Sustainable Drainage Systems (SuDS)

The consideration of how surface water is managed is coming to the forefront due to changes in weather conditions and the increase in the numbers of flood events occurring. Knowledge of SuDS is essential for all drainage engineers to work towards alleviating issues.

Dealing with surface water on a site can be challanging and starts with Source Control - dealing with the water where it falls.This is important to SuDS as implementing features assists with removing pollutants, providing water storage and slowing flow velocities throughout the overall surface water network.

What are SuDS?

• Sustainable Drainage Systems (SuDS) are how surface water is managed for maximum benefit.
• Sewer capacities are struggling, and this will only get worse with climate change.
• By working with nature and the water cycle we can reduce pollution and flooding whilst creating a great environment to live in. This is done by managing water better where it falls.
• The 4 Pillars to SuDS: Water Quantity, Water Quality, Amenity and Biodiversity.
• High quality drainage by counteracting some effects of urbanization (reduced infiltration) that can create cost savings on traditional systems if incorporated effectively.
• They can be used anywhere! New developments, re-developments and even retrofitted into existing developments.
• Doesn’t need to be loads of space, they can be incorporated with site features:
  • Permeable surfacing used for parking.
  • Rain gardens by structures or traffic calming measures.
  • Detention basins and swales with recreational uses.

Although SuDS are scrutinized from the same legislative position across England, in practice the requirements and implementation by different local authorities and attitude of approving bodies varies from place to place.  This can make it difficult to advise Contractors/Clients for budgeting at early stages of the design process and also leads to changes to the drainage system throughout the planning process.  In addition, drainage has therefore become a ‘hot topic’ in the planning process.

SuDS for Planning:

Flood and Water Management Act 2010 (FWMA)

•  LLFAs were created taking responsibility for local flood risk from EA to LA. Would have created SuDS approval bodies amongst other elements, but section 32 and Schedule 3 on sustainable drainage has not been implemented.

Planning policy was strengthened with ministerial statement in 2014

•  This made LLFA statutory consultees on major applications

Non statutory technical standards for SuDS published in 2015

• Was expected to be a technical document to level standards across the country/authorities, but was a 2 page document of high level information only. There is ongoing consultation on bringing the 4 pillars into this and water cycle strategies

 Other guidance

•   LASOO guidance on the non-statutory technical standards for SuDS published in 2016 (LASOO is now ASA)
•   Sewers for Adoption, subsequently replaced by SSG App C Design and Construction Guidance
•   Individual planning authorities guidance
•   Building Regs