Rise of the Rain Gardens

– From Portland (US) to Portslade (UK) Rain Gardens are on the rise, here in the Brighton & Lewes Downs Biosphere now following the evolution of this pioneering concept in the US. A “rain garden” is simply a low-lying area of ground containing plants tolerant of wetter conditions, that is designed to receive and retain rainfall from surface water run-off from hard surfaces, and then slowly drains away over time to leave them without any open water for most of the year. This natural way of helping to alleviate local flooding is a form of ‘green infrastructure’, that works in combination with the conventional grey infrastructure systems of drains, pipes and sewers. Rain Gardens are a type of Sustainable Drainage System, or ‘SuDS’, that can be created both in existing green spaces and as new elements of urban development, to help to reduce flood risk from heavy rainfall events – an phenomenon that is increasing with climate change. The great thing about Rain Gardens is that they not only hold back storm water and reduce flooding, but they can also help to filter pollution, attract wildlife to your neighbourhood and look colourful at the same time – making them multi-functional in nature. Although rain gardens are a relatively new idea here in the UK, they began life back in 1990 in Maryland in the United States. Dick Brinker, a housing developer building Somerset, an 80 acre (32 hectare) site for 199 new homes in Prince George’s County, had the idea of replacing four ponds with a series of landscape features, which he felt would be more appropriate in the circumstances. The US Clean Water Act (CWA) in 1977 had referred to Best Management Practices (BMPs) to control water pollution, and in urban situations the response to this tended to be the creation of sizeable ponds fed by conventional drainage. An over-reliance on ponds by some engineers is still a problem now, 25 years later, indicating how long it takes for new ideas to spread through the professions. Back in 1990, however, Brinker was aware of examples of industrial and commercial sites where space was limited, where landscaped areas had been modified to allow water to pool for a short time before infiltrating into the soil. Brinker and his daughter Theresa approached Larry Coffman, who was an official at Prince George’s County (the local drainage authority), to seek to modify the drainage plans for the Somerset site, replacing kerbs, pipes and ponds with shallow basins filled with free-draining soils in each building plot. Hanifin Associates, consultants to Prince George’s County, dubbed these infiltration features “Rain Gardens”. The rain gardens were only 25 per cent of the cost of a conventional drainage system and ponds, and the extra space freed up meant that the developer was able to add another 6 or 7 building plots to the scheme. The project was monitored for 2 years, which demonstrated its effectiveness, resulting in the county publishing the ‘Bioretention Manual’ of design for bioretention in storm water management. In 1998, Larry Coffman worked with others to start the Low Impact Development Center to promote the concept of ‘Low Impact Development’ (LID).

Roadside Rain Garden in Portland, Oregon (photo by Dusty Gedge)

The idea of rain gardens since spread to various cities across the US, most notably Portland, Oregon, where the city’s chief landscape architect Tom Liptan championed the idea, initiated various trials and produced guidance that allowed citizens to get involved by creating rain gardens in their own gardens or on adjacent verges. Tom emphasized the importance of multi-functionality, with rain gardens being promoted as attractive landscape features in their own right, as well as being drainage features. Now the rain garden concept has a foothold in the UK, with a few projects around Stroud, in South Wales, London and now in Portslade as part of the Brighton & Lewes Downs Biosphere programme of environmental improvements.

Rain Garden replacing pavement in London at Wardens Grove, Bankside (photo by Gary Grant)

Following a scoping study in Portslade – undertaken by Brighton & Hove City Council, The Ecology Consultancy and the Green Infrastructure Consultancy, with funding from Natural England – a number of green and grey spaces were identified where rain gardens could be established to help tackle surface water flooding problems by diverting some of the excess water entering the drains. The idea of the two new rain garden pilot schemes now established at Lockshill (Portslade village green) and Victoria Recreation Ground is that surface water runoff is re-directed into small basins or ‘swales’ from which it can slowly infiltrate into the underlying chalk or evaporate or transpire through plants later. These features in Portslade have also presented an opportunity to create two new wildlife habitats, by planting local wild flowers in to the chalk banks and seeding the damper hollows with wetland plants.

Creating the new Rain Garden at Portslade village green (photo by Rich Howorth)

Although these new rain garden pilots are relatively small-scale, we hope that they will be the forerunners of many similar schemes in the Biosphere in the future, to help to reduce flood risk whilst bringing more nature to town. Such natural benefits are vital to sustain our urban quality of life and help cope with the effects of climate change. Gary Grant, Director of The Green Infrastructure Consultancy & Lead Author of the UK Rain Garden Guide His new book “The Water Sensitive City” is published on the 8^th April 2016