4.3 Green and Blue Infrastructure
Related SPD sections
Key City Plan policies
• Microclimate
• Street Furniture
• Play and Recreation
31 Waterways and waterbodies
34. Green Infrastructure
35. Flood Risk
43. Public Realm
Context
In 2022, the city council published an Environmental Supplementary Planning Document (ESPD) which sought to provide guidance for developers on how they can meet the environmental policies within Westminster’s City Plan 2019-2040. One environmental topic the ESPD covers is green infrastructure and focuses on the functions and benefits that our green and blue assets can bring. This Public Realm SPD seeks to provide guidance to applicants on how to deliver high quality green and blue infrastructure within the public realm and should be read in conjunction with the ESPD which provides guidance specifically related to development for green and blue infrastructure
In the ESPD, it is acknowledged that an integrated approach is required to get the most out of our green and blue infrastructure network to maximise its benefits. Green infrastructure can be defined as a multifunctional, connected network of green spaces, and other environmental features, capable of delivering a broad range of ecosystem services and linked social and economic benefits 42 . Blue infrastructure is the network of waterways and waterbodies which forms part of the open space network. The areas are protected and enhanced to deliver ecosystem services while also benefiting biodiversity and society more widely. Green infrastructure can boost the capacity of a local environment to accommodate sustainable development and provide a wide range of environmental, social, and economic benefits, including:
• Climate change mitigation
• Carbon sequestration
• Biodiversity conservation and improvement
• Improvement of air quality
• Water quality and quantity management
• Local food provision
• Enhancing and supporting the natural character
• Socio-cultural benefits (e.g. social interactions, recreation, health)
42 Green Infrastructure Guidance, Natural England, 2009
Some of the specific ways in which green infrastructure can play a vital role in improving the quality of the environment and be a nature-based solution for climate change adaptation and mitigation include:
• Mitigate surface water flood risk
• Enhance biodiversity by developing a variety of habitat types
• Improve air quality
• Counter the heat island effect by incorporating green infrastructure into development
Green infrastructure can provide ecosystems and can provide access of species to habitats and resources when designed well. There are different types of green infrastructure - core areas are larger and more natural, such as parks and natural urban greenspaces, and smaller stepping stone green infrastructure areas can include green corridors, cemeteries, city farms, street trees and green roofs.
Policy 34 in the City Plan 2019-2040 emphasises the importance of well-designed green infrastructure that enhances to maximise its environmental, social and economic value rather than focuses on aesthetics. The effect of the Covid-19 pandemic has underlined the importance of local green space to support people’s mental health and wellbeing, and to address inequalities 44. There is a need for a drive to grow, improve and interconnect our green spaces, especially near to where people live, work and transportation links. By being accessible, these locations are more likely to be well looked after so people will perceive them to be safer. The combination of safe and easily accessible green space are important factors when planning green infrastructure, but these must also be considered alongside the desires of the local communities so that new or improved green infrastructure is suitable.
The importance that the natural environment plays in improving biodiversity and reducing the harmful effects of climate change is recognised in the City Council’s declaration of a climate and ecological emergency. There is an urgent need to develop actions to reverse biodiversity loss, enhance habitat enhancements and species richness, and regulate the climate in our city. Green and blue infrastructure plays a big role in supporting Westminster’s biodiversity and improve ecological value through parks and open spaces, community gardens, pocket parks, tree planting and other initiatives to provide for biodiversity net gain in the urban environment.
The Royal Parks are a huge asset, and they cover nineteen percent of the borough. However, there are still areas of open space deficiency in Westminster that means that not every resident has easy and convenient access to public open space. The City Council has published an Environmental Justice Measure (EJM) 45 which is a new data tool that aims to raise awareness of climate and environmental impacts and empower Westminster communities with data to help them make informed decisions, and to act to reduce negative environmental impacts in their local areas. Westminster is a densely populated and highly developed city and new green infrastructure will mainly be provided through the creation of spines and networks. Care must be taken to understand the potential impacts of actions and to ensure that provision of green and blue infrastructure is equitable, fair and does not increase inequalities in health between different social groups.
