Water sensitive design: Making cities of the future places where people want to live and work

Published 21/07/2020

Tony Wong has been Professor and Chief Executive of the Cooperative Research Centre for Water Sensitive Cities in Melbourne, Australia, since its establishment in 2012. The research centre is a social enterprise that supports the ongoing adoption of water sensitive principles and practices through broader services.

Water sensitive design - An interview with Tony Wong

By Jim McNaughton

A Civil Engineer, with a PhD in Water Resources Engineering, Tony is internationally recognised for his research and practice in sustainable urban water management. He has led a large number of award-winning urban design projects in Australia and overseas. His many honours include the prestigious Sir John Holland Award as Australia’s 2010 Civil Engineer of the Year and the IWA Global Water Award in 2018 for his leadership and lifetime achievements in developing the concept of Water Sensitive Urban Design, a unique socio-technical approach which addresses the social, environmental and economic challenges of traditional urban water management.

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Tony Wong: A global authority on water sensitive urban design

What is a water sensitive city?

It’s a place where people want to live and work. It’s a collection of inter-connected water sensitive precincts, or areas, which means that plans for each precinct are developed to respond to local opportunities and constraints. These precincts will:

  • efficiently use the diversity of water resources available
  • enhance and protect the health of urban and natural waterways
  • mitigate against flood risk and damage.

 

Public spaces are green infrastructure that harvest, clean and recycle water, increase biodiversity, support carbon sequestration and reduce urban heat island effects.

Water catchments are typically thought of as large rural or forested areas from which rainwater in rivers and dams is piped to a city. You describe cities as water catchments areas too. What do you mean by that and what are the benefits?

With global warming, continuing the conventional approach to securing water supply security, e.g., building another dam, is often not the most effective option. Although in many regions the effect of climate change on rainfall remains uncertain and may not necessarily lead to any consistent trend of reduced rainfall, it is more likely that climate change will increase the global temperature and thus have a more certain effect on soil moisture in traditional water supply catchments . So catchments will be drier and there will be less run off when it rains,

If we think of cities as water catchment areas, we can build a strategy around diverse water sources and a mixed water infrastructure that allow cities the flexibility to access a range of sources at least cost—with cost including environmental impacts and other externalities.

Typical features harnessing a diverse range of water sources include rainwater tanks integrated to building architecture, streetscape stormwater cleansing and storage, wetlands and lakes in public spaces, localised wastewater treatment and recycling units, managed aquifer storage and recovery schemes. These are features of cities as water supply catchments.

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Green infrastructure harvests, cleans and recycle water, increases biodiversity, supports carbon sequestration and reduces urban heat island effects

Do we need to be taking a broader collaborative approach to water?

Yes. Transforming cities into water sensitive cities requires a collaborative approach, cutting across many government departments and also integrating multiple public and private sectors.

Contemporary stormwater management is a good example of this inter-disciplinary nature. The transition to Water Sensitive Urban Design (WSUD) in stormwater management over the last 10 to 15 years has been quite remarkable, especially when considering that in this short timeframe we have seen the philosophy, technology and language of WSUD developed to industry standards and referenced in policies across all levels of government in Australia, and across multiple governmental departments.

Stormwater treatment technologies such as constructed wetlands and bio-retention systems (commonly referred to as rain gardens) are implemented from the small to large scale, from buildings and allotments to regional public open space. Bioswales (typically vegetated, gently sloped channels that remove debris and pollution from stormwater) as part of road infrastructure is another example of integrating these ecological landscapes into the urban form. These are essentially ‘kidneys in our cities’. Once cleansed, stormwater can be utilised as a resource and/or its flow rate controlled for downstream protection of the natural environment.

Stormwater runoff from roads carries more pollutants than other urban forms of runoff, and volume is high because roads are almost entirely water resistant. By fitting bioswales along roads, we improve drainage and flood management, water quality, and the quality of landscapes along road verges. In steep terrain, these systems could be designed as a series of cascading bio retention ponds.

Studies have defined key design procedures that ensure these systems deliver their ecosystem services effectively.

