Surface Water

When designing surface water drainage our engineers must follow a design hierarchy set out below using SUD’s principles where possible.


Soakaways are always the preferred method to discharge surface water from a site. Percolation tests must be carried out site in line with BRE Digest 365 to ensure that the ground is suitable for the use of soakaways.

Water courses

Utilising water courses or ditches running through your land can be an efficient way of discharging both restricted surface water or treated foul effluent (subject to approval by the Environment Agency)

Public sewer

In built up areas, towns and city’s connection to public sewer is more common when the existing ground conditions do not permit the use of soakaways.

Developer Enquiry applications are required to the relevant authority to ensure there is capacity in the network to cater for the additional flow.

When making new connection proposed Surface water flows are usually required to be restricted and on site attenuation provided as storage. All connections to public sewer are subject to section 106 approval, evidence that percolation tests have been carried out is required when making applications.

Rainwater harvesting

Although we cannot allow for rainwater harvesting tanks to be added to our model, councils do like to see the use of water being reused on certain projects. Please ask us for more information if you have been asked to provided a rainwater harvesting system.

Surface water modelling

All surface water drainage is modelled using modelling software to ensure your site does not flood during worst case rainfall intensities.