in sediment budget. Saltmarshes, for example, depending
on a number of interacting biotic and abiotic variables
(e.g., the accommodation space and sediment supply),
can migrate inland and accrete vertically, naturally
adjusting to rising sea levels. These intertidal habitats provide a number of ecosystem services (e.g., Luisetti et al.,
2011), such as natural coastal protection by dissipating
wave energy (Möller et al., 2007), therefore contributing
to reduced flood risk to inland areas and the associated
cost of maintaining existing flood defenses.
Geographic distribution
The first managed realignment projects were implemented
in France in 1981 and in Germany and the Netherlands in
1989 (Esteves, 2014). Managed realignment has
since become increasingly popular in northern Europe
(Mazik et al., 2010), especially in England (where the
highest number of projects has been implemented),
Germany, the Netherlands, Belgium, and France. A list
of projects implemented in Europe, including their main
characteristics, is available from the ABPmer Online Managed Realignment Guide (http://www.abpmer.net/omreg/).
The main objectives and the way projects are implemented
vary considerably between these countries.
In England, managed realignment is implemented to
create intertidal habitat and to deliver more sustainable
flood risk management, e.g., by reducing costs and aggregating environmental and amenity values (Esteves, 2013).
In Germany, managed realignment sites are found along
the coast of Lower Saxony (by the North Sea) and
Mecklenburg–Western Pomerania (by the Baltic Sea),
but the objectives differ across these two areas
(Rupp-Armstrong and Nicholls, 2007). In Lower Saxony,
managed realignment is usually implemented for compensation reasons (i.e., loss of intertidal habitats due to coastal
development, port construction etc.). In Western Pomerania managed realignment often combines the need for
improvement of flood defenses and creation of new intertidal habitats. In Belgium most projects have been
implemented along the Scheldt Estuary through the
mechanism of controlled reduced tide (Beauchard et al.,
2011; Teuchies et al., 2012) for compensation of damage
or loss of intertidal habitats.
Outside Europe, managed realignment projects exist
but are not known as such, being difficult to ascertain
how many already exist. Although the terms managed
realignment and managed retreat are often used interchangeably in the UK (e.g., French, 2001), elsewhere
managed retreat refers to the relocation of people and
assets at risk (e.g., National Oceanic and Atmospheric
Administration (NOAA) Office of Ocean and Coastal
Resource Management; http://coastalmanagement.noaa.
gov/initiatives/shoreline_ppr_retreat.html).
How does it work?
By allowing tidal waters to flow farther inland through
breached defenses, managed realignment creates new
intertidal areas (Figure 1b) and accommodation space for
sediment deposition. It is expected that the realignment
site will act as a sink for sediments, favoring the development of saltmarshes. The resulting wider intertidal profile
provides natural coastal protection through the dissipation
of wave energy (French, 1997), which tends to be significantly greater over saltmarshes than over un-vegetated
intertidal flats (Möller et al., 2007). Saltmarsh development enhances local biodiversity and the sustainability
of coastal protection and, therefore, is crucial for the
success of managed realignment as a sustainable coastal
management approach.
Information on the performance of managed realignment projects is still scarce as most projects do not benefit
from systematic long-term monitoring (Spencer and
Harvey, 2012). Although many gray literature reports
have been produced by consultants contracted to conduct
the design, implementation, and monitoring of the
schemes, only few independent monitoring studies have
been published in peer-reviewed journals. The existing
articles indicate diverse findings on the development of
saltmarshes at managed realignment sites.
Vegetation colonization at managed realignment sites is
reported to occur rapidly, most commonly dominated by
pioneer saltmarsh species, as reported in sites along the
Blackwater Estuary in England. Garbutt et al. (2006)
suggested that the low elevation of the Tollesbury site contributed to the dominance of pioneer saltmarsh recorded
6 years after the breaching of defenses. At Orplands Farm,
8 years after managed realignment, the site showed low
species saturation index and was dominated by pioneer
and low marsh species due to poor drainage and seed
availability (Spencer et al., 2008). At Freiston Shore
(The Wash, England), high sediment input favored rapid
colonization by pioneer saltmarsh vegetation (Friess
et al., 2012). However, sediment had originated from the
erosion of adjacent established habitats caused by the
unexpected growth of the tidal creeks at the breaches
(Rotman et al., 2008).
In their analysis of saltmarsh re-creation in Europe,
Wolters et al. (2005) observed that only 50 % of the
expected species were found at sites smaller than 30 ha.
The authors concluded that biodiversity increased at sites
larger than 100 ha, where the largest range of elevations
between mean high water of neap and spring tides occur.
Many managed realignment sites in England and elsewhere are small (<20 ha), low-lying, and confined by
a new line of coastal defenses. These characteristics compromise the sustainability of managed realignment sites,
as the lifetime of the newly created intertidal habitats
depends on whether sediment availability (and other variables) will allow vertical accretion at rates that will cope
with rising sea levels (Esteves, 2013). If saltmarshes are
not able to fully develop (e.g., due to the small size or
low elevation of managed realignment (MR) sites), it is
just a matter of time until water levels reach the new line
of defenses and the new intertidal habitats are again lost
due to coastal squeeze (Figure 1b).
