Alex Stephenson, Director of Hydro International’s UK Stormwater Division and Chair of the British Water Sustainable Water Management (SuWM) Focus Group, examines whether institutional barriers preventing greater update of SuDS in the UK.

Most people want to see widespread implementation of SuDS in the UK. We’d all like sustainable surface water drainage features on our own street corners. What an achievement it would be if in future sustainable drainage became as accepted in environmental terms as waste recycling has become.

The fact is we are a very long way from achieving such a vision. A recent Environment Agency (EA) report commissioned by Defra has collected together a wealth of available evidence around the challenges and barriers to wide scale SuDS implementation. Whilst there have been some opportunistic and small-scale retrofit SuDS, the report underlines there are currently no plans for any broader institutional programmes to retrofit SuDS on a catchment or regional basis in the UK.

The report: “An assessment of evidence on Sustainable Drainage Systems and Thames Tideway Standards” published in October 2013 seems to do a great job of presenting a case for the Thames Tideway Tunnel and countering the strong lobby demanding that SuDS be considered as an alternative. It asks the question:

“Do we have sufficient evidence and knowledge to be confident that Sustainable Drainage Systems (SuDS) could or could not be reasonably implemented at a scale that achieves the water quality standards for the tidal Thames?”

Having been invited to comment on the report by Waterbriefing’s editor Elaine Coles, I got to thinking about its implications. Leaving aside the specific arguments about the Tunnel itself, such a body of collected evidence and Defra’s commentary does focus the mind on some fundamental issues.

Institutional Barriers

Before I expand on those, it must first be pointed out that the historical institutional barriers to progress mentioned in the report will be addressed to a degree when regulation in England and Wales establishes Lead Local Flood Authorities as the responsible body for approving SuDS in England and Wales. The date for commencement of the regulation as part of the Flood and Water Management Act (FMWA) looks likely to be April 2014 and should provide some degree of focus.

What is not clear from the EA report is that the institutional arrangements for SuDS in Scotland are quite different and have been in force for much longer, through the WEWS Act (Water Environment and Water Services (Scotland). In Scotland the water company (Scottish Water) has responsibility for approval of above-ground SuDS whilst the council roads authority is responsible for local highways drainage. Engineering Nature’s Way recently conducted a survey and Round Table on SuDS in Scotland. The findings highlighted that institutional arrangements in Scotland have led to ‘disconnects’ that have left many SuDS in Scotland unadopted.

Water companies

On both sides of the border, regulation makes SuDS compulsory only for new development. In England and Wales water companies may also start to build more SuDS to take the pressure off their sewer assets. The Water Bill currently going through Parliament could do something to facilitate this. Equally the Highways Agency and Transport Scotland have separate responsibilities to drain their networks and have sustainable objectives of their own.

The clear inference of the EA report is that, based on the evidence, we cannot be confident SuDS alone could adequately protect a wider catchment from CSO spills into the Thames without the need for piped underground systems like the Thames Tunnel. Whether it is right or wrong in this case, this conclusion surely challenges us to go back to some fundamental ‘first principles’ of SuDS?

Sustainable Drainage Benefits

I have been involved with the development of SuDS for more than 30 years and, in my view, the crux of their sustainable benefit is that they deal with surface water as close to the point where the rain falls to prevent the need to pipe stormwater away in large quantities. They should do this by mimicking natural paths and processes. In my view there are three key points we, as a whole SuDS community, simply must be clear on:

1.            What it means for drainage to be sustainable

In the EA report (page 4) there appears to be an underlying assumption that SuDS should always be ‘natural’: For example it states that in London “many of the surface water management techniques employed would have to use underground storage attenuation schemes (which are not SuDS) and do not provide water quality treatment, or the benefits of wildlife, air quality and reduce heat island effects, and amenity.) This statement demonstrates the danger of confusing the need to achieve sustainable surface water objectives through source control with an imperative for biodiversity. I fully support the need for natural features, but in retrofit situations they may be difficult – even impossible - to achieve. We should not preclude using proprietary systems - with or without some natural features - to achieve sustainable source control through attenuation and infiltration. It may also be possible to use underground storage to achieve other sustainable benefits, for example, for recycling rainwater for re-use in public or private settings.

2.            SuDS performance must be predicted through robust evidence.

The EA report demonstrates the lack of good quality data on the effectiveness of SuDS features, especially for water quality. To successfully engineer a drainage system, you must be able to predict how it will perform over the whole of its working life. Performance data is much easier to demonstrate for proprietary systems, especially when they have independently verified certification such as BBA or WRc approvals. But how do you scientifically predict the effectiveness of a pond, swale or a wetland? There is little reliable, objective data available based on actual experience and I think the whole industry would welcome the funding of an independent databank, for example by a university or trade association. Coupled with this must be a universally-accepted definition of what a stage or level of treatment is. The new National Standards could help provide a more robust framework for England and Wales, but Scotland still lacks clarity on what is a level of treatment, according to measurable parameters e.g. sediment loadings, or key pollutant removal targets.

3.            Through-life maintenance must be planned from the outset

We are getting better at SuDS design and development, including SuDS from the earliest stages of masterplanning and involving landscape architects where appropriate. But planning and funding for long-term maintenance of SuDS also has to be built in to the initial SuDS specification. As our survey showed, in Scotland well-designed SuDS features appear to have been installed without robust arrangements for who will maintain them in the longer term. Indeed, as the Round Table debate highlighted, sometimes the responsible authority may lack the skills or resources to maintain SuDS features like wetlands and swales. It’s therefore vital that clear, predictable and achievable maintenance schedules by the designated owner should be subject to approval from the outset whether the SuDS is natural or proprietary, new or retrofit.

For anyone interested in SuDS policy and implementation, the EA report is a fascinating collection of available current thinking. Despite all the work underway with SuDS at the moment we are still only on the foothills of a very tall mountain. However, if we are ever really to get off base camp then these three fundamental principles need absolute clarity.