Environmental guidance for your business in Northern Ireland & Scotland

Sustainable Urban Drainage Systems (SUDS)

Sustainable urban drainage systems (SUDS) can be used in all types of development to provide a natural approach to managing drainage.

SUDS prevent water pollution and flooding in urban areas. SUDS also create green spaces and habitat for wildlife in towns and cities.

SUDS are a legal requirement for all new developments, except for surface water drainage from single dwellings and developments that drain to coastal waters.

This guide describes the different types of SUDS, and how and when you must use them on your site.


Additional resources


SEPA: SUDS guidance


Sustainable urban drainage systems (SUDS) are a natural approach to managing drainage in and around properties and other developments.

SUDS work by slowing and holding back the water that runs off from a site, allowing natural processes to break down pollutants.

Types of SUDS

Source control measures deal with run-off at, or close to, the surface where rainfall lands.

Site control measures manage the surface water run-off from larger areas, such as part of a housing estate, major roads or business parks.

The run-off from larger areas can be channelled to a site control measure using swales (shallow drainage channels) or filter drains.

Regional control measures downstream of source and site controls deal with the gathered run-off from a large area. These systems use the same principles as smaller scale SUDS, but can cope with larger volumes of water.

Rainwater that passes through small SUDS can feed into larger SUDS which deal with the gathered run-off from a wide area. It is best to connect the flows between SUDS components with swales, filter drains or ditches and avoid the use of pipes.

SUDS treatment and attenuation

When you design a sustainable drainage system you should consider including a number of connected components. The more likely the runoff is to be contaminated the more stages of treatment should be included. This is known as the treatment train.

You can include source control measures to capture and treat runoff close to where it lands. You can connect a number of source controls to a site control measure such as a detention basin. The overflow from site control measures can be finally treated in a regional control SUDS measure before final discharge to the water environment.

Benefits of SUDS

The benefits of SUDS are:

  • 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
  • creating green spaces for people in urban areas.

SUDS techniques

You can use the following SUDS techniques:

  • green roofs - see the page in this guideline: green roofs in sustainable urban drainage systems (SUDS)
  • permeable surfaces - see the page in this guideline: permeable paving in sustainable urban drainage systems (SUDS)
  • infiltration trenches filter drains and filter strips - see the page in this guideline: filter strips and filter drains in sustainable urban drainage systems (SUDS)
  • swales - shallow drainage channels - see the page in this guideline: swales in sustainable urban drainage systems (SUDS)
  • detention basins, purpose built ponds and wetlands - see the page in this guideline: detention basins, ponds and wetlands in sustainable urban drainage systems (SUDS)

Further information

SUSDRAIN: Videos on You Tube

CIRIA: BeST (Benefits of SUDS Tool)


SEPA: SUDS guidance

Central Scotland Green Network: Raingardens for developers

You can use sustainable urban drainage systems (SUDS) to treat lightly polluted water that runs off from your site, reducing the impact on the environment.

You must not use SUDS to treat sewage, heavily contaminated run-off or trade effluent. If you cause or allow surface water or groundwater pollution you may be committing an offence and may be prosecuted and fined or imprisoned.

In Northern Ireland

You may have to include plans for SUDS when you apply for planning permission for new developments. It is good practice to include the use of SUDS in all development plans.

In Scotland: What you must do

You must consult with the Scottish Environment Protection Agency (SEPA) before discharging any run-off from your site to surface waters or groundwater. If you discharge to a sewer you will need a consent or agreement from your sewerage provider. If you discharge any run-off without an authorisation you may be prosecuted.

In Scotland all new developments must use SUDS to control surface water run-off to the water environment, unless the run-off is from a single dwelling or is to coastal waters.

You must have a licence from SEPA if you plan to use SUDS to control run-off from:

  • a development with more than 1,000 houses
  • a development with more than 1,000 car parking spaces
  • an industrial estate
  • major roads or motorways.

