Coastal Flood Protection Research Articles

Spatial Cumulative Assessment of Impact Risk-Implementing Ecosystem-Based Management for Enhanced Sustainability and Biodiversity in the Black Sea

Marine ecosystems are becoming increasingly vulnerable to cumulative anthropogenic effects and pressures. Therefore, various methodological approaches and tools have been designed to apply cumulative impact appraisal schemes and better assess the dynamics and interactions among pressures affecting marine ecosystems. This study aims to apply the Spatial Cumulative Assessment of Impact Risk for Management (SCAIRM) tool for the Black Sea coastal waters considering human activities, pressures, and effects on different ecosystem components coupled with one management scenario development for actual and new emerging sectors. According to the SCAIRM, the primary pressure on the marine ecosystem was identified as introducing or spreading non-indigenous species from shipping. Additionally, when considering cumulative impact, activities related to coastal defense and flood protection, particularly beach nourishment works, were found to have the highest impact. This is due to the cumulative scores associated with the physical loss from permanent alteration or removal of seabed substrates, and temporary or reversible physical disturbances to the seabed. The scenario development indicated that after shipping, oil and gas exploitation is anticipated to become the second-highest risk sector for additional impact in the Romanian Black Sea. Additionally, the increased military activities related to the war in Ukraine present escalating risks that must be considered in EBM strategies. The results assess the possible effects of human activities and the associated pressures to direct management toward achieving sustainability, biodiversity protection, and the marine ecosystem’s integrity.

Development of a common conceptual framework for the adaptation of coastal flood protection systems

ABSTRACT In the context of climate change, sea level rise and land planning, systemic approaches based on resilience principles are required for the adaptation of coastal areas. In this paper, a new conceptual framework is proposed in which an area and its flood protection system are considered to be two nested social-ecological systems (SESs). Other types of networks of structures, especially transportation infrastructure (ports and waterways, roads and railways) can also be represented, in relation to the areas where they are located, as nested SESs. This conceptual framework, based mainly on the concept of social-ecological resilience, is recommended to develop a common adaptation strategy shared between infrastructure managers and land use planners. It also allows the complementary use of the concepts of technical, ecological and social resilience by different actors to meet specific objectives, which may concern the management of natural or anthropogenic structures or the revision of institutions.

Large-Scale Test Of Extreme Hydrodynamic Conditions Over Coastal Salt Marshes

Hard coastal structures such as dikes covered with asphalt or placed block revetments have been widely used in the past for coastal protection in densely populated deltas around the world. Nonetheless, in recent years the effectiveness of hard structures has been questioned in light of the inevitable effects of climate change and their static nature. Decades of research on how salt marshes can play a role within a comprehensive coastal protection scheme suggest that these low environmental impact structures (Maza et al., 2015) might have the capability of dissipating wave energy and hence be technically and formally considered within hybrid coastal erosion and flood protection systems (Borsje et al., 2011). However, only very few studies investigated wave attenuation by real salt marsh vegetation in large-scale laboratories (Ghodoosipour et al., 2022; Maza et al., 2015; Möller et al., 2014) and none of them addressed extreme hydrodynamic design conditions in terms of wave energy and water levels. As a result of this knowledge gap, salt marshes in The Netherlands and all around the world have never been formally considered within the coastal flood protection systems and the underlying risk assessment. With this contribution our aim is to provide an overview of the first worldwide large-scale test focused on the interaction between a salt marsh (i.e. vegetation and shallow foreshore) and extreme hydrodynamic conditions, the adopted measurement techniques and the preliminary results in terms of wave damping, erosion and removed biomass.

