RAB were asked to provide a Flood Risk Assessment and detailed surface water and foul water drainage design for a small residential development on a site in Nuneaton.
The first stage of this project was to complete a FRA for the proposed development to determine how flooding could affect the site and to establish suitable risk management measures. We recommended slightly raised finished floor levels to mitigate risk to properties and a Sustainable Drainage Scheme to manage risk to others.
We assessed the existing drainage condition of the site and determined the natural drainage routes. We decided that discharge of surface water to an adjacent watercourse was the preferred option for disposal, given ground testing which showed the site to have very poor infiltration potential. There were two main constraints at the site that impacted the design – the poor infiltration potential and limited available space. The drainage scheme was therefore based around a traditional piped system with the inclusion of small source control SuDS features where viable. The rooftops, access road and parking areas were designed to drain via a traditional arrangement of gullies and channel drains. The drainage design included a below-ground attenuation tank to store the surface water runoff and control the discharge rate with a vortex controller. The drainage scheme was designed and tested using MicroDrainage.
We designed a small outlet structure for discharge into the adjacent watercourse in discussion with the Environment Agency. The outlet was designed to be as small as possible to minimize the environmental impact and as such was assigned a flood risk activity exemption.
In addition, to the surface water drainage system, were also produced a detailed foul water design. This brought its own challenges as there was insufficient fall available for a gravity sewer connection into the water company’s network. We therefore worked with the client and a pump supplier to establish a suitable scheme with a pumping station.
We captured our final design in a 3D CAD drawing showing how the complete scheme worked within the development and provided a supporting report with MicroDrainage outputs and a drainage management plan in line with the planning condition.