Coastal Protection Strategies Research Articles

A combined coastal protection, realignment and wetland restoration scheme in the southern Baltic: planning process, public information and participation

Markgrafenheide-Hutelmoor covers a total area of 1000 ha (about 490 ha are coastal moor) and a coastline of about 6 km. This touristy area belongs to the city of Rostock in Germany. As response to sea level rise and heavy coastal erosion, the small seaside resort Markgrafenheide received a comprehensive storm surge protection until 2006. Subsequently, the adjacent Hutelmoor was flooded with the aim to restore it as a brackish coastal moor. Coastal protection measures at the Baltic Sea coastline were abandoned to enable natural dynamics, a coastal realignment and salt water intrusions. The entire process until full implementation took 14 years and was associated with very problematic public participation and a strong local polarization. Based on a literature and media review, two surveys, and expert interviews we retrospectively document and analyse the planning process with focus on public information, perception and participation. The local population and holidaymakers did not perceive coastal changes and if, did not associate them with climate change. Interviewees remembered single storm surges, but felt save from it and sea level rise was not perceived as a threat. 89% said that they feel insufficiently informed about the combined coastal protection wetland restoration measure, but did not use the offered information possibilities. 81% had their information from newspapers and freely distributed advertisers. It seems that insufficient information was the major reason for the problems with local acceptance and public participation. The media played a dominating role. The decline of traditional newspapers and the growths of free advertisers seemed to have a negative impact on quality of information and favoured a polarization. Additionally, we discuss local specifics like the cultural background (GDR history), traditions, frustration and the relatively old population and their role in public participation. We strongly promote a pro-active and long-term information and public relation strategy.

SWASH MODELLING OF A COASTAL PROTECTION SCHEME

The Beresford shoreline, Australia, is subject to a complex interaction of coastal processes and associated erosion. In support of the design of a coastal protection scheme a SWASH model has been set up capable of accounting for all the complex processes at hand. The model has successfully been validated against measured wave and current conditions. In the design process the validated SWASH model proved to be a valuable tool to assess the impact of various coastal protection schemes like groynes on the wave-driven current patterns and associated sediment pathways.

Governance context for coastal innovations in England: The case of Sandscaping in North Norfolk

Coastal management in Europe is shifting toward soft coastal protection strategies to deal with flood risk and erosion. In the UK, a sand replenishment in North Norfolk is planned to take place in the coming years, inspired by the Dutch ‘Sand engine’: a large-scale sand replenishment executed in 2011. Besides being faced with technical challenges, the initiative requires fine-tuning to the local conditions. In this article we present a theory guided assessment of the governance context for Sandscaping in England. We focus upon North Norfolk, where Sandscaping was included as an option to protect the Bacton Gas Terminal from cliff erosion. Our aim is to contribute to further elaboration of Sandscaping potential along other locations in England. The lessons we draw about implementing Sandscaping initiatives have emerged from real project experience and could therefore be relevant in other coastal contexts.

Hurricane damage along natural and hardened estuarine shorelines: Using homeowner experiences to promote nature-based coastal protection

Growing coastal populations, rising sea levels, and likely increases in the frequency of major storm events will intensify coastal vulnerability in coming decades. Decisions regarding how and when to fortify estuarine shorelines against coastal hazards, such as erosion, flooding, and attendant property damages, rest largely in the hands of waterfront-property owners. Traditionally, hard engineered structures (e.g. bulkheads, revetments, seawalls) have been used to protect coastal properties, based on the assumption that these structures are durable and effective at preventing erosion. This study evaluates the validity of these assumptions by merging results from 689 surveys of waterfront-property owners in NC with empirical shoreline damage data collected along estuarine shorelines after Hurricanes Irene (2011) and Arthur (2014). The data show: 1) homeowners perceive bulkheads to be the most durable and effective at preventing erosion, but also the most costly; 2) compared to residents with revetments and natural shorelines, property owners with bulkheads reported double the price to repair hurricane damage to their property and four times the cost for annual shoreline maintenance; 3) 93% of evident post-hurricane shoreline damage was attributable to bulkheads or bulkhead hybrids and a higher proportion of surveyed homeowners with bulkheads reported having property damage from hurricanes; and, 4) shoreline hardening increased by 3.5% from 2011 to 2016 along 39km of the Outer Banks. These results suggest that bulkheads are not meeting waterfront property-owner expectations despite continued use, and that nature-based coastal protection schemes may be able to more effectively align with homeowner needs.

