Sustainable Urban Drainage Systems (SuDS)

SuDS means ‘sustainable urban drainage systems’. It sets out how to use rainwater and surface water more intelligently, and – where possible –  mimic the natural environment to help reduce flood risk and improve the environment.

Any design should comply with SuDS’ four pillars.

The four pillars of SuDS

Picture Source – Susdrain, Circia Suds manual v6

What type of SuDS can be adopted?

Local councils are increasingly aware of the need to manage surface and rainwater during intense storms.

When volumes of surface water overwhelm the downstream sewage and surface water networks, it can cause severe flooding and damage. As a result, housing developments are now frequently required to be able to manage a 1-in-100-year storm rainfall event (and more, given our changing climate).

Designing drainage with SuDS in mind can help reuse the water, allow it to sink into the ground, hold back flows to reduce pressure on the network, and help the natural environment.

SuDS that meet the design and construction standards set out in the Construction Industry Research and Information Association’s (CIRIA) SuDS manual can include:

  • Swales
    Swales are open-channelled, shallow and flat-bottomed so they can carry, treat and minimise surface water flows. Their design and the vegetation used may vary.
  • Rills
    These open concrete channels keep water runoff on top of the surface until it meets another section of the network or SuDs feature. They can have a range of designs and are typically very shallow for safety reasons.
  • Ponds
    Ponds and wetlands are designed to permanently have a pool of water, and hold and treat surface water. Ponds can include a range of different vegetation and marine life.
  • Detention basins
    Detention basins are surface storage basins or facilities that control flow by reducing stormwater runoff. They also help some pollutants to settle.They are typically dry and, in certain situations, the land may also be used for recreation. However, basins can also be mixed, including a permanently wet area for wildlife or runoff treatment, and a dry area used to reduce flooding.Basins usually appear towards the end of the SuDS network, and tend to be used if extended treatment of the runoff is required, or when needed for wildlife or landscaping.
  • Tanks and flow control devices
    These are underground voids, constructed to store stormwater. They can be slow-release and come in various designs – from oversized pipes to modular or honeycomb (geocellular) storage systems.
  • Infiltration trenches
    Infiltration trenches are linear soakaways used mainly where the soil is less porous. The design can also include perforated pipes that help distribute water across the area.
  • Soakaways
    Soakaways can be considered for roof water and as part of swales, where the soil allows the water to sink in.
  • Outfall structures
    These are usually found at the end of a pipe/SuDS feature and can release water into a river to accommodate flows in extreme weather events.

SuDS that can’t be adopted

  • Watercourses as defined in law, including rivers, streams and some ditches
  • Features built primarily for draining surface water from streets or land
  • Features built to manage groundwater
  • Features that are an integral part of the structure of a street, such as a permeable street, or a channel formed by either a roadside kerb or a depression in the street’s centre
  • Household items, such as guttering
  • Green roofs
  • Permeable paving
  • Water butts

As every site is unique – soil type, ground contamination, elevation etc. –  including SuDS early on during the design process will help identify which features are most appropriate for each individual housing development.

Our expert team can help oversee their construction to ensure they meet the required standard and advise on their ongoing maintenance for peak performance.

Benefits of SuDS

Including SuDS in any site development can bring a number of benefits, including:

  • Environmental
    – Reduced flooding events
    – Protected water resources
    – Increased biodiversity
  • Long-term
    – Helps towards carbon reduction targets
    – Benefits local communities by providing community spaces, such as recreation grounds and wetlands
  • Developer partnerships
    Working together to help complete housing developments fosters professional relationships