Planting as an art form: ecologically-tuned, aesthetically aware. Planting as an essential: creating healthy cities and liveable places
Project Title: London Olympic Park 2012 Gardens Date of Completion: 2008 - ongoing Planting Design: Nigel Dunnett, James Hitchmough, with LDA Design/Hargreaves
Project File: The London Olympic Park Swales and Rain Gardens A bioswale in the Olympic Park. Prominent in flower are white Oxe-eye Daisy, Purple Loosetrife, and Ragged Robin The use of the landscape to manage excess rain water runoff following severe storms is integral to the design of North Park. Contrary to standard practice whereby all runoff is fed into drains and then into buried pipes, and transported away from site as quickly as possible, the aim of the drainage system in the North Park is to retain as much water on site as possible, and to allow to return slowly to the river network. In so-doing, the aim is to reduce the risk of flash flooding on site, or downstream, as a result of large quantities of rain water runoff overloading the conventional drainage system, by both slowing down the rate of flow of water off site, but also by reducing the total amount that leaves the site in the first place.
An important concept in this approach is to make the water cycle visible, through design features that show how water moves through the park. The most obvious features that achieve this are the ‘bioswales’ – linear elements that capture and transport water through the site in exactly the same way that a buried pipe might, but instead the water runs along the ground surface. In so-doing, a proportion of the water will evaporate back into the atmosphere, or infiltrate into the soil, thereby reducing the total amount of water running off the site. The bioswales line the main path network in North Park. Water is shed from the slopes and the path into the swale. On the right of the main path, excess rainwater sheds into the tree planting area.
The bioswales represent an excellent opportunity for introducing beautiful plantings into the park because vegetation will also take up a proportion of the water and remove it from the system. But they also introduce a significant additional biodiversity element. Because the swales run alongside all the major, paths, in visual terms, the bioswales form the bones of the park, highlighting the large-scale structure. The swales form a visible framework to the park The main path network has the following structure: a cambered hard surface impermeable surface as the main pedestrian route, which sheds water to each side. At the side may be the bioswales, which collect and move the water, or lines and avenues of trees set within permeable gravel, which again allows water to infiltrate back into the soil, or there may be both trees and bioswales.
Water from the bioswales collects rain garden areas (wider planted spaces that can fill temporarily with rain water, and ultimately into balancing ponds and wetlands which, if they fill completely, will overflow into the river.
Ragged Robin (Lychnis flos-cuculi) in the bioswales