Watching coverage of people losing their homes in the catastrophic flooding around Houston was a distressing experience. Extreme rainfall patterns are always difficult to deal with, as UK floods have also shown. When it’s raining here, conventional drainage systems – huge underground networks of sewers, pipes and structures – collect rain and wastewater and dispose of it in outfalls or treatment plants. In the past, we were less concerned about this process but now the question of where all that water goes to is becoming more worrying.
When it’s really pouring down, there’s a lot of water out there that needs to be managed – around 133 days of rain and snow in the UK. This is when the importance of efficient, effective and ethical water drainage becomes obvious.
Drainage has always had an important role to play within the structure of our towns and cities because of the way our activities interact with the natural water cycle. And over the last few decades there’s been a growing realisation that sending anything we’re unsure about to expensive treatment plants and dumping collected rainwater into streams, rivers and oceans is not sustainable. It merely shifts water-related problems like water pollution and flooding elsewhere. Better solutions need to be implemented to deal with the problem of rainwater and wastewater drainage in urban places.
The term SuDS does not only stand for sustainable urban drainage system. The reference to urban has been removed to accommodate rural sustainable water management practices.
SuDS: what they are and how they help prevent flooding
SuDS provide an alternative to conventional drainage solutions. They can be used in all types of developments, utilising and mimicking natural systems of water drainage in urban areas. In contrast to conventional drainage systems, SuDS aim to deal with rain and surface water where it falls by slowing and holding back water run-off from a site and allowing natural processes to break down pollutants. Although they are designed using the same principles of hydraulics and hydrology, SuDS adopt and integrate broader opportunities for economic enhancement, social cohesion, amenity, water, air and environmental quality and urban design.
Dr Ian Mell, a lecturer in Landscape Planning and Green Infrastructure at the University of Manchester, has written extensively on the topic of sustainable cities and the need to maximise the economic, social and environmental benefits of urban greening. He says:
SuDS come in all shapes and sizes but are predominantly nicer to look at, easier to fit (once you know how), cheaper than more engineered solutions and normally cheaper to maintain.
All SuDS schemes aim to catch and deal with water where it falls, rather than channel it into conventional drainage systems.
SuDS can be divided into two broad categories.
Soft SuDS utilise a green infrastructure-based approach to urban drainage, such as landscaped and vegetated features, swales, green roofs and detention ponds. These can be useful in delivering green space amenities to a development.
Hard SuDS are proprietary engineered systems which aim to mimic natural water drainage processes, such as precast concrete soakaways, permeable pavements, attenuation tanks and onsite treatment chambers. Hard SuDS can be good for sustainably managing water run-off without taking up valuable development space.
These different types of SuDS can be used in combination to create a SuDS scheme.
Ian Mell comments:
“There remains some reluctance to use SuDS because their results can be variable and that’s a difficult thing for developers to deal with. Where they have been developed though, they are normally landscaped features that people talk about, take an interest in (and therefore learn about Green Infrastructure and environmental systems), and are things that communities become proud of. This all sells homes and developments. It also sells business premises as people are more productive if they can look at nature. SuDS also have the capacity to increase the proportion of biodiversity in an area to make it more ecologically friendly.”
Some of the benefits SuDS can deliver to people and places include:
- Preventing water pollution
- Slowing down surface water run-off and reducing the risk of flooding
- Reducing the risk of sewer flooding during heavy rain
- Recharging groundwater to help prevent drought
- Providing valuable habitats for wildlife in urban areas
- Saving water drainage costs
- Adding value to a place by making it more attractive
- Improved physical and mental health benefits associated with green spaces for people in urban areas
- Improved air quality through greening
Selecting the right SuDS for a project
Ian Mell suggests the following when choosing the right SuDS:
“The main issues with SuDS are getting the design right, implementing the project effectively (including how it can be managed), and building a SuDS into an urban area as key infrastructure. If all these things can be achieved then, no matter what size the SuDS, they should be successful at delivering ecological, social and economic benefits to communities, nature and business.”
A key thing to remember when thinking about SuDS for a development is that it is a multi-disciplinary process. SuDS are not just about water drainage; planning, architectural and landscaping requirements, water quality and water resource will influence the decision and should complement the overall vision of the project.
A good general principle is minimising impermeable surfaces where possible whilst maximising opportunities for managing water close to the surface. SuDS should always be designed with operation and maintenance in mind.
Remember: there is no one correct answer. A SuDS scheme will always be the result of opportunities and constraints within any given project.
Legislation to be aware of relating to urban drainage
In the UK, all new housing developments are supposed to utilise SuDS – planning regulations for England and Wales (2015) expect SuDS to be included in all new housing developments of 10 or more homes. But there is concern that rules on drainage for new homes are poorly enforced. The Commons Environment Food and Rural Affairs (Efra) committee wants guidance to be tightened to prevent developers to opt out from installing schemes.
Building Regulations Part H3 (2002) emphasise the requirement to deal with surface water at source rather than dumping it into existing sewer systems.
Scottish Planning Policy (SPP) para 209 (2005): The Water Environment (Controlled Activities) (Scotland) Regulations 2005 require all surface water from new development (except single houses) to be treated by a sustainable drainage system (SuDS) before it is discharged into the water environment.
More information about SuDS can be found here: