Sustainable Urban Drainage Systems (SuDS) represent a natural approach to managing rainwater as close to source as possible, with the aim of mimicking natural drainage patterns by promoting infiltration, storage, and gradual release.

SuDS are an essential component of resilient drainage design – but what does this mean in practice?

1  When should we be involved?

It is essential for Civil Engineers to be involved in the early stages of a project. At this phase, civil engineers can work closely with architects and landscape architects to identify opportunities to integrate SuDS in the landscape. Early engagement of civil engineers ensures that SuDS are not implemented as a tick-box exercise, but that they are part of a well-considered holistic approach, considering the four pillars below:

2  What site constraints and characteristics do we work with?

Understanding the site’s characteristics and constraints is essential for successful project planning, including the selection of suitable SuDS. Identifying key risks, such as the following, is critical to the feasibility, performance, and long-term success of the development:

+ Flood zone designation and other potential sources of flooding
+ Site topographical survey levels, existing structures, natural depression and steepness of the site
+ Site conditions: geology, soil permeability, groundwater levels and contamination
+ Arboricultural, ecological and archaeological constraints
+ Existing drainage systems, underground utilities and associated easements
+ Space constraints that may limit the inclusion of open water features, rain gardens, swales and other SuDS.

3  What policies impact our design?

National Authorities

+ Consultation with the Environment Agency (EA) as required in relation to flood risk assessments (FRA), pre-planning advice services or permits to discharge to watercourses and to the ground.

Regional and Local Authorities

+ Review of Local Guidance and SuDS policies, and identify surface water discharge restrictions.
+ Engagement with the Lead Local Flood Authority, including use of their pre-planning service, is recommended to understand their priorities and expectations for the development.
+ Water Authority approval requirements, including pre-planning capacity applications, sewer easements, and potential sewer diversions
+ LAs to adopt expectations for drainage infrastructure, including responsibilities for long-term maintenance.

4  Working closely with the design team

Working closely with the design team on a project, in particular with the landscape architect, is essential  to ensure that SuDS are integrated effectively within the broader landscape vision and that they contribute to the overall quality of the site. Thus, the design team will be able to:

+ Explore rainwater harvesting opportunities
+ Coordinate SuDS with landscape features to optimise drainage performance
+ Design drainage systems that work efficiently with the site topography and green spaces available, maximising interception and reducing offsite water discharge volumes
+ Use landscape features such as ponds, swales, rain gardens, filter drains as well as permeable pavements and green roofs to provide natural treatment of runoff, improving water quality
+ Enhance the natural environment by creating habitats that contribute to increased biodiversity
+ Develop recreational opportunities by creating multifunctional open spaces that combine amenity with sustainable drainage features.