News

RAB Detailed Sustainable Drainage (SuDS) Design, Enfield London
Mar 14, 2019

Background:

RAB Consultants has developed long standing relationships with clients across the UK.  One of our London based clients approached us to design a sustainable drainage scheme to support the redevelopment of a site involving partial demolition of existing buildings to provide refurbished public house and commercial unit on the ground floor together with construction of 54 residential units over five storeys with associated car parking, cycle parking, plant, hard/soft landscaping and amenity space at first floor.

The is at low risk of fluvial, tidal and surface water flooding. 

The challenge:

Draining the site was certainly challenging given the urban fabric of the location and the proposed configuration which included pile foundations across the site. The land availability in combination with the location of the piles dictated the layout of the proposed surface water attenuation feature.

The geology of the site did not support infiltration drainage techniques.

The proposed drainage system had to comply with local policies of the London Borough of Enfield, the London Plan and National Planning Policy Framework.

The solution:

The proposed drainage scheme was modelled in Mircodrainage Source Control to fully understand the evolving flow regime under flood conditions and the potential for flooding. The Environment Agency’s flood maps along with relevant documents published by the London Borough of Enfield were used to assess the risk of flooding to the site from all sources. Local SuDS policy was applied to inform the proposed drainage scheme and ensure conformity.

The drainage solution included the installation of a cellular storage tank along with appropriate slot drainage and an oil-interceptor to ensure no oils enter the tank and the sewer downstream. The discharge rate was limited, in line with recommendations made by Thames Water, using an ACO Q-Brake flow control chamber prior to discharging surface water to the sewer. The scheme was designed not to flood during the 1% AEP plus 40% climate change scenario.

Further SuDS features such as green roofs were integrated into the design in line with the 2015 SuDS Manual philosophy.

The drainage scheme will reinstate greenfield runoff rates, in line with the local policy, while offering water quality, biodiversity and amenity benefits.

The proposed development was deemed appropriate given the flood risk integrating multiple SuDS features, in line with the 2015 SuDS Manual recommendations, and providing significant betterment to others downstream.