How to comply with Sustainable Drainage Systems (SuDS) standards

SuDS statutory standards

The six statutory SuDS standards are:

Standard S1 – Surface water runoff destination
Standard S2 – Surface water runoff hydraulic control
Standard S3 - Water Quality
Standard S4 – Amenity
Standard S5 – Biodiversity
Standard S6 – Design of drainage for construction, operation and maintenance and structural integrity

Download the full guidance on the standards from the Welsh Government

This page outlines advice to developers and SuDS Advisory Bodies (SABs) on three of the SuDs Standards: S2 hydraulic control, S3 water quality and S5 biodiversity.

Other permits you may need

Some SuDs have the potential for environmental risk. To mitigate this risk, you may need to obtain permits and consents from us. All permits and consents should be in place before approval from the SAB is sought.

The responsibility for finding out if any other permits are required lies with the developer. If a SuDs is developed without the necessary additional permits, we may take enforcement action.

If you are in any doubt about additional permits for a planning application, you should contact us for our pre-application advice.

Find out the contact details for your local advice team

S2 hydraulic control

A SuDs scheme may impact water levels and flows within an Internal Drainage District (IDD).

To find out if your proposed development is within or may affect an IDD, download the relevant map:

North Wales Internal Drainage Districts

South Wales Internal Drainage Districts

Some SuDs schemes that are outside an IDD, but drain water into its catchment, might affect levels and flows within it and could need a consent or permit from NRW.

SuDs may require other permissions:

land drainage consent
ordinary watercourse consent
Flood Risk Activity Permit

S3 water quality

Well-designed SuDs can help cleanse surface water runoff, improving or maintaining water quality in river catchments.

The following principles are considered good-practice. Demonstrating you’ve taken the steps below will contribute to complying with Standard S3 of the Statutory SuDS Standards:

All parts of the site have been assessed for pollution risk using an accepted technique, such as those in the pollution risk indices in the CIRIA SuDs Manual (free download with registration).
Avoid mixing flows from areas with different pollution risks as much as possible. Having separate sub-catchments on your development site can make your SuDs scheme more resilient to potential problems.
For rural and agricultural SuDs, schemes should be able to demonstrate to the SAB’s satisfaction that they meet the relevant principles from the Environment Agency’s RSuDs guidance. Download the EA RSuDs guidance. If you use this guidance, make sure you tell the SAB what parts of it you are referring to and why.
For proposals supporting high-pollution risk activities for example haulage yards, lorry parks, waste sites, you will need to contact us for pre-application advice.

For development proposals on brownfield or contaminated sites:

The presence of land contamination need not be a barrier to infiltration and the design of the SuDs can often be developed in line with the site’s remediation strategy.
Infiltration systems are suitable in contaminated sites where the infiltration can take place away from the contaminated area.
Where infiltration systems are discounted due to the presence of contamination, you need to explain the reason for discounting infiltration. Valid reasons are available in the standards guidance (page 9 para G1.8).
Please note that we will assess and provide detailed advice on the suitability of any remediation or treatment strategy when consulted by the Local Planning Authority at the planning application stage.

Pre-application advice

We recommend that developers contact us early for pre-application advice in relation to a planning application

Groundwater protection

Some activities pose high pollution risks to groundwater. Source Protection Zones (SPZs) around water sources (mainly used for human consumption) will require careful consideration.

See a map of Source Protection Zones on the Lle website

You should carry out a groundwater risk assessment if your proposed site is:

in a groundwater Source Protection Zone 1, or [geoscience]
is within 50 metres of a borehole, well or spring that is used for drinking water (please note that public health teams in local authorities hold information on the location of private water supplies serving individual households) and
one of the stated runoff destinations for the SuDs is infiltration and
involves draining anything other than ‘clean’ roof water (all roof water that is drained separately to other surface water sources on site)

The risk assessment must evaluate all pollution sources and pathways and demonstrate sufficient control measures to protect the water source. You should also contact us to discuss whether your activity needs a groundwater activity permit.

Deep infiltration systems

‘Deep techniques’ such as borehole soakaways, which discharge water directly into aquifers, bypassing the soil layers, pose a high risk of polluting groundwater.

We discourage deep techniques because of this high risk. They are not typically regarded as SuDs techniques because they do not mimic natural processes and provide no additional attenuation or treatment.