Hard protection structures as a principal coastal erosion management strategy along the Caribbean coast of Colombia. A chronicle of pitfalls

Over the last 50 years, coastal erosion has become a serious problem, rising in magnitude and dominance along the Caribbean coastline of Colombia. Circa 50% of this important area for the country is undergoing serious erosion problems related to a multiplicity of factors contrasted by their degree of influence and magnitude, e.g. sedimentary imbalances, extreme waves, ecosystems destruction and sea level rise. Coastal protection related with hard structures has been the first, and in some cases, the only management strategy for these erosion problems. At the beginning of 2016, at least 1484 hard structures (both cross and longshore, such as, groins, seawalls, breakwaters, amongst others) have been built along the Colombian Caribbean coast, the highest concentrations being found in tourist cities. A significant percentage (close to 90%) of these hard structures have not been very successful or have failed in their purpose. These hard structures have altered the natural conditions of the study area, producing impacts such as i) coastal armoring, 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. This paper describes and evaluates the functionality of coastal protection strategies used up to the present and delves into management aspects of coastal protection in the Caribbean coast of Colombia. It also indicates the current and future coastal protection scene for the region and highlights major trends and challenges faced by users, land owners, and coastal managers.

How do we know if managed realignment for coastal habitat compensation is successful? Insights from the implementation of the EU Birds and Habitats Directive in England.

In England saltmarshes account for less than 0.5% of the land area; however they have a very high biodiversity value and provide significant economic and social services. Climate change, continuous coastal urbanisation and port development are serious concerns for coastal protection planners, city councils and state government agencies interested in balancing the social, economic and environmental needs of these dynamic areas to ensure sustainable development. Providing habitat ‘compensation’, creating new intertidal habitats to replace those lost to developments and coastal protection schemes via Managed Realignment (MR), has been identified in the UK as the principal way to manage the loss of habitat and prevent biodiversity loss. However, the few existing studies that do evaluate the effectiveness of managed realignment projects in England indicate that they are not compensating fully for the original loss of habitat. Through an analysis of scientific and grey literature, conservation legislation, and purposive semi-structured interviews, we sought to ascertain what motivates the continued use of MR for habitat compensation in England, as well as in what ways success is defined by practitioners at various scales. We find that ambiguities in the conservation legislation, inconsistencies regarding definitions and evaluative metrics across scales, and a lack of transparency and reporting in past projects has led to confusion regarding what specifically should be recreated in MR projects for habitat compensation, and how best to instigate it. From this, we argue that to be able to evaluate whether current MR practices in England will actually preserve biodiversity, or contribute to its loss, and thus to ensure consistent and effective monitoring, evaluation and implementation of scientific best practices 1) habitat compensation needs to be rigorously defined; 2) consistent, cross-scalar success criteria and targets for MR projects need to be clearly established; and 3) transparent reporting and evaluation of MR projects by independent agencies should be promoted.

Evaluating the Benefits of Green Infrastructure for Coastal Areas: Location, Location, Location

ABSTRACTCoastal protection of communities and property using “green infrastructure” approaches is gaining popularity as the science and practice improve. Guidance is limited for decision makers interested in taking action to protect shorelines. Here, we offer practical guidance for decision makers interested in moving beyond generalities for coastal protection strategies. We present three case examples from the U.S. Gulf of Mexico and in Belize, each posing different questions, and thus using different approaches, to evaluate whether green infrastructure strategies could be useful. For basic questions about where habitat-based approaches are likely to add value, index-based models are useful in identifying priority areas for habitat protection or restoration. Process-based models are best used to examine strategies where the interest is in the likely magnitude of value from gray and green infrastructure approaches. Process-based models in coastal Texas demonstrate that marsh habitats are spatially variable in their ability to reduce the height and costs of levees necessary to protect property from storms and sea-level rise. Such spatial variation in the value of green infrastructure can be readily incorporated in a variety of decisions, allowing action now, before more science and lessons from applications emerge.

