Two documents hold up more planning applications than almost any other technical requirement: the SuDS (sustainable drainage) strategy and the flood risk assessment. Here's when each is needed and what satisfies the authorities.
SuDS: the discharge hierarchy
Planning policy expects surface water to be managed as high up this hierarchy as the site allows: infiltration (soakaways) first; then discharge to a watercourse; then to a surface water sewer; and only then to a combined sewer - normally with the rate restricted and storage (attenuation) making up the difference. A SuDS strategy demonstrates you've applied that hierarchy honestly, with percolation tests where infiltration is claimed unviable and calculations sizing the storage.
FRA: when one is required
- Any development in Flood Zone 2 or 3
- Sites over 1 hectare even in Flood Zone 1
- Sites with recorded surface water flooding or in critical drainage areas
- Whenever the local authority's validation checklist says so
A site-specific FRA assesses all flood sources - river, surface water, groundwater, sewers - sets floor levels and mitigation, and must agree with the drainage strategy (reviewers check). Both documents are core Paddick civil engineering work: we produce them together, answer the flood authority's comments, and see the conditions discharged.