You should only consider them as a very last resort if you have ruled out (with clear reasons and evidence) all other forms of SuDs drainage, such as storage and interception (for example rainwater harvesting, green roofs, tree pits) and shallow SuDs features like swales and wetlands.

We strongly recommend that you contact the SAB for advice if you are considering using deep techniques.

Discharging to combined sewer

You should consult Dŵr Cymru Welsh Water or Hafren Dyfrdwy water companies where your scheme’s exceedance flow is proposed to discharge to a combined sewer. This flow destination is the least favoured choice in the hierarchy within Standard S1, so you must provide clear reasons and evidence in your SuDs application as to why your scheme cannot discharge to alternative destinations.

S5 biodiversity

SuDs can help biodiversity by providing additional habitat to support wildlife. When designed well, they can be connected to other landscape features thereby improving species movement and resilience.

Providing and maximising biodiversity as part of SuDs components is a requirement of the Statutory SuDS Standards.

A key early step in the design stage of a project is to thoroughly consider:

whether the scale (size) and location of the proposed SuDs scheme could disrupt natural clean water flows to any nearby wetland. This could apply to large developments, or where the SuDs design means that water could be directed away from a wetland.
the implications of the proposed SuDs on the habitat and species
appropriate measures to ensure habitat and species are protected and, where possible, enhanced.
the implications upon legally protected species to ensure that they are not adversely affected
how the SuD will be managed if and when a protected species inhabits the SuD

Read further advice for developers when dealing with protected species of plants and animals

Screening for sensitive receptors

Before applying to a SuDs Approval Body (SAB) for a scheme, we advise that proposals are screened for likely impacts on sensitive receptors.

Check our map for protected sites, aquifers and geology

Where relevant, records of protected species in the vicinity of a SuDs proposal may be obtained from the relevant local biological records centre:

An ecologist can help identify the impacts a scheme may have on species and advise on measures to reduce or eliminate those effects.

If a scheme is found to have an impact on a protected species, you will probably need a licence from us.

If works are planned within a Site of Special Scientific Interest (SSSI), you must speak to us about obtaining an SSSI Consent.

Techniques and good practice that contribute to complying with Standard S5

You must be able to demonstrate that all relevant protected species licences have been granted and that existing species or habitats have been protected.

Explaining in the SAB application where guidance has been sourced and how it has been applied to the scheme will help with your application. Biodiversity guidance is available from the following organisations:

Where possible all SuDs components should be designed to be shallow, avoiding deep chambers, manholes, gulley pots, silt traps and buried structures such as geo-cellular soakaways.

Plant species

When considering which plant species to use in a SuDs, you should:

Use native aquatic and riparian plants in all circumstances where those plants, their fragments or seed could be carried over the site boundary (for example, into a watercourse)
Only use non-native plants in structures like rain gardens or bioretention areas serving buildings in urban settings, in which a modified rainfall/temperature regime is likely, and away from protected sites.
Only use native tree species sourced from within the UK and confirmed as disease-free. Check whether a species is non-native on the GB non-native species secretariat website Note: some Sedums (Stonecrops) available on the market for use on green roofs can be invasive.
The SuDs design should follow the natural, pre-developed landform to achieve better habitat connectivity and maximise opportunities to deal with variable site conditions (for example soil characteristics and pollution risk).
For uniform sites, SuDs components should be designed so they have varied topography and aspect to provide a wide range of niche habitats that support the different stages in the lifecycles of invertebrates.
Consider how your SuDs will connect to habitats outside of the development. Your scheme could provide valuable movement corridors for animals. It could also help reverse the fragmentation or disappearance of local habitats, thereby maximising biodiversity.
Use plants like hydrocarbon and metal-tolerant reeds and grasses in sites close to higher pollution risk activities (for example refuelling).

Further guidance on SuDS

Susdrain

https://www.susdrain.org/

Susdrain is an independent website for those involved in delivering sustainable drainage. It provides guidance, information and case studies to help with the planning, design, approval, construction and maintenance of SuDS.

Support is available for flood risk managers, engineers, planners, designers, landscape architects and developers.

CIRIA

CIRIA produce ‘Guidance on the Construction of SuDS’ and ‘The SuDS Manual’, which can be downloaded free of charge from their website (registration required).

Welsh Government

Sustainable Drainage Statutory Guidance (PDF download)

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