BREEAM Infrastructure rates A479 work as Excellent

BAM Nuttall Ltd were awarded the Design and Build Contract for the A479 Talgarth Relief Road and Bronllys Bypass by the Welsh Assembly Government in early 2006, with Hyder Consulting acting as designers, covering all disciplines, including environmental design, earthworks, drainage and highways aspects.

Before site clearance work began, extensive ecological surveys were carried out to ensure that the site was clear of ecological constraints. Early surveys also helped to inform the design of detailed mitigation measures. A series of archaeological excavations was conducted at the outset to investigate historic use of the scheme footprint. Finds included items of Roman pottery and a Bronze Age cist burial.

The scheme lay partly within the Brecon Beacons National Park and therefore required sensitive landscape treatment in order to achieve successful integration with the surrounding countryside. This was achieved through a combination of careful selection of the highway alignment, recreation of existing landscape features (i.e. hedgebanks and hedgerows) and appropriate planting.

Land acquisition

Acquisition of adjacent land and remnant field corners as part of the Compulsory Purchase Order (CPO) for the project was also a key factor in the project’s development. This allowed earthworks to be slackened (in comparison with normal engineering slopes), profiles to be varied and also provided room for additional landscape planting. Overall, this has resulted in a more natural roadside landscape.

As part of the landscape proposals, grass seed was sourced from local species-rich meadows, with help from the Countryside Council for Wales (CCW), to ensure that local provenance material was used. In total, approximately 20ha of species-rich grassland were created as a result of the scheme.

Protected species

The Talgarth section of the scheme included mitigation for a wide range of protected species, including lesser horseshoe bats, badgers, otters and dormice. Where possible, mitigation measures were combined and this is best demonstrated at Pendre Culvert, where an oversized culvert approximately 2m in diameter was provided. The culvert was designed to allow lesser horseshoe bats to safely cross the line of the road, but it also accommodates a seasonal watercourse, mammal ledges for badger and otter and a high-level dormouse ledge to link habitat on each side of the new road.

In addition to the dormouse shelf, the scheme includes an innovative dormouse overhead crossing at Pendre, intended as a long-term mitigation measure to address potential fragmentation effects of the road. The design of the Pendre Culvert and headwall were specifically altered to allow mature Oak trees to be retained, thereby ensuring the best possible connection with adjacent vegetation. Monitoring of the mitigation measures during construction and post-construction has shown that lesser horseshoe bats are using the bat underpass. There is also evidence that badgers and otters are present.

Rivers and ponds

Watercourses that cross the scheme or run alongside are tributaries of the River Wye Special Area of Conservation (SAC). During construction, a surface water management plan based on Sustainable Drainage (SuDs) principles was developed in conjunction with the Environment Agency to ensure that drainage from the scheme (in particular suspended solids) did not affect the SAC. The same ponds that were used during construction now form the attenuation ponds for the operational scheme.

Post-construction monitoring of aquatic invertebrates has shown that fresh-water crayfish continue to thrive within these watercourses. Indeed these populations are possibly some of the strongest in the National Park.

The BREEAM Infrastructure rating of ‘Excellent' that was awarded to this project not only recognises the efforts taken to address landscape issues, but also work undertaken throughout all stages of scheme development in relation to archaeology, ecology and sustainable construction in general.

Other key features of the scheme that have contributed to the high BREEAM Infrastructure score include the following:

• Earthworks balance – excavated material was re-used within the scheme or within landscape areas, thus reducing vehicle movements.

• Stone from a local quarry was used to face Pendre Culvert, gateway entrances and feature walling within Talgarth, reinforcing local character and reducing transport impacts.

• Retention of mature trees – including trees on both the Talgarth and Bronllys sections of the scheme.

• Extensive involvement of the local community and statutory consultees took place during development and construction of the scheme, including visits to the site by local school children.

• Implementation of a 5-year aftercare period – including long-term management and monitoring of the effectiveness of mitigation measures.