Our local principles are intended to supplement the national standards and aid in the evaluation of SuDS proposals.
There are 12 local principles, which are outlined below:
- Plan for SuDS
- Integrate with public spaces
- Manage rainfall at the source
- Manage rainfall at the surface
- Mimic natural drainage
- Design for water scarcity
- Enhance biodiversity
- Link to wider landscape
- Design to be maintainable
- Use a precautionary approach
- Have regard to the historic environment
- Show attention to detail
Local Principle 1: Plan for SuDS
SuDS should be considered as early in the planning process as is feasible.
As SuDS can impact far more visibly and dramatically on a development than conventional drainage, an integrated and multi-disciplinary approach to site planning and design is the key to a successful SuDS system.
Investing in good design and identifying the requirements, issues and opportunities for SuDS in the early stages of a project is an effort very likely to be repaid in the long-term. The advantages include:
- Early consultation with risk-management authorities can prove extremely useful and save wasted time later.
- SuDS requirements will inform the layout of buildings, roads and open spaces, which can reduce land-take and minimise potential conflicts later.
- Where soils vary across the site, SuDS features can be located on permeable soils to reduce the amount of storage required.
- Existing landscape features can be integrated into designs to reduce costs.
- Water features can be designed and located so as to enhance the desirability of a scheme.
SuDS planning advice can be provided by the Lead Local Flood Authority. This would preferably be sought prior to submitting a planning application; however, planning advice can be sought at any time during the planning application process. This is highly recommended to save time at the formal application consultation stage. Further information about this service can be found online.
The opportunity for regional control may be identified if there are existing features on or near to the development site that could provide downstream management of runoff for numerous sites or a whole catchment, or if an area has been identified for flood storage in an Action Plan as part of a Surface Water Management Plan.
Local Principle 3: Manage Rainfall at the Source
There are several distinct advantages in using SuDS in the landscape:
- SuDS maintenance can be incorporated as part a typical landscape maintenance specification.
- A range of habitats can be created.
- Obstructions and blockages are more easily detected.
- Creates a visually complex and ever-changing landscape.
- Potential to reduce construction costs.
- Makes the water cycle visible and provides opportunities for contact with nature and education.
- Can be designed as attractive features to enhance urban design.
- Water levels can be more easily monitored.
Management of surface water on the surface should include provision and allowance for infiltration. As detailed below, careful risk assessment and a design-led approach to health and safety concerns is often an effective alternative to fencing around open water.
Local Principle 4: Manage Rainfall at the Surface
Surface runoff should be captured as close to where it falls as possible.
It is worth emphasising this point. Features such as green roofs, rain gardens, soakaways and permeable paving treat and store water where it falls. They reduce the storage volumes, flow rates and treatment stages of features further down the management train.
As well as considering health and safety and flooding issues, designers should bear in mind how vegetated SuDS features in close proximity to development will be perceived. In order to slow and treat runoff effectively, the traditional neatly maintained landscape may need to give way to a more informal aesthetic. Colours, materials, height of vegetation and edges are some of the elements which can be manipulated to give the impression that a feature is intended and cared for.
Although it cannot (at present) be included in storage calculations, the role of mature leafy trees (albeit seasonally in the case of deciduous species) in intercepting rainwater before it hits the ground should not be underestimated.
Local Principle 5: Mimic Natural Drainage
SuDS networks will be designed to match natural drainage routes, infiltration rates and discharges as far as possible.
Designs should work with natural gradients so as to avoid the use of energy-consuming water-pumps wherever possible. Designs should also minimise the use of man-made materials, giving a softer and more natural feel to features and promoting infiltration.
Designing a system to match natural drainage can allow for water management close to the surface. This has many benefits, including enhanced biodiversity and amenity and the opportunity to monitor features easily and effectively.
One of the main underlying principles of SuDS is that they should mimic natural processes; there is therefore a presumption in favour of systems that avoid the use of pipes or storage tanks. Vegetated SuDS should usually be given priority over pure engineering solutions as their operation is easier to observe and maintain. Below-ground features are not sustainable in the long-term as they are not easily maintainable and have a limited life in comparison to grassed and more natural systems. SuDS systems that are reliant on electricity or any kind of pumped system requiring specialised maintenance are to be avoided.
Local Principle 9: Design to be Maintainable
Consideration should be given to ease of access and waste generation when designing SuDS.
It is extremely important to consider maintenance requirements for SuDS from the outset. It is essential to consider how features can be accessed, who will be responsible for maintaining them and how much maintenance is likely to cost. Good management and design go together.
The requirements of the adopting body should also be considered during the design process, to ensure site-specific drainage strategies that are compliant with the requirements of the Lead Local Flood Authority (LLFA) and adopting organisations. This can be discussed early in the design stage through the application advice service offered by the LLFA. Further information on this service can be found online.
SuDS must be designed to provide sufficient access for maintenance. In some instances, this will mean careful consideration to the extent of fencing, provision for gates, the location of drop kerbs to provide access for maintenance vehicles and the extent to which permanently wet features may limit crossing. A minimum easement of 3m on both sides of SuDS features should also be accounted for, to allow maintenance vehicles to access SuDS in areas of private land.
When undertaking the maintenance of SuDS, waste will be generated. This will be predominantly grass and other vegetation, and may be managed on-site in wildlife piles. The requirements of the relevant waste management legislation remain in place. These considerations gain particular sensitivity when waste is disposed-of off-site.
SuDS on industrial sites will need to dispose of hazardous waste separately. It is also important to comply with the duty-of-care requirements of the waste management legislation. This means that silt should only be removed from site by authorised carriers and should be taken to authorised disposal locations.
For more information relating to waste management licences, refer to the Environment Agency website.
Page updated: 4/03/2020