Wetland Restoration - Wallasea, GB
Location: Wallasea, UK
Date: 1997 – 2005, and 2006 - 2011
Involved parties : Defra, Environment Agency ComCoast, RSPB, ABP Mer, Westminster Dredging bv
Technology Readiness Level: 6 (Prototype system tested in intended environmental close to expected performance)
Environment: Delta lakes
Keywords: habitat creation, port development, compensation measures, additional environmental value, ecology
|Building with Nature design||Traditional design|
An EDD approach to wetland restoration implies that both location and design are highly influenced by environmental factors, but also include an integral approach. In case of Wallasea the location is carefully chosen to have the largest additional environmental value without destroying any of the existing environment. The wetlands are not only aimed to compensate for nature losses, but also to (indirectly) provide flood protection and to serve recreational purposes.
A traditional approach to compensating measures such as wetland restoration would spend as little effort as possible to just meet the requirements. Most probably, the process would be dictated by the authorities.
On Wallasea Island, large wetlands are reconstructed that simultaneously form a nature area; a flood storage facility and a recreational area.
To compensate wetlands and (bird) habitat losses caused by harbour development along the British coast, suitable locations are to be reopened to the sea.This ‘Managed Realignment’ is realized here by bank realignment, i.e. removing large parts of the existing embankment and building a new one further inland. The primary purpose in this case is to create new wetlands that will function as bird and wildlife habitat. A beneficial side effect is creating a sustainable flood corridor reducing flood and surge levels. A suitable location no too far from the lost wetlands was looked for, a location where the realignment would have a positive effect on the estuary and the existing wildlife.
The ideal location was found on the island of Wallasea. On the northern shore of the island 115 hectares of wetland was created forming the largest man-made wetland in Europe. The wetlands are supposed to provide for a new bird and wildlife habitat, add to flood protection, mitigate climate change and create recreational opportunities. Creating a buffer zone by laying back the embankment is a good solution to the re-naturalization of low-value land.
The solution at Wallasea constitutes an integral approach of PPP. The environmental factor to create (bird) habitat is the primary goal, but socio-economic goals such as flood protection and recreation are also included.
One of the governance issues was the large number of permits needed. This process was accelerated by early consultation of the public, as public perception was recognized to be of importance. Furthermore, early involvement of all stakeholders has been an essential part of the project. As such, national and local authorities were included in the planning and design phase.
After port construction at Lappel Bank in the Medway Estuary and at Fagbury Flats in the Orwell Estuary, 86 hectares of wetland were lost. In 1997 the British government ordered for these losses to be compensated. The Department for Environment Food and Rural Affairs (DEFRA) was in charge of this process.
Planning and design phase
After three years of studying, Wallasea was chosen in 2004 as the location for the creation of compensating wetlands. For various reasons: this island was chosen as the best suitable for Management Realignment, the area was large enough to compensate the wetlands lost, dredged material from maintenance dredging of a nearby port could be used, the existing sea walls were in need of improvement and studies showed that the construction itself would not damage the surrounding area or adversely impact present bird and wildlife populations.
The design was fine-tuned by Associated British Ports (APBmer), after a design by Defra, with help of numerical modelling and a study of the existing wild life. Aim of the design was also to minimize the impact on the estuary. Local authorities joined in the designing phase.
The design includes three separate areas with no water exchange between them, other than via the main estuary. Therefore, each of them could be given its own identity. Dredged materials were used to create salt marshes and to construct a new embankment inland from the old one. Attract rare lagoon habitants into the saline lagoon was part of the design.
The new wetland area will function as flood protection. The mudflats and marshlands will reduce the tidal wave energy and thus, will shape a natural flood defense.
Next to the environmental and safety issues, the design also meets a number of socio-economic goals, such as eco-tourism and fisheries. A four kilometers footpath will attract people, as will the beach. Because, most tourism is concentrated in summer, this will not interfere with the nesting season of the birds.
The total size of the new wetlands is twice as large as the required size to compensate for lost values. Moreover, the design includes multiple features to enhance the biodiversity within the wetlands.
Building with Nature?
The wetlands at Wallasea serve various infrastructural purposes (flood protection, recreation, wetland habitat) and create additional environmental value. The size of the new wetland does not only compensate for the areas lost during port construction, but is larger than required. Also, the integral design that includes environmental, social and economical is a good example of EDD.
During the construction phase dredged material from the port of Harwich was deposited behind the old sea dike to create salt marshes. Furthermore the dredged material was used to build a new, higher sea dike inland from the old one. The salt marshes and the new sea dike form an integrated flood protection system. Afterwards, the old dikes were breached to allow water at high tide to inundate the land and to let mudflats and salt marshes evolve naturally.
