Managed realignment for habitat compensation: Use of a new intertidal habitat by fishes

Managed realignment has become an increasingly common mechanism to increase the efficiency and sustainability of flood defences, reduce defence costs or compensate for habitat losses. This study investigated the use by fishes of a new intertidal habitat, created by managed realignment, intended to compensate for the loss of mudflat associated with a major port development. Although broadly similar, statistically significant differences in fish species composition, abundance, biomass, size structure, diversity and diet composition indicate that the managed realignment is not yet functioning in an identical manner to the mudflat in the adjacent estuary, most likely due to differences in habitat between sites. Notwithstanding, similarity in the species composition of fyke catches in the managed realignment and estuary increased annually during the 5-year study period, suggesting that the mudflat in the realignment is still developing. Indeed, the site will inevitably change over time with accretion, establishment of vegetation and possibly development of creeks. This will not necessarily prevent the aim of the realignment scheme being achieved, as long as sufficient suitable mudflat remains

Impacts of coastal realignment on intertidal sediment dynamics: Freiston Shore, the Wash

The impacts of land reclamation and managed realignment on saltmarsh and the adjacent intertidal flats at Freiston Shore (The Wash) are investigated. The hydrodynamic and sediment dynamics over the intertidal flats and a managed realignment site are discussed, with an extensive set of hydrodynamic, sediment dynamic and geomorphological data presented. The managed realignment has improved the coastal defence of the area; the site has been colonised by vegetation, accreted sediment and experienced limited wave activity. However, the channels within the breaches in the embankment were eroded, and a creek system over the adjacent intertidal flats experienced an enhancement in its development. This has allowed the natural and enhanced development of the creek system to be described and compared. These impacts were caused by the managed realignment site being at a lower elevation than the adjacent saltmarsh, causing high tidal current speeds as water flowed into the site and prolonged drainage of the site. This resulted in sheetflow over the intertidal flats, which caused an enhancement to the natural creek development. The water and sediment interaction between this creek system and the adjacent intertidal flats are discussed; the creeks were net exporters of sediment, while the intertidal flats were importers. The most rapid period of change was in the 2 months immediately after breaching the old embankment. The ‘Regime Theory’ was used to predict the equilibrium size of the channels within the breaches, and the time for this to be attained. Some 36 months after the initiation of the scheme, the adjacent intertidal flats appear to have adjusted to a new dynamic equilibrium, related to the managed realignment. The sheetflow over the intertidal flats has stopped and, consequently, the enhanced creek development has ceased and the creeks silted up. Despite the impacts of the managed realignment scheme, no obvious changes have been identified in the pattern or strength of tidal currents and sediment transport, over the intertidal flats adjacent to the managed realignment. In contrast, the previous creation of the embankment (for land reclamation purposes) led to an increase in tidal current speeds and erosion of the intertidal flats. Hydrodynamic and suspended sediment measurements show that, over the intertidal flats, the suspended sediment concentration increases exponentially with an increase in tidal current speed; similarly, linearly with wave height. The majority of wave activity over the intertidal zone is dissipated over the saltmarsh, with the mudflats causing little wave attenuation. Based upon the results of the present study, it appears that managed realignments can provide a successful future coastal defence, as long as certain guidelines for site selection are followed

Managed realignment: A viable long-term coastal management strategy?

Climate change and environmental and financial concerns have led to a shift from the traditional ‘hold-the-line’ approach of coastal protection towards more flexible soft engineering options. Managed realignment is a coastal management strategy increasingly implemented in Europe and other countries worldwide. It is a relatively new soft engineering alternative aiming to provide sustainable flood risk management with added environmental and socio-economic benefits by creating space for coastal habitats to develop more dynamically. The natural adaptive capacity of coastal habitats and the delivery of ecosystem services underpin the sustainability of managed realignment. However, many definitions of managed realignment exist and the understanding of what the term actually represents in practice has evolved through time and varies regionally. This book clarifies the definitions and terminology used in the literature and proposes that managed realignment is used as a general term that encompasses the many different methods of implementation worldwide, including: removal, breach and realignment of defences; controlled tidal restoration ; and managed retreat. These methods of implementation are explained and illustrated with examples from around the world. In addition to a general overview of emerging policies and current practices, specific chapters discuss approaches adopted in the Netherlands, the UK and Maui (US). The UK experience is presented from the perspectives of three sectors: the National Trust (a charity that owns 10% of England’s coastline), the Environment Agency (a government organisation responsible for implementing flood and erosion risk policy) and a private consultant involved in the design and delivery of managed realignment projects. Recent national and regional strategies worldwide give managed realignment an increasing role in climate change and flood risk management. Gaining stakeholders and public support is fundamental for the success of emerging coastal management strategies. However, public perception and stakeholders engagement are often cited as a factor limiting the wider uptake of managed realignment. Results from a recent survey are used to benchmark the current thinking about the potential, the performance and the limitations of managed realignment in the UK and elsewhere. The views of stakeholders are considerably more negative and notably contrast with the views of practitioners and researchers. The only clear and dominant agreement across all groups of respondents is that better understanding about the long-term evolution of sites is needed. Taking a wider perspective to consider the range of implementation methods, the viability of managed realignment as a long-term coastal management strategy is discussed

Valuing a managed realignment scheme: what are the drivers of public willingness to pay?

