News

Stop press! - SEPA SURFACE WATER FLOOD MAP UPDATE

On the 12 March 2025, SEPA published the latest update to their Flood Maps bringing the Surface Water (or Pluvial) Flood Map in-line with the already updated Coastal and Fluvial (Watercourse) Flood Maps.

The surface water flood maps now show:

• Surface Water and Small Watercourses Flooding: Future Medium Likelihood - By the 2070s, each year this area may have a 0.5% chance of flooding.
• Surface Water and Small Watercourses Flooding resolution at 2m grid square representation.
• Small Watercourses are those classified as having a catchment area up to 10km².

NOTE: Where catchment size is between 3km² and 10km², the Rain on Grid Pluvial Model outputs should be used over Fluvial outputs.

What’s the impact?

The updated Surface Water and Small Watercourses Flooding is derived from Rain-on-Grid 2D hydraulic modelling. With improved resolution and better LiDAR data, the new Surface Water and Small Watercourses Flooding Outputs are noticeably different, as below:

Previous                                                 Current (updated)

Conclusions

The new maps are in their infancy of understanding and their limitations need to be investigated and accounted for when reporting with them. Where the SEPA Flood Maps are to be contested the likelihood of detailed hydraulic modelling with up-to-date data and current best practice will be required.

The new SEPA update may result in additional modelling at an increased cost and time input, never-the-less a resolution of the problems on a site by site basis is enhanced with such modelling.

If you wish to know more about this topic, please do not hesitate to contact the office and we can talk you through your site-specific examples or in general the impacts of this change.