Located at the intersection of Oxford suburbia and the surrounding countryside, Barton Park was conceived as a garden suburb designed for the 21st century, a blend of high-quality urban living in harmony with its natural surroundings.
The development will be the largest new residential development in Oxford and the aim for Barton Park was to build an exemplary development that provides a benchmark for future large developments in the area. Recent changes to legislation driven by an increase in flood events have forced developers to reconsider how water is managed within their developments. The days of simply collecting water and directing it into pipe systems and then off-site via a stormwater sewer or into the local watercourse are behind us and instead, designers are rethinking the way they manage water by the application of increasingly smart integrated Sustainable Drainage Systems (SuDS) design. From the very early days of planning the development at Barton Park, Oxford City council recognised the impact of the development on the hydrology of the area. In order to manage the impact, they were determined to incorporate water management through appropriate flood protection measures and the implementation of best SuDS practices as a core objective. The Barton Area Action Plan includes separate chapters on both flood protection and SuDS and a clearly defined Policy BA16: Surface water drainage, which states: “Surface water drainage for the strategic development site should be designed as a Sustainable Urban Drainage System (SuDS) to reduce overall run-off volumes leaving the site; control the rate of flow, and improve the quality of the water before it joins any watercourse or other body of water.” The key to this is that SuDS should form the cornerstone for the water management practices employed across the site. The Action Plan prescribed that the SuDS (and the appropriate components) should be specified according to the site layout and the type of development in that particular development area. It also recognised the role that well-designed SuDS can play in not just managing water quantities but also in improving water quality and creating biodiversity and amenity assets within the development, all of which are key factors in improving the environment of the development. As is best practice, a significant number of landscaped SuDS components have been integrated within the design; these are designed to manage rainfall as close to the source as possible. However, in order to meet the stated objective of a net reduction in run-off volumes the designers realised that a significant volume of water attenuation capacity was required. The designers chose to design this as a below-ground structure constructed using modular plastic geo-cellular units. Structures such as this are formed of two elements; the skin and the structural element. The skin in this instance was an impermeable geomembrane designed to prevent water from escaping, or entering the tank (as the tank was for attenuation as the native soils were not suitable for infiltration). The structural element consisted of a combination of Wavin AquaCell Prime and Plus geocellular units. These are high void (96%) structural units designed specifically for these applications. Prime was chosen as the primary material because its recycled polymer construction fitted the requirement of the sustainability engineer; the Plus product was selected because of its accessibility tunnel allowing entry for inspection and maintenance, a key requirement for the project engineers. To achieve this the AquaCell Plus units are installed as rows within the structure forming a continual tunnel from one end of the tank to the other and is accessed through inspection chambers. Outflow from the tank was controlled by means of a flow control device located within a chamber on the outfall side of the tank. As the flow control device reaches maximum discharge the water then backs up within the tank and is held temporarily before being released at a controlled discharge rate continuing after the storm event has finished. Using this tank design as resulted in around 3,000 cubic metres of attenuation capacity being integrated into the SuDS scheme for the development, helping protect the new residents from flooding now and into the future.