SEPA has provided and outline of their SUDS expectations and changes in the light of the revised SUDS Manuals.

Sustainable urban drainage systems (SUDS) drain surface water from developments and can take many forms, including detention basins, detention ponds, swales and grassed filter strips.   SUDS provide benefits in terms of water quality, water quantity, amenity and biodiversity and often need to be combined together to  achieve the design objectives for the site.

SEPA would expect SUDS treatment proposals for surface water drainage from new developments to be designed for water quality in accordance with the CIRIA SUDS Manual (C753) (Chapters 4 and 26). This manual was comprehensively updated on 12 November 2015 and includes changes to best practice SUDS design methods for water quality. Up until now SEPA has expected SUDS proposals to be designed for water quality based on the numbers of levels of SUDS, irrespective of the type of SUDS proposed. The revised manual introduces pollution hazard and mitigation indices, ensuring that SUDS are more appropriate for a particular land use type. A Simple Index Approach Tool helps determine whether the SUDS proposed is adequate mitigation for the pollution hazard from the development.

It is essential that SUDS are considered at an early stage and are an integral part of the design process. SUDS design should be based upon the characteristics of the site and the nature of the proposed development. Priority should be given to managing water as close to source as possible through interception (section 4.3.1 of the SUDS Manual). Where a detention basin, pond, swale and/or filter trenches are proposed, SEPA encourages them to be designed to an adoptable standard in accordance with Sewers for Scotland or the SUDS Manual.

Surface water discharges are normally authorised by General Binding Rule 10 of the Water Environment (Controlled Activities) (Scotland) Regulations 2011 (CAR). However where there is a potential high pollution hazard level, such as a discharge from an industrial estate, a CAR licence is likely to be required from SEPA.

SEPA’s SUDS regulatory guidance WAT-RM-08, the SUDS Manual and the Simple Index Approach (SIA) Tool are all freely available on line.