Integrating mangrove growth and failure in coastal flood protection designs

Mangrove forests reduce wave attack along tropical and sub-tropical coastlines, decreasing the wave loads acting on coastal protection structures. Mangrove belts seaward of embankments can therefore lower their required height and decrease their slope protection thickness. Wave reduction by mangroves depends on tree frontal surface area and stability against storms, but both aspects are often oversimplified or neglected in coastal protection designs. Here we present a framework to evaluate how mangrove belts influence embankment designs, including mangrove growth over time and failure by overturning and trunk breakage. This methodology is applied to Sonneratia apetala mangroves seaward of embankments in Bangladesh, considering forest widths between 10 and 1000 m (cross-shore). For water depths of 5 m, wave reduction by mangrove forests narrower than 1 km mostly affects the slope protection and the bank erodibility, whereas the required embankment height is less influenced by mangroves. Sonneratia apetala trees experience a relative maximum in wave attenuation capacity at 10 years age, due to their large submerged canopy area. Once trees are more than 20 years old, their canopy is emergent, and most wave attenuation is caused by trunk and roots. Canopy emergence exposes mangroves to wind loads, which are much larger than wave loads, and can cause tree failure during cyclones. These results stress the importance of including tree surface area and stability models when predicting coastal protection by mangroves.

Life cycle assessment of green–grey coastal flood protection infrastructure: a case study from New Orleans

The study compared the life cycle environmental impacts of three coastal flood management strategies: grey infrastructure (levee), green–grey infrastructure (levee and oyster reef), and a do-nothing scenario, considering the flood damage of a single flooding event in the absence of protection infrastructure. A case study was adopted from a New Orleans, Louisiana residential area to facilitate the comparison. Hazus software, design guidelines, reports, existing projects, and literature were utilized as foreground data for modelling materials. A process-based life cycle assessment was used to assess environmental impacts. The life cycle environmental impacts included global warming, ozone depletion, acidification, eutrophication, smog formation, resource depletion, ecotoxicity, and various human health effects. The ecoinvent database was used for the selected life cycle unit processes. The mean results show green–grey infrastructure as the most promising strategy across most impact categories, reducing 47% of the greenhouse gas (GHG) emissions compared to the do-nothing strategy. Compared to grey infrastructure, green–grey infrastructure mitigates 13%–15% of the environmental impacts while providing equivalent flood protection. A flooding event with a 100-year recurrence interval in the study area is estimated at 34 million kg of CO2 equivalent per kilometre of shoreline, while grey and green–grey infrastructure mitigating such flooding is estimated to be 21 and 18 million kg, respectively. This study reinforced that coastal flooding environmental impacts are primarily caused by rebuilding damaged houses, especially concrete and structural timber replacement, accounting for 90% of GHG emissions, with only 10% associated with flood debris waste treatment. The asphalt cover of the levee was identified as the primary contributor to environmental impacts in grey infrastructure, accounting for over 75% of GHG emissions during construction. We found that there is an important interplay between grey and green infrastructure and optimizing their designs can offer solutions to sustainable coastal flood protection.

DETERMINATION OF CRITERIA FOR ASSESSING THE SUSTAINABILITY OF THE BLUE ECONOMY WITHIN THE FRAMEWORK OF THE PROTECTION OF THE UKRAINIAN SEA COAST

The blue economy is a key component of the global economy. It covers all economic activities related to oceans, seas and coasts. In the context of the blue economy, the interaction of the activities of the sea-coast system is considered a key source of economic potential that can contribute to sustainable innovation, the development of modern technologies and new markets. In addition, the blue economy takes into account the social, environmental and economic aspects of development, ensuring a balance between economic growth and environmental protection. The paper provides criteria and indicators for assessing the sustainable development of the blue economy. They are structured around four dimensions of sustainability, based on environmental, economic, social and governance aspects. A conceptual structure of the sustainable development of the blue economy in the subsector «Coastal defence and flood protection» for the Ukrainian sea coast has been built. The proposed criteria and indicators meet EU requirements for the sustainability of the blue economy and reflect the main aspects of sustainability.

The timing of decreasing coastal flood protection due to sea-level rise

The timing of decreasing coastal flood protection due to sea-level rise

A coupled agent-based model for France for simulating adaptation and migration decisions under future coastal flood risk

