SuDS: for better neighbourhoods

Embedding SuDS in urban design can bring substantial benefits if adopted from the outset, explains Interpave’s Chris Hodson.

Taking a holistic approach, designers can now embrace sustainable urban drainage solutions as one of the central design considerations from the very start of their projects, forming an integral part of urban design.

The importance of SuDS is highlighted in the National Planning Policy Framework, which requires SuDS to be installed for 10 or more dwellings as well as similar scale, non-residential developments in England. Wider requirements also apply elsewhere in the UK, with the onus for implementation resting with local planning authorities.

Concrete block permeable paving

After more than two decades of use, concrete block permeable paving has proved to be a predictable and reliable SuDS technique. Permeable paving also provides an inherent drainage system that requires no additional land take and addresses flooding and pollution by storing and cleaning water runoff at source.

This technology eliminates pipework, gulleys and manholes, and should therefore cost less than conventional drainage and paving. In fact, it can also accept runoff from other impermeable paving and roofs, giving further savings.

Concrete block permeable paving can simply infiltrate rainwater straight into permeable ground but, more commonly in the UK, less permeable conditions will limit infiltration and on brownfield sites embedded pollutants may preclude infiltration. In this case, permeable paving is used to collect, convey, clean and store water on site during storms, before gradual discharge to sewers or watercourses later, avoiding surcharging and flooding. As concrete block permeable paving removes water-borne pollutants, it can provide a gradual flow of clean water at the head of the SuDS ‘management train’. Water in subsequent open SuDS features can then be used safely to enhance landscape design and biodiversity.

Flow control

Water storage can be optimised for greater cost efficiency by distinct storage ‘compartments’ of permeable paving. Each compartment has a straightforward flow control chamber with a specifically-sized orifice, demonstrating compliance to local authorities as part of the approval process. Water storage is strategically deployed around developments within paving that is needed anyway, avoiding intrusive storage structures on valuable land – and their costs. This technique can maximise storage in permeable paving on sloping sites, with terraced compartments separated by simple check dams incorporating flow controls.

Flow controls can also detain water to optimise available ground infiltration, so reducing discharge. This approach is exemplified by the SuDS scheme designed by Robert Bray Associates at Parkside Civic Centre in Bromsgrove. Parking is on contaminated ground and the concrete block permeable paving is lined to form ‘tanked’ compartments, each with an orifice plate flow control chamber. Controlled flow from the car park passes down the site to perforated pipes and stone trenches for infiltration.

Accessible public spaces

The main courtyard is designed as an extensive, wall-to-wall infiltration blanket using concrete block permeable paving and flags, grass surfaces and free draining plant beds. The central lawn is lower than its surroundings, acting as a detention basin in very heavy rain. Some roof water downpipes discharge to a stainless steel spout that pours over a granite sett. It cascades into a wetland rill, for re-circulation by a solar pump. This holistic design approach applied from the start has created an attractive, accessible public space defined by water.

Paved surfaces help to form the character of any development. The growing choice of concrete block permeable paving products allows real design freedom combined with well-drained, firm and slip-resistance surfaces that are accessible to all. Rainwater ‘ponding’ is eliminated, reducing the risk of ice on the surface and preventing splashing from standing water.

These benefits are also demonstrated at Robert Bray Associates’ SuDS scheme for Bewdley School and Sixth Form Centre, again with infiltrating concrete block permeable paving. However, in addition, surface water runoff from roofs and other areas is slowed by collection and conveyance in a series of precast concrete features – including channels and rills used for planting, education and play – then stored in open basins, a pond and storage swales, before controlled release to the neighbouring stream.

Chris Hodson is a consultant to the trade association Interpave