The site comprised a previously developed commercial yard and existing warehouse located on a constrained urban-edge plot in Wiltshire. The redevelopment proposals included a convenience / food retail unit, drive-through coffee unit, two B8 trade counter units with ancillary office space, retention of the existing warehouse building, together with associated parking, servicing and access arrangements. Such proposals are considered acceptable in Flood Zone 1 as per Table 2 of the NPPG (Flood risk vulnerability and flood zone ‘incompatibility’), but still requiring a Flood Risk Assessment due to the mapped pluvial risk at the site.

The Lead Local Flood Authority (LLFA) issued a formal objection to the planning application, principally relating to the proposed surface water discharge rate and compliance with the local authority’s Betterment Strategy. The consultation response also identified a range of additional technical information requirements, including confirmation of the proposed sewer connection, CCTV survey data, groundwater risk assessment updates, exceedance flow routing, SuDS cross-sections and long-term maintenance arrangements.

The project also presented significant site-specific drainage constraints. BRE365 infiltration testing identified shallow groundwater approximately 1.2m below ground level, effectively ruling out infiltration SuDS under the 2025 National Standards for SuDS, which require a minimum 1m clearance between the base of any infiltration feature and the seasonal high groundwater table.

This was a key consideration with reference to the SuDS hierarchy as set out in the 2025 National Standards for SuDS. The hierarchy requires runoff from a development to be discharged to the following final destinations, to the maximum extent practicable, in accordance with the below hierarchy:

• priority 1: collected for non-potable use
• priority 2: infiltrated to ground
• priority 3: discharged to an above ground surface water body
• priority 4: discharged to a surface water sewer, or another piped surface water drainage system
• priority 5: discharged to a combined sewer

Water reuse was promoted within the strategy but cannot be solely relied upon meaning another discharge location is also required. The high groundwater ruled out Priority 2, nor were there any above ground water bodies to meet Priority 3. Hence – the strategy then followed the SuDS hierarchy and discharged at Priority 4.

As a result, the drainage strategy needed to balance multiple technical and policy requirements simultaneously –  including groundwater protection, restricted cover depths, compliance with the drainage hierarchy, and the local authority’s betterment requirements – while remaining practical and deliverable on a constrained brownfield site.

Following submission of the revised drainage strategy and supporting technical evidence, the Lead Local Flood Authority formally withdrew its objection and issued a recommendation of no objection subject to standard planning conditions, confirming that the Aegaea drainage strategy was compliant with the NPPF and 2025 National Standards for SUDS.

The agreed conditions covered detailed SuDS design, confirmation of the existing drainage arrangements, exceedance flow routing, construction management and long-term maintenance requirements. The principle of the surface water drainage strategy, discharge rate and downstream sewer capacity were all confirmed as acceptable.

This project demonstrates the importance of combining robust technical evidence with proactive consultee engagement on constrained brownfield developments. Through targeted ground investigation, revised hydraulic modelling and direct coordination with the sewerage undertaker and wider design team, Aegaea developed a policy-compliant drainage strategy capable of resolving complex statutory consultee concerns and supporting the progression of a commercially sensitive planning application.