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Jacobs: HS2 Colne Valley Landscape and Habitat Creation

By re-using construction materials, the project will create 127 hectares of new chalk grassland, woodland, wood pasture and wetland habitats to deliver a substantial ecological gain in the Colne Valley.

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  • What we know
  • What we’re doing
  • What it’s worth

What we know

In addition to increasing capacity on the UK’s busy railways, HS2’s primary aim is to modernise and connect major destinations across England by forming a new national backbone of state-of-the-art high-speed rail. [source]

As well as offering a fast, low-carbon option for long-distance travel, the numerous infrastructure projects that make up the wider scheme offer a multitude of opportunities to use innovation and sustainable design to ensure positive local outcomes for both people and nature.

One such project is set in England’s Colne Valley, where the new high-speed rail line traverses the western slopes of the valley between crossing the River Colne on the 3.2km viaduct and the bored tunnel under the Chilterns escarpment. Prior to HS2’s construction the area has consisted of arable farmland, however, the landscape was once home to calcareous grasslands, a chalk-based habitat that’s valuable but rapidly declining across the UK. [source]

What we’re doing

The Colne Valley project represents a synthesis of innovative landscape and ecological design alongside cutting-edge engineering best practice. More than the infrastructure needed to construct a railway viaduct, the result will include a varied landscape of tree-lined ridges, wood pasture, wetland, restored calcareous grassland, and recreational routes.

Chalk arisings from the boring of the Chiltern tunnel will be placed in layers and capped with local soils to create calcareous grasslands in the area. This presents a dual benefit of eliminating the need to remove these arisings to off-site and the associated carbon emissions in doing so, whilst creating a valuable habitat.

Noise levels from the operating railway, a sensitive issue on any transportation project, have been carefully considered and control measures developed through collaborative working amongst the design team.

With consideration to the ecological and landscape requirements the earthworks design has been refined to provide a high level of acoustic screening and eliminating the need for unsightly acoustic barriers. While these are unavoidable on the viaduct, the barriers have been carefully integrated into the design and provide the best possible acoustic performance while meeting the architectural and other design aspirations in this sensitive area.

illustration of three birds in navy

What it’s worth

The 140-ha site within the wider Colne Valley will be landscaped using 2.6 million cubic metres of chalk arisings from the 16-km long Chiltern tunnel.

The diverse landscape mosaic will support biodiversity through habitat creation and connectivity, climate change mitigation through the creation of habitats with higher carbon sequestration than the baseline, and social amenities and well-being will be supported by containing over 4 km of recreational routes.

A long-term rewilding approach will allow habitats to function naturally and require minimal management intervention. Calcareous grassland is one of the richest habitats found in Western Europe, containing over 40 plant species per square metre. It is a unique habitat, with 50% of the world’s occurrence being found in the UK, but with significant declines since the Second World War.

The landscaped improvements to the Colne Valley site will create approximately 88 ha of new calcareous grassland and 26 ha of woodland. This success story for biodiversity, along with acoustics and a multitude of other design elements will significantly contribute to HS2’s legacy.