Green and blue infrastructure is an extremely valuable asset contributing to several aspects of life in a city (recreation, health, amenity, quality of life, biodiversity, wayfinding, enhancing heritage, etc.). In 2024, Urban Design London published a collection of guidance documents on collaboration with the London boroughs of Camden and Islington, funded by National Lottery Heritage Fund, National Trust and the Ministry of Housing, Communities and Local Government, and supported by the Greater London Authority 46 These series of documents provide guidance on exploring and developing creative and innovative ways of using highways land to provide the access to nature and the green infrastructure benefits that are needed to address inequality, improve quality of life and support vital ecosystems.
43 Nature-based solutions in Europe: Policy, knowledge and practice for climate change adaptation and disaster risk reduction — European Environment Agency (europa.eu)
44 Enhancing England’s urban green spaces - Natural England (blog.gov.uk)
45 Environmental Justice Measure | Westminster City Council
46 Urban Design London guidance documents – Gren Infrastructure for Streets
A. Enhanced and additional green infrastructure is strongly supported where such initiatives are strategically implemented in appropriate locations to maximise wider benefits within the local area Key considerations are how the enhanced and additional green infrastructure relates and enhances the character of the location, how it seeks to address known environmental issues in the area, and how these impacts users of the public space and public safety.
B. All public realm schemes should contribute to the city’s green and blue infrastructure wherever feasible and possible and have minimal impact on existing infrastructure/assets
C. Green and blue infrastructure is an integral design component and should be considered and engaged on at early stages of a design proposal.
D. Early design proposals for green and blue infrastructure schemes should demonstrate how the proposals integrate with the existing green infrastructure network, seek to enhance the character of the location, specify choice of species to maximise biodiversity, including benefit to pollinators, to ensure climate resilience, identify green and blue infrastructure for different functions (where possible and multifunctional) in response to the location/ needs of area, ensure pedestrian flow and public safety is maintained and ensure ongoing management. An integrated approach to green and blue infrastructure which considers it a spatial as well as natural system, as opposed to an ad-hoc approach, should be taken.
E. All public realm schemes should have regard to the City Council’s declaration of climate and ecological emergencies. Public realm proposals should seek to minimise damage or removal of existing biodiversity and should deliver biodiversity net gain as mandated under Schedule 7A of the Town and Country Planning Act 1990 (as inserted by Schedule 14 of the Environment Act) which regulate the climate and should, wherever possible, maximise biodiversity opportunities.
F. Careful consideration should be had of the effect of landscaping (i.e. location and types of selected species) upon crime prevention. Designers should aim to minimise opportunities for concealment and should use landscaping positively to deter graffiti and prevent scaling on boundary walls.
G. Effective and timely evaluation of the total cost of including greenery in the project, against the long-term economic benefits which greenery can generate and balancing this with long-term sustainability and management should be undertaken, thus enabling optimisation of space and other resources for landscaping.
H. Watercourses and Sustainable Drainage Systems (SuDS) should be integrated into the design of public realm schemes.
I. Green and blue infrastructure should enhance walking and cycling routes, to support active travel and recreation. Where possible, these should be designed to provide for public access for all types of users.
J. Public realm proposals should seek, where possible, a partnership approach to enhancing and maintaining Westminster’s green and blue infrastructure to ensure integration, connection, diversity, and usability of the whole network.
K. Hanging baskets make a limited contribution to biodiversity and are unlikely to contribute to the biodiversity offer of a public realm development or scheme.
Westminster’s ESPD incorporates general requirements for all green space typologies that are set out in the Wild West End (WWE) Value Matrix, which includes requirements for the public realm.
Publicly accessible green spaces
Major developments are required to consider incorporating elements of publicly accessible green spaces. These can also be at different levels within the development, including rooftops. Connectivity between existing and new publicly accessible green spaces, great squares, piazza spaces etc. should be made when preparing early design proposals within the public realm.
