Coastal Flood Protection Research Articles

Characterization of SDGs towards Coastal Management: Sustainability Performance and Cross-Linking Consequences

The Sustainable Development Goals (SDGs) and associated targets focus on a wide range of global issues and can be useful in coastal challenges such as climate change and green economic growth. The aim of this study is to tailor the SDGs, as a universally recognized policy framework, to assess the sustainability performance for coastal flood protection management to enhance climate-resilient and adaptable coastal development. To operationalize this aim, the SDG Sustainability Impact Score (SDG-SIS) framework was developed. Based on system functionalities for the land–sea interface, 38 SDGs were identified in the SDG-SIS framework. Given the availability of public numeric data, only 12 SDG targets are connected with Key Performance Indicators (KPIs). The SDG-SIS framework was applied to two different sets of cases, including five coastline and five sand nourishment cases. This study shows that the geographical and socioeconomic characteristics of the two sets of cases should be considered in the selection of system functionalities as well as the consideration of SDG targets. Moreover, cross-linking cumulative consequences of SIS do not directly indicate the level of sustainability, but the individual SDG target data are essential to reveal the underlying details. This stresses the importance of prioritizing SDGs to serve as leverage for policymakers to optimize the climate resilience and adaptation of coastal management. The SDG-SIS framework enables the support of coastal policy by addressing long-term measures and providing a sustainable vision for future implementation.

Regional economic analysis of flood defence heights at the German Baltic Sea coast: A multi-method cost-benefit approach for flood prevention

Mean and extreme sea-level uncertainties, as well as uncertainty about future flood exposure, hinder the risk-based optimisation of flood protection investments. To deal with these uncertainties, cost-benefit analysis (CBA) and methods for robust decision-making can be combined. This paper sequentially applies CBA, robust optimisation methods and info-gap analysis to find efficient and robust coastal flood protection strategies for the German Baltic Sea coast. The CBA results suggest that – under flood risk assumptions – a share of the coast of Schleswig-Holstein (9.3–10.1%; 60–65 km) and Mecklenburg-Vorpommern (4.1–10.0%; 78–189 km) with relatively high flood exposure, might currently be under-protected from a social welfare perspective. Present Value estimates of regional investment costs of five regret or loss minimising strategies range from 1.7 to 4.8 billion Euro across robustness metrics at 3% discounting. The info-gap analysis suggests that some of these strategies will fail to prevent large-scale damages under high-end scenarios. We conclude that a multi-method cost-benefit approach can be used to narrow down the number of solutions that are both potentially efficient and sufficiently robust by investigating strategy performance within, across and beyond predefined scenarios.

Dune Systems’ Characterization and Evolution in the Andalusia Mediterranean Coast (Spain)

This paper deals with the characterization and evolution of dune systems along the Mediterranean coast of Andalusia, in the South of Spain, a first step to assess their relevant value in coastal flood protection and in the determination of sound management strategies to protect such valuable ecological systems. Different dune types were mapped as well as dune toe position and fragmentation, which favors dune sensitivity to storms’ impacts, and human occupation and evolution from 1977 to 2001 and from 2001 to 2016. Within a GIS (Geographic Information System) project, 53 dune systems were mapped that summed a total length of ca. 106 km in 1977, differentiating three dune environments: (i) Embryo and mobile dunes (Type I), (ii) grass-fixed dunes (Type II) and (iii) stabilized dunes (Type III). A general decrease in dunes’ surfaces was recorded in the 1977–2001 period (−7.5 × 106 m2), especially in Málaga and Almería provinces, and linked to dunes’ fragmentation and the increase of anthropic occupation (+2.3 × 106 m2). During the 2001–2016 period, smaller changes in the level of fragmentation and in dunes’ surfaces were observed. An increase of dunes’ surfaces was only observed on stable or accreting beaches, both in natural and anthropic areas (usually updrift of ports).

