Column | Mainstreaming blue-green infrastructure

Climate-resilient urban planning is centred on water. The consequence of the increase in impermeable surfaces brought on by urbanisation includes reduced vegetation cover and increased stormwater runoff. Regular flooding lowers property values, discourages investment in flood-prone areas, and restricts societal development. Traditional drainage systems, which are used to quickly transport and discharge stormwater in order to prevent flooding, not only increase the risk of flooding downstream, but also reduce aquifer recharge and harm the water bodies that receive it. The focus of conventional piped systems on managing stormwater quantity rather than its remediation and re-use has exacerbated environmental degradation in urban areas.

It is critical to have a thorough understanding of both the urban and natural water systems when evaluating spatial interventions. Many cities around the world are considering a paradigm shift in urban drainage from hard engineering to blue-green infrastructures (BGI), such as rain gardens and constructed bioswales (vegetated channels for filtering stormwater). BGI takes advantage of the benefits of working with the natural water cycle and urban green spaces to reduce urban flood risk, particularly pluvial flood risk.

Sustainable drainage systems (SuDS) employ a holistic approach to mimic the pre-development hydrology of the site. Stormwater is viewed as a valuable resource rather than a nuisance that must be addressed. Water quantity and quality, as well as biodiversity conservation, increased urban amenity, and a sense of 'place', are prioritised. Water control at the source, such as through the use of pervious pavements or green roofs, takes precedence over local and regional controls, such as the use of wetlands. Local stormwater management reduces not only the amount of water that must be managed at any one point, but also the amount of water that must be transported off the site. Vegetated SuDS offers additional ecosystem services, including water filtration and carbon sequestration and storage. By considering stormwater as a resource instead of as a waste product, BGI may be able to potentially compensate cities with scarce ecosystem services.

Urban flooding can be effectively solved by combining green (vegetation-based) and blue (water resources-based) approaches. By prioritising flood management in areas of high precipitation and stormwater recovery in areas of water stress, this can also enable the coordination of water demand and availability. BGI can therefore maintain resource balance while also assisting in resilient climate change adaptation. Integrating drainage infrastructure with open space systems is a practical solution given the scarcity of available space in urban areas and the competition for it.

A place-based design approach assesses and interprets the local socio-ecological context for BGI development. The most significant barriers to widespread adoption of BGI are socio-institutional rather than technical in nature. Narratives that inspire collective action at the city level have the potential to mainstream the practices necessary to establish regenerative urban built environments. Community participation is essential to the success of BGI projects. Stakeholder perceptions, aspirations, and potential interactions should all be considered when designing BGI. Communities must be viewed as active participants in BGI projects rather than passive 'recipients' when developing guidelines. It is necessary to address the power dynamics that influence their participation.

Aesthetics and improvements to community facilities are significant factors in influencing BGI acceptance. The inclusion of recreational features in BGI has the potential to increase community participation and thus contribute to its long-term viability. Stakeholder acceptance will encourage government officials to include SuDS in development plans, assisting in the concept's mainstreaming. Residents willing to pay a premium for BGI maintenance will also encourage property developers to invest in them. BGI has intrinsic economic value because of the plethora of co-benefits it provides, such as free recreational space, energy savings from urban cooling, and improved psychological well-being. They also significantly improve urban public health.

Local stewardship is critical for BGI's long-term viability. In this context, stewardship entails refraining from destructive behaviours such as littering and vandalism and engaging in constructive behaviours such as monitoring and upkeep. This may be influenced by awareness of the purpose and function of BGI, risk perceptions, and its positioning in the public sphere.

BGI development has the potential to empower communities by enabling them to participate in the design of public spaces. Participation from the community can assist with demand analysis, design inspiration, implementation support, and monitoring. Community co-production may improve public preferences, accountability, and effectiveness for BGI. Community members may require stewardship competencies and materials, which may be provided through capacity-building programmes. Increased citizen participation in blue-green infrastructure projects can be facilitated through the use of legal, policy, and market-based tools. Infrastructure that is ‘blue-green’ has the potential to enhance the long-term liveability and prosperity of cities.

(Ann Rochyne Thomas is a bio-climatic spatial planner and founder of Centre for Climate Resilience - a sustainability and climate change advisory.)