A monumental example of environmental infrastructure is emerging at the Olympic Park in east London. It is approaching its peak of 11,000 workers on-site per day, in what the Games project sponsor for the public realm John Hopkins describes as "our most challenging year".
Apart from the iconic sports venues and athletes' village rapidly rising from the former industrial landscape, the softer side of the £9.3bn project, designed to provide the area with a more lasting legacy, is also taking shape.
Around 45 of the park's 105ha are designated as habitat. Hopkins says: "It will be a park that really mixes people and wildlife."
Central to this is the rejuvenation of the river Lea, which flows through the site on its way from the Hertfordshire countryside to the Thames estuary. Within the park, two wetland bowls and a wet woodland are being created along the stretch of the river through the northern half of the park.
Hopkins explains: "The wetland bowls provide a transition between the urban southern park, as well as forming part of the 42km Lea Valley River Park and the Mayor's East London Green Grid."
Previously lined with scrubby slopes of bramble and elder out of view behind factories and depots, it has been extensively cleared and dredged. However, in common with the rest of the site, contamination of soil and groundwater was a huge problem to be overcome.
"The level of contamination was severe, but with innovative decontamination techniques, 90 per cent of material has remained on site," says Hopkins, stressing the project's sustainability credentials.
Five soil-washing machines were employed across the site to clean more than two million tonnes of soil under the guidance of specialist soil consultancy Tim O'Hare Associates.
"The subsoil, topsoil and drainage are critical to the success, so we have taken great care over them," Hopkins says. He explains that the widespread presence of Japanese knotweed has entailed a three-year programme of removal: "We are watchful for it and it will be part of the maintenance contracts. In areas around rivers and railways, it's virtually impossible to keep out."
Further specialist consultancy was employed to find a design suitable for plants, animals and people. Mike Vaughan, principal engineer at consultants Atkins, says: "I did a lot of river modelling for this to understand the twin effects of tide and rain. That showed heavy rain could inundate the paths, so we moved them further up."
Vaughan also trialled a wide range of plants under different conditions last year, including on the site. He says: "We have ended up using 47 species of wetland plants, including common reed, yellow iris, purple loosestrife and sedges.
"It was a question of planting the right levels. As the river is impounded, it rises and falls by 400mm every day."
Of the resulting planting, Vaughan explains: "It will evolve and some species will over-colonise. But in on-site trials we only got one Himalayan balsam, and no Japanese knotweed at all."
Replanting such a large area in a relatively short time frame required an innovative approach. Water planting specialist Salix has produced around 300,000 wetland plants, which were mostly propagated from seed and cuttings harvested from local plants before site work began.
These were seeded in root trainers at the Salix nursery in south Wales, then grown on for a year in custom-made coir mats at the Salix Norfolk nursery, before being rolled up, labelled and re-laid on the site's native alluvial soil, and pinned with wooden stakes.
Salix technical director David Holland says: "It's been the largest growing programme of its type in the UK - we had to double the size of the nursery to accommodate them."
Vaughan adds: "The rolls can be laid quickly on-site - it's a bit like carpeting your living room."
The vegetation will not form an unbroken carpet because, as Vaughan explains, "spilings" made of woven hazel will preserve channels of open water for fish to colonise and shelter in. He says: "We have found examples of them here already, dating from Mediaeval times. And there are already carp in the river."
Other wildlife will be accommodated in the park in 700 wildlife installations including bird and bat boxes and even artificial holts for otters.
These species will also benefit from the creation of a 4,000sq m wet woodland on the river, which has been identified as a priority habitat in the Government's UK Biodiversity Action Plan. This is about to be planted with semi-mature native trees such as willow and alder, as part of Hillier Nurseries' contract to supply more than 4,000 trees to the site.
And, besides conservation value, the area will be able to cope with rainwater from storms of a severity likely only once every 100 years, through swales and other forms of water attenuation.
"It will protect around 5,000 neighbouring properties," says Hopkins. "It's an absorbent landscape - and the swales are good for wildlife such as frogs."
Its role in alleviating the urban heat-island effect makes it a key component of east London's "environmental infrastructure", he adds. "The river area will be finished in three months, then we'll close it off and let it mature for the Games."
However, the area will not benefit solely wildlife. Spectator lawns around the wetland bowls will allow for external seating during the Games - courtesy of huge video screens - and incorporating benching that can later be used as part of outdoor classrooms. According to LDA Design partner Neil Mattinson: "The soil is very sandy, which means the grass can be used immediately after a heavy shower."
The nearby Olympic Village, which will revert to housing after the Games, also contains a small wetland and around two thousand trees - further blurring the distinction between the park's conservation, infrastructural and amenity roles.
What remains unclear is how exactly the park will be run after the big event. "It's designed as a managed landscape, and its ongoing management will be very important, though it's for the legacy company to decide how do that and how to fund it," says Hopkins. He adds that an outline 10-year management and maintenance plan has already been drawn up, which "will need to be refined as the park develops".
Contractors on the site have gained valuable experience from the construction work. Banking is being formed with a high degree of accuracy using GPS-guided diggers, for example.
"We will take that and other things away from the work here," says White Horse project manager Steven Ayres. "It's a legacy for us too, in things like health and safety and office procedures."
Hopkins adds: "The Olympic Delivery Authority's procurement policies are pretty tough, therefore everyone here has upped their game - and that's exactly what we wanted."
GARLANDED WITH GARDENS
Other landscape elements around the Olympic Park are beginning to take shape. "You will feel you're in a park, even during the Games," says Games' project sponsor for public realm John Hopkins, who has engaged Sheffield University specialists Nigel Dunnett and James Hitchmough to design temporary planting around the main stadium. The swathe of yellow, orange and red annual wildflowers will call to mind the Olympic gold, he says, adding: "August isn't a good time for them, but they will be sown late. It will be a splash of colour for the Games, then turned into perennial meadows afterwards."
The Olympic medals also provide inspiration for the nearby Great British Garden, for which the Olympic Delivery Authority has submitted a planning application. It is based on designs by two winners of an RHS competition who, together with a panel of experts including LDA Design and Hargreaves Associates, developed a scheme with bronze-, silverand gold-themed areas.
The Sarah Price-designed 2012 Gardens will take a more botanical approach. "It will tell a story of the world's plants and Britain's role in collecting them," says Hopkins. It will have four different botanical zones comprising 60,000 plants within the 1km-long garden."
These two designed gardens will be the only areas of the park to be permanently irrigated, via a ring of treated runoff water.