Potential Impacts of Future Urbanization and Sea Level Rise on Florida's Natural Resources

Abstract As urban development continues to encroach into natural systems, these ecosystems experience increasing degradation to their form and function. Changing climatic conditions further compound the losses in biodiversity and ecosystem function. The state of Florida is known for its biodiversity but has experienced declines in species populations and habitats because of urbanization and sea level rise. Because Florida benefits from a multibillion-dollar income from natural resources tourism, these declines challenge the state's economy. In this study, we assessed the potential future impacts of urbanization and sea level rise on a suite of conservation targets that have been set for the state. We developed six scenarios of all combinations of intermediate and high sea level rise paired with two types of urbanization, sprawling and compact, in both 2040 and 2070 to examine the potential future threats to conservation targets in High Pine and Scrub, Coastal Uplands, and Freshwater Aquatics ecosystems. Our results show projected decreases in extent and area of these priority ecosystems into the future. Under Florida's current trends in urbanization practices, projections indicate a greater impact on conservation targets than if sprawl reduction practices are implemented. Projections indicate that Coastal Uplands will experience the greatest loss in area, at up to 47%. Conservation-focused urban planning and climate adaptation strategies can help protect Florida's natural resources with benefits to Florida's tourism economy as well as critical ecosystem functions and services such as coastal flood protection and storm surge risk reduction.

Valuing natural habitats for enhancing coastal resilience: Wetlands reduce property damage from storm surge and sea level rise.

Storm surge and sea level rise (SLR) are affecting coastal communities, properties, and ecosystems. While coastal ecosystems, such as wetlands and marshes, have the capacity to reduce the impacts of storm surge and coastal flooding, the increasing rate of SLR can induce the transformation and migration of these natural habitats. In this study, we combined coastal storm surge modeling and economic analysis to evaluate the role of natural habitats in coastal flood protection. We focused on a selected cross-section of three coastal counties in New Jersey adjacent to the Jacques Cousteau National Estuarine Research Reserve (JCNERR) that is protected by wetlands and marshes. The coupled coastal hydrodynamic and wave models, ADCIRC+SWAN, were applied to simulate flooding from historical and synthetic storms in the Mid-Atlantic US for current and future SLR scenarios. The Sea Level Affecting Marshes Model (SLAMM) was used to project the potential migration and habitat transformation in coastal marshes due to SLR in the year 2050. Furthermore, a counterfactual land cover approach, in which marshes are converted to open water in the model, was implemented for each storm scenario in the present and the future to estimate the amount of flooding that is avoided due to the presence of natural habitats and the subsequent reduction in residential property damage. The results indicate that this salt marshes can reduce up to 14% of both the flood depth and property damage during relatively low intensity storm events, demonstrating the efficacy of natural flood protection for recurrent storm events. Monetarily, this translates to the avoidance of up to $13.1 and $32.1 million in residential property damage in the selected coastal counties during the ‘50-year storm’ simulation and hurricane Sandy under current sea level conditions, and in the year ‘2050 SLR scenario’, respectively. This research suggests that protecting and preserving natural habitats can contribute to enhance coastal resilience.

Fish assemblages associated with coastal defence structures: Does the surrounding habitat matter?

Artificial structures are sprawling along seashores due to growing populations, coastal use and greater need for coastal erosion and flood protection. The impacts of these anthropogenic modifications of coastlines on fish populations are poorly described, and little is known about factors affecting the ecological performance of these novel habitats for fish. We compared the abundance and community structure of fish assemblages associated with artificial coastal defence structures built in either rocky or sedimentary contexts at two locations along the coast of Sicily, to explore whether the performance of the artificial habitats for fish changed in relation to the characteristics of the surrounding natural habitat. We also quantified how fish associated with artificial structures in either habitat contexts differed from that at nearby natural rocky reefs. We found that fish assemblages differed in abundance and structure between artificial coastal defences deployed in sandy contexts vs natural rocky reefs, with different ecological taxa showing greater (i.e. benthic carnivorous) or lower (i.e. serranids) abundances in the artificial habitat. We also found that fish assemblages associated to artificial structures built on rocky bottoms had inconsistent outcomes, more frequently grouping with artificial sandy habitats at one location and with natural rocky reefs at the other. These results suggest that the surrounding environmental setting could have an overriding, and so far largely overlooked, importance in affecting the performance of artificial structures as habitats and in facilitating the development of fish assemblage with distinctive composition and structure.

