Case study:Medmerry Managed Realignment Scheme

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Location: 50° 44' 10", -0° 48' 42"
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Project overview

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Status Complete
Project web site http://www.gov.uk/government/publications/medmerry-coastal-flood-defence-scheme/medmerry-coastal-flood-defence-scheme
Themes Flood risk management, Habitat and biodiversity, Land use management - agriculture, Monitoring, Social benefits
Country England
Main contact forename Lee
Main contact surname Spicer-Howard
Main contact user ID User:Leespicerhoward
Contact organisation Environment Agency
Contact organisation web site http://www.gov.uk/government/organisations/environment-agency
Partner organisations RSPB
Parent multi-site project
This is a parent project
encompassing the following
projects
No
Whole Medmerry site aerial view - March 2012

Project summary

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Medmerry is the largest managed realignment of the open coast in Europe, on the stretch of coast that was most threatened by coastal flooding in South East England. The Environment Agency (EA) has built 7km of new flood embankment on higher ground and has breached the existing defence, creating intertidal habitat to compensate for Natura 2000 (N2K) loss elsewhere around the Solent. The scheme mitigated for the loss of freshwater SSSI and the impact on important populations of protected species, and created an accessible landscape-scale nature reserve in collaboration with the RSPB and the local community. The Medmerry scheme had 3 key objectives:

1) sustainable flood risk management: It will provide a higher standard of protection to 348 properties in Selsey, as well as key infrastructure such as the main road and waste water treatment works. 2) creation of compensatory intertidal habitat: Delivering 183ha of intertidal habitat, including mudflat, saltmarsh and transitional grassland. 3) involvement of local communities: Creating new access routes and viewpoints for walkers, cyclists and horse riders, and linking Selsey to Bracklesham.

The original flood defence was an artificially maintained shingle bank. This 'hold the line' option offered little opportunity for ecosystem functioning and services. The new Medmerry site is delivering 500ha of functional intertidal, freshwater and terrestrial habitats. The scheme has been designed to be resilient to sea level rise for at least 100 years.

Ecosystem services that the site will provide include: a sustainable and natural approach to flood risk management, in which the habitat will absorb and dissipate the sea's energy; important fish spawning and nursery areas; low intensity mixed farming both seaward and landward of the flood embankment, working in partnership with local graziers and tenant farmers who are helping to develop these opportunities.

As part of the EIA, a Health Impact Assessment (HIA) was undertaken. This highlighted that a new nature reserve, with 10km of new, well managed access for walking and cycling, offers the human health benefits of physical activity and exposure to natural environments. There are educational opportunities for local schools and colleges, which will focus on wildlife and habitats, heritage and flood risk management and sustainability.

Rising sea levels and the economic challenges of maintaining coastal sea defences will make coastal realignment an increasingly sustainable option in the future and will be vital for protecting the integrity of the N2K network. The project demonstrates adherence to the 3 pillars of sustainable development. Social benefits include: a higher standard of flood risk protection to 348 homes and key infrastructure in the local town of Selsey; a greater sense of place and identity for the area and improved recreational facilities with health and educational benefits. Through the creation of the stakeholder group Medmerry Stakeholder Advisory Group (MStAG), and extensive wider community engagement the Medmerry project has given local people the opportunity to influence the creation and development of this reserve.

Economic benefits include: vastly reduced ongoing EA maintenance costs of flood defences, as the shingle beach is no longer the primary defence; benefits to local businesses from the establishment of a new tourist attraction; a fish nursery to help sustain the local fishing fleet; and potential extension of the tourist season through enhanced opportunities for green tourism. The flood defences were completed in Sept 2013 and within months have withstood well some of the worst coastal storms the area has seen for over 20 years. Environmental benefits include: maintenance of the regional N2K network; contribution and enhancement of biodiversity resulting from the creation of new habitats; and improved connectivity between this new reserve and Pagham Harbour nature reserve, as well as providing a stepping stone between Pagham Harbour and Langstone and Chichester Harbours. In addition, the clay for the new embankment was excavated from within the site, ensuring that little material was imported, whilst the borrow pits contribute to the habitat creation.

Work started in September 2011, and on Monday 4 November, 2013, on one of the highest tides of the year along the south coast, Environment Agency Chairman, Lord Chris Smith, unveiled a plaque to celebrate the completion of the Medmerry flood defence.

Innovative ecological mitigation techniques developed during this project, including the problems encountered and solutions adopted, have been documented and can therefore inform the design of future managed realignment schemes, reducing cost and increasing the chances of success.

The Royal Society of the Protection of Birds (RSPB), who helped the Environment Agency design the habitat, is taking on this long-term management role. A 5-year rolling management plan will ensure the scheme habitat and mitigation objectives are met, with an overall aim of maximising biodiversity across the site.

Works included: Building new sea defences inland then breaching the original shingle bank, with habitat creation inland of new defences (including drainage ditches; ponds and reedbeds).

https://www.therrc.co.uk/sites/default/files/projects/sc120015_case_study_6.pdf

Monitoring surveys and results

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This Environment Agency lead scheme has created a naturally functioning and developing mosaic of intertidal, transitional, freshwater and terrestrial habitats which will protect the regional integrity of N2K habitats along the south coast, and contribute to and enhance the conservation status of UK priority habitats and species. It will also contribute to the achievement of Biodiversity 2020. The habitats are designed to be resilient to climate change so that they are sustainable long-term. The originally intensively managed arable farmland which supported a vulnerable population of valuable farmland bird species is now converted to low intensity mixed farmland around the perimeter of the scheme. Birds such as corn bunting, grey partridge and lapwing will thrive in the new farmland mosaic, and ongoing sympathetic management will continue to protect these vulnerable species.

