A Short Paper for the Second Asia Pacific Forum on Urban Resilience and Adaptation (2nd March 2016)

 

Introduction

Climate shocks and stresses affect many urban centres worldwide. Resilience involves a number of measures including provision for storm floods and droughts. Rather than conventional stormwater drainage systems, an eco-system approach can be more effective as not only is a natural buffer formed to alleviate peak flow but surface water can be conveyed, cleansed and stored for local reuse through multifunctional green infrastructure.

The Eco-System Approach

The concept of an ‘ecosystem approach’ according to the Convention on Biological Diversity’s (CBD) definition: ” is a strategy for the integrated management of land, water and living resources that promotes conservation and sustainable use in an equitable way”, which aspires to maintain the natural structure and functioning of ecosystems.

Ecosystem approaches address the crucial links between climate change, biodiversity, ecosystem services and sustainable resource management and thus have the potential to simultaneously contribute to the avoidance and reduction of greenhouse gas emissions and the enhancement of sinks through increased carbon sequestration. These approaches also maintain existing carbon stocks, regulate water flow and storage, maintain and increase resilience, reduce vulnerability of ecosystems and people, help to adapt to climate change impacts, improve biodiversity conservation, promote livelihood opportunities and provide health and recreational benefits.

Blue Green Infrastructure

Green infrastructure is based on the principle that the same piece of land can frequently offer multiple benefits if its ecosystems are in a healthy state and the spatial structure of natural and semi-natural areas are retained. Investments in green infrastructure are generally characterized by a high level of return over time, job opportunities and a cost-effective alternative, which can be complementary to ‘grey’ infrastructure and intensive land use change.

Blue-green infrastructure combines the water component with an eco-system approach using a stormwater management model that seeks to avoid or minimise development impacts on the natural environment and environmental value. This approach protects, restores, or mimics the natural water

cycle and allows a way of managing surface water as close as possible to where it falls. There is usually a connection between the built landscape with locally-generated water resources and this serves to provide a mechanism to reconnect individuals and local communities with the natural landscape.

Blue-green infrastructure includes protected areas, areas of high nature value outside protected areas, natural landscape features, restored habitat patches, artificial features such as eco-ducts or eco-bridges, multifunctional zones where land uses maintain or restore healthy biodiverse ecosystems, areas where the general ecological quality and permeability of the landscape can be improved, and urban elements such as green parks, green walls and green roofs.

Examples of the advancement of blue-green infrastructure include:

  • National promotion in USA by the US EPA via the Green Infrastructure Strategic Agenda 2013
  • Best Practice demonstrated by the successful application of blue green technologies in Philadelph
  • In Melbourne, Water Sensitive Urban Design (WSUD) is be used for storm water planning policy
  • In the UK, Sustainable Drainage Systems (SuDS) is mandated in all new developments via legislation and planning approval framewo
  • The new wastewater discharge permit issued by the Milwaukee Metropolitan Sewerage District is the first in the S. to mandate green infrastructure.
  • Instead of using electric-powered water treatment plans, New York City brings its drinking water through aqueducts connected to protected areas in the nearby Catskill/Delaware forests and wetlands –demonstrating how protecting watersheds can provide residential areas with drinking water and flood and pollution protection at low cos
  • New national ‘Sponge City Construction Guidelines’ provides a clear framework for delivery of a Low Impact Development City in Chin National Funding is being provided for ‘Sponge City’ pilot provinces and cities that implement ‘Sponge City’ projects.

We explore three areas of blue green infrastructure, namely river revitalisation, retention facilities and sustainable drainage systems.

River Revitalisation

Rivers offer economic development prospects for urban centres as well as ways of reinvigorating social and cultural heritage. At the outset, engagement with multiple stakeholders and the local community is crucial in establishing clear design goals and objectives during the planning and design process. Revitalisation involves the enhancement of diverse environments – although the design should be tailored to suit specific locations – as well as opportunities to test new technology and techniques. Experience with river revitalization shows that water quality (especially odour) may be a significant influencer in the delivered design outcome.

Case study – Kallang River, Singapore

The naturalisation of the Kallang River and park surrounds involved transformation of the concrete drainage channel into a naturalised meandering river. An application of soil bioengineering techniques (a combination of vegetation, natural materials and civil engineering techniques) was used to stabilise the banks and prevent erosion, which resulted in an expansion of the effective maximum river channel width. The profile of naturalised river and surrounding park area was transformed such that river flow is confined to a narrow stream during dry weather; and the park areas adjacent to the river become a flood plain and conveyance channel (i.e. natural retention facility) during heavy rainfall. The new riverbed can now reportedly hold 40 percent more water than prior to the redevelopment.

Retention Facilities

In designing storm retention facilities like retention lakes, controlled storage areas and retention parks, encouraging the successful co-use of land requires multiple engagement avenues – hence early community engagement in the design process is essential. During operation and maintenance, optimisation of flood management strategy and hydrological aspects may be required following construction so as to minimise maintenance through design and to allow standardisation of maintenance and management activities. Other items of importance concern risk management measures to ensure public safety and security around waterways and flood waters. Ecological compensation may be required as part of EIA approval conditions.

Case Study – Boronia Park, Sydney

Boronia Park is a high-use community space, located adjacent to a local library, basketball stadium and playgrounds. As a valued community space, upgrade works to the Boronia Park Retarding Basin involved community consultation as part of the planning and design process, with the basin specifically intended to encourage public access and interaction. The new Boronia Park Retarding Basin design hence encourages public access, with designated areas specifically built for the community to enjoy. The basin upgrade includes an outdoor classroom, amphitheatre, trees and vegetation, a boardwalk, and recreational zones for locals to sit and enjoy the ambience as well as new features such as landscaping, rockworks and connecting pathways. The wetland at the base of the retarding basin was also designed to provide amenity to the community.