In this study, we couple an integrated flood damage and agent-based model (ABM) with a gravity model of internal migration and a flood risk module (DYNAMO-M) to project household adaptation and migration decisions under increasing coastal flood risk in France. We ground the agent decision rules in a framework of subjective expected utility theory. This method addresses agent’s bounded rationality related to risk perception and risk aversion and simulates the impact of push, pull, and mooring factors on migration and adaptation decisions. The agents are parameterized using subnational statistics, and the model is calibrated using a household survey on adaptation uptake. Subsequently, the model simulates household adaptation and migration based on increasing coastal flood damage from 2015 until 2080. A medium population growth scenario is used to simulate future population development, and sea level rise (SLR) is assessed for different climate scenarios. The results indicate that SLR can drive migration exceeding 8000 and 10,000 coastal inhabitants for 2080 under the Representative Concentration Pathways 4.5 and 8.5, respectively. Although household adaptation to flood risk strongly impacts projected annual flood damage, its impact on migration decisions is small and falls within the 90% confidence interval of model runs. Projections of coastal migration under SLR are most sensitive to migration costs and coastal flood protection standards, highlighting the need for better characterization of both in modeling exercises. The modeling framework demonstrated in this study can be upscaled to the global scale and function as a platform for a more integrated assessment of SLR-induced migration.

Coastal Defense Megaprojects in an Era of Sea-Level Rise: Politically Feasible Strategies or Army Corps Fantasies?

Storm surge barriers, levees, and other coastal flood defense megaprojects are currently being proposed as strategies to protect several US cities against coastal storms and rising sea levels. However, social conflict and other political factors add a layer of complexity that casts doubt on their status as practical climate adaptation options. The specific mechanisms responsible for some projects not progressing beyond initial planning stages remains unclear. In this study, we examined the outcome of two USACE storm surge barrier proposals to explore the political reasons why some coastal flood protection megaprojects break ground in the US, while others do not. Using original archive research, we concluded that storm surge barriers are politically challenging climate adaptation options because of modern environmental laws that provide avenues for expression of oppositional views within the decision process and the allure of alternative options that are more aesthetically pleasing and cheaper and faster to implement. To better allocate public resources and utilize the expertise of USACE, future flood protection megaprojects should first achieve broad support from the public, nongovernmental organizations (NGOs), and elected officials before beginning serious planning. This support could be achieved through new innovative designs that simultaneously address adverse environmental impacts and provide cobenefits (e.g., recreation). New designs should be studied to better understand the level of protection offered and their associated reliability so that USACE has confidence in their use.

Mangrove forests as a nature-based solution for coastal flood protection: Biophysical and ecological considerations

Nature-based coastal protection is increasingly recognised as a potentially sustainable and cost-effective solution to reduce coastal flood risk. It uses coastal ecosystems such as mangrove forests to create resilient designs for coastal flood protection. However, to use mangroves effectively as a nature-based measure for flood risk reduction, we must understand the biophysical processes that govern risk reduction capacity through mangrove ecosystem size and structure. In this perspective, we evaluate the current state of knowledge on local physical drivers and ecological processes that determine mangrove functioning as part of a nature-based flood defence. We show that the forest properties that comprise coastal flood protection are well-known, but models cannot yet pinpoint how spatial heterogeneity of the forest structure affects the capacity for wave or surge attenuation. Overall, there is relatively good understanding of the ecological processes that drive forest structure and size, but there is a lack of knowledge on how daily bed-level dynamics link to long-term biogeomorphic forest dynamics, and on the role of combined stressors influencing forest retreat. Integrating simulation models of forest structure under changing physical (e.g. due to sea-level change) and ecological drivers with hydrodynamic attenuation models will allow for better projections of long-term natural coastal protection.

The role of mangroves in coastal flood protection: The importance of channelization

The historical, present, and projected future risk of coastal flooding necessitates measures to protect coastal communities and environments, including using natural defences such as mangroves. Estimates of extent of flood protection provided by mangrove forests range widely, probably because of differences in growth characteristic of trees combined with variations in local geomorphology in each case study site. Here we use a Delft3D model of a mangrove forest in Tauranga, Aotearoa New Zealand, with vegetation flow resistance parameterized by frontal area, as a basis of idealized scenarios designed to explore and generalize the impact of channels, vegetation density, and forest slope on long wave (surge/tide) attenuation. Previous models often parameterise the frictional effect of mangroves with high bottom friction, which we show using theoretical arguments, becomes increasingly problematic with larger amplitude flood events. However, the contorted forms of the shrubby Avicenna mangroves at the field site necessitate new ways to quantify vegetation density more accurately for modelling. Nevertheless, modelling experiments show that vegetation distribution and channelization have a greater impact on flood attenuation than vegetation density, with large events resulting in less attenuation than smaller events due to the increased hydraulic efficiency associated with increased water depth. Additionally, a forest with sloping topography reduces the rate at which long wave attenuation occurs. Implications are that mangroves can only be effective coastal flood protection if the larger scale (forest-scale) distribution of vegetation also contributes to reducing the landward flow of water.