For all other developments, you may not need to contact SEPA, but must comply with General Binding Rule requirements. See The Water Environment (Miscellaneous) (Scotland) Regulations 2017, schedule 3, Activities 10 and 11 - Discharges of water run-off  (GBR 10 and 11)

SUDS must be:

  • designed to prevent pollution of the water environment
  • designed to protect the bed and banks of the receiving surface water
  • maintained in good order
  • protected from materials that will damage or block the system.

If your site was constructed after 1 April 2007, you must not discharge untreated surface water which contains run-off from:

  • fuel delivery or refuelling areas
  • areas where potentially polluting materials - such as chemicals and oil - are delivered, handled or stored.

If you discharge surface water run-off from a construction site, you must use suitable SUDS techniques.

Good practice (NI and Scotland)

Run-off from hard paving is likely to be contaminated by oil, organic material or toxic metals. Where there is a high risk of contamination by oil, you may need to install an appropriate oil separator in the drainage system.

PPG 3 Use and design of oil separators in surface water drainage systems (Adobe PDF – 78.6KB)

Where possible, you should design SUDS to increase biodiversity and provide habitats for wildlife in the area they drain.

For further information on measures to control water pollution, see our guideline: Preventing water pollution.

Further information

CIRIA: The SUDS Manual (2015)

Susdrain: Water Assessment and Drainage Assessment Guide


SUSDRAIN: Videos on You Tube

SEPA: SUDS guidance

Central Scotland Green Network: Raingardens for developers

Green roofs are an example of source control. Source control measures deal with run-off at, or close to, the surface where rainfall lands. You may need to use additional sustainable urban drainage systems (SUDS) components to control any overflow.

Green roofs have a layer of vegetation or patches of vegetation as part of the roof cover and can:

  • reduce or eliminate run-off from roof areas
  • extend the life of your roof
  • add insulation to your building during the winter months
  • cool your building during the summer by evaporation
  • provide sound insulation
  • reduce the heat island effect in cities
  • provide a habitat for wildlife.

You can use a variety of green roofs, including:

  • intensive systems - deep soil capable of growing shrubs and even trees
  • extensive systems - thin layer of vegetation, such as sedum mats.

Green roofs add weight so you should consider them at the construction stage of a new build. For an existing building, an extensive system is recommended as it adds less weight, but you should always consult an engineer to make sure that the structure is safe.

Further information

The Scottish green roof forum

Filter strips are strips of ground where water running off a site can pass, allowing some or all of it to soak away. The rest often enters a swale - shallow drainage channel - or another sustainable urban drainage systems (SUDS) component. This strip of ground can also be used to filter grit and other particles from the run-off.

Filter drains or filter trenches can be used beside roads and other impermeable surfaces, but should be avoided at busy road junctions or where rainwater can become heavily contaminated. Filter drains allow the run-off to soak away into the surrounding soil. Filter drains are filled with stones or gravel. This stone fill collects particles and helps to prevent pollutants from entering groundwater. You can use a filter strip or swale to reduce the level of pollutants entering the filter drain.

You can use filter drains for source control and to convey run-off between SUDS measures.

You can use permeable or porous paving as a source control measure for small roads, pavements, car parks and yards. Source control measures are sustainable urban drainage systems (SUDS) that deal with run-off at, or close to, the surface where rainfall lands.

Rain passes through the surface, either through gaps between individual blocks or permeable material such as gravel or porous asphalt, trapping pollutants below. Once there, many pollutants are broken down by natural processes.

By using permeable paving you can also prevent water pooling on impermeable surfaces, avoiding puddles and ice on car parks.

Large amounts of water can be stored temporarily under the surface. This reduces the chances of flooding.

A swale is a shallow drainage channel with gentle side slopes in the ground where water running off a site can collect and soak away.

Swales can be used to channel run-off from roads, yards and car parks where it collects into pools before soaking away. You can also use swales to carry water through a site.

