Are we on the path to better SuDS?

Reflections on the LHE breakfast roundtable

February 2026

In early February, Paul Davis joined Lewis Hubbard Engineering and a small group of engineers, landscape architects, planners, and developers for a breakfast roundtable on the state of SuDS in the planning system. The conversation was framed around LHE’s working paper, The case for a smarter, simpler approach to SuDS in planning, which makes a bold argument: that the requirement for software-based hydraulic modelling is a primary driver of poor SuDS outcomes, and that replacing it with a quick storage estimate (QSE) approach would unlock better, more landscape-integrated design.

It was a genuinely good morning. The room was well-chosen: people who care about this, who have the project experience to back their opinions, and who are not interested in talking around the edges. And LHE deserve credit for putting a clear, argued position on the table and inviting it to be tested.

We came away with a great deal of agreement on the destination, and a meaningful disagreement about the route.

Where we agree

The SuDS actually being built are too often too limited. End-of-pipe solutions, including pipes, gullies, basins and underground tanks, dominate new development when they should be the exception, not the default. The national standards, the NPPF, and most local policy now articulate a clear ambition for multifunctional, landscape-integrated SuDS. The gap between that ambition and what gets built is real, persistent, and worth talking about seriously.

We also agree that the QSE, supported by clear conveyance diagrams, is a proportionate and entirely legitimate basis for demonstrating drainage compliance. For progressive design teams working with engaged clients, removing the obligation to produce a full hydraulic model in proprietary software can genuinely free up the design process. Modelling software was built for piped drainage networks. It struggles to represent overland flow, vegetated systems, and the kind of connected, sequenced SuDS components that actually make places worth living in. When you are trying to co-design drainage and landscape in a collaborative, iterative process, the demand to remodel every time a swale moves three metres is a real constraint. On sites where good design is genuinely in play, we think LHE are right.

Where our perspective differs

The paper is written from the position of a capable, committed engineer working with clients who want to do better. In that context, modelling can be a straitjacket, and the QSE plus good design logic can unlock genuine collaboration. Everyone around that table, broadly, already operates this way, or wishes they could.

But that is not the modal condition for the rest of the UK.

End-of-pipe SuDS are not primarily chosen because they model well. They are chosen because they are familiar, low-effort to design, low-risk to programme and phase, easy to price, and easy to subcontract. The choice is made before the drainage engineer opens the software. Modelling does not steer designers towards basic SuDS. In much of the industry, designers are already heading there. Modelling, when it happens at all, just rubber-stamps a decision that was taken for entirely different reasons.

This matters, because it changes what the solution looks like.

If you remove the modelling requirement from a project with a strong design culture, you may well unlock better outcomes. But if you remove it from a project where the end-of-pipe solution was already locked in by fee structure, programme pressure, and a developer with no long-term interest in the site, nothing changes. The cheapest compliant solution still wins. In the weakest design cultures, modelling may actually be one of the few things preventing outright underprovision. Remove it, and you have removed the last checkpoint.

The deeper problem is procurement and value

The discussion summary from the roundtable touched on developer incentives, cost pressure, and the short-termism of most housebuilders. This is where the real diagnosis lives, even if it was not the paper’s primary focus.

Drainage has been commoditised. On most projects, it arrives as a fixed-fee line item, scoped late, often subcontracted to whoever will do it cheapest. Landscape is value-engineered out early. The multifunctional benefits of good SuDS are real: biodiversity, amenity, water quality, flood resilience. But they are hard to price and easy to delete. Planning policy does not always translate into high-quality delivery on the ground. Programme favours certainty over ambition.

Modelling does not create these conditions. It operates within them.

The market rewards minimum compliance. Until that changes, through stronger minimum standards, genuine enforcement of quality conditions, smarter procurement by public clients, and a better-evidenced case for the long-term value of good SuDS, the technical route to planning approval is a secondary variable. Simplifying it is not nothing, but it will not move the dial on its own.

What we are doing about it

At EGY, this is exactly the territory our SuDS Compliance Framework is designed to address. Rather than treating SuDS compliance as a binary pass/fail against a single technical threshold, we are working towards a graduated, four-tier structure that makes the quality of SuDS visible at the planning stage, not just its hydraulic adequacy. We will be publishing more on this shortly.

The LHE paper, and the conversation it generated, has sharpened our thinking. The problem is real. The appetite for change is there. If we are serious about better SuDS, we need to focus not just on technical process, but on the incentives that shape what gets built.

Reference: https://www.lewishubbard.com/research