EMPOWERING GEO-BASED AI ALGORITHM TO AID COASTAL FLOOD RISK ANALYSIS: A REVIEW AND FRAMEWORK DEVELOPMENT

Abstract. Climate change and current susceptibilities exacerbated the coastal flood loss and damage resulting in livelihoods and property damage. Urban areas in the Low to Lower-Middle Income Countries are expected to be disproportionately impacted by the disaster, given a higher share of citizens living in the Low Elevation Coastal Zone, limited financial resources, and poorly constructed disaster protection. Documentation of historical coastal floods, population, and property affected, could advance the assessment by considering those parameters in risk analysis. Besides, incorporating such geographic features e.g., mangroves as the ecological solution for alternative coastal flood protection in the prediction is also essential. Mangrove is considered fit for the LLMIC primarily situated in the tropical zone. The prediction utilizing spatial Machine Learning (ML) could aid climate-related disaster risk analysis and contribute to risk reduction and policy suggestions to improve disaster resilience. The research aims to archive recent studies on the application of geospatial science empowering Artificial Intelligence, notably ML in coastal flood risk assessment, so-called GIS-based AI. Another aim is to document population, property, and mangrove distribution across the LLMIC. Artificial Neural Networks were mostly utilized for disaster risk assessment in past research. The number of 58 historical coastal flood events and 908 expected coastal flood hotspots for 2006 to 2021 has been documented. Over 1,2 million Km2 falls under vulnerable areas toward coastal flood in LLMIC under different settlement types where Large City (urban areas) dominates it. Mangrove distribution is mainly distributed across tropical regions mostly distributed along the Southeast Asia coast.

Exploring Methodological Approaches for Strengthening the Resilience of Coastal Flood Protection System

Coastlines are subject to multiple developments related to land use planning and the effects of climate change. These developments generally lead to an increase in the risk of coastal flooding. This article focuses on systems to protect against this hazard, and presents a bibliographical analysis on methods and operational tools to strengthen their resilience. This analysis is carried out by considering that a system of protection is a component of the territory to which it provides protection and that it is therefore necessary to study in depth the relations between this system and the various components of the territory (the natural environment, the built environment and the social and institutional environment). Based on this hypothesis, the concepts of risk and resilience applied to floods are specified and the protection and adaptation strategies commonly used in recent decades are described. This retrospective on concepts and strategies leads us to structure the state-of-the-art analysis on methods and operational tools in relation to two issues: 1) understanding risks; 2) adapting and transforming protection systems. In each case, the use of the concept of resilience implies a clear distinction between systemic and analytical approaches. Finally, this bibliographical analysis reveals the need to revise the protection system concept in order to promote the integration of these systems in the territories. Accordingly, new methodological developments could be considered using ecosystem and socio-economic approaches.

Mapping and assessment of future changes in the coastal and marine ecosystem services supply in Lithuania

Assessing and mapping ecosystem services (ES) became an integral part of coastal and marine management practices. Hence, quantitative and validated approaches are lacking, especially to address future conditions. The objective of this study is to apply further existing and develop new methodological frameworks to quantitatively assess and map the current and future supply of 3 ES in the coastal zone of Lithuania: coastal flood protection, nutrient regulation, and maintenance of nursery conditions. For coastal flood ES modelling, 2 time periods (1990 and 2018) and 4 scenarios (A0, A1 A2, A3 - based on future socio-economic changes in Lithuania) were analysed. The coastal flood protection ES model was validated (r2 = 0.30) using tree cover density. The results showed spatial differences among the analysed periods but no statistical differences. High supply areas are located in the southern coastal area, while the central part displays a low supply. For nutrient regulation and maintenance of nursery conditions, 7 time periods were analysed: a historical period and 6 scenarios based on Representative Concentration Pathway 4.5 and 8.5 and 3 Shared Socioeconomic Pathways. The nutrient regulation ES model was validated (r2 = 0.85) using in situ nutrient. Statistical differences were observed for this ES, but a similar spatial distribution of high and low supply areas. A decrease in the supply was observed comparing the historical period and future scenarios. Maintenance of nursery conditions was validated (r2 = 0.72) based on the protection status of the coastal zone. Results show no statistical differences and similar spatial patterns among the periods. Rocky and sandbank areas show a high supply for this ES. Limitations of our work are mainly related to the resolution of the utilised indicators. Nevertheless, the information obtained from our models can support spatial planning and decision-making processes.