Swales can run alongside roads so that run-off from the road surface can drain directly to the swale. You can also use them in the treatment of lightly contaminated run-off from hard standing around farmyards and farm roads.

When building a swale, you can include check dams to slow the flow of water. This allows the sediment to settle out. You can also use swales to carry water between sustainable urban drainage systems (SUDS) features instead of using pipes. This can reduce the cost of construction and maintenance.

Swales can be used for linking SUDS dealing with run-off from individual sites and SUDS that manage the run-off from large areas.


Further information


SEPA: SUDS guidance

Susdrain: Swales

Where rainfall lands on a surface, you can use source control sustainable urban drainage systems (SUDS) techniques to control run-off at, or close to, the source. This includes permeable or porous surfaces such as permeable paving, swales and filter strips.

To deal with heavy or persistent rain which produces more ,run-off, you can use site control SUDS, which are downstream of source controls, to manage the surface water run-off from larger areas, such as:

  • parts of housing estates
  • major roads
  • business parks.

Detention basins

You can use detention basins to store run-off from large areas. Water usually runs into these from conventional drainage systems or from upstream SUDS.

Detention basins let run-off spread across a wide floor area and only fill after heavy rainfall, when they will hold large volumes of water. This lets pollutants settle out before the water soaks away or discharges slowly downstream.

Ponds and wetlands

If you want to store water for longer, you can use ponds instead of detention basins. This allows natural processes, using bacteria and sunlight, to break down pollutants before the water eventually flows into downstream watercourses. Ponds can also be a welcome addition to urban areas, encouraging plants and wildlife.

You should never use existing ponds or wetlands to treat run-off. Always create new ponds to avoid damaging or disturbing the wildlife that is already in the area.

You can also connect a number of ponds, or include wetland areas in tackling run-off from large areas. Wetlands contain a larger amount of vegetation and are more suitable for treating contaminated run-off. Newly created ponds and wetland areas are ideal for treating lightly contaminated water from farmyards and farm roads.

Further information

Scottish Government: Constructed farm wetlands

The Constructed Wetland Association

SEPA: Ponds, Pools and Lochans

The Scottish Environment Protection Agency (SEPA) is the statutory agency responsible for protecting the water environment. SEPA requires the use of effective, appropriate sustainable urban drainage systems (SUDS) features in new developments.

SEPA: SUDS guidance

Susdrain: Water Assessment and Drainage Assessment Guide

The Construction Industry Research and Information Association (CIRIA) is an independent member-based, not-for-profit association. CIRIA promotes good practice in the use of SUDS with its Susdrain website. You can now download the "Benefits of SUDS" tool (BeST).


SUSDRAIN: Videos on You Tube

CIRIA: The SUDS Manual (2015)

SUSDRAIN: Climate Proofing Housing Landscapes (SHORT FILM)

The Sustainable Urban Drain Systems Network provides a UK-wide network for researchers, practitioners, agencies, developers and all those who are interested in SUDS.

SUDSnet: UK wide network for all involved with SUDS

Central Scotland Green Network has produced a guide for developers that describes simple measures to incorporate SUDS features into garden design.

Central Scotland Green Network: Raingardens for developers

Environmental management systems

If you are implementing an environmental management system for your business, you'll need to compile a legislation directory. In Scotland you may need to add the Water Environment (Controlled Activities) (Scotland) Regulations 2005 (SI 2005/348) to your directory. These regulations require that all new developments use SUDS to control surface water run-off to the water environment, unless the run-off is from a single dwelling or is to coastal waters.

Scottish SUDS Legislation

The Water Environment (Controlled Activities) (Scotland) Regulations 2011 Read the section on the Pollution Control Regime for information on the levels of authorisation you may need if you intend to use SUDS in a development.

The Water Environment (Controlled Activities)(Scotland) Amendment Regulations 2013These regulations amend the rules governing a number of activities that affect the water environment, including works close to or in watercourses, certain agricultural activities and the storage and use of pesticides.

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