Mendora Road

In order to compensate for the loss of permeable green space that would previously have alleviated the risks of excess stormwater, Polypipe Civils & Green Urbanisation [Polypipe CGU] was able to supply its unique geocellular system at Mendora Road, a typical suburban street in Fulham.

Polypipe CGU’s Permavoid geocellular system was installed as a retrofit SuDS solution for source control, creating an engineered stormwater solution, designed to alleviate the flood risk from the existing combined sewer system.

Permavoid was installed beneath permeable paving under car parking bays on both sides of Mendora Road. Harnessing Permavoid’s 95% void fill ratio, 3,600 cells form two attenuation tanks, providing 136m³ of stormwater storage.

Due to the tanks’ location, directly beneath residents’ cars, Permafilter geotextile was installed beneath the permeable paving at the top layer of the tank to treat any stormwater contaminated by oils and pollutants from the vehicles parked above, before the water enters the storage tank. The sides and bottom of the tanks are surrounded in a geomembrane to allow for the attenuation of stormwater.

The tanks were designed to fit the footprint of the narrow street, taking into account the existing underground services and the load bearing requirements of the parked vehicles. Due to the Permavoid’s strength and its capability as an interlocking ‘raft’, the shallow tanks reduced excavation requirements and needed only 130mm over cover, which minimised disruption to residents during the staggered installation process.

Mendora Road is part of a three-street scheme designed to alleviate flood risk in streets built over the Counters Creek river system. Monitoring performance on the street will provide evidence to show how joint engineered and soft SuDS systems will provide a viable solution that can be applied across a wider area.

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 to 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 have been able to work collaboratively to provide such an innovative solution.”