Applying Uncertain Science to Nature-Based Coastal Protection: Lessons From Shallow Wetland-Dominated Shores

Climate change and associated sea-level rise alongside the potential for alterations in the magnitude and frequency of extreme storm events, rapidly rising coastal populations, and a legacy of coastal land reclamation have led to the consideration of nature-based approaches towards coastal flood and erosion protection over recent years. The descriptions of such approaches highlight the flood protection value of natural coastal features but examples of their implementation remain few and far between and nature-based solutions to the rising coastal flood and erosion risk can certainly not (yet) be considered mainstream. One key problem around the implementation of these types of approaches has, arguably, been the relative lack of perceived scientific certainty, amongst stakeholders, surrounding the efficiency with which natural landforms reduce wave action on landward lying structures and the persistence of such landforms in an uncertain future. This makes nature-inclusive approaches less attractive to more traditional engineering-only approaches that rely solely on one ‘hard’ structure with a well-defined impact on waves and a specified design life. Using existing evidence for the coastal protection function of salt marshes, this paper offers a new perspective on this apparent lack of scientific certainty by offering a ‘no-regret’ application of existing science that allows decision makers and coastal planners to implement nature-inclusive approaches to coastal flood and erosion risk reduction measures with greater confidence.

Attenuation of Storm Surges by Coastal Mangroves

AbstractThe interaction between mangroves and storm surges is explored using an analytical solution. A simplified momentum equation, balancing vegetation drag and pressure gradient, is combined with the continuity equation resulting in a diffusion equation. Assuming a simplified environment, a one‐dimensional analytical solution is obtained to predict peak surge level across a forest. The solution accurately reproduces peak water level of a 10‐year return period flood event in mangroves in the Firth of Thames, New Zealand, and in Ten Thousand Islands, Florida, during Hurricane Charley. Vegetation properties that determine the capacity of mangroves to reduce surges are forest density and cross‐shore extent. Storm characteristics—flood duration and peak water level at the forest fringe—also influence surge attenuation. Mangroves are shown to be an effective form of coastal flood protection if forests are sufficiently wide/dense, relative to the surge decay length scale, to restrict water exchange during a storm.

Maintaining Tropical Beaches with Seagrass and Algae: A Promising Alternative to Engineering Solutions

Tropical beaches provide coastal flood protection, income from tourism, and habitat for flagship species. They urgently need protection from erosion, which is being exacerbated by changing climate and coastal development. Traditional coastal engineering solutions are expensive, provide unstable temporary solutions, and often disrupt natural sediment transport. Instead, natural foreshore stabilization and nourishment may provide a sustainable and resilient long-term solution. Field flume and ecosystem process measurements, along with data from the literature, show that sediment stabilization by seagrass in combination with sediment-producing calcifying algae in the foreshore form an effective mechanism for maintaining tropical beaches worldwide. The long-term efficacy of this type of nature-based beach management is shown at a large scale by comparing vegetated and unvegetated coastal profiles. We argue that preserving and restoring vegetated beach foreshore ecosystems offers a viable, self-sustaining alternative to traditional engineering solutions, increasing the resilience of coastal areas to climate change.

A review of coastal management approaches to support the integration of ecological and human community planning for climate change

The resilience of socio-ecological systems to sea level rise, storms and flooding can be enhanced when coastal habitats are used as natural infrastructure. Grey infrastructure has long been used for coastal flood protection but can lead to unintended negative impacts. Natural infrastructure often provides similar services as well as added benefits that support short- and long-term biological, cultural, social, and economic goals. While natural infrastructure is becoming more widespread in practice, it often represents a relatively small fraction within portfolios of coastal risk-reducing strategies compared to more traditional grey infrastructure. This study provides a comprehensive review of how natural infrastructure is being used along the United States Atlantic, Gulf of Mexico, and Caribbean coasts related to four habitats – tidal marshes, beaches and barrier islands, mangroves, and biogenic reefs. We compare information on the benefits, opportunities and challenges of implementing natural, grey and hybrid infrastructure in the coastal zone. In addition, we present a suite of actions to increase information and reduce uncertainty so that coastal mangers and planners are aware of the full suite of options for restoration, conservation and planning that maximize ecosystem services over short- and long-term planning horizons.

