MLM Consultant Engineers
Permavoid Cells; Permavoid Biomat; Permachannel; Permafilter
The Walthamstow Stadium housing development, adjacent to the River Ching, required a stormwater attenuation system in order to manage stormwater on the site. The 294 new homes incorporate sustainable drainage features, including brown roofs and permeable paving.
The site required a sub-base replacement system in order to avoid deep excavation at the site which contained contaminated ground and a high water table.
Polypipe’s Permavoid geocellular stormwater attenuation system was specified for the stormwater management system. Utilising the high-strength Permavoid system, Polypipe designed and supplied the system beneath 4,500m² of permeable paving to provide 1,500m³ of stormwater attenuation to meet the requirements of the Environment Agency.
The design featured 150mm-deep Permavoid cells, with Permafilter geotextile laid on top between the cells and the permeable paving. The Permafilter acts as a barrier to capture and treat surface water run-off at source from the permeable paving above, before entering the tank. The sides and the bottom of the tank were wrapped in a geomembrane to allow for stormwater to be attenuated, before discharging at a rate set by the Environment Agency into the river with the use of flow control devices.
In areas of hard standing, without permeable paving, Permachannel and Permavoid Biomat were installed to capture, treat and attenuate surface water run-off.
Despite being so lightweight, the strength of the Permavoid cells allows them to support structural loads across heavily trafficked areas, making them suitable to withstand the compressive and dynamic loads produced by vehicles at the site.
The Permavoid system is capable of handling rainfall in the event of a ‘1 in 100’ year storm, and reduces urban stormwater run-off from the site by 80%.