Sustainable drainage systems (SuDS)

Guidance

The Council, as the lead local flood authority (LLFA), has been designated as the statutory consultee on surface water drainage for major developments.

We have produced a number of guides that sets out the framework for integrating SuDS into development layouts:

Sustainable drainage design and evaluation guide

• part 1 
• part 2
• part 3
• part 4 

All developments within the borough should follow this guide and incorporate SuDS.

The London sustainable drainage proforma

For all major developments, you’ll need to send this proforma together with the sustainable drainage strategy submitted with planning applications. It forms part of planning application validation requirements.

It sets a clear standard for the information that should be provided in a sustainable drainage strategy for all development in London. It ensures that key information is provided with the initial planning application, reducing the need for additional information throughout the assessment process and preventing delays in approval.

Minor developments should complete this form and are encouraged to discuss their drainage strategy with the lead local flood authority (LLFA). This is of particular importance to sites located in critical drainage areas (CDA) and / or a surface water flood risk areas.

• Hackney-SuDS-Proforma (spreadsheet)

Please submit your completed form to: floodsandsuds@hackney.gov.uk. For more information, or a pre-application discussion, please contact us using the details below.

SuDS and planning policy

SuDS are now a planning requirement for major developments (ie developments of ten dwellings or more and equivalent non-residential schemes).

Developers need to provide SuDS on major developments, where appropriate, while paying due regard to the following:

• surface water drainage checklist – surface water drainage information required by LLFA as part of the planning application
• SuDS management and maintenance requirements guide
• planning practice guidance, updated to reflect these changes
• non-statutory technical standards for the design, maintenance and operation of SuDS, published by Defra
• non-statutory technical standards for sustainable drainage – practice guidance
• guidance on flood risk and sustainable drainage systems (SuDS) for planning applications

London Plan Policy 5.13 Sustainable Drainage states that development should utilise SuDS unless there are practical reasons for not doing so, and should aim to achieve greenfield runoff rates and ensure that surface water runoff is managed as close to its source as possible in line with the following drainage hierarchy:

1. Store rainwater for later use
2. Use infiltration techniques, such as porous surfaces in non-clay areas
3. Attenuate rainwater in ponds or open water features for gradual release
4. Attenuate rainwater by storing in tanks or sealed water features for gradual release
5. Discharge rainwater direct to a watercourse
6. Discharge rainwater to a surface water sewer/drain
7. Discharge rainwater to a combined sewer

The benefits of SuDS

SuDS provide a range of benefits over conventional drainage systems and use a variety of techniques to slow (attenuation) or store (detention) the flow of runoff and improve the quality of water by natural cleaning processes. SuDS can also be used to reduce the flow and volume of surface water runoff by providing infiltration / evapotranspiration and / or reuse.

Reduced flood risk

SuDS features such as rainwater harvesting, bioretention systems and detention basins etc. can slow down or eliminate the flow of rainwater from a site by filtering and storing it. This reduces pressure on the traditional drainage system within Hackney (which mainly consists of combined sewers) and therefore reduces the risk of flooding, especially after heavy rainfall. This is particularly important as our drainage system is under increasing pressure due to urbanisation, the effects of urban creep and the increased risk of heaving rainfall due to climate change.

Improved water quality

SuDS features such as filter strips, filter drains, green roofs and pervious pavements provide a natural cleaning and filtering process, therefore managing the quality of surface water runoff so that receiving surface waters and / or groundwater are protected. A well-designed SuDS treatment train can deliver a cost effective system in providing adequate treatment and pollution removal while at the same time, providing conveyance, attenuation and infiltration, particularly within vegetated surface-based systems.

Benefits for people and wildlife

SuDS can improve the quality and, in most cases, aesthetics of the public realm and private developments by creating attractive and multi-functional landscape features. In addition to surface water attenuation and / or detention, well-designed SuDS features can provide education and amenity opportunities for local users.

Water reuse systems such as rainwater harvesting and water butts can retain surface water for irrigation of landscaped areas or toilet flushing, thus reducing water demand for the development / property.

A number of comparative studies on the costs and benefits of traditional drainage and SuDS were undertaken under the DEFRA’s Water Availability and Quality Evidence Programme as part of the work on the Flood and Water Management Act. Clients, designers, engineers and quantity surveyors compared the capital costs for draining sites using sustainable drainage and more traditional approaches. All of the sites in these studies showed that the inclusion of SuDS was cheaper than a traditional drainage system.

Based on the studies, the capital and maintenance costs associated with most of the above ground features tend to be more cost effective than conventional drainage systems, therefore providing potential cost savings.