Integrating Stormwater Management with Coastal Flood Protection

Integrating Stormwater Management with Coastal Flood Protection

Potential of marshes to attenuate storm surge water level in the Chesapeake Bay

AbstractStorm surges from tropical and extratropical storms frequently impact coastal communities globally. While the potential of natural and nature‐based features for coastal defenses has gained increased attention as a viable option for coastal flood protection, the lack of in situ measurements of storm surge attenuation has delayed their widespread utilization. We present the findings of a 3‐yr water level monitoring campaign that resulted in a large collection (52 flood events) of attenuation rates from marsh transects located in two natural preserves in the U.S. mid‐Atlantic region. Results show that the overall marsh attenuated water levels, exhibiting values up to 0.02 cm/m at Eastern Shore of Virginia National Wildlife Refuge (ES) and 0.03 cm/m at Magothy Bay Natural Preserve (MGB). In general, the greatest attenuation rates were observed at the marsh edge section. The reach close to the coastline revealed an amplification of the water level followed by water level attenuation toward the backside of the marsh. However, analyses of five major storms at ES demonstrated that, within each event, the ability of the upper marsh to attenuate water level decreased with higher inundation heights. Additionally, small spatial scales of the marsh platform, geomorphological features such as channels, elevated surrounding forests and levees seem to play a major role in reducing the attenuation rates provided by the marshes. These results indicate that, while this type of marshland would provide storm surge attenuation during low inundation heights, these ecosystems would be less effective attenuating higher water depths from extreme events.

Influence of risk factors and past events on flood resilience in coastal megacities: Comparative analysis of NYC and Shanghai

Coastal flood protection measures have been widely implemented to improve flood resilience. However, protection levels vary among coastal megacities globally. This study compares the distinct flood protection standards for two coastal megacities, New York City and Shanghai, and investigates potential influences such as risk factors and past flood events. Extreme value analysis reveals that, compared to NYC, Shanghai faces a significantly higher flood hazard. Flood inundation analysis indicates that Shanghai has a higher exposure to extreme flooding. Meanwhile, Shanghai's urban development, population, and economy have increased much faster than NYC's over the last three decades. These risk factors provide part of the explanation for the implementation of a relatively high level of protection (e.g. reinforced concrete sea-wall designed for a 200-year flood return level) in Shanghai and low protection (e.g. vertical brick and stone walls and sand dunes) in NYC. However, individual extreme flood events (typhoons in 1962, 1974, and 1981) seem to have had a greater impact on flood protection decision-making in Shanghai, while NYC responded significantly less to past events (with the exception of Hurricane Sandy). Climate change, sea level rise, and ongoing coastal development are rapidly changing the hazard and risk calculus for both cities and both would benefit from a more systematic and dynamic approach to coastal protection.

Usability of the climate-resilient nature-based sand motor pilot, The Netherlands

Coastline maintenance in the Netherlands, formally in place since 1990, aims at a sustainable preservation of coastal flood protection. Over 25 years annual assessments, comparing the actual coastline positions with the 1990 reference position of the coastline, have governed the execution of sand nourishments following an adaptive management method. This method involves yearly assessment of the coastline based on measurements, design and adoption of nourishment strategies and measures and execution of the nourishments. This management approach has enabled learning and introduction of innovations in coastline maintenance. For instance, in comparison to the early nineties, nourishments are now placed more on the foreshore and the yearly nourishment budget has doubled. The most recent innovation in coastline maintenance is the ‘Sand Motor’, a nature-based nourishment approach, which concentrates the regular nourishments in space and time, given that natural processes should redistribute the sediment over the wider coastal system. In contrast to regular nourishments, the Sand Motor combines flood protection with nature and recreational objectives and is much larger in dimensions. Five years after the construction of the Sand Motor we investigate its usability in this article. We present the results of first Sand Motor evaluation and draw conclusion on the adoption and usefulness of it for coastline management from the perspective of the adaptive management method used in coastline maintenance. Recent evaluation of the monitoring data shows that the large amount of sand used for the Sand Motor has a positive impact on coastal protection. Bridging between the Sand Motor pilot and daily nourishement practice is however not yet achieved.

