Water management is a major issue in large urban areas, where after heavy rainfall, rooftops, streets and pavements act as funnels. This sends huge volumes of water very quickly into drainage systems, putting pressure on rivers and increasing the risk of flooding. In contrast, undeveloped land absorbs and utilises water, thus slowing its progress to rivers. It is this natural bioretention that our towns and cities must learn to mimic. Rain gardens do just that. In its most basic form a rain garden is a planted depression in the ground, providing porous and absorbent materials into which water can soak, with plants that can withstand occasional temporary flooding.
Water management is a major issue in large urban areas, where after heavy rainfall, rooftops, streets and pavements act as funnels. This sends huge volumes of water very quickly into drainage systems, putting pressure on rivers and increasing the risk of flooding.
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In contrast, undeveloped land absorbs and utilises water, thus slowing its progress to rivers. It is this natural bioretention that our towns and cities must learn to mimic.
Rain gardens do just that. In its most basic form a rain garden is a planted depression in the ground, providing porous and absorbent materials into which water can soak, with plants that can withstand occasional temporary flooding.
Portland in the USA is a city that has utilised rain gardens since the early '90s, and Philadelphia, Pennsylvania, has embraced green infrastructure and water management extensively as part of its Green City, Clear Water plan. In Seattle, municipal funding - alongside the efforts of local NGOs -has helped produce neighbourhood champions who maintain their own local rain gardens.
Dusty Gedge, famous for his pioneering work with green roofs, is a strong proponent of rain gardens. He says the UK lags behind by 'at least a decade'.
In South London, Owen Davies, an engineer working for Lambeth council, is starting to change all that. An inner city borough, most of Lambeth is paved, leaving very little green open space, Victorian sewer systems and only the Thames as an open water channel. Davies, Lambeth's Sustainability Engineer for Environmental Services & Highways, says: '15% of [Lambeth's] land use is public highway; it is a public open space and I think it should be looked at not just as a place to drive through; it should also be enjoyed.'
Existing traffic calming measures are often simply concrete structures, he points out, but councils could be much more creative with the way they manage roads.
On a town - or city - wide scale rain gardens can also help support and even improve biodiversity. They will mitigate the urban heat island effect and help to create more pleasant places to live. Measures like bioretention strips and tree pits use absorbent materials to slow and absorb water run-off from roads and pavements, while Bioswales - those long depressions often seen running parallel to roads - can be used to manage water runoff or to collect and channel water across a garden or park.
Read more at The Ecologist.
Rain garden image via Wikipedia.