See section 4.1 Highway Space, Road Safety and Parking above for guidance on Parklets
Retrofitting greening in the existing public realm
The City Council supports the incorporation of green and blue infrastructure into existing public open spaces, great squares, piazza spaces, play areas and the public highway where this does not negatively affect pedestrian movement,
servicing, and essential transportation functions. Opportunities to provide for greening in the public realm should be taken where the benefits can be demonstrated
Green Infrastructure Audit and Greening and Biodiversity Strategy
The City Council commissioned a Green Infrastructure Audit 47 which aims to produce a robust evidence base of Westminster’s green assets to support the implementation of the City Plan. The findings have been used to inform the recently published Greening and Biodiversity Strategy 48 and remains relevant to proposals affecting or creating public realm schemes in providing new or enhancing existing green infrastructure. The Green Infrastructure Audit identifies a number of priority recommendations, including:
• Address areas of green space deficiency in the north west and south east of the borough
• Address gaps in the active travel network
• Reduce the impact of high visitor pressures on existing green spaces
• Integrate new green infrastructure into key streets experiencing declining footfall
• Maximise green infrastructure opportunities provided by Westminster’s historic environment
• Mitigate impacts of the urban heat island effect, particularly where these are disproportionately higher in areas to the north west of the borough
• Restore lost rivers
• Deliver a bigger, better, more joined up SINC network
• Deliver nature recovery and climate change resilience
• Address the risk of surface water flooding in the borough
• Protect existing trees and woodland
• Encourage new tree planting within the borough
• Adopt and encourage tree pit designs that optimise SuDS benefits
The Greening and Biodiversity Strategy builds on this activity, providing a vision and framework for collaborative action to protect and enhance the local natural environment. It promotes a city ‘ecosystem’ approach where nature and people can thrive, through six outcome priorities:
• Protect and enhance nature in the city
• Establish corridors for nature and people
• Make our streets cleaner and more liveable
• Improve resilience to climate change and pollution
• Ensure access to nature for all
• Empower local stewardship
Trees
Trees are one of the principal components of green infrastructure in Westminster. They are integral to Westminster’s townscape and have an enormous amenity value, as well as being a major contributor to the environmental, social, and economic benefits delivered by green infrastructure. To maximise the benefits of trees, it is essential that they are protected and well managed. The following additional guidance applies only for trees in the public realm and should be read in conjunction with the ESPD.
47 https://www.westminster.gov.uk/media/document/westminster-green-infrastructure-audit-
48 https://www.westminster.gov.uk/media/document/a-greening-and-biodiversity-strategy-for-westminster
Trees Guidance:
Existing trees
A. New development should be designed to retain and protect existing publicly owned trees of amenity, ecological and historic value and those which contribute to the character and appearance of the townscape, in line with Policy 34H of the City Plan.
B. Trees in the public realm should be included in the arboricultural details submitted to support new developments, in accordance with British Standard 5837:2012 “ Trees in relation to design, demolition and construction –Recommendations” (or successor document) 49
C. The proposed method of construction of development in relation to existing trees and their roots should be considered at an early stage to avoid conflict with construction requirements such as scaffolding, gantries, site accommodation and construction access.
D. Any elements of development which overhangs or otherwise encroaches on the public realm, such as façade maintenance equipment or projecting canopies should be carefully designed to avoid conflict with existing trees.
New trees
E. New trees should be planted in order to optimise canopy cover, and according to the principle of the ‘right tree in the right place’ (see ESPD and Trees and the Public Realm 2011).
Site specific constraints on new tree planting in the public realm include:
F. Footway safety - new tree planting should ensure sufficient pavement width is provided to allow unimpeded passage of pedestrians, particularly those with accessibility needs, subject to the guidance in the Highway Space and Street Furniture sections of this SPD.
G. Road safety - The anticipated ultimate height and spread of new trees should be considered to ensure the safe passage of vehicles. For example, small-growing broad-headed trees on busy routes where lateral branches could come into contact with vehicles should be avoided.
