Surface Water Drainage is the system that collects and conveys rainwater run-off from roofs, paved areas and other hard surfaces. UK surface water drainage is designed to Building Regulations Approved Document H and BS EN 752, and must increasingly incorporate Sustainable Drainage Systems (SuDS).
Discharge hierarchy
UK Building Regulations Approved Document H sets a clear hierarchy for surface water discharge — designers must demonstrate why higher options cannot be used before specifying lower ones:
- 1. Infiltration (soakaway) — preferred where ground permeability and water table allow.
- 2. Watercourse — discharge to surface water (river, stream, ditch) with appropriate consent.
- 3. Surface water sewer — connection to the public surface water network.
- 4. Combined sewer — last resort, only where no alternative is available.
Design return periods
| Event | Return period | Performance |
|---|---|---|
| Routine design | 1-in-30 years | No surcharge of pipework |
| Exceedance | 1-in-100 years (with climate change) | No flooding of property |
| Greenfield run-off rate | 1-in-1 year (Qbar) | Discharge limit at outfall |
SuDS integration
Modern UK surface water drainage on new development is no longer just a pipe network. It is a SuDS scheme that delivers water quantity control (attenuation), water quality treatment, amenity and biodiversity benefits. Source control is preferred over end-of-pipe attenuation.
The Lead Local Flood Authority is the statutory consultee on surface water drainage for major planning applications.
Related ViaCon solutions
ViaCon delivers the complete surface water drainage system — conveyance, attenuation, treatment and infiltration — through ViaCon Storm Solutions and the wider stormwater solutions range. Related glossary entries: underground drainage systems, SuDS, attenuation tank and stormwater management.
Frequently asked questions about surface water drainage
What is surface water drainage?
Surface water drainage is the system that collects and conveys rainwater run-off from roofs, paved areas and other hard surfaces to a discharge point — a soakaway, watercourse, surface water sewer or (as last resort) a combined sewer. UK design follows Building Regulations Approved Document H, BS EN 752 and SuDS principles.
What is the difference between foul and surface water drainage?
Foul drainage carries wastewater from toilets, sinks and other plumbing fixtures to a sewage treatment works. Surface water drainage carries rainwater from roofs and hard surfaces to a soakaway, watercourse or surface water sewer.
What return period is used for surface water design?
UK practice uses two levels. The routine design event is the 1-in-30 year storm. The exceedance event is the 1-in-100 year storm plus climate change allowance.
Where should surface water discharge?
Building Regulations Approved Document H sets a hierarchy: infiltration to ground via a soakaway is first preference; second is discharge to a watercourse with consent; third is connection to a surface water sewer; combined sewer is last resort.