Making SuDS mandatory – some dos and don'ts

Wales made it compulsory to build sustainable drainage systems (SuDS) into new developments four years ago. As England prepares to follow suit next year, what can it learn from the neighbours? Ian Titherington shares some tips

Schedule Three of the 2010 Flood and Water Management Act will hopefully arrive in England next year, requiring new developments to build in sustainable drainage systems (SuDS). Using our devolved powers, we did this in Wales back in January 2019. It’s fair to say that in my last role as a council drainage engineer, that decision kept me busy.

A proposed new development triggers the legislation. The drainage systems need approval. The developer must apply to the nearest SuDS Approval Body (SAB) within the 22 local unitary authorities of Wales. The application must demonstrate that the project meets six statutory standards:

• Destination
• Hydraulic control
• Quality
• Amenity
• Biodiversity
• Who owns and maintains the scheme.

Wales’ strong, focused legislation is grounded in technical standards. Although seeking SAB approval is quite similar to making a planning application, the decision rests on an engineering assessment. In my four years as a senior SAB officer, the best advice I could give developers was to make all their applications reasonable and consistent.

Every application is unique. Although there are general principles to follow, SABs must treat each design on its own merits, based on these six parameters. However, The Environment has asked me to suggest three dos and don’ts – and I’m always up for a challenge.

Do

• Complete a pre-application check

A SAB pre-app is similar to, but not the same as, an outline planning application. The pre-app checks the design is viable before you submit the plan or finalise the site layout. A good SAB pre-app will minimise loss of development density and offers you your best chance of SAB approval success. It simply leads to better design.

• Design for human nature, not just hydraulics

When you design the site’s layout for SuDS, think about how residents, employees, visitors and passers-by interact with their surroundings. Position features so that people will not walk, build or drive over them, to reduce the risk SuDS features get messed up.

Always think about the desire paths that people and vehicles follow – don’t stick to the letter of the highway-design manual. Put up signs to explain how local SuDS features work. If the project is a retrofit, consult until you drop. The more conversations you have, the more chance you have to win over residents.

And the more widely the design is accepted, the more people will look after it once it’s built. Always cost adequately for consultation.

• Support and supervise installation

A rain garden is civil engineering that is landscaped, not the other way around. But many contractors, who have never installed SuDS features, dismiss them as end-of-contract “green stuff”. I don’t mean to criticise. But until we build up wider understanding and acceptance of SuDS, this is how construction contracts work.

Contractors need advice and support on how to install and price for SuDS. They should not be picking up the tab for a poor design. Soil specifications and levels, even plant locations, are critical to SuDS installations; do more to support the contractor.

Don’t

• Apply for planning first

Any competent SAB officer will reject any project that submits its full planning application ahead of the SAB pre-app meeting. Being rejected forces you to withdraw your planning application. That delays development.

This mistake is the most common reason why SAB applications are rejected. The SAB process exists so that you design for surface water at the start – not the end – of a design. Don’t expect sympathy if you get it the wrong way round.

• Take shortcuts with designs

I recently stumbled on the worst SuDS installation I have seen in the UK – and that’s quite a boast. I’ve seen some shockers. The designer had clearly never visited the site and simply assumed its levels, slopes and soil levels. Perhaps they used Google Earth or Google Maps?

They kept very quiet about the consequences – my tip-off came from a contractor. The scheme was an embarrassment that defied every SuDS principle – and the basic laws of gravity.

Always visit the site – your design and installation success depend on it. Yes, you can use video to check the site when you’ve finished. But you can’t design SuDS remotely and expect success.

• Be high-maintenance

In my experience, high-maintenance leads to no maintenance. I have never signed off a SAB approval that demanded significant or frequent maintenance. I’ve worked long enough in this industry to know that maintenance will not take place.

In SuDS designs, conveyance, quality and storage happen between the finished-floor level (FFL) and the outlet-invert level. That’s where the magic happens with SuDS. Schemes’ designs stand or fall on where you install hydraulic head. The deeper you go, the higher your costs and the fewer your maintenance options.

The more visual you can make the maintenance – keeping it at surface level – the easier it becomes to spot problems and to solve them. Once you bury a maintenance feature, out of sight is out of mind. Yes, there are exceptions to that rule – but not many.

What can we learn?
As a SAB engineer, I could offer any number of top tips to design and implement great SuDS schemes. But these six main points should help budding English SAB officers to embrace their new roles.

Wales recently completed a four-year review of national SuDS laws. Government plans numerous small changes in coming years to improve Welsh drainage legislation having proved, beyond doubt, that statutory SuDS leads to better design.

We need to see surface water as just one of many supply services a new site will need – along with telecoms, gas, clean water and electricity. Out of all of these, surface water is the hardest to design in. Schedule Three ensures developers design for surface water first, not last. And that in doing so, they deliver multiple benefits.

Ian Titherington is the Welsh government’s senior advisor on sustainable drainage. A former drainage expert with Cardiff Council, he led the capital’s SuDS Approval Board (SAB) when Wales made sustainable drainage systems mandatory

This story was first published in The Environment magazine in June 2023