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The great outdoors

Around the dome: The organisers of the Millennium Experience want people to enjoy themselves outside the Dome as well. Margo Cole reports.

On a windswept day in January the Greenwich peninsula is not the ideal spot for a gentle stroll, but later in the year visitors will appreciate the walkways, riverside park and sculpture area which are wrapped around the Dome. Hardy children are already making the most of an imaginative play area.

Most of the ground around the Dome is hard landscaped. There is a huge paved main plaza between the underground station and the front entrance, and block paved walkways surround the building. However, the 73ha of the peninsula taken up by the Millennium Experience includes the linear Meridian Park and a riverside walkway which runs the length of the river frontage.

The river works are part of English Partnerships' masterplan for the entire 121ha peninsula, designed by the Richard Rogers Partnership. This puts a lot of emphasis on public open space and includes 20ha of parkland, mostly in the form of a central 'alluvial marsh' park. There is also an ecology park and 2.2km of new river terraces. At the end of this year, when the Experience is over, the river walkway alongside the Dome will become public park, and will be incorporated into the Thames Path.

Existing river defences on the peninsula consist mainly of sheet piled walls, many of which were badly in need of replacement when English Partnerships took over the site. The Environment Agency provides financial assistance to replace flood defences if they have less than five years life left in them - as was the case here.

Traditionally, the solution would be to simply install a new row of sheet piles in front of the existing wall, but that would have involved considerable encroachment into the Thames. Both English Partnership and the Environment Agency accepted that this was not the best solution, and worked closely with lead consultant WS Atkins to come up with a new, more environmentally sensitive approach.

This was to build a sheet piled flood defence wall 8m back from the original line and fill the gap with a series of planted terraces. The old sheet piles were cut down to river level and capped with timber, and then the terraces built behind on a slope of 1:7 to a reinforced concrete retaining wall at the back.

Ground behind the old sheet piles was excavated out and replaced with clean material to form the terraces. They are faced with gabions containing clean stone fill, topped with a growing medium and planted with reeds and other plants that thrive in a salt water environment, most of which came from local sites up and down the Thames.

'The capital costs are not much different to a conventional solution,' explains English Partnerships technical director Simon Wright. 'We did an economic study and we think this is a viable solution.

'It would be difficult for a private developer to do this because we have had to give a lot of land back to the river. As a public authority we can do that, but we also believe there are benefits in terms of the value of the adjoining properties and the ecology and environment.'

Elsewhere on the peninsula natural shingle beaches have been enhanced and new mudflats built to create more diverse habitats for invertebrates, fish and birds, including gulls, oyster catchers, cormorants and herons.

The aim of the £11M flood defence improvements is to restore some of the habitats that used to exist in this area of the Thames estuary before it was developed in the 19th century.

At that stage the site was nothing but marsh, and it is this heritage that led the landscape architects to opt for an 'alluvial marsh' philosophy for the tree planting in the central park. Rows of hornbeams interspersed with other species have been planted on concentric grids based on lines radiating from a central point in east London. English Partnerships has also reintroduced a rare species - the Lewisham Black Poplar - on to the peninsula.

The trees are planted in 10m wide trenches filled with a depth of 1.2m of well-drained clean material and lined with a membrane to restrict the roots and stop them pushing out and disrupting the services.

An automatic irrigation system will keep the trees watered and should ensure the roots stay within the trenches rather than growing down into the contaminated ground below. The water comes from a borehole sunk into the underlying chalk at the north end of the site.

In all, 12,000 new trees, 50,000 shrubs and a further 60,000 other plants have been planted on the peninsula.

The public open spaces are part of what is predominantly an urban environment: the peninsula will eventually be developed for residential, commercial and light industrial use, as well as housing the Dome.

Hard landscaping areas reflect this philosophy, with extensive use of granite (for kerbs, edgings and seating), and of bound gravels for cycle tracks and parking spaces. Many of the footways have been built using stone paving slabs which can be lifted easily to gain access to the services trenches below.

All the main utilities buildings are clustered together at the centre of the site, including a communications centre and mobile phone tower. Power supply to the site comes from the other side of the river, with a new tunnel excavated by London Electricity to deliver the 11kV cables for both the new development and the Dome.

The 2.1m diameter surface water pipes were installed using microtunnelling - predominantly pipe jacking. These techniques are often too expensive for services installation, but here there were so many constraints - including constant construction traffic and contamination in the ground - that it offered a cost effective solution.

WS Atkins managed to re-use an existing tunnel as the outfall for the surface water. The structure was originally a cooling water intake for an old power station on the site, and ends in an outfall under the dolphin of an old coaling jetty.

While the Dome and its immediate surroundings were designed to remain after the end of the year, Atkins designed the 300-space coach park for short- term use. Arisings from the Jubilee Line Extension excavation were stabilised with both lime and cement to create a suitable material for laying over the whole coach park area. The process was done in two stages - first the lime then the cement - using an injection technique. This material was then capped with a 14mm thick 'fibre deck' - bitumen over a fibre glass mat. The final surface is gravel.

All around the peninsula is a range of street furniture carefully designed to reflect the urban environment. Along the river walk the parapet rails are made of stainless steel, and there are low-level street lamps designed specifically for the site which cast a white light downwards, with minimum light pollution. A network of cycle and pedestrian routes is designed to ensure that visitors can make the most of the open spaces.

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