Constructing and inspecting SuDS: are we still missing the point? 

Sue Illman, Managing Director, Illman Young Landscape Design and CIRIA trainer

Sustainable Drainage Systems (SuDS) are no longer a niche concept. They are embedded in policy, expected in major developments, and widely recognised for their role in managing flood risk, improving water quality, and delivering wider environmental benefits. Across the UK, there are many excellent examples of SuDS delivering exactly what they were designed to do—and doing so beautifully. But alongside this progress, my experience on site suggests there is still more to do.

I continue to come across SuDS that don’t quite perform as intended—not because the design is flawed, but because the original vision hasn’t fully translated into construction reality. Components may be installed slightly differently to how they were designed, sequencing can be overlooked, or features intended to provide multiple benefits are simplified. These aren’t always major failures, but they can reduce the effectiveness of what should be high-performing systems. 

I don’t think this reflects a lack of effort or commitment. In many cases, it highlights a gap in understanding. SuDS are fundamentally different from conventional drainage systems. They are not just about moving water away quickly—they are about managing it thoughtfully, often at source, and frequently in visible, multifunctional ways. That shift requires both a change in mindset and a stronger appreciation of how these systems should be built, protected during construction, and inspected before handover.

Encouragingly, awareness is improving. More practitioners recognise that SuDS require a different approach on site, and there is growing interest in learning from both good and less successful examples. However, some common challenges still arise. For instance, infiltration systems can be unintentionally compromised by compaction or contamination, and features like bioretention areas may not always receive the attention needed in terms of soil specification or planting. Even relatively small issues—such as levels and falls—can influence long-term performance.

Inspection plays a key role in addressing this. Done well, it provides an opportunity to catch issues early and ensure systems meet their intended purpose. But without a clear understanding of what “good” looks like for SuDS, inspections can risk becoming a tick-box exercise rather than a meaningful quality check.

So, how do we continue building on the progress already made?

In my view, it comes down to strengthening the link between design intent and site delivery. Better communication between designers, contractors and inspectors is essential—but so too is practical, experience-based learning. Those involved in delivering SuDS benefit greatly from understanding not just what to build, but why it matters and how systems behave in reality.

It’s been encouraging to see more opportunities emerging for practitioners to develop this knowledge, particularly through training that focuses specifically on construction and inspection. By sharing real-world examples and common pitfalls, these initiatives help translate guidance into practice and support more consistent delivery across the industry.

SuDS have already proven their value. If we can continue to improve how they are constructed and inspected, we can ensure they deliver their full potential—not just in theory, but on the ground.

What steps can we take, as an industry, to keep closing that gap?

CIRIA offers a one day Constructing and inspecting SuDS training course to address the issues raised by Sue. 
Register now for the next scheduled course on 8 July 2026 in central London (venue TBC).