Overview and Design Considerations of Storm Surge Barriers

The risk of flooding in coastal zones is expected to increase due to sea level rise and economic development. In larger bays, estuaries, and coastal waterways, storm surge barriers can be constructed to temporarily close off these systems during storm surges to provide coastal flood protection. Worldwide, 18 storm surge barriers have been constructed thus far, but they are increasingly being considered as a future solution for other coastal locations. This study provides a systematic overview of existing storm surge barriers. It analyzes information about the main functions of each barrier, the type of gates used, and the associated costs. It also shows that functional requirements determine the design and layout of the barrier. The main design challenges are discussed. The study results may be of use in future planning and preliminary storm surge barrier design

Coastal flood protection by a combined nature-based and engineering approach: Modeling the effects of marsh geometry and surrounding dikes

As ecosystem-based adaptation to global change is gaining ground, strategies to protect coastal and estuarine areas from increasing flood hazards are starting to consist of natural tidal wetland conservation and restoration in addition to conventional coastal defense structures. In this study, the capacity of tidal wetlands to locally attenuate peak water levels during storm tides is analyzed using a two-dimensional hydrodynamic model (TELEMAC2D) for a 3000 ha intertidal marsh (SW Netherlands). Model results indicate that peak water level reduction largely varies between individual flooding events and between different locations in the marsh. Model scenarios with variable dike positions show that attenuation rates can be minimized by blockage and set up of water levels against dikes or other structures confining the marsh size. This blockage only affects peak water level attenuation across wetlands if the duration of the flood wave is long compared to the marsh size. A minimum marsh width of 6–10 km is required to completely avoid blockage effects for the storm tidal cases assessed in this study. If blockage does not affect flood wave propagation, variations in attenuation rates between different locations in the marsh and between tides with varying high water levels can be explained with a single relationship based on the ratio between the water volume on the marsh platform and the total water volume on the platform and in the channels. Attenuation starts to occur when this ratio exceeds 0.2–0.4 and increases from there on up to a maximum of 29 cm/km for a ratio of about 0.85. Furthermore, model scenarios with varying marsh channel depth show that marsh scale attenuation rates increase by up to 4 cm/km if the channel elevation is raised by 0.7 m on average. Conversely, marsh scale attenuation rates decrease by up to 2 cm/km for scenarios in which the channels are lowered by 0.9 m on average. The marsh platform elevation has little effect on the maximum attenuation, but it determines which tides are attenuated. In particular, only overmarsh tides that inundate the platform are attenuated, while undermarsh tides that only flood the marsh channels are not attenuated or even amplified. These findings may assist coastal communities and managers in the optimization of the coastal defense function of tidal wetlands in combination with dikes.

English

The determination of the borders and the internal structure of a coastal flood protection system, then the understanding of its behavior during past events contribute widely to determine actions to improve its performance. To set up in this domain a proven methodology, transposable in other places prone to episodes of marine floods, four sites with contrasted configurations were chosen for case studies. These sites are representative of most of the situations met during the storm Xynthia which hit the French Atlantic coast in February, 2010: - Loix is a peninsula surrounded by a set of basins and marshes, - Les Boucholeurs extends in border of a vast bay and presents houses on the sea front directly exposed to waves as well as setback constructions on the location of former leveed marshes, - Boyardville-La Perrotine is an urbanized zone crossed by a leveed canal connecting the sea front with a vast zone of swamp and a marina, - Batz-sur-Mer is characterized by salterns along which urbanization developed. These sites are structured by a network of natural features, levees, canals and ditches, road and railway infrastructures, involving many actors for their management. This paper presents case studies conclusions. It focuses on the way the main identifiable stakes were actually protected during the passage of the storm Xynthia.