Offering several advantages over traditional “hold the line” flood defences, including increases in the supply of ecosystem services such as carbon sequestration and habitat provision, managed realignment is increasingly being used as a flood defence option. This paper seeks to add to the growing literature on public perceptions of the benefits of managed realignment by examining local resident's knowledge of estuarine management issues and identifying their willingness to pay towards a new managed realignment scheme on the Tay Estuary, Scotland. Results showed that the majority of respondents were not aware of flood risk issues on the estuary or of different flood defence options. Household mean willingness to pay for a specific managed realignment scheme was calculated at £43 per annum. Significant drivers of willingness to pay included respondents perceived flood risk and worries about the state of existing flood defences. There was also spatial heterogeneity with those living closest to the scheme being willing to pay the most. Prior knowledge of flood risk issues were found not to significantly influence willingness to pay

Tourists’ representations of coastal managed realignment as a climate change adaptation strategy.

In coastal destinations climate change adaptation is needed to address coastal erosion due to a combination of sea level rise and more frequent extreme weather events leading to loss of natural features and tourism infrastructure. Managed realignment is increasingly adopted as a strategy to address coastal change; however, this has often proved a contentious strategy with stakeholder groups. This study explores tourists' representational framework of managed realignment and how this frames understanding of the concept, understanding of how coastal resources might change and implications for future visitation. Data compiled using a questionnaire adopted a social representations theory perspective to analyse how collective tourists’ ideas may serve to mobilise the public in various ways. In general tourists have a poor understanding of managed realignment anchored to historic coastal management strategies and contextualised by use values with consequent implications for tourism planning and coastal management decision making

Physicochemical changes to soil and sediment in managed realignment sites following tidal inundation

PhDThe recognition of the value of salt marshes and concerns over salt marsh loss has led to the adoption of managed realignment in coastal areas. Managed realignment involves the landward relocation of the seawall, allowing an area of agricultural land to be tidally inundated. It is believed that managed realignment sites can act as a sink for contaminants. However, these sites may also act as a contaminant source and pose a risk to estuarine biota. In this thesis, the potential for metal and herbicide release from agricultural soil and dredged sediment in managed realignment sites was investigated by laboratory microcosm experiments. The agricultural soil and dredged sediment were subjected to two different salinities and drying-rewetting treatments. Results indicate the release of metals (Cu, Ni and Zn) and herbicides (simazine, atrazine and diuron) was dependent on their strength of binding to the soil and sediment, and complexation and competition reactions between seawater anions, cations and the sorbed metals. The release patterns indicated that metal and herbicide release into overlying water may continue for extended periods of time after an initial rapid release. The total metal and herbicide loads released into the overlying water followed the order: Cu < Zn < Ni and diuron < atrazine < simazine with a greater release from the soil than sediment. The increase in CO2 release, mineralisation rates, total metal and herbicide loads after drying and rewetting the soil suggested an increase in the mineralisation of organic matter and the release of organic matter associated metals and herbicides. Results of linear regression analyses provided evidence that the release of the metals and herbicides as DOC-complexes was important for soil but not for sediment. These findings indicate that there is a lower potential for contaminant release from managed realignment sites where dredged sediments are beneficially re-used

Governance and stakeholder perspectives of managed re-alignment: Adapting to sea level rise in the Inner Forth estuary, Scotland

With climate change, coastal areas are faced with unprecedented sea level rise and flooding, raising questions as to how societies will choose to adapt. One option is to strengthen existing sea walls to maintain current land uses; however, scientists, policy-makers and conservationists increasingly see the benefits of managed realignment, which is a nature-based coastal adaptation that involves the conversion of reclaimed farmland back to wetlands, allowing periodic local flooding in designated areas to reduce the risk of flooding downstream. We interviewed 16 local organisations, landowners and farmers and held workshops with 109 citizens living the Inner Forth estuary in eastern Scotland, to examine how managed realignment is supported by stakeholder attitudes and their engagement. Most of the farmers we interviewed prefer strengthened sea walls, to maintain their livelihoods and agricultural heritage. Citizens and local organisations were mainly supportive of managed realignment, because it provided wildlife and flood regulation benefits. However, we identified several barriers that could present obstacles to implementing managed realignment, for example, uncertainty whether it would support their principles of economic and rational decision-making. Our findings suggest that the local capacity to cope with rising sea levels is limited by lack of engagement with all relevant stakeholder groups, the limited scope of existing stakeholder partnerships and poor short-term funding prospects of landscape partnerships that would facilitate collaboration and discussion. We suggest that including citizens, landowners, farmers and industries would strengthen existing stakeholder deliberation and collaboration, and support the Inner Forth’s transition towards a more sustainable future shoreline