Transcript

Rivers

Narrator

One of the most time-critical sub projects of the Terminal 5 construction programme has been the twin river diversion scheme.Until April 2004 two rivers ran right through the middle of the site, literally bisecting it. It was imperative that the rivers be sensitively moved at the earliest opportunity. The Duke of Northumberland’s river, is manmade and was constructed in the 1530s to divert water from the River Colne to feed the River Crane and the royal residence at Syon House. The Longford River also manmade, was built in 1638 by Charles I to feed the fountains at Bushey Park and to take water to Hampton Court Palace. The Duke of Northumberland’s river belongs to the environment agency and the Longford River to the crown. BAA worked closely with the Environment Agency and the Royal Parks Agency to agree a scheme that would both improve the rivers and divert them into two new channels around the western perimeter of the airport. This meant also diverting 4 kms of the airport’s western perimeter road without causing disruption to local traffic or site delivery.On-site, the original rivers had run in tunnels under the northern and southern runways and in open channels through what was then the sewage treatment works.When construction began the rivers were protected from the surrounding T5 construction by a 10 metre exclusion zone and endangered wildlife species were carefully relocated.The newly-built river channels are 3 kms long, longer in fact than the original rivers. 2/3 of the channels have been created in some vertical concrete walls and the other 1/3 enjoys natural river banks.Locally-sourced materials including clay and terrace gravel were used to line the new channels and in-channel enhancements were introduced to improve the ecology and flow of the rivers. These include reclaimed timber and stone filled baskets to provide new habitats for fish, plants and macro invertebrates.When everything was in place the new channels were filled with water from the original rivers. Fresh water duck muscles, about a thousand of them were translocated from the old river beds to the new. Thousands of fish too including pike, dace, perch and even eels were carefully caught and then set free in the rivers to naturally repopulate the new channels.Silt and gravels from the original rivers, rich in macro invertebrates such as shrimp and snails, were also translocated to the new channels. Pallets of pre-grown native plants were placed on the river beds and on banks to provide additional ecological value. The area has also been carefully landscaped with trees, shrubs and plants to provide a high quality landscape.Just 18 months after work commenced, both the Longford and Duke of Northumberland rivers were switched to the new channels. Back on site the old river channels could then be made available to T5's archaeology team for further exploration; an unmissable opportunity before eager construction teams complete the works between the main terminal and the first satellite building.The new rivers are now thriving.