Building standard 3.3 - flooding and groundwater guidance review: research

Appendix E City of Edinburgh Guidance

Design Principles: SUDS Components

• Protect and maintain or enhance existing trees and green space.
• Create small rain gardens or bio-infiltration areas.
• For buildings consider fitting water butts or rain planters
• New SuDS trees, infiltration strips, and filter drains
• Roads or paths with adjacent green space could introduce swales.
• Disconnect building down pipes to feed into adjacent bio-infiltration areas
• De-pave areas of hardstanding to introduce trees, bio-infiltration areas or rain gardens
• New or re-purposed existing green space to provide swales, ponds, or wetlands.
• Hard surface or green multi- purpose basins as parking or recreation areas with capacity for storing water during high rainfall.
• Avenues of trees planted in SuDS trenches and filtration drains in hard landscaping
• Porous road surfaces and paving
• Green roofs on buildings and other structures,
• Formal water features such as rills or canals.
• New woodland planting in semi-rural locations

Design Out Risk

• Do carry out risk assessments at each design stage
• Do create banks and shallow edges to waterbodies with gentle stepped gradients of less than 1 in 4 (if planted up) or 1 in 6 (if grassed) that allow easy access and escape.
• Do Avoid trip hazards within 1m of the water’s edge
• Do ensure path surfaces close to water are safe and even
• Do provide clear sightlines to the waters Do ensure engineered outlets and control points are safe and set well back from areas of public access
• Do consider the needs and risks to the main users of the area through consultation and address local concerns.
• Do avoid the need for danger signs and lifesaving equipment by designing out risk
• Do avoid creating gullies, catchpits and other sumps that can be a risk to people and wildlife
• Don't create high vertical drops or headwalls
• Don't provide a maximum central depth of more than 1 m for ponds and a maximum of 600mm in other features
• Don't create steep sided banks or steeply shelving waterbodies
• Don't create fast flowing water or areas that will flood quickly.

Designing with Nature

• Do provide clean water for wildlife by including features that filter pollutants.
• Design a sequence of SuDS features to filter pollutants and sediment to ensure a controlled flow of clean water before the water enters a wetland SuDS or pond features to create conditions for wildlife to flourish.
• Do create connections to surrounding green networks.
• Proximity or indirect links between existing and proposed wetlands or ponds will enhance natural colonisation and habitat resilience for wildlife.
• Do create a range of different habitats
• Providing a varied range of landforms, slopes and water depths will provide a greater variety of potential habitats. Include opportunities for wildlife (such as woodlands, hedgerows or meadow) beyond the wetland areas to provide connections and integrate nature into the overall design of the site.
• Do provide gentle slopes and shallows to waterbodies
• Gentle slopes and shallow shelving edges to ponds and other waterbodies provide safe access for both wildlife and people and creates opportunities for marginal planting
• Do provide undisturbed sections of bank along water features
• Provide undisturbed areas away from public access to encourage nesting birds and wildlife.
• Do control nutrient levels in soil and water
• In general, lower soil fertility will support a diversity of native habitats and reduce maintenance costs. Most native trees and wild plants will thrive on low nutrient top soils while ponds can develop algal problems if fertility is too high.
• Do create ponds, or wetland areas within flying distance of similar habitats
• Do use native plants
• Using plants of local or Scottish provenance will protect and enhance our natural heritage while maximising the benefits to wildlife.
• Do consider access for toads
• Consider access for toads to SuDS ponds and wetlands during their breeding season. In the local vicinity consider temporarily covering gullies or grills with mesh to aid safe migration
• Do Mix native and non native plants
• Use a diverse range of plant species to enhance biodiversity and increase climate resilience.
• Don’t Plant Invasive Species
• Avoid planting invasive species near waterways and transport routes
• Do plant flowering and berrying plants
• Designing with Nature
• In more formal locations where informal native planting might not be suitable choose species that provide berries and flowers attractive to wildlife (including cultivars or garden varieties of native species).
• Do manage your wildlife areas
• Use mown access paths and edges to create public access and an acceptable appearance to wildlife friendly SuDS areas of vegetation and meadow grasses. Grass areas of different heights can create a network of different interlinked habitats (mosaic habitats).
• Do use existing established trees as part of your design
• Established mature trees are environmental assets, important habitats and attractive features that will provide multiple benefits if incorporated into the design of the site
• Do link hedge patterns, avenues of trees or woodland planting
• To encourage birds, bats, small animals and insects.
• Don't economise on soils in SuDS Tree pits
• It’s a false economy to use cheaper sand-based soils instead of proprietary engineered SuDS soil mixes. The tree is unlikely to thrive and will either need to be replaced or will never reach the level of growth which will deliver meaningful SuDS benefits.
• Don't directly link SuDS water features to protected natural areas
• Avoid direct links from the SuDS to environmentally sensitive waterbodies or wildlife areas to avoid transferring pollutants or sediment.
• Don't excavate too close to the roots of established trees
• Cutting or damaging roots may destabilise or kill existing trees. See British Standard 5837 (2012) – Trees in relation to design, demolition and construction.