The services of Cowan Consultancy were required to provide drainage design on Imperial Homes’ nine unit residential development in Aldingbourne, West Sussex. Planning conditions, relating to the surface water and foul drainage, were attached to the planning permission of the development and were in need of discharging prior to the commencement of any building work.

Initial infiltration testing on site, carried out by Cowan Consultancy, showed that the site was not suitable for discharging the surface water into the ground. Therefore, a ditch to the northern boundary was identified as an appropriate discharge point for the surface water. An Ordinary Watercourse Consent Application to Arun District Council was obtained for this.

Due to the topography of the site and the location of the outfall into the ditch, a shallow attenuation system underneath the access road and parking areas was necessary to allow a gravity system to work. The adequacy of the surface water drainage design was determined by computer modelling software. This also enabled for the most economic design to be implemented.

As part of the planning conditions a Surface Water Maintenance & Management Manual was required to ensure the effective long-term operation of the surface water drainage system. Financial management and arrangements for the replacement of major components, when necessary, was detailed within the manual for the owners or Management Company to adhere to.