SuDS

The term SuDS is used to group together a range of ‘Sustainable Urban Drainage Systems’. The aim is to use rain water and surface water more intelligently, and to mimic the natural environment (where possible) to help reduce flood risk & improve the environment.

Their design should comply with the Four Pillars of SuDS.

The Four Pillars of SuDS

Picture Source – Susdrain, Circia Suds manual v6

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What type of SuDS are adoptable?

Local councils are becoming increasingly aware of the need to manage surface & rainwater in extreme flooding events. It is often a requirement for a housing development to be able to manage a 1-in-100-year storm rainfall event (plus an uplift for climate change) within the site boundary. In intense storm events large volumes of surface water can overwhelm the downstream sewage & surface water networks, causing severe flooding & damage. SuDS should be designed to help re-use the water, allowing it to infiltrate into the ground, or hold back flows which reduces the pressure on the network and helps the natural environment.

SuDS that are built to the design and construction standards within the CIRIA SuDS manual would be considered for adoption, these include:

1. Swales

Swales are open channelled, shallow and flat bottomed in design to enable them to convey, treat and minimise surface water flows. They can vary in profiles, with different designs and vegetation used.

swales
c.5 swales and conveyance channels canals and rills 2

2. Rills

These are open concrete channels used to keep water run-off 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 often very shallow for safety reasons.

3.Ponds

Ponds & wetlands are designed to permanently have a pool of water and to hold and treat surface water. Ponds can include a range of different vegetation and marine life.

pond3
baisns

4. Detention Basins 

Detention basins are surface storage basins or facilities that provide flow control through attenuation of stormwater runoff. They also facilitate some settling of particulate pollutants.

Detention basins are normally dry and in certain situations the land may also function as a recreational facility. However, basins can also be mixed, including both a permanently wet area for wildlife or treatment of the runoff and an area that is usually dry to cater for flood attenuation.

Basins tend to be found towards the end of the SuDS management train, so are used if extended treatment of the runoff is required or if they are required for wildlife or landscape reasons.

5. Tanks and flow control devices

Tanks and flow control devices, are below ground voids constructed to create storage for storm water. These can be slow release and can come in a range of designs and can include over sized pipes through to geocellular storage systems.

tanks and flow
trenches

6. Infiltration trenches

These are linear soakaways and are better for areas where the soil is less permeable. Perforated pipes can also be included in the design to help with the distribution of water across the area.

7. Soak aways

These can be considered for roof water and also as part of swales where infiltration is possible (with permitting soil types).

soakaways
olympus digital camera

8. Outfall Structures

These are usually the end of pipe / SuDS component and can release water off into a river as part of a design for exceeding flows in extreme weather events.

SuDS components that cannot be adopted:

  • Watercourses as defined in law (these include rivers, streams and can include some ditches)
  • Components built primarily for the drainage of surface water from streets or for the drainage of land
  • Components built to manage groundwater
  • Components which are an integral part of the structure of a street (e.g. a permeable street or the channel formed by the kerb of a conventional road or a channel formed by a depression in the centre of a street) or household items
  • Green Roofs
  • Permeable Paving
  • Water Butts

Every site has various unique features such as soil type, ground contamination, elevation etc. Therefore, early involvement in the design of SuDS will assist in identifying adoptable features, and ESP overseeing the construction of SuDS will help ensure they are built to an adoptable standard. The ongoing maintenance of SuDS features vary. ESP Water will consult on the best SuDS features for each individual housing development, to ensure the long term maintenance of SuDS is successful.

Benefits of SuDS

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long term 2
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