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Closer look: Reducing HS2's environmental impact in the Colne Valley

Words: The Planner

HS2 has been criticised for its environmental impacts. But at least one approach to limiting – and mitigating – harm has received a thumbs-up from environmentalists

Read the related article: Leader of the track: An interview with Paul Gilfedder

As HS2’s Head of Planning, Paul Gilfedder  juggles a myriad of challenges. He tells Huw Morris about working on the UK's biggest transport and regeneration project.

1. Environmental impact: The environmental effects of HS2 are a source of contention. The Woodland Trust says phase 1 will directly affect more than 32 ancient woodlands and indirectly affect another 29 through noise and air pollution. Six have already been felled, according to the Trust, and another – Jones’ Hill Wood in Buckinghamshire, which is thought to have inspired Roald Dahl’s Fantastic Mr Fox – is about to lose 1.7 of its 4.4 hectares. One of the ways HS2’s planners are looking at mitigating this damage is through ‘translocation’ of plants, soils, stumps that can regrow, and dead wood to a nearby location.





2. Ancient soils: Soil complexity is a defining characteristic of ancient woodland. These are woodlands that have existed since at least 1600 and have taken centuries to evolve into our richest terrestrial habitats. Typically, they have developed ecological communities of plants and animals that are not found elsewhere, including many of our threatened species. Once vast, they now cover just 2.5 per cent of the UK. Ancient woodland indicator plants include bluebell, primrose, the wild service tree and herb paris. Watch a short Woodland Trust video about ancient woodland.



3. New planting: In mitigation, HS2 points out that damage will be minimal and that 730,000 new trees have already been planted as part of landscaping that will create 33 square kilometres of new woodland and wildlife habitat en route – a 30 per cent increase over what currently exists. Critics say new planting is no replacement for ancient woodland.









4. Chiltern Tunnel project: The Woodland Trust has, however, given a cautious thumbs up to the Chiltern Tunnel scheme in the Colne Valley, which will save nine hectares of ancient woodland while creating 127 hectares of new grassland, woodland and wetland. The twin-bored 16-kilometre tunnel will carry passengers beneath the Chiltern Hills. The scheme will also incorporate the 3.4km Colne Valley viaduct, Britain’s longest railway bridge.







5. Meet Florence and Cecilia: Two tunnel boring machines – Florence and Cecilia – arrived in the UK last December. At 17 metres long and 2,0000 tonnes each, they will be the largest ever used in the UK and will operate non-stop for three years. As they dig, they’ll line the tunnel with 56,000 concrete wall segments, all made on site. Watch a two-minute video on the tunnel-boring process.








6. A new landscape: The tunnelling will produce around three million tonnes of chalk spoil, which will be the foundation for 90 hectares of new chalk grassland, which once thrived on the valley slopes. This mitigation scheme has been designed by Align JV, an ecological consultancy set up for the purpose by infrastructure companies Bouygues Construction, Sir Robert McAlpine and VolkerWessels.






7. Soil profiling: Align has commissioned Cranfield University and Tim O’Hare Associates to research the physical and chemical characteristics of the soil profiles that will support resilient, biodiverse grasslands and conduct field trials during construction. “A key challenge with habitat creation is how to establish and then maintain the habitats over the long term,” says Matt Hobbs, ecology lead from Jacobs, on behalf of Align.

Among other features being added to the Colne Valley western slopes are S-shaped sparsely vegetated banks for reptiles and invertebrates, and hibernacula to provide refuges for reptiles and amphibians.


8. A home for skylarks: Lime-rich but low in nutrients, the thin soil of chalk grassland is poor for grasses, allowing smaller plants to flourish. This is a habitat noted for flowers such as small scabious and common bird’s foot trefoil, as well as rarer plants like the monkey orchid. It’s also home to beetles and bees, rare butterflies and threatened birds such as the stone curlew and skylarks, which nest on chalk grassland. The UK has lost 80 per cent of its chalk grassland since the Second World War. The Colne Valley mitigation scheme goes at least some way to returning this important habitat to one of its native locations.



Photos | HS2; Alamy; iStock