Name: Mayer Brown
Address: Lion House, Oriental Road, Woking, GU22 8AR, GB
Telephone: 01483 750508

The challenge of a large sewer and buried manholes

We liaised with a number of stakeholders to ensure the relevant checks were carried out and permissions in place to facilitate the discharge of the drainage related planning conditions. This included liaison with Southern Water to agree suitable points of connections for the surface and foul water systems, and Medway Council as the Lead Local Flood Authority to ensure the proposed discharge rates were in accordance with their policy for sustainable development.

The site was heavily constrained by the presence of a large Southern Water surface water sewer running along the south-western boundary, with a diameter ranging from 750Ø to 1050Ø and requiring an easement or 4-5m either side.

Southern Water records identified indicative location of manholes within the site, some of which, however, had not been recorded by the initial topographic survey.

Another Successful SuDS-friendly Drainage Design

Establishing the exact location and depth of the sewer was key in finalising the proposed drainage design and to adequately position the underground attenuation tank required to achieve greenfield discharge rates.

We provided mark ups of any additional information required, which enabled the Client to find the missing (buried) manholes and then accurately survey them.

The final surface water design consisted of connecting to the on-site Southern Water 1050Ø sewer via a saddle connection, restricting discharge rates to greenfield run-off, i.e. matching surface water run-off rates prior to the development. This was achieved by installing a flow control device just upstream of the connection point, and by building an underground attenuation tank in the car park adequately sized to store excess surface water run-off during heavy rainfalls without increasing the risk of flooding on site or elsewhere.

We also produced a Drainage Verification Note to ensure the as-built surface water drainage was in line with the planning approved design, which enabled all drainage planning conditions to be discharged.

We offer key Flood Risk Assessments and Drainage services, working with a range of clients and industries across both the private and public sectors. Contact us to discuss your project by using our online form or call us on 01483 750508.