Islington goes retro with SUDS

A retrofit SUDS system that’s one of the UK’s first, is capturing more than rainwater. Natasha Wiseman went to take a look

But for the public information notice, passersby might fail to notice the tiny, newly landscaped garden on a residential estate in Islington, north London. However, the project is actually one of the UK’s first retrofit SUDS systems and is capturing not only rainwater, but the interest of UK water companies.

Paul Shaffer, an associate of construction industry association Ciria says that the project, which was completed in June, signals a new phase for SUDS. Rainwater falling on the roof of the apartment block in Ashby Grove is now diverted into the system, retrofitted into the passive space that separates the pavement from the building frontage.

A simple disconnected downpipe leads roof water to a small depression, resplendent with summer flowers and planted as a ‘rain garden’. Most day-to-day rainfall collects for short periods of time in the rain garden and soaks into the ground. When heavy rainfall occurs, there is a simple grated overflow that directs surplus water to the sewer.

For such a simple concept and minimal development, this pilot is born of a sophisticated partnership between the local authority, the housing association, designer Robert Bray Associates and developer Murphy.

According to case study notes from Ciria, internal agreement within the council was a major challenge and this was achieved through the persistence of a local champion of the scheme.

The rain garden’s success in reducing flooding and sewer flows is being monitored by Thames Water and a PhD student at Middlesex University. Work will focus on the volumes that are held by the rain garden, the quality of water entering and leaving the rain garden, and the soil moisture content, recorded over a 12-month period.

This kind of technique will be particularly important in inner-city areas like Islington where there is little green space and the Victorian drainage system is under increasing pressure as new homes are built and climate change brings heavier rainfall.

By storing rainwater for short periods of time, after heavy storms, the amount of rainwater rushing off roofs and roads and into drains is reduced, leading to a lower risk of flooding.

The rainwater naturally waters the plants in the garden and encourages rainwater to soak into the ground.

Dry periods too can cause problems for buildings, especially in South-east England, as shrinkable clay soils and thirsty trees give rise to subsidence. Rain gardens can facilitate the rehydration of clay soils, particularly in summer. Shaffer says that five other water companies have expressed an interest in retrofitting SUDS systems to reduce the pressure on drainage systems.

New guidelines for best practice on retrofitting have recently been published by Ciria.

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