Recommendations to Update Non-Statutory Technical Standards for Sustainable Drainage Systems (SuDS)

The aim of this research project is to report whether updating the current Non-Statutory Technical Standards (NSTS) (Defra, 2015a) could help provide for multiple benefit (also referred to as multi-functional) sustainable drainage systems (SuDS), and if so, what those updates should be.
The research included the following:
• An investigation into the understanding, interpretation and application of the current NSTS. This included a review of existing literature and an online survey with stakeholders.
• An evaluation of current hydraulic design methods and investigation into how the current NSTS could be updated to improve consistency and effectiveness of
delivery of the water quantity standards.
• A review of current and evolving drivers, barriers and enablers for delivering
multiple benefit SuDS. This included a review of the implementation of Schedule 3 of the Flood and Water Management Act 2010 in Wales.
Based on the findings from this research, recommendations have been made to replace S1 to S6 in the current standards with a new suite of six standards. Although it is recognised by stakeholders that S7 to S14 in the current NSTS would also benefit from a review, this was outside the scope of this project.
The new standards cover the following:
• Standard 1: Runoff destinations
• Standard 2: Everyday rainfall
• Standard 3: Extreme rainfall
• Standard 4: Water quality
• Standard 5: Amenity
• Standard 6: Biodiversity
Each standard is accompanied by a set of clarifications that provide guidelines to support the interpretation, delivery and evaluation of the standard. In addition to the standard and clarifications, it is also recommended that three key principles are applied when planning and designing schemes to meet the new standards. These are:
1. Use of ‘a SuDS approach’
2. Early and integrated design
3. Embedding SuDS within the development planning process.

Draft versions of the standards and clarifications were shared with stakeholders via a focus group workshop and an online survey. The response received was positive and the feedback was used in preparation of the final versions, as presented in this report.
The successful implementation of these new standards will require:
• Appropriate supporting guidance and tools (including new metrics for e.g. amenity)
• Alignment with and referencing within other national policy and guidance to
maximise outcome value;
• Processes that facilitate the design, approval and adoption of integrated and
multiple benefit SuDS that meet the new suite of standards; and
• Increased awareness and skill development of those designing and approving
SuDS.
The research approach and findings, plus the resultant recommendations from the Contractor are summarised in Part 1 of this report. The recommended updates to the NSTS are provided in Part 2 of this report.
This report is accompanied by eight separate annexes that present in detail the findings from the research and the evidence base for the recommendations.