H. Proximity to adjacent buildings - Planting locations should be planned to take into account existing building features such as windows, doors, and projecting balconies.
49 BS 5837:2012 | 30 Apr 2012 | BSI Knowledge (bsigroup.com)
I. Existing street furniture and other highway infrastructure, including street lighting and below ground infrastructurePlanting locations should be chosen in order to minimise conflict with existing street furniture, or where appropriate, street furniture and below ground infrastructure should be rationalised to allow for new tree planting. In order to limit conflict with street lighting, a minimum distance of 5 metres minimum, and optimal 7 metres from existing street lights is recommended. See also guidance in the Power and Lighting section.
J. Important views - Tree planting which would impede strategically important views (identified in the council’s adopted City Plan) should be avoided
K. Respect for the local townscape – new tree planting should ensure that the trees contribute to the character and appearance of the area.
Trees in planters
L. Trees in raised planters are not a sustainable approach to greening. They are usually short lived and rely on artificial irrigation for the duration of their lives. Where provision of trees in planters is proposed, they will need careful justification on the grounds of the aesthetic or other benefits that they have the potential to provide. (see Street Furniture for more details).
Lighting of trees
M. Lighting of trees should only ever be used on exceptional specimens or in exceptional locations, see Power and Lighting section for more details.
Tree pruning
N. Street trees will not normally be pruned for the following reasons, but if it is possible to address issues through general maintenance, this work will be carried out at the appropriate time as part of our cyclical maintenance programme:
• Obstruction of light, and/or a view
• Leaf-fall
• Issues associated with flowers, fruit, seeds, pollen or honeydew
• To accommodate renewable energy systems such as solar panels or wind turbines
• To improve television reception
• Birds in trees and/or their droppings
• Insect activity
• Where a tree is perceived to be too large
• Offers of payment for tree removal and/or replacement
• To create space for new trees
• Disturbance to pavements, kerbs, walls or paths, except where an engineering solution to these problems is inappropriate
• Perceived risk of future subsidence damage by property owners
Tree Removal
O. Street trees should only be removed for good arboriculture reasons, including trees which are:
• Dead or dying
• Dangerous, or with significant disease and/or defects
• Demonstrated to be causing significant structural damage
• Considered by the City Council to be inappropriate in their location
P. Trees should also be removed or pruned:
• As part of an agreed management plan or as part of an approved public realm improvement project
• When planning permission has been granted for tree removal and all pre-commencement conditions and legal obligations have been satisfied
• In the interest of national security
When trees are removed, they should usually be replaced, according to the principle of the ‘right tree in the right place’ (see ESPD).
Privately owned trees and vegetation
Q. Owners of trees which encroach on the public highway should manage their trees, hedges, and shrubs so they do not impede the safe passage of pedestrians or vehicles. The highway authority may undertake work to overhanging vegetation and, if necessary, recoup the cost. Overhead clearance from trees, hedges and shrubs should be a minimum of 2.1 metres to the underside of signs, 2.5 metres over footways and up to 5.5 metres over carriageways and regularly managed to maintain theses clearances, remembering that wet foliage hangs lower. Hedges, trees, shrubs or bushes should be cut back to the boundary line to ensure the highway is free of obstruction
The City Council’s Trees and the Public Realm (2011) provides guidance on townscape character, as do the council’s adopted conservation area audit SPDs 50
Tree pits
See Paving Materials section for guidance on tree pit materials.
Tree inspection and management
Council owned trees are managed in order to meet legal responsibilities and to limit risks to safety. The overall risk from trees and branches falling is extremely low, but trees are living organisms so risks from trees cannot be removed entirely. The City Council shall manage trees to ensure that risks to safety are as low as reasonably practicable.
