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Staying close to nature

T5 Rivers

Airport expansion generally draws the wrath of environmental campaigners. Alan Sparks finds out how the team on T5's twin channel diversion has produced an ecological haven.

Bisecting the heart of the T5 site are two ancient man-made waterways, the Duke of Northumberland's and Longford Rivers. (See box) Temporary bridges for site traffic currently cross these at strategic locations.

But, come 14 May, the rivers' routes must be handed over to the army of excavation plant already transforming the T5 terrain.

Simply culverting the rivers beneath the site was a non-starter.

'Adding value is an essential requirement, ' says T5 landside project leader Phil Wilbraham.

'Taking the easy option would have had a detrimental effect on the river's ecology, but by adding value, we will actually see it thrive.'

So instead of enclosed diversion, the rivers running southwards have been re-routed a total of 6km along the western boundary of Heathrow Airport to meet up with their original route on the southern edge of the site. Only 170m of their length has had to be enclosed, to negotiate road links.

These works will cost £75M in total.

Hitting the 14 May deadline is imperative, as any delay will hold up critical path earthworks. 'But worse than this would be to deliver a fortnight early and not give the earthworks team sufficient warning, ' adds Wilbraham.

'That would be an opportunity missed and display poor programme control. This is why we constantly monitor progress so that if we can reshuffle and add value elsewhere we are aware early enough to do something about it.'

A series of considered additions to the new 8m wide, gravel-lined concrete channels will increase their similarity to natural river systems.

Thought, time, effort and money have all been invested - not to appease planners, but to deliver the highest quality within the programme's constraints.

'BAA has made a huge commitment to protecting and developing the local ecology. No other river improvement schemes have come close to matching the level of commitment we have here, ' says Black and Veatch lead river engineer Dave Palmer.

'As an example, over £250,000 was spent on pre-planted pallets that will be brought in from Norfolk.

These will have better developed root systems than conventionally planted alternatives and should flourish quicker.'

Developing interesting habitats for fish and micro-invertebrates has been a priority. 'To replicate a natural river system we have placed naturally felled trees and gravel beds in the channel bottom, ' says Palmer.

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