Preparing for SuDS How new sustainable drainage guidelines will impact the construction industry

Sewers for Adoption: A design and Construction Guide for Developers, is set to change the face of UK drainage forever. It will be instroduced in April 2020, and will outline standards regarding the adoption of sustainable drainage systems (SuDS) by water companies across the country. Here, Martin Lambley, Product Manager for stormwater management at Wavin, explains the changes and what they mean for the industry.

With flooding and heavy rainfall hitting the UK headlines more than ever, it is becoming increasingly clear that using pipes to collect rainwater and then distributing it into rivers is no longer a sustainable solution to the UK’s drainage needs. In order to combat this, the eighth edition of Sewers for Adoption (SfA8) is setting out new standards for SuDS, clarifying what is expected of developers if their drainage systems are to be adopted by water and sewerage companies (WaSCs) across the country.

To allow sufficient time for WaSCs, planning authorities and developers to update their policies and procedures to comply with the new manual, a pre-implementation version of SfA8 was published in 2018. Since this initial publication, WaSCs have been looking at a range of SuDS techniques that greatly improve on existing assets, such as oversized pipes and tanks. These more sustainable techniques include swales, basins and geocellular systems, which are installed under green areas and are made up of modular crates that control surface water runoff either as a soakaway or storage tank.

Positive progress The concept of SuDS is nothing new to the industry. They’ve been around since the early 1990s and their benefits are plentiful - not only do they ensure flood resilience, but they also improve the urban environment through improved air quality and biodiversity. However, despite these benefits, they are still not a conventional feature of urban developments.

There are a number of reasons for this, but it essentially boils down to there being no formalised route to adoption. There is also a longstanding misconception that SuDS are less easy to maintain when compared with conventional piped drainage systems and cost comes into play - where SuDS are easy and cost-effective to install, they will often be implemented; however, if a less expensive option is available, developers will often default to more traditional methods.

SfA8 aims to change such perceptions and set a standard for better levels of flood protection, ultimately leading to greater use within infrastructure design. There are many steps within the guidelines that should help to protect against even the heaviest rainfall events and elements like the abolishment of the five- metre rule for infiltration could actually treble the capacity of water storage. But is it all positive?

A flaw in the plan Any efforts made to improve the sustainability of UK drainage should be supported, and it’s promising that under SfA8 designers will need to fully consider installation, health and safety risk assessments, maintenance and access requirements of both hard and soft SuDS as part of their designs. However, there is a justified argument that the guidance doesn’t go far enough to effect real change. And there are some SuDS that are notable absent from the manual, such as green roofs and permeable pavements.

Although the document will be mandated by Ofwat, making it the strongest edition to date, there is still the potential for WaSCs to deviate somewhat from the guidelines as some of the wording is open to interpretation. Geocellular tanks are expected to be a particularly tricky area as some water companies have historically been against their installation, mistakenly claiming they are difficult to maintain. In hope of avoiding any backlash, there has been constant engagement with water companies to gain their feedback and agree on the proposed standards but, of course, widespread uptake of the guidelines cannot be guaranteed.



What does the future hold?

Over the years there has been real progress when it comes to sustainable drainage and the new guidelines are certainly a step in the right direction. A commitment to a more sustainable future has been seen at all levels, from government bodies to installers - take the government’s 25-year surface water action plan, for instance. However, we need to see this commitment put into practice across the board and in a potent way if SuDS are to be universally adopted and rid of their specialist status. As an industry, we need to embrace this change and quickly, especially as the flooding caused by climate change becomes ever more common.

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