Guidelines for Analysing Coastal Flood Protection Systems after a Submersion

Storm Xynthia, which hit the French Atlantic coast on 28 February 2010, flooded vast territories despite coastal defences. This disaster highlighted the need to further study the behaviour of the coastal flood protection systems at an adapted geographical scale by considering the kinematics of the events. This objective has been achieved through a combination of conceptual input on the definition of protection systems, significant breakthroughs in the knowledge of the mechanisms governing the flooding, and via the improvement of strategies and methods dedicated to flood analysis and representation. The developed methodology was successfully tested on four sites submerged during Xynthia (Loix, Les Boucholeurs, and Boyardville, located in Charente-Maritime, and Batz-sur-Mer, located in Loire-Atlantique). This work is intended to guide the diagnosis of sites prone to marine flooding from the first investigations until the delivery of study reports. Beyond the usual focus on hydraulic structures, it provides guidelines to better analyse the interactions with the natural environment (sea, soil, dune, wetlands, etc.) and with the built environment (roads and urban networks, ponds used for fish farming, buildings, etc.). This systemic approach, which is applied to a territory considered as a complex adaptive system, is fundamental to understanding the reaction of a territory during a marine submersion event and subsequently developing adaptation or transformation strategies.

Heterogeneity of values for coastal flood risk management with nature-based solutions

The purpose of this study was to understand preferences for different coastal flood protection measures and the factors that influence such preferences, to inform management and policy. The Discrete Choice Experiment applied to Wales residents revealed that there is willingness-to-pay for coastal flood protection, especially through Nature-based Solutions (NbS) including expanding saltmarsh area and increasing saltmarsh with high vegetation. The preference for NbS provides evidence for including specific coastal area targets in financial schemes initially aimed at other benefits from natural habitats, such as habitat creation for biodiversity. This joint action will maximise the benefits from NbS and ensure integrated and concerted efforts across, often disjointed, sectors. There were also high levels of heterogeneity for preferences in different groups of people. For instance, results support that direct flood experience and damage severity can give rise to behavioural intentions that support mitigation and adaptation measures. Findings also highlight how crucial environmental education and direct contact with the object of study are for securing support and buy-in for flood protection measures. This work is original in that it considers the different types of management for a habitat as NbS and the heterogeneity of preferences within a population. Results are significant in providing a basis for future NbS developments and in supporting flood risk policy and management.

Ecohydraulics of Surrogate Salt Marshes for Coastal Protection: Wave–Vegetation Interaction and Related Hydrodynamics on Vegetated Foreshores at Sea Dikes

Vegetation on foreshores in close vicinity to sea dikes may prove beneficial as regulating ecosystem service in the context of coastal defense, dike safety, and flood protection by reducing loads on these defense structures. Predominantly, a decrease in wave heights and bottom shear stresses is hypothesized, which calls for an inclusion in design procedures of coastal defense structures. In contrast to heterogeneous and variable salt marsh vegetation, this study uses surrogate vegetation models for systematic hydraulic experiments in a wave flume, without modeling specific plant species a priori. Froude-scale experiments are performed in order to investigate the effect of salt marsh vegetation on the wave transformation processes on the foreshore and wave run-up at sea dikes. The effect of plant and wave properties on wave transmission, energy dissipation, and wave run-up at a 1:6 sloped smooth dike are presented and discussed, focusing on the wave–vegetation–structure interaction. Vegetated foreshores can contribute to wave attenuation, where an increasing relative vegetation height hv/h results in decreased wave run-up on the dike by up to 16.5% at hv/h = 1.0.

