SuDS – a Matter of Definition?

Written By: Market Development Director, Hydro International.

If you asked a developer, a planning officer and a consulting engineer for a definition of SuDS, do you think you would get the same answer?

I have a suspicion that their answers might well be significantly different.  In a recent parliamentary inquiry into future flood resilience, it was suggested that we have a problem with the definition of SuDS.

If this is true, then how can we hope to use SuDS effectively to protect our infrastructure, property and our environment from flood risk and water pollution, when those who regulate, design and deliver SuDS have different impressions of what they are?  Not to mention environmentalists, politicians, academics, proprietary equipment manufacturers like ourselves, landscape architects and so on.

The point was made during an oral evidence session on 25 May  to the Environment, Food and Rural Affairs (EFRA) select committee’s inquiry into Future Flood Prevention by Steve Wielebski, speaking on behalf of the Home Builders Federation.  He said: “SuDS is 4,000 years old.  There is nothing new about it.”  He continued: “The view that we have always taken as engineers – others might disagree – is that SuDS just about embraces everything.  It can be above ground.  It can be below ground.”

In his evidence to the committee Philip Barnes, Director for Land and Planning, Barratt Developments Plc, suggested there could be a “definitional issue”. He pointed out that 67% of Barratt schemes involve some above-ground drainage solutions. “The policy is clear that that is where we should go.” The reasons for not doing so might be because it was not technically possible, or because the planning authority might actually prefer a below-ground solution that enabled more houses to be built, he said.

“A below-ground solution is still sustainable drainage in Barratt language, because we use hydro breaks [sic] to hold back the water from either a natural watercourse or the ground or the public sewers, which is very rare for Barratt. It is still sustainable in the sense that it does not involve any more run-off than the predevelopment condition.”

I acknowledge that these are just short extracts from a thorough and far-reaching inquiry with many expert contributions, which has still to publish its conclusions. However the comments did make me stop to think for a moment about what exactly we mean by “sustainable” in the context of drainage.

Do we mean a drainage scheme is sustainable if it ensures that no more water is discharged from a site than the predevelopment or greenfield rate? In this sense, sustainable means they avoid unnecessary discharge to our already overloaded sewer network.

Or should sustainable be interpreted principally as the use of ‘natural’ or ‘green’ above-ground structures and techniques? Or is a sustainable drainage scheme better described as one that closely mimics natural drainage paths and processes? We might describe this as “Engineering Nature’s Way”, in fact.

At Hydro International, we believe our proprietary stormwater products, such as Hydro-Brake® Flow Controls and the Hydro StormTrain® Series contribute to this process and are sustainable, not least because they do not need power and require minimal maintenance. They can also be used to enable soft-engineered above-ground features.

To look elsewhere for a balanced definition, we could turn to the four pillars of SuDS, as defined in The SuDS Manual (CIRIA C753), suggesting SuDS should aim to achieve not just water quantity, but also water quality, amenity and biodiversity.

To me, the four pillars are the right aspirations for a sustainable outcome, with which few would disagree, although it may not be possible or necessary to achieve that outcome in each case.

However, using the best means to achieve that outcome is an entirely different matter. Seeing SuDS only as above-ground or ‘natural’ can be very limiting and could restrict our ability to encourage their wider use. Equally using only hard-engineered, below-ground components may miss opportunities for making our urban environments more liveable, as well as promoting green spaces and wildlife in our towns and cities.

So, a toolbox of components and approaches must be available according to site-specific opportunities, the soil and ground conditions and the topography of a site. There may also be hard choices to be made in terms of land-take and construction costs to avoid making a development unviable.

The Government’s commitment to review SuDS delivery in England was prompted during the progress of the Housing and Planning Bill after pressure to reinstate previously-ditched proposals to remove the developer’s right to connect to the sewer.

But if SuDS are to be mandatory without exception – according to exactly what definition? On the basis of the sustainable outcomes they achieve, or according to the components used?

If we get the definitions wrong, there is a danger we could end up applying above-ground SuDS inappropriately without fully understanding their engineering performance and thereby compromising flood resilience.

So, should the Government provide a cast-iron definition as part of its review? Should we have much more detailed and prescriptive technical standards to regulate the use of SuDS components of techniques? (so far the devolved regions all have different responses to this) Should we have more regulation – or less, leaving more to the the judgement of local communities?

It feels like these issues are still not completely resolved. Could it be that addressing the need for a more robust long-term solution to ownership and maintenance for SuDS might be the missing link in achieving a framework that will make matters clearer?

For further details of the EFRA enquiry visit the Future Flood Prevention Inquiry page on the parliament website.



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The SuDS proponents made a rod for their own back when they coined the term with the word ‘sustainable’ in it. I never agree with Steve Wielenski normally, but in this case I do. Yes, in some cases buried infrastructure may be the more sustainable option. Why? Because there is no objective way of measuring sustainability. We have the classic 3 pillars but no agreed way of assessing how sustainable any project is. We do know that a full LCA is required Sadly a number of other countries are using the term, although USA now uses ‘SCM’: Stormwater control measures. See our paper on definitions:
and the CIRIA WaND project report: if you want more info on this topic.

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