Coastal flood protection systems – concepts and analysis

Storm Xynthia, which hit French coasts on February 28th, 2010, flooded vast territories despite coastal defences. This disaster highlighted the need of studying the behaviour of our coastal flood protection systems at an adapted geographical scale and by taking into account the kinematics of the events. The research project led by Cerema has made significant breakthroughs in the knowledge of mechanisms governing the flooding and in strategies and methods dedicated to their analysis and their representation. The developed methodology was successfully tested on four sites submerged during Xynthia (Loix, Les Boucholeurs and Boyardville in Charente-Maritime, Batz-sur-mer in Loire-Atlantique). It is intented to guide the diagnosis of sites prone to marine flood, since the first investigations until the delivery of study reports.

Ranking coastal flood protection designs from engineered to nature-based

Compared to traditional hard engineering, nature-based flood protection can be more cost effective, use up less raw materials, increase system adaptability and present opportunities to improve ecosystem functioning. However, high flood safety standards cause the need to combine nature-based structures with traditional civil engineered structures. This increases complexity assessing when and how ecological and engineering objectives of such flood protection systems are achieved. This study classifies the degree to which coastal designs are nature based using criteria for ecosystem-based management (EBM). For the engineering criterion the distinction between main and supporting structures is introduced. To evaluate the ecological criterion five design concepts have been introduced, ranging from completely engineered to completely nature-based.The method results in an EBM-ranking of the coast, showing where a particular flood protection design stands on the range between completely engineered (low EBM-rank) and nature-based (high EBM-rank). It thus facilitates comparison of different flood protection systems.The method was the applied on the North-Sea coast of Belgium, the Netherlands, and Germany. The results show that combinations of civil-engineered and nature-based structures are widely applied. However, due to the overall low contribution to flood protection by the nature-based structures, about 85% of the coast is dominated by engineered structures. The majority of these stretches is located in relatively sheltered areas. Improving the flood protection capacity of the nature based structures in these areas is hard to achieve. Therefore, application of more nature-based design concepts on the main structures is the most promising way to improve the EBM-rank of many flood protection systems.

Interannual Variability of Two Offshore Sand Banks in a Region of Extreme Tidal Range

Lewis, M.J.; Neill, S.P., and Elliott, A.J., 2015. Interannual variability of two offshore sand banks in a region of extreme tidal range.Offshore sand banks play important roles for coastal flood protection and fisheries, and they are sources of marine aggregates. An 11-year record (1991–2002) of annual bathymetric surveys from two sand banks (Nash and Helwick) in the Bristol Channel (U.K.) were analysed. Both sand banks have a history of commercial dredging, and have dimensions of the order 10 km by 1 km, with a crest height rising to around 20–25 m above the surrounding sea bed. The crest at Nash Bank is exposed on the lowest spring tides, while Helwick Bank is always covered to a depth of at least 3 m. The volume of Nash Bank decreased over 10 years, and dredging was estimated to be responsible for around one third of this reduction. The volume of Helwick Bank also decreased over an 8-year period, but at a rate six times greater than the loss due to dredging. Significant interannual variability of sand bank morphology was calculated at both sites. The time during which waves alone could induce sediment transport over the sand banks was calculated between each survey date (the effective wave climate). The change in sand bank volume correlated well to the effective wave climate: a linear regression score of 77% (−0.88 Pearson correlation at the 95% significance level) and 69% (0.83 Pearson correlation at the 95% significance level) were found at Helwick and Nash, respectively. A one-dimensional morphodynamic model (UNIBEST-TC), simulated storm wave–induced changes to sand bank morphology that were consistent with those observed. Therefore, the interannual variability within storm wave events could be responsible for the observed natural variability of sand bank volume and morphology observed at both sites. We conclude that it is important to understand anthropogenic impacts upon sand banks within the context of natural variability.