Residential SuDS in East Anglia

A detailed sustainable drainage design for a proposed residential development in King’s Lynn, Norfolk.

RAB Consultants was commissioned to undertake the FRA and drainage design (surface water and foul water) for a residential development on a site at King’s Lynn, Norfolk. 

The first stage of the project was the collation of readily available data, including Environment Agency flood risk data, Local Authority and County Council site-specific data, and Anglian Water Asset mapping. An initial assessment of the data followed by a visual inspection of the site, undertaken by RAB, helped identify the site constraints. 

With no infiltration potential, and a lack of sewer network, a heavily vegetated and mostly undefined ditch at the boundary of the site proved the most appropriate option. Given the size of the development and the land availability, the four pillars of SuDS (water quantity; water quality; aminity; biodiversity) determined the drainage design.

The four pillars of SuDS set out in the 2015 SuDS Manual

A combination of permeable paving and lined infiltration trenches provided the necessary runoff filtration, especially during first flush events, and promote water quality while controlling the outflow to ensure utilisation of the system. The final receptor of the surface water design was a wet pond which would polish the runoff and entrap sediment bound contaminants while promoting the treatment of liquid bound pollutants.

The system provided a significant betterment in terms of runoff rate, offering a reduction of 78% during the critical 1% Annual Exceedance Probability flood event plus 40% climate change allowance. The design therefore reduced the risk downstream while providing water quality improvements, amenity, and biodiversity benefits. The permanent pool within the pond was designed to be 150 mm in depth with the maximum depth during flood conditions was designed to be 1.1 m, reducing health and safety risks to the residents.

The design was tested within Microdrainage_SuDS in order to ensure reliability. The foul water design was then undertaken in line with the Sewers for Adoption 7th edition recommendations. The final product was a supporting report with MicroDrainage outputs including a maintenance schedule of the proposed SuDS features.

Case Studies

1. A detailed sustainable drainage design for a proposed commercial facility in Uttoxeter, Staffordshire. More...

2. A conceptual surface water SUDS drainage design for a proposed school in Bedfordshire.

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