For safety and maintenance reasons, recreational spaces in the park are located just outside areas of potential inundation. The park design, however, is not fenced, and footpaths are purposely located in close proximity to the water edge to encourage people to interact with park elements such as the wetland areas.

Key features of the proposed works include:

  • Upgrade of the storage capacity and flood protection performance of the retarding basin from a 15 percent risk of flooding to 2 percent likelihood
  • Creation of a new path into the basin across a new ‘meadow’ and wetland garden
  • Integration of stormwater quality treatment, in the form of a wetland, at the base of the retarding basin
  • Creation of more useable areas in the park to walk, meet and relax – new north and west facing sloping lawns to maximise sunny areas to sit and rest
  • Installation of new seating and feature trees
  • Creation of a new multipurpose plaza space

Sustainable Drainage Systems (SuDS)

SuDS –which includes green roofs, rainwater harvesting, water reuse, porous pavement, bioswales and rain gardens – is part of Water Sensitive Urban Design (WSUD), the process of integrating water cycle management with the built environment through planning and urban design.

SuDS can be adopted to contribute to broader sustainability and greening space objectives. Pilot testing of SuDS designs is valuable in optimising the design and demonstrating compliance with standards although there are practical challenges with procurement of soils and plant species and meeting water quality standards. Researchers have found that a simple mixture of soil, sand and bark works extremely well at reducing toxins in storm water runoff. In terms of operation and management, establishment of bioretention facilities or similar SuDS measures will have different requirements over the life of the asset. Effective routine maintenance is essential to maintaining SuDS function.

Case Study – North West Cambridge, UK

North West Cambridge is Europe’s largest rain water harvesting system based on a series of swales to collect, convey and cleanse storm water falling on 3,500 homes in a green field site in Cambridge. This is then stored in a new lake and reticulated back round for non-potable reuse. This reduces potable water demand to under 80 litres per person per day and also helps reduce downstream flood risk. The project was designed to meet 1 in 100 flooding under the Code for Sustainable Homes Level requirements. Some level of water recycling was required but driving the project was the desire to become a sustainability exemplar using international best practice.

Connections and transitions were important in the SuDS strategy to ensure that runoff is captured and filtered using a treatment process of at least two SuDS features. All runoff therefore is directed towards the Western Edge, where it is slowed and treated during its journey. Runoff from properties is connected to the surface water sewer only after passing through initial SuDS measures where possible. Connections made at the front of the property can be done via front sloping roof to avoid passing pipework beneath the house. Connections from the back are installed where properties back onto communal courtyards or green spaces. Features to keep water above the surface and help take pressure off the subterranean environment include:

  • Brown, Green and Blue roofs
  • Permeable paving in courtyards
  • Disconnection from the down pipe

Surface water drainage networks offer other benefits such as a pleasant environment, cycling routes and biodiversity.

Conclusion

Blue green infrastructure consists of new ways to address flood risk in the urban environment offering opportunities for delivering multiple benefits. These include:

  • Linking urban water infrastructure (blue) to urban vegetation (green)
  • Reversing urban creep
  • Greater climate change resilience
  • House, street, community and city-wide applications
  • Reduced flood and drought risk
  • Efficient use of water (recycling)
  • Lower temperatures in summer (reduced heat island effect)
  • Lower pollution levels
  • Better biodiversity
  • Increased amenity and health
  • Generation of local jobs

However, capturing these benefits, which are very local, is still difficult, making putting forward business cases for funding beyond flood risk management problematic. New legislation will be required if more sustainable drainage solutions are to be established in new developments. Retrofitting in urban areas offers local benefits but local authorities and communities will need to be proactive and seek opportunities.

Costs of blue green infrastructure such as bioswales and rainwater collection systems are in fact not much more than typical good quality landscape features. The design and materials used to construct these elements are the same as for typical landscape planters, except with more specific requirements for certain items (e.g., soils, drainage, planting stock). On the whole, they are generally seen as cheaper to construct and maintain, particularly as they are on the surface. As these are landscape solutions,

costs are sometimes doubled up, mainly for the drainage systems which will entail a higher landscape specification – however the landscape solutions should reduce the demand and therefore amount of grey infrastructure needed. Much also depends on the targets being set i.e. the volume of attenuation, the water quality improvement targeted, the pollution in the source water etc. Maintenance costs are comparable to typical good quality landscape.

It is also important to think of cost in terms of total value. Often for new builds it is cheaper to use natural processes. However, they can take up more land where the rule of thumb is 2-5% of impermeable areas. If not planned properly or retrofitted, it is as always more costly. The benefits often go to the water company rather than to the developer – so it is also a question of who pays.

The establishment period for blue green infrastructure is in the range of a few weeks to months. In terms of how quickly they take to establish, most of the benefits are actually derived through the soil structure, so as soon as they are constructed they will provide attenuation and some water quality improvements. Planted solutions provide added benefits from the microbes living in the root structure. These would take as long as a normal landscape to establish.

 

Author:

Dr Thomas S.K. Tang

DIRECTOR, SUSTAINABILITY, ASIA

sk.tang@aecom.com

 

The author would like to acknowledge with thanks the following AECOM staff for their contribution to this short paper: Michael Henderson, David Gallacher and Katrie Lowe.