Wellington will need a new drinking water source in the next 10-20 years, unless we significantly reduce per capita usage. Could our small city transition into a catchment area that produces as much water as another traditional source?

All cities transition to water sensitive cities progressively as they undergo urban renewal. The key enabling factor is good planning policies and principles for practice.

It is not simply about comparing the total volume of water harvested but about capitalising the opportunities to diversify the water sources and introducing flexible local solutions that can respond quickly to changing future circumstances and development timing and patterns. This approach is relevant and appropriate for cities of any size.

A study undertaken to assess the security of existing water supply for the City of Melbourne recommended a strategy to transition to a more diverse portfolio.  The optimal share of harvested stormwater came to 11 -14 per cent of the total water supply. The assessment revealed potential cost savings of between $43 million and $463 million per year, depending on the three future climate scenarios evaluated.

Redevelopments at a precinct-scale are often the best starting point for catalysing city transition to a more balanced portfolio of water sources. In Melbourne, the inner-city redevelopment at Fishermans Bend, adding up to 80,000 residents into the new precinct, is one such example.

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Brylee Reserve, Auckland: A recently completed constructed wetland integrated with a public park and houses

Would environmental and social benefits offset increased financial cost of transitioning Wellington into a water sensitive city?

We need to explore the ‘economic return on investment’ rather than the traditional financial benefit-cost assessment when asking the cost of transitioning into water sensitive cities. We also should not simply look at the transition as one of converting cities into a water supply catchment. There is also the ecosystem services that such cities can provide to the built and natural environment, and the broader whole-of-water cycle sustainability and resilience.

From a water supply security perspective, the recycling of wastewater and harvesting urban stormwater through the use of green infrastructure provides added water security. These actions deliver a range of ecosystem and social services that are highly valued.

A study undertaken by South East Queensland Healthy Waterway’s Water by Design Program estimated that the potential property premiums to be around 90 per cent of the capital cost of WSUD assets. Also, figures from the Commission for Architecture & the Built Environment (CABE) in the United Kingdom show that property values increase near green spaces, with houses close to parks averaging 8 per cent higher prices than similar properties further away. These types of studies show the community’s willingness to pay for the amenities associated with green infrastructure.

There are other widely acknowledge positive economic benefits that are difficult to monetise. These include increased biodiversity and ecological health of the aquatic ecosystem, improved physiological health of people who are more connected with green space by being more physically active (such as walking through green corridors in their suburbs).

Water management influences many elements of a city’s productivity and liveability, not all of which are necessarily directly tangible or market-driven economic values. It is for this reason that the CRC for Water Sensitivity embarked on a major project to develop a framework and accompanying database to document the non-market values derived from a water sensitive approach

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Waitangi Park is Wellington’s first water sensitive urban design

What water opportunities do you see for Wellington?

Wellington’s first water sensitive urban design is the development of Waitangi Park. That project was a good example of seizing the opportunity to introduce ecosystem services to cleanse stormwater conveyed in a main drain (what was formally Waitangi stream). For as long as a city is growing, re-developing and undergoing renewal, there will be opportunities at a range of scales, whether it is about the fit-for-purpose recycling of grey and wastewater, to rain and stormwater harvesting, groundwater replenishment and micro-climate management or the incorporation of water sensitive building design with landscape design.

Community participation and co-design can create unique places that reconnect community with the intrinsic value of water, its cultural and environmental significance—beyond just a commodity. Achieving water security does not have to be mutually exclusive from recreating a more harmonious balance between the social, environmental and economic values of society.

Water sensitive design guideline

Wellington Water has released a new technical guideline for water sensitive design, developed after working with green infrastructure specialists and holding a series of interdisciplinary workshops. Water sensitive design typically involves using natural processes to mimic healthy hydrological cycles and provides a better way to manage freshwater in our cities and restore the mauri of our regions’ waterways, harbours, and estuaries. The new guideline is a tool to ensure standardised and successful design outcomes, which means that green infrastructure devices designed using this guideline are optimised for maintenance, safety, and perform their function over the entire asset lifecycle. 

The guideline can be found here.