Buckshaw Village required the use of SUDS techniques to remove all standing water from new access road to landmark housing development.
1. System to minimise below ground infrastructure.
2. Low-carbon, locally sourced recycled materials to be used.
3. Easy to install, clean and maintain.
In granting permission to develop the site both Borough and County Councils stipulated that the existing site access had to be upgraded to relieve the predicted increased traffic loading on the surrounding villages and on the main A49 link to the M6. Combining this within Redrow’s commitment to include the highest degree of sustainability in its development of the site lead to a Sustainable Urban Drainage System (SUDS) being proposed for the new site access.
The adopted design introduces swales on both sides of the carriageway along 80% of its 2km length. Each has a depth of 400-800mm and an effective width of 2.5m. The profile provides the required attenuation and groundwater recharge characteristics to cope with the surface run-off from a 100 year storm. Seeded with a hard-wearing grass, the velocity of the water is minimised and the primary filtration improved within the swale by maintaining a cut length of 50mm.
As ground levels across the site do not fluctuate significantly, the majority of the swales achieve near static attenuation of the run-off by simply following the contour of the road surface. However, a short section of the road close to the link with the main A49 has a gradient of 1 in 20. Under heavy rainfall conditions, run-off velocity within the swale would cause ‘scouring’ of the surface and potential flooding downstream. This has been overcome by ‘stepping’ the bottom profile of the swale, effectively reducing the overall gradient to 1 in 80.
“A critical element of the design is the method used to control the flow of run-off into the swale,“ says Steve Openshaw, technical manager at Redrow. “We needed a system that would be easy to install and maintain, minimise visual impact and not require any additional excavation within the proposed swale. It would also need to allow surface water to return to ground as close to the point at which it fell – a vital criteria for SUDS.
A further advantage came from the system being manufactured in a range of sizes. The mid-capacity KerbDrain 305 unit has a reduced overall height of just 305mm. Originally developed to ease installation around utility services, the effective ‘raised’ height of the rear outlets meant that the depth of the swale could be reduced – minimising excavation, reducing visual impact and speeding up installation.