Many lessons have been learned, to such extent that the principle of Managed Realignment is becoming a reliable practice. Nevertheless, as several systems need more time for ‘full response’ more lessons can still be learned from log-year monitoring campaigns.
Design / technical issues
- The planning process is complex and often causes long delays, both in terms of technical details and obtaining consents. Many of the issues seem to be due to the relatively novel nature of Managed Realignment. Experience from these early cases could be documented to provide useful information for future cases and accelerate the process (DEFRA, 2008).
- There is a need to better understand risks and uncertainty associated with Managed Realignment, particularly when compared to “traditional” Hold the Line schemes. Uncertainties include the lack of ability to predict physical processes, anticipation of longer periods required to obtain consents and licences and estimating long-term maintenance costs or other similar factors. Quantifying these would assist decision-makers, who are usually risk-averse, in bringing forward more schemes (DEFRA, 2008).
- Technical issues about how best to help natural succession of habitats, model channels and the development of creeks, as well as obstacles such as the presence of heritage resources and how best to protect them, can be costly and timeconsuming to resolve. It appears that much could be gained from a better monitoring of intertidal environments (both natural sites and those resulting from human intervention) and from EU-wide collaboration / exchange of technical information (DEFRA, 2008). See below for succes factors.
- Monitoring periods of five to ten years, commonly required as permit conditions, may provide valuable information on whether the site is evolving as anticipated. However, this period is generally not long enough to inform improvements in planning and design of future projects (Williams, 2004).
- The design of many early restoration projects was focused on the achievement of vegetated marsh functions as rapidly as possible and, in doing so, discounted the value of interim habitats and the value of a mosaic of evolving habitats (Williams, 2004).
- Early restoration projects were not planned and designed following a rigorous methodology that clearly established the linkage between design decisions and predictions of how the site would evolve to meet restoration objectives. This has sometimes made it difficult to assess performance in a way that would help us improve design decisions (Williams, 2004).
- Some early restoration projects were based on goals for developing suitable habitat for a particular target species. Overall project objectives should be clear at the outset with due consideration given to the needs of other target species and the marsh as a part of the whole ecosystem (Williams, 2004).
Succes factors for wetland restoration
Wolters et al (2005) evaluates the success of many de-embankments in north-west Europe, especially in the UK, Netherlands and Germany. In this (scientific) review, success has been measured as a saturation index, where the presence of target plant species in a restoration site is expressed as a percentage of a regional target species pool. Also factors that affect restoration success are determined as well as recommendations for future restoration schemes.
Factors that affect restoration are:
- Surface elevation
In salt-marsh systems, elevation in relation to tidal inundation is generally accepted as the major abiotic factor governing the establishment and survival of halophytes at different zones within the range from mean high water neap (MHWN) to mean high water spring (MHWS) tide levels. Other studies reveal that the rate at which vegetation develops in de-embanked sites is determined by the initial elevation or that sites lower than 1.5 m below high water spring tides will fail to colonise with salt-marsh vegetation. However, initially low elevation in itself may not be a problem if sedimentation rates are high enough. For the sustainability of re-created and established salt marshes it is required that rates of surface elevation change are at least equal to local rates of relative sea-level rise.
Williams (2004) further suggests that:
- Restoration projects (and unplanned restorations) that took advantage of natural sedimentary processes to form an accretionary marsh that evolved over time have performed as well or better than highly engineered projects that attempted to replicate the form of a mature marsh.
- Many early restoration projects had unrealistic expectations of the rate at which a fully vegetated marsh would form. One should expect restoring wetland sites to take at least several decades to evolve towards a mature state in balance with sea level rise and sedimentation.
Size of restoration sites
It has been established that, for a variety of organisms and habitats, a linear relationship exists between the number of species and the size of the area (plotted on a log scale). Therefore, the size of restoration sites may be an important determinant of success in restoration sites. The best results are found for sites larger than 100 ha. It should be noted however, that the width of a site (i.e., the line perpendicular to the coastline) is likely to be more important than the length(i.e., the line parallel to the coastline), due to zonational processes leading to higher species diversity.
Soil salinity is an important factor affecting the composition of salt-marsh vegetation. High salinities for example may prevent germination and seedling establishment, whereas low salinities allow glycophytes to outcompete halophytes.
2) Accessibility of the site
A prerequisite for the successful restoration of salt marsh communities is the availability of a target species source and the ability of the species to reach the target area. The best results may be expected when the target species are still present in the community species pool of the target area, which consists of the established vegetation and the soil seed bank.
It is generally assumed that the distance between the target area and a target species source will largely determine the chance of a species arriving in the target area. Thus, better results may be expected when an established salt marsh (i.e., local species pool) is directly adjacent to a de-embanked site.
Construction and maintenance of drainage structures
At the start of the restoration, artificial creeks may be required to improve drainage, increase colonisation rates and may assist in supplying sediment to the salt marsh surface. In some restoration sites therefore, meandering creeks are dug deliberately. Another factor affecting creek development is the composition of the soil subsurface. Apart from the role of creeks, drainage is also affected by the size of the opening in the embankment. For example it is reported that enhanced salt-marsh vegetation development when culverts were enlarged by ca. 1m in diameter. Lowering of the elevation at which the culverts were placed did not increase success.
Grazing or mowing regimes
Species diversity may be maintained over time by the implementation of a grazing or mowing regime. The dominance of tall species results in the suppression or disappearance of species of shorter statue and loss of diversity, so the level of species diversity must be maintained over time. Apart from the effect on the vegetation, grazing may also affect soil salinity and surface elevation change. So, the implementation of a grazing or mowing regime creates create heterogeneity in the soil and vegetation and prevent dominance of a single species. A prerequisite for this type of management is that the sites are high enough for the establishment of vegetation communities suitable for grazing or mowing regimes.
