What are Sustainable Drainage Systems?

If you are submitting a planning application, then chances are you may have read the term Sustainable Drainage Systems or ‘SuDS’. But what makes SuDS different than any other normal drainage?

Conventional surface water drainage has one principal aim, to remove water from a particular location as quickly as possible. Increased development and removal of permeable areas for water to seep away within our urban landscapes puts huge pressures on our drainage assets, leading to increased flooding. With higher intensity storm events becoming more commonplace due to the effects of climate change, water quality is also affected due to the effects of pollutants and sediments being washed into the sewer system.

SuDS (Sustainable Drainage Systems) takes a fundamentally different approach to conventional drainage by replicating natural processes to provide multiple benefits both on site and in the downstream catchment.

The SuDS Manual was first published in 2007, with a major update released in 2015 CIRIA C753. The SuDS Manual defines SuDS as:

“Sustainable drainage Systems (SuDS) are designed to maximise the opportunities and benefits we can secure from surface water management.”

The opportunities and benefits have been classified into four sections known as ‘The four pillars of SuDS’, these are:

• Water Quantity
• Water Quality
• Amenity
• Biodiversity

A good SuDS system will provide betterment within all four of these pillars, which will be covered individually in upcoming blog posts.

When are SuDS required?

During the planning process the Lead Local Flood Authority (LLFA) is a statutory consultee for all Major developments. This principally means:

• Developments with 10 or more dwellings;
• A development site of 1 ha or greater;
• Non-residential development with additional floorspace of 1000 m² or more

Developments of all sizes within Critical Drainage Areas (CDAs) and those within areas of flood risk can provide the greatest benefit to reduce flood risk overall. In these cases, a SuDS scheme will be incorporated into a Flood Risk Assessment.

For all developments, SuDS will need to be incorporated into the scheme wherever possible as part of a scheme to reduce surface water runoff from the site in accordance with the local council’s policies. Often SuDS schemes are cheaper and easier to maintain over their conventional counterparts.

What is Required?

All development will need to demonstrate water reuse has been prioritised. This could be in the form of rainwater harvesting, where grey water is reused for toilets. Water butts are a simple solution and effective solution to encourage water use for garden irrigation.

The drainage hierarchy should be used when determining how surface water will be disposed on the site, prioritising more sustainable approaches (infiltration) over connections to sewers. Local authorities may have slight adaptations of this hierarchy but covers the same principles.

Mimicking natural processes, a SuDS scheme will need to demonstrate how development aims to meet greenfield (pre-development) runoff rates. The preference is to slow water down by providing as many ‘source control’ measures as possible. These are measures which manage water where it falls, such as green roofs and pervious paving. The more source control measures used will reduce the overall attenuation volume requirements. In addition, source control measures provide multiple benefits. For example green roofs provides benefit to surface water runoff in terms of quantity and quality as well as increasing biodiversity and amenity value. A series of SuDS techniques will be discussed in future blog posts.

A SuDS strategy ultimately needs to show the regulator how the development will manage its surface water using SuDS techniques and throughout its lifespan, taking climate change into account. Conveyance and attenuation of surface water through the site will need to prioritise above ground features, such as swales and ponds over below ground solutions such as pipes and tanks as far as is practically possible.

An important aspect in a good SuDS strategy is providing a robust maintenance regime to ensure the system performs as intended throughout the developments lifespan.

Each LLFA or local authority may have slightly different requirements. The detail required will be dependent on the planning stage and type, development proposals and any specific site constraints.

How We Can Help

Here at Lustre we can provide SuDS strategies for planning applications of all sizes and development types.

Working with our Land Team we have extensive experience in undertaking infiltration testing to BRE365 and BS EN ISO 22282. This allows us to provide you with confidence that infiltration testing has been undertaken to suit any future onsite drainage, ensuring a more robust design process.

We will work with your design team to provide options on how the SuDS requirements can be incorporated into your site, providing our recommendations on how multiple benefits can be achieved. We will prepare a report detailing our methodology providing calculations using the latest software and rainfall data to be included alongside the strategy.

SuDS are most effective when considered as an integral part of the development design process. The earlier we get involved, the greater opportunity there is to maximise the opportunities and benefits from the surface water management of your site.

Contact us today so that we can help get your site approved and built.