Best practice in sustainable drainage design: what’s holding SuDS approaches back — and what to do about it

As urban areas densify and climate-driven flood risk increases, Sustainable Drainage Systems (SuDS) have shifted from “nice to have” to essential — and in many places, effectively planning-required. Yet many organisations still struggle to deliver SuDS consistently due to fragmented processes, inconsistent requirements, skills shortages, and slow approvals.

In our latest webinar, which was hosted by New Civil Engineer in partnership with Autodesk, four experts explored what “best practice” really looks like – from policy and approvals, to research, modelling, delivery, and long-term maintenance. We put together the main takeaways from the webinar, which you can watch here on the One Water Blog.

Speakers featured in the webinar

• Peter Holt, Stormwater & Blue-Green Infrastructure Expert, Arup
• Dr Simon De-Ville, Lecturer in Water & Environment Engineering, University of Liverpool
• Javier Soto, Product Manager, Autodesk (InfoDrainage)
• Pankit Shah, Flood & Water Management Lead, London Borough of Haringey (LLFA)

SuDS is maturing — but policy clarity still matters

A recurring theme was the need for clear, consistent expectations. Peter Holt reflected on the value of the Welsh approach to SuDS (where requirements are clearer), and pointed to ongoing debate in England over whether to enact Schedule 3 or continue with a “planning-plus” system.

Several speakers highlighted that consistent rules create a “level playing field”:

• Developers and designers know what’s required
• Reviewing authorities can apply standards more consistently
• The industry can scale delivery with fewer surprises mid-design

Peter also referenced recent improvements to national standards, noting that updated guidance is more comprehensive than previous versions and could help drive better outcomes, even while still non-statutory.

Best practice means designing for the real world: space, utilities, and retrofit constraints

If new build SuDS can be challenging, retrofit SuDS is often harder — especially in dense urban environments where space is tight and buried utilities are everywhere.

Autodesk’s Javier Soto shared a practitioner’s perspective from years delivering SuDS retrofit across London: opening survey data and seeing dense utility corridors is a familiar moment for many teams. But he argued that the opportunity is also enormous, especially when civil engineers and landscape architects collaborate:

• Civil engineers bring hydraulic understanding and performance thinking
• Landscape teams bring integration, planting, and place-based design
• Together, SuDS can become infrastructure people see and value, not just hidden storage

Peter adds that utilities and SuDS don’t have to be mutually exclusive. With the right approach, SuDS can even improve future access and reduce risk; for example, restoring a verge-like condition above utilities with appropriate protection layers.

The research base is strong — and now it’s feeding practical tools

Dr Simon Deville outlined how SuDS research has matured over the last decade, driven by national and EU projects and supported by major research infrastructure, including specialised facilities focused on green infrastructure and SuDS performance.

This research is building confidence in:

• Understanding physical processes within SuDS devices (from micro-scale media structure to full-field outcomes)
• Field monitoring that proves performance over time, particularly in large programmes like Mansfield

Simon noted that modelling capability has advanced to the point that, in many contexts, designers can now treat blue-green systems with confidence similar to traditional “grey” infrastructure, and that research insights have helped refine tools used by practitioners.

Proof at scale: Mansfield and the impact of multiple interventions

A standout reference was the Mansfield retrofit programme, which delivered 343 interventions. Peter shared that post-project modelling showed 402 properties experiencing reduced flood depth or improved resilience, alongside improved spill volumes and spill frequency.

The Mansfield programme also illustrates a key best-practice point: scaling SuDS requires moving beyond “one big asset” thinking. Distributed source control interventions — designed well and repeated many times — can deliver substantial cumulative impact.

Capacity is the next big challenge — design skills, review skills, and maintenance

As SuDS demand rises, the panel agreed that capacity is a serious constraint — especially for local authorities and approval bodies.

Pankit Shah said it clearly: many authorities face resource and skills shortages, which makes scaling review, delivery, and maintenance difficult. He emphasised the need to invest in people — from graduate pathways to structured training — and warned that adopting new regulatory frameworks without adequate resourcing could be difficult.

