Managed realignment is a measure that usually results in the creation of a salt marsh by removing costal protection an allowing for an area previously protected from flooding to become flooded. Managed realignment is a measure dealing with sea level rise and coastal erosion. It is also often a method that replaces hard coastal defense measures with soft coastal landforms. Rather than relying on hard structures for defense, managed realignment depends on natural defenses to absorb or dissipate the force of waves.
Based on kindly provided information by the ClimateTechWiki and the TNA Guidebook on 'Technologies for Climate Change Adaptation' by Matthew M. Linham & Robert J. Nicholls
Managed realignment effectively forms intertidal habitats. Intertidal habitats are effective in absorbing wave energy and reducing offshore sediment transport or erosion. Extensive root networks created by saltmarshes also help to prevent erosion.
Managed realignment sometimes requires the complete removal of existing coastal defense structures. In some cases managed realignment is an introduced alternative measure when existing coastal defenses can no longer be maintained and are abandoned.
Conditions to consider in undertaking managed realignment according to Gardiner et al., 2007 are:
1) presence of coastal defences
2) availability of low-lying land
3) desire or need to improve flood or coastal defence systems
4) presence of a sustainability-oriented coastal management attitude
5) desire or need to create intertidal habitats
6) societal awareness about the benefits of managed realignment
Advantages of the technology
Realignment is considered a soft measure and can significantly reduce the cost of protection against coastal flooding and erosion. Intertidal habitats such as saltmarshes, or mangroves, are effective in reducing the energy and inertia of incoming waves and thus the damage that they do. With intertidal habitats the need for intrusive hard defenses is reduced and often avoided. In addition to protecting against floods and buffering storms, rich intertidal zones can improve the resilience of the local ecosystem and provide environmental benefits such as absorbing carbon dioxide and methane emissions which are stored in the sediment deposits.
Increasingly intertidal habitats are implemented in areas that have been surrendered or abandoned. In these cases, degraded land or land that would otherwise be used for development is used to create an intertidal habitat. Intertidal habitats are important ecosystems for a variety of flora and fauna. Realignment in the UK for instance has created new opportunities for ecotourism with activities such as walking and bird watching.
Intertidal habitats can also improve water quality in nearby urban areas. In situations where drinking water is threatened by sea level rise, intertidal habitats can help avoid saltwater intrusion from inappropriate land use and reduce the effects of eutrophication.
Disadvantages of the technology
When managed realignment is implemented, land is effectively relinquished to the sea. One of the greatest disadvantages or barriers is the loss of the land itself and the potential necessity of relocating important coastal infrastructure which can be expensive.
Although experience in the application of managed realignment is increasing, the approach is still relatively new and uncertainties still exist. For example, it is not fully understood how long it will take to create typical intertidal habitats that deliver the full benefits of naturally occurring systems. Moreover, managed realignment is not well monitored which has not built up an evidence base for future projects.
The approach is also not appropriate for all environments as wetlands and saltmarshes tend to occur in locations where wave energy is low and where high volumes of sediment are available. It is therefore important to carefully evaluate the feasibility and effects of this approach in specific locations.
Barriers to implementation
Relinquishment of land by the coastline is also often met by a lack of public acceptance and conflicts among those that own the land. In densely populated coastal areas this may be very difficult. Conflicts between users and landowners bring about legal and financial difficulties. For example the creation of intertidal habitats is often at sectoral odds with social and economic factors when the proposed land area is used for agriculture production. One way to navigate conflicts of interest is to ensure a participatory process in decision making and planning.
The potentially high cost of managed realignment also poses a barrier. The relocation of infrastructure and/or compensation to landowners in the managed realignment zone is potentially costly.
Managed realignment can only take place in certain areas and contexts. It is especially beneficial to have low-lying land that is sheltered by existing coastal defences as well as societal willingness.
Opportunities for implementation
Managed realignment is an extremely effective soft measure that replaces or reduces the need for constructing hard measures. When implemented managed realignment creates space for new habitats that are beneficial for flora and fauna and that preserve land. They are an effective soft measure to the coastline dealing with sea level rise and extreme weather events and also reduce the need for additional climate change measures to be implemented behind them.
Managed realignment usually requires significant amounts of coastal land. The beneficial environmental impacts of this are complimented also open up new opportunities for the creation of a new nature reserve and ecostourism.