Sustainable Drainage Systems

What are sustainable drainage systems?

Sustainable flood drainage systems are processes which regulate water in a way that imitates natural drainage systems.

Designed to control water flow and the distribution of polluted water in developed, urban areas, SuDS work by enabling water to soak into the ground (infiltration systems), slowing down the flow of water into watercourses (retention systems), storing and transferring water from vegetation into the atmosphere (evapotranspiration) and removing pollutants from water (filtration).

Faced with a future of climate uncertainty, SuDS are a far more competent water drainer, container and manager than their traditional counterparts like underground pipe systems, borehole soakaways and drainage bricks. 

What are the types of sustainable drainage systems?

Sustainable drainage solutions come in several forms, each of which have different purposes and suit a specific type of landscape.

Variations of surface water drainage solutions examples include:

• Linear wetland – gullies leading to a wetland downstream, where excess water is stored and vegetation aids the breakdown of pollutants. 
• Detention basins – a dry or naturally waterlogged area, formed into a concave shape which reduces the flow of excess rainwater during and after storms. They can also be referred to as an attenuation basin or SuDS attenuation pond.
• Green roofs – a specially-developed or landscaped roof which is designed to harvest rainwater or attenuate stormwater flow via plant matter or drainage mechanisms.
• SuDS paving – gravel and porous pavement in urbanised areas which allow water to soak into the ground rather than cause surface water flooding.
• Swales – a shallow vegetated channel that collects water runoff from a road and delivers it to a storage pond.
• Wetland and retention ponds – water-saturated plains which provide a valuable ecological amenity into which swales and channels can drain.
• Vegetative filtration – the absorption and transferral of water through plants into the atmosphere through the process known as evapotranspiration.

What are the benefits of sustainable drainage systems?

SuDS provide many advantages to people, society, wildlife and the environment alike due to their variety. 

• The benefits of sustainable drainage systems include:
• Conserving and producing natural habitats through the use and creation of green areas like wetlands and ponds.
• Providing more natural areas for species to breed, shelter and eat.
• Decreasing the risk and presence of flooding by removing and managing surface water.
• Better home drainage protection and an improved surface water drainage design.
• Improving the quality of fresh water in local rivers, ponds and wetland areas by reducing the transferral of pollutants from urban areas.
• Improving urban sewage systems and providing a better drain flow.
• Filtering and removing pollutants from watercourses, the local environment and urban areas.
• Improving the appearance of towns and cities – sustainable urban drainage systems often include vegetation and plant life.
• Relieving the pressure on traditional urban drainage systems which will struggle to cope with heavier quantities of stormwater.
• Encourage natural groundwater or aquifer recharge.
• Maintaining the natural flow regimes of rivers.
• Adapting communities to the projected increase of heavier rainfall caused by the climate crisis.

What are the disadvantages of SuDS?

Whilst the positives of sustainable drainage systems far outweigh the negatives, there are a couple of downsides to SuDS.

Firstly, the room for further urban development can be difficult where sustainable drainage systems have been integrated as green spaces.

Wetlands and marshland offer a wealth of biodiversity as well as managing water efficiently so being granted permission to build on such areas would be difficult.

Another downside to SuDS outlined by the British Geological Survey (BGS) is the requirement of permeable matter beneath the ground for infiltration drainage systems to function correctly.

According to the BGS, the areas where these types of SuDS are limited to places where gravels, sands and other free-draining mediums are present.

If surface water is unable to soak through the ground, it will cause flooding or could transfer pollutants into local watercourses.

How do SuDS benefit developers and architects?

There are several ways that developers and architects profit from sustainable drainage systems.

Firstly, from a financial perspective, the construction and maintenance of SuDS has been proven to be a cheaper alternative to traditional drainage systems.

In addition, SuDS can improve the financial value of land and property with the integration of green, natural spaces which combat flooding and pollution in a more attractive way.

Developments constructed in an area with sustainable drainage systems will also improve their aesthetic value and offer wellbeing benefits to potential occupants.

Furthermore, the presence of SuDS will reduce the time taken for planning permission to be granted, especially in instances where SuDS schemes are key to drainage strategies of local planning authorities.

Are SuDS a legal requirement?

Most local authorities will require a SUDS report to be undertaken before any construction can take place, even in areas with a relatively low flood risk.

If SuDS are to be incorporated into the layout of your development, you will need to submit plans for them, usually in the form of a sustainable drainage strategy, to your local planning authority.

England

According to part C of paragraph 167 in the National Planning Policy Framework, local planning authorities should only permit developments if the area “incorporates  sustainable drainage systems, unless there is clear evidence that this would be inappropriate.”

In paragraph 169, the policy additionally states that major developments need to incorporate SuDS unless it would be inappropriate to do so. The policy outlines that the SuDS should:

1. Take account of advice from the lead local flood authority.
2. Have appropriate proposed minimum operational standards.
3. Have maintenance arrangements in place to ensure an acceptable standard of operation for the lifetime of the development.
4. Where possible, provide multifunctional benefits.

Wales

Under the ‘Distinctive & Natural’ chapter of Planning Policy Wales, it is stressed that the Welsh planning system should ensure that SuDS are an “integral part” of a new development’s design, and should be “considered at the earliest possible stage when formulating proposals for new development.”

In cases where new developments of more than one dwelling are planned for construction, or in instances where the area that will be covered by the development equals or exceeds 100 square metres, approval is required from the SuDS Approval Body (SAB) prior to any construction.

The SAB approval will also require developers to demonstrate:

• Arrangements for the adoption and management of SuDS.
• How maintenance of the SuDS and its drainage elements will be funded.

Moreover, in cases where infiltration SuDS are not suitable, the policy states that “consultation with drainage bodies and NRW should be undertaken and relevant evidence and information drawn from Area Statements taken into account.”

Scotland

The Scottish Planning Policy states that the planning system should promote avoidance of increased surface water flooding through requirements for Sustainable Drainage Systems (SuDS) and minimising the area of impermeable surface.

Proposed arrangements for SuDS should be adequate for the development and appropriate long-term maintenance arrangements should be put in place.

According to the policy, planning should support developments which showcase six qualities, one of which integrates SuDS “to conserve and enhance natural features whilst reducing the risk of flooding.”

What is a sustainable drainage report?

Sustainable drainage reports are a comprehensive analysis of a site to determine its suitability for SuDS, the topography of the site land and data relating to sewage systems in the vicinity.

GeoSmart’s SuDSmart Drainage Reports are offered in three variations, each of which are able to support architects, developers, planning consultants and the legal market.