Failure of coastal protection concrete armour units due to alkali–silica reaction

The 1993 Clacton Coastal Defence Works included a 1·4 km length of sloping revetment formed of precast concrete armour units. The revetment was designed for a service life of greater than 50 years, but severe cracking of the armour units necessitated its entire replacement after only 22 years. This paper describes an investigation that determined the primary cause of the armour unit deterioration to be alkali–silica reaction (ASR), which appeared to have been exacerbated by the choice of cement, leaching action and the geometry of the units. In addition, sustainable reuse of the concrete units within the rock armour fishtailed groynes of a replacement coastal protection scheme is described. This case study is of particular importance as it is notable that the failed concrete armour units complied with the current UK guidelines for prevention of ASR. As such, it demonstrates the importance of considering the potential action of leaching and the associated alkali migration when designing concrete structures to resist alkali–aggregate reactions. In particular, designers of marine/coastal structures should be aware of the potential leaching and alkali migration implications of specifying hollow concrete armour units with relatively low surface area to volume ratios.

Global coastal wetland change under sea-level rise and related stresses: The DIVA Wetland Change Model

The Dynamic Interactive Vulnerability Assessment Wetland Change Model (DIVA_WCM) comprises a dataset of contemporary global coastal wetland stocks (estimated at 756×103km2 (in 2011)), mapped to a one-dimensional global database, and a model of the macro-scale controls on wetland response to sea-level rise. Three key drivers of wetland response to sea-level rise are considered: 1) rate of sea-level rise relative to tidal range; 2) lateral accommodation space; and 3) sediment supply. The model is tuned by expert knowledge, parameterised with quantitative data where possible, and validated against mapping associated with two large-scale mangrove and saltmarsh vulnerability studies. It is applied across 12,148 coastal segments (mean length 85km) to the year 2100. The model provides better-informed macro-scale projections of likely patterns of future coastal wetland losses across a range of sea-level rise scenarios and varying assumptions about the construction of coastal dikes to prevent sea flooding (as dikes limit lateral accommodation space and cause coastal squeeze). With 50cm of sea-level rise by 2100, the model predicts a loss of 46–59% of global coastal wetland stocks. A global coastal wetland loss of 78% is estimated under high sea-level rise (110cm by 2100) accompanied by maximum dike construction. The primary driver for high vulnerability of coastal wetlands to sea-level rise is coastal squeeze, a consequence of long-term coastal protection strategies. Under low sea-level rise (29cm by 2100) losses do not exceed ca. 50% of the total stock, even for the same adverse dike construction assumptions. The model results confirm that the widespread paradigm that wetlands subject to a micro-tidal regime are likely to be more vulnerable to loss than macro-tidal environments. Countering these potential losses will require both climate mitigation (a global response) to minimise sea-level rise and maximisation of accommodation space and sediment supply (a regional response) on low-lying coasts.

Large-scale 3-D experiments of wave and current interaction with real vegetation. Part 1: Guidelines for physical modeling

The growing interest in incorporating nature-based solutions and ecosystem services as part of coastal protection schemes has recently increased in the literature and focused on the understanding and modeling of wave and current interactions with natural coastal landforms, such as salt marshes. With this purpose, using flumes or basins has been one of the preferred options in experimental modeling under controlled conditions. However, due to the inherent complexities associated with this approach, most of the previously published experiments are based on wave-flume experiments using vegetation mimics. The current demand for understanding the relevant processes requires a step forward, which includes experimental modeling with real vegetation on both a relevant large scale and at a sufficiently large water depth. In response to foreseen needs, this study provides useful guidance based on the experience gained from a unique set of experiments conducted in a large wave basin, including wave and current interaction with real salt marsh vegetation. This study reports on plant collection and growing strategies, plant properties, physical set-up, instrumentation, and experimental strategy and dismantling, providing guidelines aimed at being helpful for future experimental efforts at the interface of engineering and ecology.

Climate Change, Coastal Vulnerability and the Need for Adaptation Alternatives: Planning and Design Examples from Egypt and the USA

Planning and design of coastal protection for high-risk events with low to moderate or uncertain probabilities are a challenging balance of short- and long-term cost vs. protection of lives and infrastructure. The pervasive, complex, and accelerating impacts of climate change on coastal areas, including sea-level rise, storm surge and tidal flooding, require full integration of the latest science into strategic plans and engineering designs. While the impacts of changes occurring are global, local effects are highly variable and often greatly exacerbated by geophysical (land subsidence, faulting), oceanographic (ocean circulation, wind patterns) and anthropogenic factors. Reducing carbon emissions is needed to mitigate global warming, but adaptation can accommodate at least near future change impacts. Adaptation should include alternatives that best match region-specific risk, time frame, environmental conditions, and the desired protection. Optimal alternatives are ones that provide protection, accommodate or mimic natural coastal processes, and include landforms such as barrier islands and wetlands. Plans are often for 50 years, but longer-term planning is recommended since risk from climate change will persist for centuries. This paper presents an assessment of impacts of accelerating climate change on the adequacy of coastal protection strategies and explores design measures needed for an optimum degree of protection and risk reduction. Three coastal areas facing similar challenges are discussed: Abu-Qir Bay, Nile River delta plain, Egypt; Lake Borgne, New Orleans, Louisiana delta plain; and the New York City region.

Dyke design, floodplain restoration and mangrove co-management as parts of an area coastal protection strategy for the mud coasts of the Mekong Delta, Vietnam

The dynamic coastlines in the Lower Mekong Delta of Vietnam are threatened by the impacts of climate change, particularly by the increased intensity and frequency of storms and floods, as well as by rising sea levels. The most effective coastal protection systems consist of different elements arranged in series, for instance natural floodplains vegetated with mangroves and a sound dyke line. However, the unsustainable use of natural resources and development in the coastal zone are threatening the protection function of the mangrove forest belt. In sites where severe erosion has destroyed the mangrove belt, restoration of floodplains and mangrove rehabilitation is only possible after the wave energy has been reduced by physical barriers. This can be achieved with bamboo fences, which reduce erosion and stimulate sedimentation. Restoration of the eroded floodplains creates the pre-conditions for rehabilitation of the destroyed mangrove forest. Mangrove management is an important element of an area costal protection strategy.

Going with the flow or against the grain? The promise of vegetation for protecting beaches, dunes, and barrier islands from erosion

Coastlines have traditionally been engineered to maintain structural stability and to protect property from storm‐related damage, but their ability to endure will be challenged over the next century. The use of vegetation to reduce erosion on ocean‐facing mainland and barrier island shorelines – including the sand dunes and beaches on these islands – could be part of a more flexible strategy. Although there is growing enthusiasm for using vegetation for this purpose, empirical data supporting this approach are lacking. Here, we identify the potential roles of vegetation in coastal protection, including the capture of sediment, ecological succession, and the building of islands, dunes, and beaches; the development of wave‐resistant soils by increasing effective grain size and sedimentary cohesion; the ability of aboveground architecture to attenuate waves and impede through‐flow; the capability of roots to bind sediments subjected to wave action; and the alteration of coastline resiliency by plant structures and genetic traits. We conclude that ecological and engineering practices must be combined in order to develop a sustainable, realistic, and integrated coastal protection strategy.

HYBRID SHORELINE MODELLING OF SHORELINE PROTECTION SCHEMES, PALM BEACH, QUEENSLAND, AUSTRALIA

In this study the use of a hybrid shoreline model, namely the Mike21FM Shoreline Model, has been applied to investigate the effectiveness of three different coastal protection schemes for Palm Beach in Southern Queensland, Australia. The yearly littoral drift on this shoreline is approximately 500,000 m3 to the north. The three coastal protection schemes are: Nourishment, Nourishment plus a submerged control structure and Nourishment plus artificial headlands. The coastal impact due to the three schemes is quantified and compared using the shoreline model. The results assisted the Gold Coast City Council in their decision on which option to bring forward to the detailed design phase.

EVALUATION AND DEVELOPMENT OF COASTAL PROTECTION MEASURES FOR SMALL ISLANDS IN THE WADDEN SEA

The Northfrisian Halligen are small undiked marsh islands and located in the German part of the UNESCO - World Natural Heritage Wadden Sea. The houses of the inhabitants are built on dwelling mounds and during storm events these mounds are the only places which are not inundated on the islands. With respect to climate change and related changes in mean and extreme water levels, new coastal protection measures and strategies have to be developed. At the Institute of Hydraulic Engineering and Water Resources Management (IWW) of the RWTH Aachen University different tools are used to evaluate and to develop new coastal protection measures and strategies for these islands. Within this project several new coastal protection measures and strategies for the Hallig islands have been developed and existing protection measures have been technically and economically evaluated. In addition, social accompanying measures were set-up to rise flood awareness and acceptance.

Hydraulic Stability of Interlocking Concrete Unit-V (ICU-V)

Continuous research is conducted to improve the available coastal protection scheme, including to develop an innovative concrete armor unit with interlocking capability. Interlocking Concrete Unit-V (ICU-V) has light weight characteristic and developed specifically for mild wave condition. This paper discusses the performance of ICU-V represented by the Stability coefficient,KDand results of the damage progression investigation under different wave conditions. These were achieved by conducting a 2-D physical model investigation by using JONSWAP random wave spectrum. The damage ratio method was used to assess the damage progression. The optimumKDobtained was 12 with highest damage level of 0.4%, which is comparable with available armor units

Long-term assessment of an innovative mangrove rehabilitation project: case study on Carey Island, Malaysia.

