molise shoreline has undergone significant erosion during the last 60 years that prevailingly affected the coastal segments including the major river mouths (Trigno and Biferno). Erosion has been faced mainly through engineering interventions and, nowadays, nearly 62% of the shoreline is covered by hard defence structures. In this study, the numerical model GENESIS is used to assess the potential shoreline trends, in order to evaluate the potential interference of hard defence structures. The wave climate has been reconstructed and the concept of Littoral Drift Rose (LDR) has been employed to achieve the wave parameters responsible for littoral transport. Results indicate that defence structures most likely have played a key role in shoreline recession whereby their removal could positively influence the Molise littoral regime.

Are We Managing in the Right Way the Coastal Erosion along the Caribbean Coast of Colombia?

Rangel-Buitrago, N., 2020. Are we managing in the right way the coastal erosion along the Caribbean coast of Colombia? In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 930–934. Coconut Creek (Florida), ISSN 0749-0208.Coastal erosion has become a severe problem, rising in magnitude, dominance, and extension along the Caribbean coast of Colombia. Circa 55% of this critical area for the country is undergoing severe erosion problems related to a multiplicity of factors contrasted by their degree of influence and magnitude. The management of the coastal erosion processes has been implemented via traditional hard defense options. During the last 30 years, the necessity to protect the coast with hard structures has been driven by the growing coastal zone population and political - economic pressures. At the beginning of 2019, at least 15000 both cross and hard longshore structures have been built along the coastline. These hard structures have altered the natural conditions of the study area, producing impacts such as (i) coastal hardening, (ii) reduced sediment supplies to downdrift areas, (iii) intensification of erosion processes, (iv) generation of nearby new erosion hot spots, (v) deterioration of coastal scenery quality, among others. Direct and indirect experience indicates that optimal results, on money and a time basis, can be achieved using a combination of other coastal erosion management options, such as, “accommodation,” "planned retreat," or “do nothing” solutions delivered through legally adopted coastal management plans, coordinated by one government department is urgently required. This work describes and evaluates the functionality of current coastal erosion management strategies used up to the present. It also indicates the current and future coastal erosion management scene for the region and highlights major trends and challenges faced by users, landowners, and coastal managers.

Computational Modelling of the Impacts of Saltmarsh Management Interventions on Hydrodynamics of a Small Macro-Tidal Estuary

Saltmarshes are considered as natural coastal defences. However, owing to the large context dependency, there is much discussion over their effectiveness in providing coastal protection and the necessity of additional coastal defence interventions. The macro-tidal Taf Estuary in south-west Wales was chosen as the case study in this paper to investigate the effects of anthropogenic coastal defence interventions such as construction of hard defences, managed realignment, and altering land use of the saltmarshes on the complex hydrodynamics of the estuary. A coupled flow–wave–vegetation model, developed using the Delft3D coastal modelling software, was used. The wave and current attenuation role of saltmarshes during two contrasting storm conditions was modelled, with and without saltmarsh management interventions. The study reveals that certain saltmarsh management interventions can have widespread impacts on the hydrodynamics of the estuary. Altering the land use by allowing extensive grazing of saltmarsh by livestock was found to have the largest impact on wave attenuation, where wave heights on the marsh almost doubled when compared with the no-intervention scenario. On the other hand, managed realignment has a significant impact on tidal currents, where tidal currents reached 0.5 m/s at certain locations. Changes in estuarine hydrodynamics can lead to undesired impacts on flooding and erosion, which stresses the importance of understanding the effects of localized anthropogenic coastal management interventions on the entire estuarine system.

Mortality during Hurricane Sandy: the effects of waterfront flood protection on Staten Island, New York

Hard defenses, such as levees or land berms, are often considered the most effective approach to reduce flood risk. This study reveals a potential increase in mortality when hard protections cannot defend a location against low-probability, extreme flood events. Staten Island, New York, suffered devastating damage from Hurricane Sandy, including 23 fatalities, of which 18 occurred in the neighborhoods along the island’s eastern shore. This study demonstrates that the elevated berm along the eastern shore may have contributed to the concentration of fatalities in the area by increasing the speed at which seawater rose, causing some people to be trapped in places where they could not escape rising waters. The study uses a hydrodynamic model to simulate Hurricane Sandy flood conditions, providing water depth, rise rate, and velocity. Statistical analyses show that water rise rate influences mortality, while other flood characteristics and several demographic and socioeconomic factors do not. A model experiment that qualitatively examines flood conditions in the presence of a lower discontinuous berm that historically existed at the location in Midland Beach finds that the increased height and continuity of the berm increased probability of mortality by worsening the water rise rate during Sandy by about 50%. The potential increase in mortality needs to be taken into account when designing coastal protections. If a protection strategy does not prevent low-probability, extreme floods, then there is a trade-off between protection against more frequent floods and increased risk of mortality during extreme floods.