With sustainable drainage systems set to become mandatory for all new developments in England, Dr Netsanet Mebrate, Product Owner for Causeway Flow at Causeway Technologies, discusses their benefits and shares tips for implementation.
Following a review into surface water management by the Department for Environment, Food and Rural Affairs (Defra), the government announced plans earlier this year to make sustainable drainage systems (SuDS) mandatory for all new developments in England.
The regulations are expected to come into force in 2024 – five years after they were introduced in Wales to reduce flood risk and improve water quality.
Some regions in England, including Cambridgeshire and Oxfordshire, have already implemented a mandate for SuDS. However, there is still work to be done to encourage the adoption of SuDS more widely.
Drainage is now a top priority in the construction design process and the mandate announcement has placed added pressure on housebuilders to explore the possibilities of installing SuDS on all new sites – not just those consisting of more than 10 homes, as is currently the case.
Arguing the case for SuDS
Since the Building Act 1984 was passed, there has been a requirement for UK housebuilders to conduct hydraulic analysis to identify where drainage systems would be best placed to deal with rainfall.
Software was developed to address this requirement and facilitate the design of traditional drainage systems such as pipe-to-pond or pipe-to-tank solutions, which are still widely implemented today. However, these systems can result in deep ponds and basins with steep sides, tanks, and pumps that are unsightly and provide few additional benefits to developments.
Sustainable drainage expert Anthony McCloy argues that we need to change our attitude towards rainfall and rather than view it as an issue – something that must be addressed to meet a planning condition – we should embrace it as an asset and make it a critical consideration in planning and design stages.
According to Anthony, by harnessing rainfall as an asset housebuilders can improve climate change resilience, facilitate biodiversity, and create more interesting, usable and multi-functional amenity spaces within their developments.
Anthony’s point is that if we can replicate what the National Planning Policy Framework (NPPF) is telling us and acknowledge what the guidance is there to relay, keep the water at source and allow it to slowly move through the site, it becomes something that’s much more in-keeping with the local landscape and a real asset.
What’s more is all the research that’s been done to date shows that SuDS don’t cost more – they can either be cost neutral or even cost less than traditional drainage solutions.
Tips for implementing SuDS
It’s true that SuDS should inform the layout of a development, but they should also be informed by the layout. Developers shouldn’t get as far as the detailed design stages before they decide they need to implement SuDS.
There is a wide range of data that can inform SuDS design and flood risk assessments, from planning information that planners would use as a screening tool, to more detailed data which can be accessed via the government website about surface water and reservoirs, so we can understand flood from a variety of different mechanisms.
It is also possible to access Strategic Flood Risk Assessment – site-specific flood risk assessments – and look at all the documents the local authority may have, such as the Local Flood Risk Management Strategy (2019 – 2029), which may contain data about particular areas of flood risk that might not be representative within the modelling.
Lessons from Wales
With any significant change to the status quo, there are bound to be some teething problems and the implementation of a SuDS Approving Body (SAB) with the mandate in Wales in 2019 took some readjusting.
SAB has drastically affected drainage implications and how sites are developed to ensure there is enough room for SuDS features.
We spoke to representatives from Caerphilly County Council and a Welsh civil engineering, environmental and building consultancy who stressed the importance of early engagement between clients and architects during the pre-design stage(s). They said this helps to avoid any unforeseen site issues when it comes to drainage, and mitigates the risk of needing changes to the development due to unforeseen drainage issues, ie lack of space for attenuation or lack of green areas for SAB approval.
How technology can help with the design of SuDS
Technology also exists to support the design and integration of SuDS. Cloud-licensed platforms such as Causeway’s Flow, which provides a hydraulic modelling solution for the design and analysis of optimal, compliant, and cost-effective storm and foul water drainage networks, are ideal.