Wave energy and storm surges threaten coastal ecology and nearshore infrastructures. Although coastal structures are conventionally constructed to dampen the wave energy, they introduce tremendous damage to the ecology of the coast. To minimize environmental impact, ecofriendly coastal protection schemes should be introduced. In this paper, we discuss an example of an innovative mangrove rehabilitation attempt to restore the endangered mangroves on Carey Island, Malaysia. A submerged detached breakwater system was constructed to dampen the energy of wave and trap the sediments behind the structure. Further, a large number of mangrove seedlings were planted using different techniques. Further, we assess the possibility of success for a future mangrove rehabilitation project at the site in the context of sedimentology, bathymetry, and hydrogeochemistry. The assessment showed an increase in the amount of silt and clay, and the seabed was noticeably elevated. The nutrient concentration, the pH value, and the salinity index demonstrate that the site is conducive in establishing mangrove seedlings. As a result, we conclude that the site is now ready for attempts to rehabilitate the lost mangrove forest.

Asset anchoring as a constraint to sea level rise adaptation

It can be argued that there is presently a disparity between the theory of coastal climate change adaptation and the large-scale or mass implementation with respect to adaptation to sea level rise. From a theoretical perspective, rising sea levels will effectively move the coastline landward and hence the most seaward parts of the built environment, which often feature the highest physical asset value and intensity and hence economic density, will become inundated more often and therefore perhaps need to be relocated landward under the guidance of planned retreat policies. By contrast, evidence of active large-scale planned retreat policies being developed and implemented is sparse, and often being rejected in favour of coastal protection strategies. It is argued here that this lack of uptake of coastal retreat strategies is partially a result of a phenomena coined here as ‘asset anchoring’ where major community infrastructure acts to anchor seaside communities in place and inhibit the implementation of coastal retreat strategies.

Hydrodynamic and sediment dynamic modifications of tidal flow in the near-field area of offshore breakwaters

Numerical modeling was used in order to study the effect of tidal currents within a breakwater scheme that has reached morphodynamic equilibrium. Tidal flow is simulated, using a downscaling procedure from a regional numerical model, in order to investigate the small-scale hydrodynamic modifications caused by the structures in the absence of waves. Sediment transport processes at different stages of the neap and spring tidal cycle are also considered over the entire scheme. Significant modifications to the tidal currents were identified, caused by the presence of the following structures: (1) obstruction of the main tidal flow and (2) flow channelization between the structures and the coastline, leading to flow acceleration over the salients. Furthermore, the effect of the modified tidal regime on bedload sediment transport processes was investigated. The design characteristics of the scheme (i.e., gap width, offshore distance, and relative angle with respect to the tidal currents) are found to influence locally the tidal flow and the bedload transport, over the top of the salients, modulating their growth. Despite being located in a mixed-energy, wave-dominated environment, the shear stress ratio between currents and waves show a dominance of tidal processes at the sheltered areas of the scheme (i.e., behind the breakwaters) that diminishes as the incident wave period increases. Hence, in order to correctly predict the morphological evolution of such coast under the influence of coastal protection schemes, the tidal processes have to be studied in addition to the wave processes.

Adaptation to climate change: A combined coastal protection and re-alignment scheme in a Baltic tourism region

ABSTRACT Weisner, E. and Schernewski, G. 2013. Adaptation to climate change: A combined coastal protection and re-alignment measure in a southern Baltic tourism region. The German federal state of Mecklenburg-Vorpommern has an outer Baltic coastline of 354 km of which 70% is subject to erosion with an average retreat of 0.34 m/yr. Altogether 135 km of coastline is protected by wooden groynes, beach and dune nourishment, protective dunes and forests, dykes, seawalls and breakwaters at an annual maintenance cost of about 15.5 mio €. During the last decades the sea level rose at a rate of 1.2 mm/yr and an accelerated rate of rise is likely in future. A combined coastal protection and managed re-alignment scheme was implemented in an area of about 1000 ha, which aimed to adapt to the challenges associated with climate change, to reduce costs for coastal protection and to support environmentally sustainable development. The scheme covers 6 km of coastline comprising the seaside resort Markgrafenheide and the w...