Tree inspection regime
The City Council undertakes regular inspections of trees in the public realm in order to meet legal responsibilities and in the interest of tree safety. Trees on highways are inspected every 2 years. Trees in parks, on housing estates and in out of borough cemeteries are inspected every 2 to 3 years. Guidance provided by the London Tree Officer Association’s (LTOA) Risk Limitation Strategy and the National Tree Safety Group’s ‘Common Sense Risk Management of Trees’ (or successor documents) are taken into account with regard to respect to tree inspection.
Tree management
The City Council carries out routine tree maintenance based on the results of regular tree inspection regime. In addition to this, there are planned tree management interventions which include:
• Removal of growth at the base of trees annually
• Work to address Massaria disease of London plane trees on an annual basis
• Cyclical reduction of tree canopies in order to limit the risk of tree related subsidence, taking into account guidance provided by the London Tree Officer Association’s (LTOA) Risk Limitation Strategy (or successor documents).
Other types of planting
Vertical Rain Gardens / Green Walls Guidance:
A. Public realm schemes should clearly demonstrate their contribution to the city’s green infrastructure network, particularly in terms of climate adaptation, water management and biodiversity.
B. Public realm schemes that are purely aesthetic with species to look attractive but not necessarily the right type for vertical rain gardens/green walls and will require disproportionate maintenance with the sole intensive use of clean potable water will generally not be accepted. See ESPD for further guidance to potable water.
C. Public realm schemes should incorporate and maximise rainwater runoff collection and reuse. See ESPD for further details.
D. Public realm proposals should demonstrate that they have selected appropriate species that can thrive in the microclimate of the space they are to be located within. London Plan guidance advises using natural vertical habitats and mimic plan groupings and structure into wall designs 51
E. There are structural and fire safety implications for green walls and green roofs that will need to be carefully considered and mitigated for. Advice should be sought from the appropriate specialists as part of development proposals.
F. Non-living green walls will generally not be accepted.
G. ‘Living pillars’ (attached to lamp columns) are generally not supported due to the difficulty in maintaining them and their negligible contribution to biodiversity.
50 Conservation area audits, maps and guidance, from A to K | Westminster City Council
Conservation area audits, maps and guidance, from L to Z | Westminster City Council
51 urban_greening_and_bng_design_guide_march_2021.pdf (london.gov.uk)
Context
When rainwater does not drain away either by soaking into the ground or through the drainage system on roads and around buildings, surface water flooding occurs. Increasing rainfall and intensity of rainstorms due to climate change is likely to increase surface water flooding in the future. Sustainable Drainage Systems (SuDS) incorporate a range of measures which can help to better manage surface water run-off from buildings and hard standings now and in the future, by employing a combination of infiltration (allowing surface water to soak into the ground) and attenuation (storing surface water and releasing it slowly) before it enters the drainage system. Along with water quantity, SuDS are also designed to deliver benefits in water quality, amenity and biodiversity.
Carefully integrated and well-designed SuDS can make a major contribution to the public realm; not only reducing flood risk but also numerous environmental benefits in addition to improving character and appearance. SuDS can create or improve habitats for biodiversity, improve air quality, contribute to amenity value, help mitigate the urban heat island effect, improve the quality of run-off entering rivers and create a sense of place 52 Even small SuDS features can make a contribution to reducing flood risk and providing additional benefits, and as such all public realm developments should consider opportunities for SuDS. Examples of SuDS in the public realm include permeable paving, green/blue roofs or walls, rain gardens, tree pits, downpipe planters, swales, and detention ponds.
Although not currently set in place, legislation is set to come in 2025 (Schedule 3 of the Flood and Water Management Act 2010) which will see Westminster City Council designated as a SuDS Approval Body (SAB). This will mean that all projects larger than 100sqm or more than one property that have a drainage implication will need to incorporate a SuDS based drainage scheme that complies with new standards and be approved by the SAB before construction can commence. Once legislation comes into effect, this will need to be applied to the relevant public realm schemes.
