The site is located in Flood Zone 1 at low risk of flooding from the River Roding. However, due to its proximity to the river, the flood risk from a breach of the river wall was assessed.
Residential dwellings were located above ground level to ensure the residential element would remain safe in the event of a breach. The new riverside walk would remove a section of the river wall, so it was necessary to demonstrate that this would not increase the flood risk to the site. A method of raising the river wall crest level in the future was considered, which would ensure the development remained safe for its lifetime.
Although the EA’s preferred set-back distance could not be achieved for the whole site, it was demonstrated that vehicles and machinery would be able to access the river wall for maintenance purposes in the future.
Mitigation measures were included to reduce the surface water flood risk to the site, by raising the ground floor finished floor levels and including planted and landscaped areas around the development to direct flows away from buildings.
The proposed drainage strategy included sustainable drainage features in the form of green and brown roofs to improve biodiversity, and lined permeable paving to improve water quality. A cellular storage crate system was also required to provide the required attenuation on-site. The attenuation provided by the new drainage system reduced the surface water runoff rate by 50% compared to the existing site. The restricted outfall to the River Roding meant that there would be a reduction in flows entering the public surface water sewer network, therefore also providing a benefit to the wider area.
Planning permission was granted in June 2019.
Preparation of a Flood Risk Assessment and Drainage Strategy, Negotiation with the Environment Agency
Former Abbey Retail Park, Abbey Road, Barking, London