SuDS should be treated as an early design input on development in Southampton, not a final drainage calculation. Southampton schemes can combine coastal groundwater influences, dense urban development and constrained outfalls. Drainage proposals should test whether infiltration is genuinely feasible and provide a clear alternative where groundwater, contamination or site layout limits that route.
What matters on a Southampton site
- groundwater and seasonal conditions that may limit infiltration depth
- the effect of historic or made ground on infiltration and water quality
- the proposed receiving system and any flow restriction
- coordinating drainage levels with highways, basements and coastal flood considerations
The current drainage framework
For development in England, the 2025 National Standards for Sustainable Drainage Systems set out a runoff hierarchy and design expectations covering flood risk, water quality, amenity and biodiversity. Local planning and flood-risk requirements still need to be addressed for the individual site.
National Standards for SuDS provides the national framework; the project still needs a site-specific strategy and evidence appropriate to the proposed development.
Where infiltration testing fits
If infiltration is being relied upon, testing should be located and designed around the proposed drainage features rather than used as a generic site-wide assumption. Where previous land use or made ground could affect water quality, review the ground-risk information alongside the drainage proposal.
What to send us
Send the site boundary, proposed layout, levels or topographical survey where available, drainage concept, planning or flood-risk comments, and any previous ground investigation. We can then identify whether infiltration testing, drainage support or linked environmental work is needed.
View SuDS, drainage and flood support · View infiltration testing · Ask about a Southampton project