Practitioners from Atkins and the Blackwater Valley Countryside Partnership describe how green infrastructure can mitigate significant environmental effects
The Blackwater Valley is an area of open space, dominated by a chain of lakes, separating urban areas on the Surrey, Hampshire and Berkshire borders. Rapid urban expansion led to the degradation of the landscape and traffic congestion along the valley.
The Blackwater Valley Countryside Partnership was formed in the 1960s to tackle neglect and pollution, and now works to increase the valley’s importance for biodiversity and as a recreational resource for local people. The partnership was involved throughout the construction of the Blackwater Valley Road and remains responsible for management of the green infrastructure retained and created as part of the scheme.
The Blackwater Valley Road comprises 17km of high-speed dual carriageway linking the A30 with the A31 and M3. It was conceived in the 1960s and built in four stages between 1985 and 1996 by Hampshire and Surrey County Councils. Each of the four stages was the subject of a separate environmental impact assessment (EIA); making them some of the earliest road schemes to be subject to EIA in the UK.
The EIAs recognised the road would have significant effects on ecology as a result of:
- a net habitat loss of 38 hectares;
- habitat fragmentation reducing the effectiveness of the valley as a wildlife corridor;
- noise disturbance;
- pollution of the River Blackwater from surface water run-off;
- effects on legally protected species due to habitat loss and severance; and
- loss of recreational facilities.
To mitigate significant effects, the two county councils purchased substantial areas of land alongside the scheme. This enabled a comprehensive package of green infrastructure measures to be designed and constructed, including:
- the avoidance of existing sensitive areas where possible;
- temporary fencing to prevent damage to adjacent areas during construction;
- river diversions to improve riparian habitat;
- habitat creation, resulting in an increase in water bodies and woodland of 90 hectares;
- habitat management, such as tree removal from grassland and swamp areas;
- translocation of heathland, aquatic and marginal vegetation and individual rare plants;
- natural regeneration of chalk grassland communities;
- the capture and translocation of reptiles, amphibians and fish;
- new drainage ponds to provide wildlife habitat;
- construction of a tunnel for roosting bats and erection of bat and bird boxes;
- measures to protect the water quality of the river; and
- a public footpath, doubling the area of open access land and improving the quality of an angling lake.
Monitoring exercises in 2004 and 2011 indicated the habitat creation schemes were largely successful, although some of the new habitats would take many more years to be of equal quality to those lost.
Wildfowl populations have largely benefited from the borrow pits, which provided new water bodies, and woodland bird populations use new tree belts. Translocation of aquatic plant species was successful, whereas few of the translocated grassland plants survived.
Populations of protected species have been retained including, for example, a number of common bat species. The habitat changes brought about by the road scheme also helped species not targeted by the mitigation work, such as the wildfowl that benefited from new water bodies.
However, some species have been adversely affected by the changes both directly and as a result of the changes to the overall balance of habitats within the valley. For example, attempts to translocate common spotted orchid were unsuccessful.
Three key factors were identified as being instrumental in the success of the mitigation for this scheme:
- Ecologists worked closely with the highway engineers during design and construction of mitigation.
- The Blackwater Valley Countryside Partnership works closely with local authorities, private landowners and local community groups to manage the green infrastructure.
- Maintaining a flexible approach to management, based on monitoring of habitats and species, helped to direct and reshape mitigation measures while continuing to focus on the original overall aims. For example, trees were removed from a number of plantations to allow naturally regenerating grassland flora to flourish.
Long before the phrase “green infrastructure” came into common use, the Blackwater Valley Road scheme retained, created and managed 117 hectares of land to provide multi-purpose benefits for people and wildlife.
This green infrastructure was placed in local authority ownership and is being managed to ensure it provides green space for local people, habitat for wildlife and mitigation against the impacts of the road.
At a time when budget constraints are likely to have an increasing influence on road and other major infrastructure schemes, it is essential that mitigation is as efficacious as possible. Green infrastructure with its multi-purpose approach to realising benefits is an excellent way of ensuring this and EIA is a robust method of identifying what mitigation is required, and can provide guidance on what should be included in the green infrastructure design.
This article was written as a contribution to the EIA Quality Mark’s commitment to improving EIA practice.
Suzanne Glencross and Claire Wansbury are senior ecologists at Atkins and Steve Bailey is the manager of the Blackwater Valley Countryside Partnership