Final breaching work Mud is pumped into a retaining bund to settle
Operation and Maintenance
In the first year after completion, the ownership of the land was handed over by Defra to local authorities and the Royal Society for the Protection of Birds (RSPB). In the wetlands first signs of results were found, such as bird, wildlife and wetland vegetation. The expectations are that the wetlands need at least 5 years to mature and to get all the expected flora and fauna. During these 5 years the wetlands will be monitored closely and the interesting lessons learned will be shared with the public.
The initial monitoring is still ongoing, and the full results remain to be reported. However, from the interim progress reports that have been produced by ABPmer and Jacobs up to the end of 2010 (i.e. up to four years after the breaching), the following general observations can be made:
Breaches and channels
The breaches and channels through them are very stable which confirms the effectiveness of the approaches underlying their design.
Within the site, sediment accretion has occurred relatively consistently and evenly due to the slow flows and stable internal creek/channel configurations. In the first year after breaching (2006 to 2007), accretion was around 10 cm (of which about 50% is considered internally relocated materials and 50% externally imported sediments). In each subsequent year, annual accretion assumed to consist predominantly of imported sediments amounted to 3 to 5 cm on average (specifically 5 cm in both 2008 and 2009, and 3 cm in 2010).
The accretion and the relatively stable and depositional nature of the environment has helped to promote rapid benthic invertebrate colonization of the mudflat (about 80 ha in extent). After the first, year invertebrates abundance was at 20,000 organisms/m2 and has ranged between 10,000 and 20,000 organisms/m 2 in each successive year. The benthic assemblages have been dominated by large numbers of mud snail (Hydrobia ulvae) and although the patterns of organism recruitment are clearly complex and variable, there is evidence that the assemblages are maturing over time. One indication is the increase of bivalve species over time (representing 2%, 4%, 14% and 26% of the populations in each successive year).
The bird monitoring (by CJT Ecology) shows that in the first four years of the monitoring programme the site has been supporting very good numbers of waterbirds. This was already the case in the first winter survey (2006/07) when the site supported around 7,000 waterbirds and included good numbers (i.e relatively high in a national or international context) of many key species such as Shelduck, Dunlin, Black-tailed Godwit, Ringed Plover and Golden Plover. In the following two winters the value of the site continued to grow as the abundance of waterbirds increased to around 10,000 and then 12,000. In the winter of 2008-2010 the overall abundance levels declined slightly. These overall trends are strongly influenced by some major inter-annual changes in the abundance of certain species which, in turn, are likely to be influenced by the weather conditions.
Fixed-point photographs showing
the rate of saltmarsh development.
In 2009/10, for instance, particularly bad weather conditions were experienced as compared with other years. Moreover a range of other factors influence the natural variability of bird populations (e.g. breeding success, timing of migrations, national population trends and inter-annual or inter-generational changes in roosting/feeding site selection).
It is worth noting however, that the numbers of birds using the site as a roost reduced in 2009/10, whereas the number of birds feeding increased. This may indicate that the habitat and the relationship with migratory birds are still developing and maturing, or that under adverse weather conditions the site's feeding and roosting functions exhibit opposite trends.
Saltmarsh coverage of elevated areas of the sites (approx 25 ha in extent) has occurred relatively rapidly. On average plant coverage (i.e the amount of marsh plant compared to bare mud at any given location) has rapidly increased from less than 1% in 2007 via 6% in 2008 and 60% in 2009 to ultimately near 100% in 2010.
The project at Wallasea is considered successful; the parties involved have indicated a number of success factors of the project and its process, factors that can each be considered a lesson learned.
The first success factor mentioned is the (early) involvement of the broad public, NGOs, the Harwich Harbour Authorities and Westminster Dredging, as supplier of the 'construction' material. Early and continuous consulting and informing of the public has led to them to accept and support the project. It is emphasized that especially clear graphics and visuals have to be integrated in the communication process. Involvement of other stakeholders has enhanced the integral approach of the project. Moreover, handing over the ownership to local authorities has also led to close involvement and success.
The integral approach can be considered another success factor. Important aspects mentioned are:
- Seek multiple benefits beyond the principal project objectives
- Consider impacts on and benefits to the expected users of the area
- Use a range of relevant techniques and tools to select suitable sites and develop effective designs.
A third lesson learned concerns the project governance. An involved and enthusiastic coordinator and a good management structure have proven to be crucial to a successful project.
At least two out of these three lessons learned closely relate to the EDD approach described in the BwN Guideline, viz. early stakeholder involvement and an integral approach.
- Maunsell, F., 2006. Wallasea Wetland Creation Project - Submission for RSPB/CIWEM Living Wetlands Award 2007
- ABP Marine Environmental Research Ltd, 2011. Case Study on the Wallasea (North) Managed Realignment Scheme (England)
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