This section is a brief summary of many of the key components or elements of SUDS that are commonly quoted and used (There are others – see CIRIA The SuDS Manual). It should be noted that many can be combined and arranged in a number of ways.
This guide is not a definitive “how to” or provision of “standard details” that is for you guys to develop. But this might help.
SOURCE CONTROL – Local to the site and looking at controlling and treating water where it falls.
SITE CONTROL – When water needs to be conveyed to other areas or grouped
SuDS principles can be applied to any site, it’s just a case of using the right methods and approach for the site conditions you have. That is not to say that the consideration stated, and others, are not important to how a site is drained, as long as they are considered.
There are a number of types of green roof (Brown, Extensive and Intensive).
A roof does not need to be entirely one type or another or even planted. Other equipment could be included (solar arrays etc) but the design needs to be a joined up process to agree the needs of the structure (biodiversity requirement, drainage function, public access and amenity) with the physical constraints.
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Biodiverse and Brown Roofs - replicate an ecological environment and provide a natural living habitat to encourage a wider species of flora, insect and fauna. – note this option may not be green at all.
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Extensive - lightest weight option available with hardy, pre-cultivated sedum vegetation for instant greening of the roof – note, again may not be green all the time
Extensive Substrate-based Systems - greater depth of substrate allowing for a broader range of self-sufficient plants including grasses, herbs and succulents – note, a “proper green roof” as most would recognise it.
Intensive Roofs - where the design may include lawns, flowerbeds, shrubs, trees all intermixed with paths, driveways and patios. These roofs also include vegetable plots, sports grounds, and park land. – Note, this could be a podium deck in which case paving and landscaping could form part of the “roof”.
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Simply put, this is a green roof hat has been designed to retain/detain as much water as possible from a rainfall event – usually within a reservoir media below the surface
There are a number of methods of infiltrating surface water into the ground.
This can be via discrete point sources such as house, trench and ring soakaways where the infiltration is usually designed to flow from the sides of the structure through to modular, blanket and basin soakaways where infiltration is predominately from the base of the structure.
Pervious pavements can come in many forms, both in terms of the surface treatment as well as the sub-surface construction.
The paved surface can itself be “porous” such as porous blocks or porous asphalt or the structure as a whole is pervious such as block paving (with the joints providing the pathway for water) and reinforced grass systems (using spaces to allow plant growth and permeability)
Determine underlying permeability and ground conditions (contamination and groundwater levels etc) and hence which paving “system” is to be designed.
How close to structures is the paving and taking additional inflows (roofs or other paved areas etc)?
Make sure paving is greater than 5m from the structure or use System C.
Is the paving separate from other surface water drainage?
Do you want to use the paving as attenuation for other areas?
Is the paving linked to other paving areas (more important for Systems B and C)
Where does the paving sit in the “SuDS Treatment Train”?
To maximise the storage within the sub-base, some form of flow control is required to simulate a virtual tank and maximise the utilisation of the available volumes.
A traditional way to provide additional storage volume on a drainage network can be by increasing the size of the pipework or manholes or providing tanks. Although not meeting all the requirements of SuDS, they can provide attenuation to a system when outflows are restricted.
There are many types and configurations for tanks and each has to be considered in relation to its location, the loading it is likely to be subject to, how deep it is.
When considering the use of a tank, of any manufacture, consider its structural components and loadings. NOT ALL TANKS SYSTEMS ARE THE SAME
Shallow landscaped longitudinal depression using vegetation to filter runoff
Shallow gradients and side slopes
Primarily conveyance but offers some attenuation
Can allow infiltration along its length or be lined if ground condition require separation of the surface water from the underlying soils.
Can include an infiltration trench or conveyance pipework beneath to increase capacity and allow crossings of the swale by footpaths, driveways etc.
Typically alongside highways but can be used in landscaped areas
Need to consider utilities and other crossings (as all SuDS components should)
On steeper sites, consider check dams to restrict flows between swale sections
Retention ponds can provide both stormwater attenuation and treatment.
They are designed to support emergent and submerged aquatic vegetation along their shoreline.
Runoff from each rain event is detained and treated in the pool. The retention time promotes pollutant removal through sedimentation and the opportunity for biological uptake mechanisms to reduce nutrient concentrations.
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.
Wetlands provide both stormwater attenuation and treatment.
They comprise shallow ponds and marshy areas, covered almost entirely in aquatic vegetation.
Wetlands detain flows for an extended period to allow sediments to settle, and to remove contaminants by facilitating adhesion to vegetation and aerobic decomposition.
They also provide significant ecological benefits.
