Wallis Road, Hackney, London

Water Environment Limited was commissioned to undertake a Flood Risk Assessment with a Flood Evacuation Plan and prepare a strategic Sustainable urban Drainage System (SuDS) for the proposed mixed use redevelopment for 75-89 Wallis Road and 59 Berkshire Road in Hackney, London.

The site lies partially within Flood Zone 3 (less than 0.1% annual probability of flooding) of the River Lea. Due to heritage reasons the development had to set finished floor levels at existing levels. The development proposed to implement flood resilient construction techniques, a flood warning system, flood doors to basement levels and internal access to higher levels. A flood evacuation plan was also developed for the users of the development explaining flood risk and the route to take to safety when flooding occurs.

A detailed drainage strategy was developed, incorporating the use of SuDS to ensure that runoff from rainfall events with return periods up to 100 years (including climate change) is managed on-site, and peak runoff rates meet the requirements of Tower Hamlets, London Legacy Development Corporation and the London Plan. As the site was compact, the SuDS strategy had to use a number of elements to ensure no additional runoff from the site. The strategy included green roofs, permeable paving with granular subbase, cellular storage and allowing the yard area to flood to 60mm in the largest design storm event.