Olympic Legacy: Otters and Trees along the River Lea

Soil is shaken free of contaminants on the conveyor belt of a soil washing machine.

When the London 2012 Olympic and Paralympic competitors have departed, they will leave behind a new urban park—at more than 111 acres (45 ha), one of Europe’s largest—with lush meadows, lawns, wetlands, woodlands, and wildlife habitat where a brownfield formerly stood.

An Isolated Brownfield

When the 2012 Games were awarded in 2005, the Lower Lea Valley in East London was an underserved community with low-income housing and industrial areas—some of them heavily contaminated—dating back hundreds of years. The valley’s local landmark was the notorious Hackney Fridge Mountain, a 20-foot-high (6 m) heap of broken appliances.

River Lea channels and a few bridges isolated the Lea Valley community, though the site is mere miles from Canary Wharf—a London financial center—and the Docklands, a thriving commercial and residential area. The moribund Lower Lea Valley changed dramatically as it became the site of the nearly 1-square-mile (2.6 sq km) Olympic Park.

In 2005, the Olympic Delivery Authority (ODA) selected London-based Atkins as the official engineering design services provider for the 2012 Games, which included delivery of the site’s “enabling works"—the preparation and remediation a site undergoes before development. Between 2006 and 2009, more than 1,000 engineers, project managers, ecologists, soil scientists, and sustainability experts worked with subcontractors and team partners under extraordinarily tight deadlines to ready the site for construction of sports facilities.

After businesses and residents were relocated from the valley site, 215 buildings were demolished and the ground was assessed. More than 3,000 exploratory holes were drilled across the site to determine the nature of soil contaminants. During the assessment, 140 archaeology trenches were excavated, which revealed a 19th-century boat, an 18th-century roadway, Iron Age skeletons, a Bronze Age hut, and numerous other artifacts and remains.

Chemicals, glue, and other industrial landfill debris had tainted the underlying soil and groundwater. With evidence of contaminated soil, a remediation plan was developed that divided the park into zones so that sports facility sites requiring longer construction times—such as the Olympic Stadium—could be completed first.

Soil Hospitals

Running Water, by Canadian artist Peter Lewis, is one of many artworks commissioned for Olympic Park by the Olympic Delivery Authority.

To ensure the environment sustainability of the London 2012 Games, one of the ODA’s goals was to reuse, repurpose, or recycle 90 percent of the soil and material at the site. Recovering contaminated soil for reuse was problematic, in part because of the carbon dioxide footprint trucks would have generated by hauling the soil from the area. Instead, a cut-and-fill strategy was deployed to use excavated materials in foundations beneath several sports venues.

The remediation of the Olympic Park became the U.K.’s largest-ever soil washing operation. Over 2.6 million cubic yards (2 million cu m) of soil were excavated with around 80 percent of the cleaned soil reused in earthworks or recycled as fill material. Contaminated soil was treated using a variety of techniques, including bioremediation, soil washing, and chemical and geotechnical stabilization. Two “soil hospitals” were set up to test, process, and treat excavated contaminated soil for reuse, and five washing plants treated the soil for a range of contaminants.

When the enabling works were completed, the ODA’s ambitious target of reusing and recycling 90 percent of material from demolition was exceeded, with 98 percent of the materials reclaimed for recycling and reuse.

A new bioremediation technique was applied for the first time in the U.K. to treat ammonia-contaminated groundwater under Olympic Stadium. Archaea—microorganisms that thrive in extreme conditions and that biologically degrade ammonia—were inserted into specific boreholes. As archaea “ate” ammonia, several other reagents, including oxygen-released compounds, were injected into other groundwater areas to remove contaminants.

At the same time as the soil was being remediated, over 1.9 miles
(3 km) of rivers and canals weaving through the site were revitalized to create an urban park. In 2008, Atkins began a four-year project to help reengineer riverbanks. However, before riverbanks were re-created, flood risk had to be gauged through hydraulic modeling. A river lock, built in 2008 to improve navigation along the River Lea, caused tidal water levels to fluctuate by as much as 13.1 feet (4 m) twice a day. With modeling data, the new slope of the river banks was planned to include a wetland barrier and wet woodlands to help elevate the area—and 5,000 properties nearby—to a 100-year flood level.

Landscaping the restored banks presented challenges because plants had to stabilize the riverbanks, withstand tidal fluctuations, attract birds and wildlife, and bloom profusely for the 2012 Games. A 12-month trial planting was carried out along a 164-foot (50 m) wetland area. Various native species were planted using different bioengineered installation techniques at different elevations along the riverbanks. Trial results determined that grasses and sedges, yellow irises, and purple loosestrife fared well when planted in coir (coconut fiber matting) instead of directly in soil.

Nearly 380,000 individual plants were cultivated off site by Salix River & Wetland Services Ltd. at nurseries in Swansea, Wales, and Thetford, England. When planting began, 300 trucks—each with 1,000 pallets—arrived with detailed descriptions of where to install the plants. Planting the riverbanks was done via pontoon boats for greater control during the landscaping.

Creating Wildlife Habitat

An Olympic Park biodiversity action plan—one of the planning conditions for the park’s development—provided a blueprint to create sustainable wildlife habitats, protect indigenous wildlife, and attract new species to the area.

Before buildings were demolished and remediation began, the bird species and animals were cataloged, tree cuttings and seeds from native vegetation were collected for replanting, and some species—including smooth newts, toads and common lizards—were relocated.

A variety of habitats were created: 24.7 acres (10 ha) of native trees and shrubs; reed beds and ponds covering nearly 4.9 acres (2 ha); restored riverbanks; 49.4 acres (20 ha) of species-rich grassland; and 2.2 acres (9,000 sq m) of rare native wet woodland (indigenous to boggy northern climes) to support willow, alder, and black poplar trees. In general, native trees were chosen to withstand changing climate conditions.

Species to populate the new park encompass bugs, fish, amphibians, reptiles, bats, and birds. Otters, currently rare in London, were singled out for a specially planned habitat of soft riverbanks planted with reed beds and wet woodland, where it is hoped they will form a colony.

London’s Legacy

After September, the 2012 Games site is to be transformed within a year into one of Europe’s largest urban parks. The park will have two areas: the South Park, with lawns, gardens, and mature trees, and the North Park, with meadows, wetlands, and woods.

Public access to the park was designed to accommodate a range of ages and disabilities through wide, smooth paths and shallow gradients. After the Games, however, some temporary walkways will be removed, enabling woodlands and plantings to thrive. Several sports venues will remain in the park, including the velodrome and basketball venues, though trees have been carefully planted to screen them. The effect will provide visitors with a more sylvan setting.

Minimal maintenance will be required for the park’s landscape because of the careful planning and bioengineering methods used during its creation. A new wastewater facility will supply nonpotable water for irrigation of new—mostly native—plants and trees. To provide moisture for and enrich the wetland woods, Atkins designed a system that allows the River Lea to overtop its banks once a month.

Creation of Olympic Park has been key to revitalizing this section of East London. Even before the Games began, new building and economic development on the park’s perimeter was attracting businesses and residents. After the flame is extinguished, the reclaimed land will attract a variety of species —including human visitors—to what had been an uninhabitable brownfield.