The new Jennett’s Park housing development in Berkshire has embraced a pioneering method of underground drainage to minimise the risk of flooding to the area.

The surface water attenuation system installed at Jennett’s Park, which is the largest of its kind in the UK, comprises over 29,000 individual polypropylene AquaCell infiltration modules, developed by Wavin Plastics and installed in conjunction with WSP Development and Transportation, Thames Water, Persimmon Homes and Redrow Homes (Southern Ltd) consortium, Ashridge Construction and SEL Environmental. The innovative structure has been designed to cope with the drainage requirements of this substantial development of up to 1,500 houses.

Originally manufactured for use within sewerage systems, these purpose-built attenuation tanks have been designed to cope with future storm patterns and will capture and store the high volumes of water associated with extreme weather conditions.

Modules are clipped together to form two box-like structures which, once encapsulated in an impermeable, watertight geo-membrane, form two large underground tanks. These tanks are together capable of storing up to 5,500m³ of storm water run-off. The water is then stored and slowly released to prevent flooding to the development and surrounding areas, which include a Site of Special Scientific Interest (SSSI) located immediately downstream of the Jennett’s Park development.

On a typical housing development, surface water run-off can increase to 80% of rainfall compared to a figure of 20% typical of Greenfield sites, resulting in large volumes of stormwater flowing into traditional drainage systems. In the absence of suitable conditions for the use of infiltration drainage, it was evident that a large development site like Jennett’s Park would require a substantial storage tank to prevent an increase in flow to the SSSI.

The entire drainage system for this site had to be planned very carefully. The overall design also had to take into account the fact that all the water from the system drains directly into the SSSI, where prevention of flooding, water erosion damage and pollution is essential. As surface water run-off in urban areas may contain small quantities of oil or petrol, an oil interceptor has been installed at Jennett’s Park to ensure the water is stripped of these pollutants before it drains into the SSSI downstream.

Lightweight and simple to install, the system offers a low risk solution to urban drainage, lessening the hydraulic impact of a housing development on a previously rural site.