Sustainable Drainage Systems (SuDS) Guidance:
A. All new developments and interventions in the public realm should aim to achieve greenfield runoff rates and ensure that surface water runoff is managed as close to its source as possible. SuDS should be implemented unless there are clear practical reasons for not doing so.
B. SuDS components should be considered from early on in the design process, taking account of the topography and use of the site/area. Consideration should be given to SuDS which aim to deliver multiple benefits in biodiversity, water quality, water quantity and amenity.
C. Public realm proposals should refer to the Construction Industry Research and Information Association (CIRIA) SuDS Manual, London Sustainable Drainage Action Plan, TfL ‘SuDS in London’ Guide, the City Council’s published Strategic Flood Risk Assessment (SFRA) and Environment Supplementary Planning Document (ESPD) as part of the early design stage for new development proposals.
D. Developers are encouraged to contact Thames Water as early as possible to discuss their development proposals and intended delivery programme to assist with identifying any potential water and wastewater network reinforcement requirements
E. Public realm proposals should encourage natural drainage in the public realm wherever possible whilst maintaining a healthy balance between the other functions within the public realm. For new developments located in Surface Water Management Zones (previously known as Surface Water Flood Risk Hotspots), as identified within the SFRA, proposals will be required to actively explore opportunities to incorporate SuDS or other methods of mitigating surface water runoff. Due to the constrained nature of Westminster’s built environment, public realm proposals should consider innovative solutions to incorporate SuDS, including consideration of opportunities within residual spaces such as building setbacks or areas outside of pedestrian desire lines.
F. Porous materials can provide rainwater with an alternative route into the drainage system, lessening the likelihood of surface water flooding. Porous materials should be designed into schemes whenever possible. Permeable asphalt,
52 Guidance from the Mayor of London (http://content.tfl.gov.uk/sustainable-urban-drainage-november-2016.pdf ) to be read alongside CIRIA C753 The SuDS Manual 2015, which provides industry standards in this area.
for example, allows water to infiltrate into the ground, and therefore reduce demand on waste-water drainage. See Materials Guidance in this SPD.
G. All new public realm developments should prevent harm to existing trees and allow sufficient soil volume for new trees to grow to maturity.
H. Public realm proposals should explore innovative, non-traditional drainage solutions in the public realm including a range of types of SuDS. Examples include raingardens, permeable surfaces, green/blue roofs, rainwater harvesting, underground water storage, water squares, tree pits, swales, detention ponds, and other ways of storing and slowing down the flow of surface water.
I. Different types of SuDS may be more or less appropriate depending on specific local circumstances or constraints. Proponents should carefully consider and justify their proposed drainage solutions to the City Council.
J. We strongly encourage ‘opportunistic interventions’ to integrate or retrofit SuDS where other public realm works are being planned.
K. The design of SuDS should ensure they do not restrict the use of the public realm to any groups or individuals, particularly vulnerable people.
L. Design of new public spaces should be carried out in line with the concept of the ‘sponge city’, where urban areas utilise good design and nature-based solutions to absorb rain and prevent flooding.
M. Robust funding, management and maintenance plans should be agreed in advance of scheme delivery.
N. Applicants should ensure appropriate management and maintenance arrangements for relevant green spaces and features are in place for the lifetime of the development.
O. The decision to take on management/maintenance responsibilities and/or ownership will be at the City Council’s discretion.
Funding and Management/Maintenance
The following should be considered as part of the funding and management/maintenance for all green infrastructure proposals:
• Depending on individual circumstances, the City Council will use planning conditions or obligations as appropriate to secure funding and delivery of green infrastructure, including for monitoring and management where required.
• For major developments, arrangements for funding the long-term sustainable management and maintenance of green infrastructure should be identified as early as possible and factored in alongside consideration of costs and benefits.
• Where the council is requested to take ownership and/or management and maintenance of green infrastructure proposals, funding will be provided for by the developer to cover management/maintenance for the lifetime of the development via contributions secured by planning obligations or a commuted sum. If this route for funding, management/maintenance is chosen, developers will need to engage with the council at the earliest opportunity.