Javier added a cautionary note about technology: making tools easier is good, but it doesn’t replace fundamentals. If tools become “too easy,” there’s a risk that users generate outputs without understanding hydraulics or design intent — reinforcing the need for review, competence, and engineering basics.

And maintenance came up repeatedly. Many SuDS assets look great early on, but performance can degrade due to neglected maintenance, sediment build-up, or vegetation issues — a challenge that grows as SuDS scales.

Simon shared future research directions aligned to these concerns:

• Aggregation/simplification approaches that let engineers model many devices more efficiently
• Understanding long-term performance impacts from sediment, seasonal effects, and changing catchment conditions

Practical design debate: variable discharge rates, Qbar, and cost vs complexity

One audience question focused on variable discharge controls (matching greenfield hydrographs rather than simply capping at Qbar). The discussion highlighted a real-world trade-off:

• Yes, variable control strategies can reduce required attenuation volume
• But complex controls can be expensive and harder to maintain
• For many schemes, it may be better to reduce volumes through upstream source control rather than a complicated end-of-pipe solution

Pankit also pointed out the commercial reality: complex flow controls can add significant cost, and teams often seek simpler arrangements where acceptable.

Javier confirmed that tools like InfoDrainage can model variable outflows using staged control structures at different water levels, but stressed that users still need a solid grasp of hydraulics to apply such approaches safely.

Geology and infiltration: don’t treat it as a checkbox

Another strong thread was the role of geology and groundwater. Simon explained that infiltration is one of the biggest opportunities for volumetric control, but conditions can vary dramatically even over short distances.

Pankit reinforced how critical groundwater and seasonal water table variation are, particularly in London boroughs where groundwater can be a live issue.

Peter and Javier both cautioned against overly conservative defaults like lining systems automatically just because clay is present. Even limited infiltration can help, provided risks to structures and foundations are managed. The message: avoid turning infiltration into a simplistic yes/no decision — design for what’s actually happening beneath your feet.

Source control expectations vs viability and space constraints

A final audience question asked how feasible it is to meet source control and interception expectations in the new standards, including demonstrating “no runoff leaves site” for smaller storms.

Pankit’s view was candid: in practice, many developers still prioritise maximising built area, often defaulting to underground storage and arguing that more visible SuDS features aren’t financially viable. He suggested stronger requirements and fewer “escape routes” may be needed to make best practice the norm.

Peter agreed that early engagement and clear expectations are key, and pointed to the Welsh experience as evidence that higher standards are challenging but achievable.

Key takeaways for SuDS best practice

The discussion between these experts unveiled six key takeaways for doing SuDS right:

1. Standardisation helps scale: Clear requirements support better design and faster approvals.
2. Retrofit needs collaboration: Civil + landscape coordination is critical in constrained environments.
3. Research-backed modelling is ready: Tools and methods have matured, and confidence is growing.
4. Capacity and maintenance are the bottlenecks: Skills shortages and long-term upkeep must be addressed.
5. Don’t oversimplify infiltration: Geology, groundwater, and seasonality matter — and even partial infiltration can add value.
6. Optimise the whole system: Upstream source control can reduce reliance on complex end-of-pipe controls

Using InfoDrainage in your work

• We are big fans of SuDs and have articles about all of the SuDS features inside InfoDrainage detailing how they work, including rain gardens, bioretention systems, swales, infiltration trenches, cellular storage, porous pavement, soakaways, and wet ponds and infiltration basins.
• Do you follow CIRIA’s guidance for SuDS? Download a copy of our CIRIA 753 SuDS manual for InfoDrainage.
• Dig into the InfoDrainage Technical Information Hub and examine how the software conforms to industry standards.
• New to SuDS? Watch our ‘Fundamentals of Drainage Design’: a framework with 8 steps video.
• Try InfoDrainage yourself by downloading a free trial for 30 days (no credit card required). Are you a student or educator? You can use our water software for free.