SUDS – Greening urban drainage
publication date: Jul 17, 2008
|
author/source: David Harris
Phil Chatfield who is the Policy Advisor on Diffuse Pollution for the Environment Agency explains:
The summer of 2007 saw an unprecedented amount of rainfall that put managing flood risk high on the agenda. Over the devastatingly wet summer months, 35,000 of the 57,000 homes and businesses flooded were flooded by surface water. Getting to grips with surface water drainage needs to be a priority for planners and developers, especially as the unavoidable impacts of climate change take effect. Incorporating sustainable drainage systems (SUDS) into new and existing developments is one way we can start to deal with the likelihood of more extreme rainfall events.
Though SUDS may not prevent flooding during times of exceptionally heavy rainfall, such as that which we saw last summer, using the SUDS approach will help manage flood risk. SUDS techniques such as green roofs, rainwater harvesting, soakaways and permeable paving all provide ways of managing rainwater locally in high-density developments, helping to keep surface water runoff from site at or even below greenfield runoff rates. Wetlands and swales can also be introduced to absorb surface water runoff, and alongside green roofs, create valuable habitats for wildlife.
The benefits don’t stop there, by implementing SUDS and reducing surface water flooding we can make our drainage systems cleaner and healthier. Inadequate surface water drainage effects water quality by increasing the likelihood of water pollution. Pollutants can be picked up by rainwater flowing through the streets, and sewers can overflow, resulting in polluting human, commercial and industrial waste discharging from sewers and into the watercourse. By better managing where rainwater goes, we can help prevent these situations.
Interest in the many benefits that SUDS has to offer is widespread and recently we have seen government and public bodies acting to raise awareness of SUDS techniques. The Planning Policy Statement for England on Development and Flood Risk (PPS25), published by Communities and Local Government, recommends that councils give priority to SUDS when deciding planning applications. PPS25 is accompanied by a Practice Guide Companion document that offers practical advice and good practice case studies, helping planners and developers to implement SUDS in their work.
Government’s new water strategy published this January, Future Water, also highlighted the importance of tackling the issue of surface water drainage. It has a strong emphasis on managing rainwater on the surface and preventing surface water from entering underground drainage systems. Individuals planning to pave their front gardens will be encouraged to use a SUDS approach by a change to permitted development rights which will exempt permeable systems from the need for planning permission. We fully back such initiatives and hope that permeable surfaces will become the default option for such hard surfaces.
The Environment Agency has promoted the SUDS approach to drainage for some time and we work with a range of institutions and developers to increase their understanding of SUDS. We have just introduced a SUDS training course for our own staff, which is also available to local authorities on request. Local Authorities themselves increasingly include SUDS related information into their policies, and we are now seeing more examples of successful developments incorporating SUDS techniques.
In Bristol, permeable paving has been retrofitted in a number of streets close to the city centre as part of a “Home Zones” project in the city. Oxfordshire County Council has pioneered the use of SUDS for streets and other areas in new housing developments across the county. They have emphasised the savings for developers in laying flat, permeable paving, without the need for gullies and associated drainage systems, when negotiating commuted sums for future maintenance.
The use of green or living roofs has also grown. Developers recognise the multiple benefits they offer in addition to attenuating and reducing rainwater runoff
They can help reduce energy use and extend the life of the roof by insulating it and protecting the waterproofing, they can provide valuable habitat or amenity benefits and help reduce the urban heat island effect. Green roofs can be seen on housing developments and commercial sites as far apart as Canary Wharf in London and at Waverley Gate in the centre of Edinburgh. They have also been widely used in schools.
The UK Rainwater Harvesting Association has reported growth in the market for rainwater harvesting systems. But there is a lot of scope for this SUDS technique, which is often seen as little more than a water butt used for watering the garden. This is despite the clear benefits of using rainwater to replace water treated to a drinking water standard from the water mains. In the UK about one third of the water used in our houses flushes our toilets. Rainwater stored in an underground tank could replace all or most of this, reducing the pressure on both water resources and our drainage systems. Future climate change predictions forecast more times of drought, and we need to match this with the fact that in times of heavy rain, we have a problem disposing of flood water. The Environment Agency’s flagship office development, Red Kite House in Oxfordshire, not only has permeable car parks and wetlands for surface water drainage, it also harvests enough water to satisfy 40 per cent of the building’s water needs.
With increasing concerns over both flood risk and water resources, SUDS look set to stay. Nevertheless, there is still much work to be done. It is important that drainage is considered right from the start of new developments.
Developers tend to see the benefits of SUDS, but difficulties in arranging adoption of SUDS scheme part-way through the development process is still causing problems and resulting in too many compromises being made. Fortunately, there is a wealth of practical advice on SUDS available, planning guidance has been enhanced and resources supporting SUDS have been improved in the last year. We are increasingly seeing SUDS successfully incorporated into new and existing developments, and here at the Environment Agency, we are confident that the SUDS approach will continue to gain acceptance and reduce the risk of water pollution and surface water flooding.
Pictures courtesy of the Environment Agency.
