Urbanisation, coupled with climate change, has led to a disturbed water cycle and an increase in flood events in the UK. This has placed immense stress on London’s combined sewer systems, which were developed over old river culverts.
To compensate for the loss of permeable green space that would have alleviated the risks of excess stormwater, Polypipe CGU was able to supply a unique SuDS geocellular solution at Melina Road – a busy residential street in Hammersmith, which includes a local school and public open space.
2,345 Permavoid cells were installed to create four separate storage tanks which sit beneath new rain gardens. These tanks will provide 88m³ of rainwater storage.
Each of the Permavoid tanks feature a top layer of Permafoam cells to upwardly irrigate the rain garden above. Permafoam cells contain a phenolic foam that is highly absorbent and water retentive, providing 31 litres of water storage for on-demand irrigation.
Each tank is wrapped in a geomembrane at the sides and bottom, along with Permatex 300 Geotextile at the top of each tank to allow for infiltration into the tank to feed plants and allow for water capture.
Each rain garden is also connected to the local sewer network to allow excess water to discharge back into the network at a lower flow rate, managing water at source. Installation had to be carefully planned and considered due to existing services on the street, while shallow tanks were used to reduce excavation time and to fit within the footprint of the street.
This method helps to reduce water volumes into the local sewer network, whilst improving the visual environment of the street. The effective water management at source provides multifunctional benefits to the design and meets recommendations of the CIRIA SuDS manual, dealing with the quantity and quality of water, adding amenity and biodiversity.
Martin Bennett, Project Director of the Counters Creek Sewer Flooding Alleviation Scheme, said: “The implementation of the SuDS solutions marks an important milestone in the delivery of the wider project, which will help alleviate the misery of sewer flooding for local residents. Together with the proposed storm relief tunnel, which will run under both local authority areas, upgrading the existing local sewer network and the SuDS schemes, the ability of the sewer network to cope with heavy rainfall will be greatly improved and we are delighted that, in this instance, we’ve been able to work collaboratively to provide such an innovative solution.”