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Greenfield sight

Roads : Environmental mitigation

Environmental concerns are dominating the construction of a village bypass. Dave Parker reports from the depths of Norfolk.

To paraphrase the refrain of a famous Gilbert & Sullivan song, the 3.3km Broome-Ellingham bypass in Norfolk is the 'very model of a modern major road project'. There was a time when unblocking the last bottleneck on the busy A143 would have involved the construction of a long loop of dual carriageway, far from the obstruction, complete with bridges, viaducts and underpasses.

Trees would have been felled, hedges bulldozed, ditches culverted, all with the aim of smoothing the passage of convoys of sugar beet trucks heading for Great Yarmouth. Not any more.

Twenty-first century bypasses are much less obtrusive and much more environmentally aware. Norfolk County Council's solution to the challenge posed by the only remaining unimproved stretch of the A143 - a twisty section through two villages further restricted by a particularly narrow bridge - is a deceptively simple single carriageway road with few major structures. Total project value is £6M. 'And 10% of that is earmarked for environmental mitigation measures, ' reports NCC site supervisor Tim Ellis.

'That is the highest proportion we have ever spent on a road project.'

One of the main reasons why this is the last project on the A143 is the environmental challenge. Half the route is in the Norfolk Broads National Nature Reserve. There are two county wildlife sites and a site of special scientific interest. Five species of bat, plus otters, water voles, badgers, slow worms and lizards live in the varied terrain. And, almost in the middle of the chosen route, lies the borehole that extracts drinking water for nearby Bungay.

Mott MacDonald environmental supervisor Graham Searle says the environmental objective was to maintain the characteristics of the traditional Norfolk landscape. 'We go through a major carr [the local name for an area of peaty wet woodland] and nearby wet meadows will be converted back to carr to replace what is lost to the bypass.'

Landscaped and planted bunds alongside the road should keep the flight paths of owls above traffic. Near the borehole the sands and gravels outcrop through the peat to form a haven for snakes and lizards, and this had to be cleared of these vulnerable herpetofauna before work began.

'We first erected special fencing to keep the snakes and lizards from coming back, ' explains Jackson Civil Engineering site agent Andy Sullivan.

'When road construction is finished we will replace the sandy topsoil and remove the fencing so the site should be recolonised.'

Inevitably, some sections of the extensive network of dykes have to be diverted or piped under the new road. New dykes will be 'inoculated' with silts from the existing sections, transferring most of the 70 species of aquatic invertebrates that have been recorded in the area.

Strangely, these dykes are at a lower level than Broome Beck which crosses the route and discharge directly into the River Waveney to the south.

A 10.5m span crossing of the beck is the only significant structure on the bypass. The insitu concrete structure is remarkable mainly for the two 'otter runways' formed on each abutment.

Some might wonder why an amphibious animal like the otter needs such special provision, but it seems that during floods otters very sensibly prefer terra firma. Unfortunately, such common sense does not extend to road safety, so the bypass will be lined with anti-otter netting.

Jackson Civil Engineering started work in February this year, under a 52 week, £4.1M partnering contract with NCC and Mott MacDonald. Most of the route runs across nearly 1.8m of peat overlying sands and gravels, but, says Jackson site manager Colin Garrod, the exceptionally wet weather during the early part of the year had no real effect on progress.

'Rather than attempt to dewater the peat we chose to excavate it in its saturated state. This worked well and we only used bog mats in a couple of areas.'

He adds: 'One of the biggest problems during construction is avoiding the contamination of groundwater via ditches and dykes. All our insitu concrete had to be poured onto impermeable polythene membranes.'

Where the road crosses a critical zone within a radius of 300m from the borehole it sits on a 600m long by 21m wide 'nappy' of Monoflex 1000 medium density polyethylene. Elsewhere road drainage is led into new lagoons planted with reeds moved from elsewhere on the site.

Generally, the 7.3m wide road will sit some 1-1.5m above existing ground levels - 'to keep it off the floodplain', Ellis explains. The bunds alongside will reach 1.5m above road level.

To the south a new bridlepath is being established, part of it using the route of a disused railway, to recreate a long lost link between the two villages.

Residents of Broome and Ellingham have been campaigning for a bypass for many years.

Traffic eases considerably during the winter months, so the real benefit of the new bypass will be felt first next summer.

Instead of clogging up with an intractable mixture of tourist traffic and HGVs the two villages should enjoy a long forgotten tranquillity. And the traffic thundering by the herpetofauna sunning itself on the verges should also appreciate the benefits. So should the otters.

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