Communication / public perception
Appropriate consultation and public participation are important in developing any scheme (DEFRA, 2008). Involving stakeholders is not easy. It is time consuming, intensive in management time and can lead to outcomes that are not in the best interests of strategic flood management. Managed Realignment is a complex issue, which needs to be explained, and expectations need to be managed. Constructive ways to inform and involve the local communities both at an early stage of the scheme, and for monitoring purposes need to be explored. This can help to reduce delays, for example resulting from a Public Inquiry. The difficulty is in finding how best to “sell” the scheme to local communities, as this will vary across the sites.
CIRIA (2004) provides some recommendations on reporting and the use of the media:
- As the managed realignment scheme develops, periodic reports should be issued in an easily understood and accessible format. The frequency of reporting should be in proportion to the size, complexity and sensitivity of the project and the extent to which the scheme has developed. For large or sensitive projects, quite frequent reports may be required at inception, perhaps annually for the first five years and subsequently at significant milestones. The timing of reporting might also be aligned to monitoring requirements and the provision of updated or new information about the project.
- The reporting should include the problems faced and how they were overcome. It is advisable to be open and transparent about what has occurred, including detrimental outcomes or where the reality of what occurred differed from what was expected, both during and after the scheme implementation. This approach is more likely to reduce problems with the local community in future years, especially if part of the scheme develops differently from the project expectations and changes have to be made. Also, understanding the issues will help professionals to develop further tools and techniques to support managed realignment and to share best practice solutions to problems. This will help reduce uncertainty and risk in future schemes and would provide a positive contribution to future R&D work.
- Particularly for large or sensitive sites (or several smaller linked sites) public perception issues should be addressed through local or national media.
- Local television and newspapers are important additional media that can deliver messages regionally, while for large schemes with high risks it may be helpful to include national television and newspapers.
- It is important to ensure that messages come from an identified individual (a spokesperson) for consistency and familiarity.
Finance and regulations
Some lessons learned on finance and regulations are:
- Financial compensation to landowners appears to have been a key factor in the success in some earlier projects. The desirability of increased provision of financial compensation to individual stakeholders such as landowners who are adversely affected by Managed Realignment is a strong theme identified (DEFRA, 2008).
- Apart from land acquisition, the largest restoration cost is usually earth moving. Many design decisions have significant grading cost implications yet are based on very limited data and analysis (Williams, 2004).
- Environmental benefits and costs should be included explicitly in economic appraisals of schemes and be taken into account by the scheme prioritisation system, while taking care that there is no overlap between the economic and environmental criteria (DEFRA, 2008).
- The Habitats Regulations and planning process are likely to cause significant delays, especially where European nature conservation sites are involved. Experience suggests that Managed Realignment schemes will almost always take longer than hold the line (or non-intervention) schemes, which can be an important issue in the context of urgent flood works. A realistic time scale needs to be allowed for at the outset (DEFRA, 2008).
- Reducing the political sensitivity of Managed Realignment would contribute to enabling more balanced consideration with other coastal defence options and therefore better integration into the strategic planning process. Mechanisms for this could include public education about benefits of Managed Realignment in situations where it is appropriate and providing financial compensation to landowners, so as to reduce the perception that such benefits are achieved at the expense of private loss (DEFRA, 2008).
Do they work?
New salt marshes created as part of managed coastal realignment are failing to meet European conservation regulations, according to a recent study by Mossman et al. (2012) from the University of East Anglia (UEA), http://www.guardian.co.uk/environment/2012/sep/20/man-made-saltmarsh-plants.
Under the EU Habitats Directive, new salt marsh must be created each time natural salt marsh is lost to coastal development or to coastal erosion caused by sea-level rise. The new marshes must display “equivalent biological characteristics” to their natural counterparts – but the new findings, published in the Journal of Applied Ecology, reveal that artificially created salt marshes suffer significantly reduced biodiversity.
The UEA researchers analysed the vegetation of 18 marshes created through deliberate coastal realignment since 1991 and 17 marshes created accidentally by storm surges since 1881. They compared the salt-tolerant plants at these sites with those at 34 natural salt marshes and found that some key species were very poorly represented. These included sea lavender, thrift, sea arrowgrass and sea plantain.
“Salt marshes such as those in North Norfolk, Essex and around much of the coast of England are loved by naturalists and tourists alike for their natural beauty and rare/rich ecology,” said lead author Dr Hannah Mossman of UEA’s School of Environmental Sciences. “These unique tidal areas also provide vital habitat for invertebrates, a staging post for migrant birds, and the only environment in which a number of salt-tolerant plants can survive.”
Prior to this in-depth five-year study it had been assumed that this process caused no loss of species richness and that manmade marshes compensated well for the loss of natural ones. The researchers found, on the contrary, that plant life on artificially created salt marsh tended to be dominated by early-colonizing plants such as marsh samphire because of a lack of oxygen in the sediment. Shrubs such as sea purslane can also quickly become unduly dominant. The sites tended to be flat and featureless with scrappy vegetation. Even the older accidentally-created marshes were deficient in the characteristic salt marsh perennials such as sea lavender, thrift, sea arrowgrass and sea plantain.
“Our findings demonstrate very clearly that marshes created by managed realignment are not biologically equivalent to natural ones and therefore fail to satisfy the biodiversity requirements of the EU Habitats Directive,” said co-author Prof Alastair Grant, of UEA’s School of Environmental Sciences.
Prof Anthony Davy, of UEA’s School of Biological Sciences, added: “These created marshes are certainly better than losing our precious natural salt marsh altogether, but they are not a good enough replacement. We are currently developing ways of enhancing their biodiversity, such as improving local drainage conditions and planting the deficient species.”