MANAGED REALIGNMENT
391
on a number of interacting biotic and abiotic variables
(e.g., the accommodation space and sediment supply),
can migrate inland and accrete vertically, naturally
adjusting to rising sea levels. These intertidal habitats provide a number of ecosystem services (e.g., Luisetti et al.,
2011), such as natural coastal protection by dissipating
wave energy (Möller et al., 2007), therefore contributing
to reduced flood risk to inland areas and the associated
cost of maintaining existing flood defenses.
Geographic distribution
The first managed realignment projects were implemented
in France in 1981 and in Germany and the Netherlands in
1989 (Esteves, 2014). Managed realignment has
since become increasingly popular in northern Europe
(Mazik et al., 2010), especially in England (where the
highest number of projects has been implemented),
Germany, the Netherlands, Belgium, and France. A list
of projects implemented in Europe, including their main
characteristics, is available from the ABPmer Online Managed Realignment Guide (http://www.abpmer.net/omreg/).
The main objectives and the way projects are implemented
vary considerably between these countries.
In England, managed realignment is implemented to
create intertidal habitat and to deliver more sustainable
flood risk management, e.g., by reducing costs and aggregating environmental and amenity values (Esteves, 2013).
In Germany, managed realignment sites are found along
the coast of Lower Saxony (by the North Sea) and
Mecklenburg–Western Pomerania (by the Baltic Sea),
but the objectives differ across these two areas
(Rupp-Armstrong and Nicholls, 2007). In Lower Saxony,
managed realignment is usually implemented for compensation reasons (i.e., loss of intertidal habitats due to coastal
development, port construction etc.). In Western Pomerania managed realignment often combines the need for
improvement of flood defenses and creation of new intertidal habitats. In Belgium most projects have been
implemented along the Scheldt Estuary through the
mechanism of controlled reduced tide (Beauchard et al.,
2011; Teuchies et al., 2012) for compensation of damage
or loss of intertidal habitats.
Outside Europe, managed realignment projects exist
but are not known as such, being difficult to ascertain
how many already exist. Although the terms managed
realignment and managed retreat are often used interchangeably in the UK (e.g., French, 2001), elsewhere
managed retreat refers to the relocation of people and
assets at risk (e.g., National Oceanic and Atmospheric
Administration (NOAA) Office of Ocean and Coastal
Resource Management; http://coastalmanagement.noaa.
gov/initiatives/shoreline_ppr_retreat.html).
How does it work?
By allowing tidal waters to flow farther inland through
breached defenses, managed realignment creates new
intertidal areas (Figure 1b) and accommodation space for
sediment deposition. It is expected that the realignment
site will act as a sink for sediments, favoring the development of saltmarshes. The resulting wider intertidal profile
provides natural coastal protection through the dissipation
of wave energy (French, 1997), which tends to be significantly greater over saltmarshes than over un-vegetated
intertidal flats (Möller et al., 2007). Saltmarsh development enhances local biodiversity and the sustainability
of coastal protection and, therefore, is crucial for the
success of managed realignment as a sustainable coastal
management approach.
Information on the performance of managed realignment projects is still scarce as most projects do not benefit
from systematic long-term monitoring (Spencer and
Harvey, 2012). Although many gray literature reports
have been produced by consultants contracted to conduct
the design, implementation, and monitoring of the
schemes, only few independent monitoring studies have
been published in peer-reviewed journals. The existing
articles indicate diverse findings on the development of
saltmarshes at managed realignment sites.
Vegetation colonization at managed realignment sites is
reported to occur rapidly, most commonly dominated by
pioneer saltmarsh species, as reported in sites along the
Blackwater Estuary in England. Garbutt et al. (2006)
suggested that the low elevation of the Tollesbury site contributed to the dominance of pioneer saltmarsh recorded
6 years after the breaching of defenses. At Orplands Farm,
8 years after managed realignment, the site showed low
species saturation index and was dominated by pioneer
and low marsh species due to poor drainage and seed
availability (Spencer et al., 2008). At Freiston Shore
(The Wash, England), high sediment input favored rapid
colonization by pioneer saltmarsh vegetation (Friess
et al., 2012). However, sediment had originated from the
erosion of adjacent established habitats caused by the
unexpected growth of the tidal creeks at the breaches
(Rotman et al., 2008).
In their analysis of saltmarsh re-creation in Europe,
Wolters et al. (2005) observed that only 50 % of the
expected species were found at sites smaller than 30 ha.
The authors concluded that biodiversity increased at sites
larger than 100 ha, where the largest range of elevations
between mean high water of neap and spring tides occur.
Many managed realignment sites in England and elsewhere are small (<20 ha), low-lying, and confined by
a new line of coastal defenses. These characteristics compromise the sustainability of managed realignment sites,
as the lifetime of the newly created intertidal habitats
depends on whether sediment availability (and other variables) will allow vertical accretion at rates that will cope
with rising sea levels (Esteves, 2013). If saltmarshes are
not able to fully develop (e.g., due to the small size or
low elevation of managed realignment (MR) sites), it is
just a matter of time until water levels reach the new line
of defenses and the new intertidal habitats are again lost
due to coastal squeeze (Figure 1b).
MANAGED REALIGNMENT
391