Environmental benefits of managed realignment

Experts from Black and Veatch describe how managed realignment will provide multiple environmental benefits at Hesketh Out Marsh

The Environment Agency, in partnership with Natural England and the Royal Society for the Protection of Birds (RSPB), is proposing to realign a section of the Ribble Estuary coastline at Hesketh Out Marsh East (HOME). The scheme will restore 154ha of agricultural land to inter-tidal habitat, reversing the land reclamation that occurred in 1981.

Situated on the south bank of the Ribble Estuary the site is adjacent to the Ribble and Alt Estuaries special protection area (SPA), Ramsar site and site of special scientific interest (SSSI) and the RSPB Hesketh Out Marsh West Nature Reserve. The nature reserve was created through a similar managed realignment scheme in 2008.

The scheme will maintain a one in 200 year standard of flood protection (ie providing protection during a flood with a 0.5% chance of happening each year) to more than 140 properties in the nearby village of Hesketh Bank.

To achieve this, approximately 2km of the existing inner flood embankment will be refurbished using material excavated from the site. The material will be won from the network of historic creeks and a number of new lagoons. The final element of the scheme will involve cutting the breaches in the outer embankment to reconnect the site with the estuary.

Material for refurbishment of the embankment will be sourced entirely from within the site. This not only minimises the impact on the local population and road network during construction, but also significantly reduces the carbon footprint of the scheme compared with importing material.

Potential environmental impacts were assessed and mitigated through the design development, consultation and preparation of a Habitats Regulations assessment and a statutory environment statement. Black & Veatch provided environmental, planning and engineering design consultancy services for the project and a planning application was submitted in September 2013.

As many realignment schemes, the HOME scheme will result in the residual loss of a large area of agricultural land which cannot be mitigated. However, the refurbished inner embankment and fronting inter-tidal habitat will provide a sustainable flood defence for the next 100 years.

The HOME scheme will:

Provide an improved standard of flood protection and provide an adaption to climate change and associated sea-level rise. Frequent tidal inundation of the site and the subsequent creation of intertidal saltmarsh habitat will serve to dissipate tidal energy and reduce physical forces on the embankment during storm surges.

Deliver Water Framework Directive mitigation measures for the Ribble and Douglas water bodies under the North West river basin management plan. The project delivers a specific action to carry out managed realignment of flood defences on the Ribble by 2027 preserving and, where possible, enhancing the ecological value of marginal aquatic habitat. Saltmarsh habitat also has water quality benefits by locking in nitrogen and phosphate, which derives from land-use diffuse pollution within the Ribble catchment.

Restore saltmarsh habitat. The scheme will provide significant biodiversity benefits and will help the Environment Agency to meet its biodiversity targets under Defra’s Biodiversity 2020 strategy. Saltmarsh creates valuable nursery grounds for juvenile fish and habitats for eels. It is also an important feeding and roosting habitat for waders and wildfowl, and supports diverse plant communities. The significant size of this habitat creation (>150ha) is considered to be important on a landscape scale, and will help to restore the natural morphology of the estuary, restoring connections between disparate landscapes along the coastline. This will make an important contribution to the improvement of sub-regional landscape character.

The provision of saltmarsh habitat is also considered to have a positive impact on human welfare through the provision of numerous ecosystems services. Benefits include:

  • primary production and nutrient cycling;
  • global and local climate change regulation through carbon sequestration;
  • improved tourism and recreation through an extension of the RSPB nature reserve, which will in turn help provide education on our understanding of saltmarsh ecology, and;
  • increased aesthetic value by matching the neighbouring Hesketh Out Marsh West site.

The scheme will be subject to a monitoring and management plan to ensure the anticipated benefits are delivered. It is likely that the Ribble Estuary SPA/SSSI designation will eventually encompass the HOME site.

Managed realignment can provide multiple benefits to both the human and natural environments and a sustainable approach to flood risk management.

This article was written as a contribution to the EIA Quality Mark’s commitment to improving EIA practice.

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