Managed retreat refers to the purposeful, coordinated movement of people and buildings away from risks. This may involve the movement of a person, infrastructure, or community. It can occur in response to a variety of hazards such as flood, wildfire, or drought. In the context of coastal erosion, managed realignment allows an area that was not previously exposed to flooding by the sea to become flooded by removing coastal protection. This process is usually pursued in low-lying estuarine areas and almost always involves flooding of land that has at some point in the past been claimed from the sea. The type of managed retreat depends on the location and type of natural hazard. In the United Kingdom, managed realignment through removal of flood defences is often a response to sea level rise exacerbated by local subsidence of the land surface due to post-glacial isostatic rebound in the north. In the United States, managed retreat often occurs through voluntary acquisition and demolition or relocation of at-risk properties by the government. In the Global South, relocation might occur through government programs. Some low-lying nations, facing inundation due to sea level rise, are planning for the relocation of their populations, such as Kiribati planning for "Migration with Dignity."
Managed realignment
In the United Kingdom the main reason for implementation of managed realignment is generally to improve coastal stability, essentially replacing artificial ‘hard’ coastal defences with natural ‘soft’ coastal landforms. According to University of Southampton researchers Matthew M. Linham and Robert J. Nicholls "one of the biggest drawbacks of managed realignment is that the option requires land to be yielded to the sea." One of the benefits, however, is that the process can help protect areas of land further inland by creating natural spaces that act as buffers to absorb water or dampen the force of waves. Managed realignment has also been used to mitigate for loss of intertidal habitat. Although land reclamation has been an important factor for salt marsh loss in the UK in the past the majority of current salt marsh loss in the UK is believed to be due to erosion. This erosion may involve coastal squeeze, where protective sea walls prevent the landward migration of salt marsh in response to sea level rise when sediment supply is limited. Salt marshes are protected under the EU Habitats Directive as well as providing habitat for a number of species protected by the Birds Directive. Following this guidance, the UK’s biodiversity action plan aims to prevent net losses to the area of salt marsh present in 1992. It is, therefore, a legal requirement that all losses in marsh area must be compensated by replacement habitat with equivalent biological characteristics. This equates to the need to restore approximately 1.4 km² of salt marsh habitat per year in the UK. One of the major reasons cited for the slow pace of current salt marsh restoration in the UK is the uncertainty associated with the practice. There are no agreed protocols on the monitoring of MR sites and, consequently, very few of the sites are being monitored consistently and effectively. Due to the low levels of monitoring there is little evidence on which to base future managed realignment projects. This has led to the results of Managed Realignment schemes being extremely unpredictable.
Relocation programs
Managed retreat in the form of relocation has been used in inland and coastal areas in response to severe flooding and hurricanes. In the United States, this often takes the form of "buyout" programs, in which government acquires and relocates or demolishes at-risk properties. In some cases, individual homes are purchased after disasters. In other cases, such as Odamah and Soldiers Grove, Wisconsin, or Valmeyer, Illinois, the entire community has relocated. Managed retreat can be very controversial. A law suit in Del Mar California brought on by residents was initiated to stop a managed retreat program based on worries that home values, insurance costs and restricted home expansion have been effects of the policy. Some areas included in Managed Retreat are above sea level and are recommended based primarily on estimated and by studies financed by the California Coastal Commission itself. Despite the controversy, as the costs of climate change adaptation increase, more communities are beginning to consider managed retreat.
Realignment examples
In the UK, the first managed retreat site was an area of at Northey Island in Essex flooded in 1991, followed by larger sites at Tollesbury and Orplands, Freiston Shore and Abbott's Hall Farm, at Great Wigborough in the Blackwater Estuary, it is one of the largest managed retreat schemes in Europe. It covers nearly of land on the north side of the estuary and a number of others. The programme was started by the Essex Wildlife Trust who own Abbott's Hall Farm. They made five breaches in the original old sea wall to allow the held-back sea to flood through to create salt marshland. The marshland over time reverted to its original state before cultivation, providing excellent bird habitat and breeding grounds.