A genetic monitoring programme, undertaken in partnership with Brighton University, will provide valuable information about how well the founder population of water voles establishes in the new freshwater habitat. Genetic data has been taken from the water voles that were translocated and from others that remained in the site during the inundation. Future projects will therefore be able to use this information to help develop appropriate mitigation strategies for water voles.

The project team has worked with local voluntary groups and Universities, to involve students in long-term monitoring of the habitat and species establishment. Brighton University currently have masters and PhD students undertaking research that includes the Medmerry scheme. There is also the potential to include Medmerry in core environmental and wetland modules. The team continue to work with local wildlife and heritage groups to ensure their ongoing involvement in the site.

Further monitoring will be undertaken, as part of the RSPB management plan, to understand how the ecosystem services such as fish spawning and nursery areas and public enjoyment of the site develop over the coming years. d.

Lessons learnt

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The key learning points:

• Good planning required to fully understand a large site, ensure surveys are specific from an early stage, understand the difficult areas in detail • Good communications internally and externally are essential, consider using a RACI tracker for large project teams • Involve archaeology fieldworks as early as possible to understand risk and investigation techniques such as GPR and intrusive works.

We have worked with voluntary groups and Universities, to involve students in long-term monitoring of the habitat and species establishment. Brighton University currently have masters and PhD students undertaking research that includes Medmerry. There is also the potential to include Medmerry in core environmental and wetland modules.

Lessons from translocating water voles, have been published in 'In Practice' to ensure good practice is circulated amongst professionals. This includes specifications of water vole exclusion fencing; for example, the mesh size formerly recommended in the water vole conservation handbook proved to be too large, allowing juvenile water voles to pass through. A full lessons learnt exercise and an CIWEM site visit are planned for the summer of 2014.

As expected the shingle beach, which used to be the flood defence, has rolled backwards and has been flattened by the sea. This does not impact the flood risk because the inter-tidal area that the scheme has created acts to absorb and dissipate the sea's energy.


Image gallery


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Catchment and subcatchment

Catchment

River basin district South East
River basin Arun and Western Streams

Subcatchment

River name Broad Rife
Area category Less than 10 km²
Area (km2)
Maximum altitude category Less than 100 m
Maximum altitude (m) 9
9 m
0.009 km
900 cm
Dominant geology Siliceous
Ecoregion Great Britain
Dominant land cover Arable and Horticulture
Waterbody ID GB107041006580



Site

Name
WFD water body codes GB107041006580
WFD (national) typology coastal
WFD water body name Broad Rife
Pre-project morphology
Reference morphology
Desired post project morphology
Heavily modified water body No
National/international site designation
Local/regional site designations
Protected species present No
Invasive species present No
Species of interest
Dominant hydrology
Dominant substrate
River corridor land use
Average bankfull channel width category
Average bankfull channel width (m)
Average bankfull channel depth category
Average bankfull channel depth (m)
Mean discharge category
Mean annual discharge (m3/s)
Average channel gradient category
Average channel gradient
Average unit stream power (W/m2)


Project background

Reach length directly affected (m)
Project started 2011/10/01
Works started
Works completed
Project completed 2013/10/01
Total cost category
Total cost (k€) £30m
"£" is not declared as a valid unit of measurement for this property.
Benefit to cost ratio
Funding sources Flood Defence Grant-in-Aid

Cost for project phases

Phase cost category cost exact (k€) Lead organisation Contact forename Contact surname
Investigation and design
Stakeholder engagement and communication
Works and works supervision
Post-project management and maintenance
Monitoring



Reasons for river restoration

Mitigation of a pressure Coastal Flood Risk Management
Hydromorphology Shingle bank vulnerable to storm damage, Management was unsustainable with high cost to maintain
Biology Intertidal habitat creation; Offsetting losses of internationally designated habitat associated with Coastal Flood Risk Management schemes in the Solent. 183ha of inter-tidal compensatory habitat (Outcome Measure 4) created. Freshwater habitat creation; network of freshwater habitat created to mitigate scheme impacts on water voles etc.
The wikipage input value "Intertidal habitat creation; Offsetting losses of internationally designated habitat associated with Coastal Flood Risk Management schemes in the Solent. 183ha of inter-tidal compensatory habitat (Outcome Measure 4) created. Freshwater habitat creation; network of freshwater habitat created to mitigate scheme impacts on water voles etc." contains invalid characters or is incomplete and therefore can cause unexpected results during a query or annotation process.
Physico-chemical
Other reasons for the project


Measures

Structural measures
Bank/bed modifications
Floodplain / River corridor Built new sea defences inland then breached original shingle bank, Habitat enhancement, Drainage ditches, Reedbed creation, Creation of pond
Planform / Channel pattern
Other Constructed new freshwater outfall structures
Non-structural measures
Management interventions
Social measures (incl. engagement) The Medmerry Stakeholders Advisory Group (MStAG), which includes representatives from local councils, residents’ groups, access groups and conservation organisations, guided the scheme design.
Other


Monitoring

Hydromorphological quality elements

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative

Biological quality elements

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative

Physico-chemical quality elements

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative

Any other monitoring, e.g. social, economic

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative


Monitoring documents



Additional documents and videos


Additional links and references

Link Description
http://www.gov.uk/government/publications/medmerry-coastal-flood-defence-scheme/medmerry-coastal-flood-defence-scheme Fact sheet
http://www.youtube.com/watch?feature=player embedded&v=x7jemyJujg8 YouTube link to Medmerry Scheme
http://www.flickr.com/photos/environment-agency/sets/72157631063812816/ Flickr pictures

Supplementary Information

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