HS2 reveals plans to create huge area of chalk grassland at the edge of the Chilterns in Colne Valley
An ambitious scheme, designed by HS2’s landscape architects, ecologists, engineers and soil specialists, aims to reuse construction materials to create 127 hectares of new chalk grassland, woodland, wood pasture and wetland habitats that will substantially enhance the local natural environment.
It is hoped The Colne Valley Western Slopes project will go some way to help meet HS2's Carbon reduction targets.
HS2 hope it will deliver a 'significant ecological gain' in the area.
Plant species and habitats are being carefully selected to be resilient to a changing climate.
Almost 65,000 trees and shrubs of 32 species will be planted together with nearly 3.5km of new hedgerows, say HS2.
Around 90 hectares of calcareous grasslands which once thrived on the valley slopes will be established and areas of historic woodland reinstated.
It is also claimed that the project, being designed and delivered by HS2’s civils contractor Align, will provide wider health and recreation benefits for neighbouring communities including the provision of new connected green spaces and around 4.5km of new footpath, cycling and horse-riding routes.
Arable land that is initially needed for a major works compound to construct the Colne Valley Viaduct and Chilterns Tunnel will be transformed through the re-use of existing soils and recycling of three million m3 of chalk taken from the tunnel excavation, as well as concrete and limestone aggregate materials used in the construction process.
HS2 said: "Reusing materials rather than transporting them away by road will significantly reduce carbon output.
"The excavated material will be used to re-establish the locally distinctive chalk valley landscape, replicate natural drainage flows and establish the right growing conditions for calcareous grassland across the site.
"Calcareous grasslands, which develop on shallow soils overlying chalk or limestone, are a valuable, scarce and rapidly declining habitat in the UK, with this decline reflected in both the Colne Valley and adjacent Chiltern Hills. The neighbouring Chilterns Area of Outstanding Natural Beauty is currently thought to support around 700 hectares of chalk grassland. This collaborative project will provide a unique opportunity to create one of the largest extents of such habitat in this area.
"New planting and seeding will create an extensive mosaic of habitat that will potentially be colonised by hundreds of species of flora and fauna, including invertebrates, birds, mammals, reptiles and amphibians."
HS2’s Environment Director Peter Miller said:
“This project forms a major part of HS2’s Green Corridor programme to establish better connected, sustainable and biodiverse landscapes along the route of the new railway that will contribute substantially to HS2’s carbon reduction target. It demonstrates HS2’s approach to addressing many of the complex issues surrounding climate change and which are central to protecting our environment, and is a great example of how good design and planning can mitigate the effects of climate change.”
Matt Hobbs, Ecology lead from Jacobs (on behalf of Align-D) said:
“The Colne Valley Western Slopes is a unique opportunity to give something back for wildlife by creating a large new reserve dedicated to nature in the Colne Valley. The design will deliver habitats that are the biggest and best possible, and those that will succeed and thrive over the long term with minimal human input.
“We initially focussed on soils and substrates, the essential building blocks for the habitats, and ensuring they are provided using site-won soils, chalk and temporary works materials. The key challenge is creating the necessary physical and chemical characteristics of the soil profiles to support resilient, biodiverse grasslands and the specialist species that thrive there. This is the subject of an innovative research study with Cranfield University and Tim O’Hare Associates that will involve both laboratory and field trials during construction to fine-tune the design.
“A key challenge with habitat creation is how to establish and then maintain the habitats over the long term. The team’s approach uses local land managers who will let natural processes operate and introduce free-roaming livestock to graze the habitats year-round. This will reduce management inputs, increase soil health, soil carbon, and overall biodiversity, while creating a dynamic landscape of wood pasture and wetland over time. The designs include all the necessary infrastructure to support grazing animals year-round including fencing, cattle grids, management areas and wetlands for watering.
“Numerous small-scale features have been included to diversify the habitat further. These include s-shaped sparsely vegetated banks for reptiles and invertebrates, and hibernacula to provide refuges for reptiles and amphibians, as well as localised variations in topography to provide niches for many species to colonise.”
Align is currently preparing the site for the launch of the two tunnel boring machines that will excavate the 16km-long Chiltern Tunnels. Once launched in 2021, the site will receive a continuous supply of chalk until tunnel completion in 2024. Field trials are in preparation ahead of final seeding, and planting of trees and shrubs in 2025. At peak, around 1,200 people are expected to be employed in the design and construction of the Chiltern tunnels and the viaduct, with 50 opportunities for apprentices.
Once detailed design is complete, the local community will be able to see the full plans at our online ‘you said, we did’ webinars which are currently planned for:
Webinar 1 – 23 March, 12:30pm
Webinar 2 – 25 March, 18:30pm