Flood Plain? – ‘It had to be SUDS’

Written By: County Drainage Engineer, Oxfordshire County Council

Whitney Housing Development

My first thought when the Henry Box Development got planning permission was ‘how on earth are we going to drain it?’ The site was within the flood plain, and generally had a very high water table. My next thought was: this had to be a SUDs site.

Up to this time we really had only touched the surface using SUDs techniques, this was a chance to try anything and everything.

I then sat down with WS Atkins, the developer’s consultant, who was happy to work closely  to develop a design on a challenging site constructed within the flood plain.

Design Policy

  • We had to allow the site to flood
  • The drainage had to be as close to the surface as possible
  • The road construction had to contend with the high water table
  • The road design used minimum radius to keep traffic speeds low
  • Discharge to water course kept to green field run off rates,

Since all the house floors were suspended, holes were placed in all walls, so flood water could flow throughout the site, across roads and in and out of houses and gardens.

We decided to go for a standard road construction using a ACO kerb drain system to drain the roads. Having ACO on board from the start was extremely useful in helping to design a cost effective drainage system for the development. Having designed the system we had to choose the online storage to reduce the flows. So we selected Stormcell® from Hydro International, which is sealed in a membrane to store the excess flows. I chose this system because of the minimum maintenance requirements. This then discharged to a swale with an overflow to a pond.

For the access road into the development we used an over the edge system discharging to swales, which are all planted and maintained by the developer.

This site is memorable for several reasons:-

  • The first fully SUDs site in Oxfordshire
  • When the Contractor removed the peat layer under the top soil, the whole site became an open air swimming pool
  • We connected all the house down pipes into the backs of the kerb drain units. These additional flushes help cleanse the kerb drain and keep maintenance costs down.
  • Working together with a Consultant and a Manufacturer has many benefits including obtaining A Constructing Excellence Award for the Development
  • Also working closely with a manufacturers like ACO and Hydro gave the opportunity to suggest new products which would complement their range as well as helping the  Drainage Designer and Planning Authority.      

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