Green infrastructure for coastal flood protection: The longitudinal impacts of green infrastructure patterns on flood damage

The importance of implementing green infrastructure (GI) for flood protection is supported by multiple substantial cross-sectional analyses. Yet, limited longitudinal research has been conducted which addresses how to maintain and improve the configuration of GI in order to minimize the cost of losses resulting from flooding. Structural damage from devastating storm events has repeatedly imposed substantial financial burdens on local governments in coastal regions. This study longitudinally examines the impacts of changes in GI patterns on flood damage cost in coastal Texas areas. Major flood events in the 36 Texan coastal watershed counties along the Gulf of Mexico were monitored from 2000 to 2017. Along with non-spatially weighted panel data models, we developed an advanced statistical model controlling for spatially correlated errors in flood loss and predicting flood loss with a set of time-series socioeconomic and environmental control variables. The results of the spatial panel data model reveal that long-term maintenance of larger, more irregular, more dispersed, less fragmented, and less connected patterns of GI will help to reduce county-level flood damage costs per capita over time. Most importantly, protecting larger patches within a closer proximity was found to be of the utmost importance for retaining the flood regulation services provided by GI. These findings suggest that planners and natural resource managers should enhance supportive land use policies to preserve existing GI and strategically locate new implementations in order to achieve long-term flood protection.

Analysis of coastal storm damage resistance in successional mangrove species

AbstractUse of mangrove ecosystems for coastal flood protection requires reliable predictions of mangrove wave attenuation, especially if this capacity lessens due to storm‐induced forest damage. Quantifying and understanding the variation in drag forces and mechanical properties of mangrove vegetation can improve assessment of mangrove protective capacity. We studied five mangrove species common in the subtropical Pearl River Delta, south China. The studied species range from typically landward‐occurring to more seaward‐occurring pioneer species. We sampled across seven sites in the delta to study the impact of salinity on mechanical properties. We quantified strength and flexibility of branches (branch strength and flexibility related to branch diameter, modulus of rupture and modulus of elasticity), leaf strength (leaf attachment strength related to leaf size, and leaf mass per area) and drag properties (drag force related to surface area and drag coefficient). For all tested species, larger branch diameters resulted in higher mechanical strength. Larger leaf size resulted in larger peak pulling forces and larger branch surface area resulted in stronger drag forces. Notably, species that generally occur lower in the intertidal zone, where exposure to wind and waves is higher, had relatively stronger branches but more easily detachable leaves. This may be regarded as a damage‐avoiding strategy. Across the seven field sites, we found no clear effect of salinity on mangrove mechanical properties. This study provides a mechanistic insight in the storm damage process for individual mangrove trees and a solid base for modeling storm (surge) damage at the forest scale.

Flood risk reduction by parallel flood defences – Case-study of a coastal multifunctional flood protection zone

In this paper the safety of a double-dike system (or twin dikes) is assessed. Such a system consist of two parallel lines of flood defences. During storms the combined strength of the parallel flood defences must prevent flooding of the hinterland. A culvert can be implemented for the tidal exchange of sea water to enable new land-uses in the area between the dikes such as aquaculture, saline agriculture, salt marsh restoration and clay extraction. We develop a general framework for assessing the safety of such double dike systems and apply a simplified version to the Double Dike between Eemshaven and Delfzijl (The Netherlands) to test this method. In doing so, we aim to quantify the flood protection benefits of parallel flood defenses and enable their use in multifunctional flood protection strategies.Within the framework the transmission of hydraulic loads by the seaward dike to the landward dike in the case-study was described by overtopping, overflow and erosion of the outer slope, alongside discharge through the culvert in the event of a non-closure. For the subset of coastal double dike systems with a tall seaward dike (as in the case-study), the results show only a negligible improvement in flood protection compared to a single dike system. With the addition of a culvert in the first dike, flood risk will only be reduced by the second landward dike if its height is sufficient to retain water in the event of a non-closure during common storm events. These double dike systems are implemented for potential uses of the inter-dike zone, e.g. for nature restoration, rather than as a measure to primarily improve flood protection.