RAB Consultants undertook a Flood Risk Assessment for the construction of a new 1ha storage and office facility for AFS Earthmoving and Aggregates in Uttoxeter. As part of the work a drainage impact assessment was performed. This involved calculating pre-development Greenfield runoff rates and volumes and recommending a suitable attenuation storage volume such that betterment from the existing condition was achieved. We provided a conceptual surface water drainage design to demonstrate the viability of the development. Once planning permission was agreed, AFS engaged our services to work up the concept to a detailed design.
There were various challenging constraints at the site that required an innovative approach to drainage. A geotechnical investigation revealed that ground water was located reasonably close to the surface, making the use of infiltration methods unsuitable. Water discharge from the site needed to be into an existing drainage system discharging to a nearby watercourse. There was an extremely limited fall available from the site to the discharge point. In addition no ground raising was allowed on site to limit the impact on adjacent businesses, as the industrial estate was within a river floodplain.We found a solution, working in close cooperation with our client that made use of a swale system linked to an attenuation pond. An impermeable swale was created where vehicular access was required, connected to a landscaped swale, which in turn discharged water to the pond. Special attention was taken to the landscaped swale and pond to create a valuable amenity for works staff and neighbouring businesses. The pond was designed as a series of linked units, to promote water treatment prior to discharge into the river.
We supplied detailed plan and cross-section drawings to the client, suitable for construction, along with a report detailing the design with supporting calculations. We have remained in contact with AFS during the build stage to offer technical assistance as required.