Sustainable drainage system for new housing developments

The trade association Interpave has published a new case study showing how concrete block permeable paving provides a comprehensive sustainable drainage system (SuDS) for new housing developments without additional land-take.

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leetwood Crescent is the 28-home first phase of a new development in the Eastfield Area of Peterborough for award-winning housing association Cross Keys Homes. It makes extensive use of concrete block permeable paving, reflecting Peterborough City Council’s desire to incorporate SuDS in developments. The estate road is a trial site for the adoption of permeable paving by the Local Highway Authority and will be adopted under the ‘Section 38’ process, and its performance monitored.

Storing rainwater on site

The 0.87ha brownfield site – formerly a secondary school – has a 0.8m depth of made-up ground with underlying clay and sand, giving a low permeability. The drainage is designed to temporarily store rainwater runoff on site and remove pollutants before gradual discharge to an existing surface water sewer that eventually outfalls into a nearby watercourse.

The adopted estate road is ‘System C’ concrete block permeable paving with an impermeable membrane effectively forming a tank, due to the low soil permeability. A perforated pipe collects water, running the length of the road and connecting to the sewer. Here, water discharge from the development via the permeable paving is restricted to ‘greenfield’ runoff rates by an orifice plate flow control chamber. Surface water storage volumes on the site are designed to cater for rainfall events exceeding the one in 100-year storm, plus 30% allowance for climate change.

Un-adopted driveways next to dwellings and shared parking areas are also constructed in concrete block permeable paving, linked to the permeable road construction with pipes below the footpath. Rainwater from all roofs drains into the adjacent driveway permeable paving via perforated diffuser pipes. Services are generally accommodated in ‘corridors’ within the footpaths, with an impermeable block paved road crossing.

Interpave technical guidance

All the concrete block permeable paving has been designed and constructed in accordance with Interpave technical guidance (available from www.paving.org.uk). This scheme demonstrates how concrete block permeable paved drives, parking and adopted roads on a typical new housing development can attenuate, store and treat runoff from all the hard surfaces without any additional land-take or other SuDS features. Addition of a simple orifice plate flow control protects the local sewer from overloading.

By its very nature, concrete block permeable paving is uniquely placed to help meet requirements for SuDS on developments. Of course, hard surfaces are necessary on housing schemes anyway – whether for traffic, parking, pedestrians or play. But permeable paving also provides an inherent drainage system, addressing both flooding and pollution issues by attenuating and cleaning water runoff at source. This technology largely eliminates pipework, gulleys and manholes, and should cost less than conventional drainage. Concrete block permeable paving can simply infiltrate to the ground where conditions allow or collect water for transmission to other SuDS features along the ‘management train’ or to conventional drainage, as here.

Predictable and reliable

Following some 25 years of use in the UK and abroad, concrete block permeable paving has proved to be a predictable, reliable and low-cost SuDS technique. Its capability to attenuate water flow during rainfall for gradual discharge is well known. But this principle is optimised for greater cost efficiency by considering distinct storage ‘compartments’ of permeable paving using straightforward flow control devices with an orifice – accurately sized and accessible for observation or adjustment if needed – on the outlet.

This technique enables water storage to be strategically deployed around a development within compartments, each with a flow control demonstrating compliance to local authorities as part of the SuDS design approval process.

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