Sponge cities - transforming urban water cycle management

Dr Veljko Prodanovic and Dr Kefeng Zhang (Research Manager), Sino- Australian Centre on Sponge City, Water Research Centre (WRC)Sponge Cities is an urban water management approach that captures stormwater for re-use through detention, infiltration, evapotranspiration, treatment, harvesting and recycling. The beneficial effects are many. It combats flooding, reduces water run-off, reduces urban heat, improves water quality, increases water storage, vegetates the urban environment, increases property values and enhances the quality of urban living. 

Similar concepts have been employed all around the world over the past 30 years, e.g. in Australia Water Sensitive Urban Design (WSUD), in the USA Low Impact Development (LID), and in the UK Sustainable Urban Drainage System (SUDS). Two things make Sponge City unique. One is the name that describes in simple poetics what it is hoping to achieve: to absorb the water we have previously let escape. Second is the determined and widespread implementation in China, driven by government support. Sponge City is the most holistic plan to date as it includes a whole range of urban water cycle management, not only stormwater, and is supported by strong concepts, broad principles and latest technologies.

The Chinese government sees Sponge City as an alternative to expensive and disruptive retro-fitting of drainage systems. Rapid urbanisation in China has demanded a rapid response. By 2016 Sponge City programs were active in thirty cities, mainly attempting to reduce flooding. Great successes have been achieved, and the country is targeting to achieve 70% of runoff to be adsorbed and reused in 20% of urban areas by 2020, and 80% of urban areas by 2030.

As research manager of the Sino-Australian Centre on Sponge City (SACSP), Dr Kefeng Zhang is responsible for overseeing the direction of one of the leading consulting bodies on Sponge City research and practice. Dr Zhang is an emerging but already highly awarded engineering academic. He has developed the first framework for validating WSUD treatment systems, and has also been involved in development of the Water Sensitive Cities Toolkit (developed through the Cooperative Research Centre for Water Sensitive Cities) that quantifies the benefits to community and environment of a Water Sensitive Cities approach.

SACSC at the School’s Water Research Centre is an international partnership between UNSW, Monash University and EastHigh Environmental Holdings, a Chinese company acting as the implementation arm of this partnership. SACSC is growing at a fast rate, with new research and engineering staff facilitating a constant flow of information between Australian researchers and China. The centre has three main research areas: Green technologies, urban water modelling and novel technologies.  Green technologies are visible in any city with a restorative urban water plan and can include green walls and roofs, stormwater biofilters (also called raingardens and bioretentions), tree pits, wetlands and other bio filtration and retention systems. They are composed of two main components: plants and media. Professor Ana Deletic, UNSW Pro Vice-Chancellor (Research) and director of SACSC has recently developed clear and simple adoption guidelines for practitioners and has improved the applicability of bio-filtration systems by adapting media and plants to local environmental conditions.

This immediate and conscious connection between research and implementation makes SACSC an attractive funding proposition and they have leveraged this financial capital into cultural capital as their reputation grows and they are increasingly sought after as a hub of expertise on the research and implementation of green technologies.

Currently Dr Zhang is heading a two-year project on the development of Biofiltration Technology (rain-gardens, living walls) for Stormwater Management in Jiangsu, China, supported bilaterally by Australian and Chinese government bodies.  This research is timely for Sydney as well, as the 2030 Vision of the City of Sydney is to reduce stormwater pollutants by 50%, part of the 2011 City’s Raingarden Policy. As of 2015, 140 Sydney street scaping projects had included raingardens. It has almost doubled since then and is expected to keep growing exponentially. Integrating raingardens into capital works reduces cost and disruption and this is a key interest to SACSC and Dr Zhang.

Raingarden efficiency and analysis is at the heart of his research. Stormwater has been wasted in the past. Gathering it and filtering it of pollutants provides a community with two resources. Nutrients filtered out become a good source of food for plants, either within the bio-filtration system itself or to local plantings. The purified water can be either redirected to infiltrate local soils or it can be used as water for irrigation or other urban necessities. Even if the water does eventually become run-off it will be purified and will cause less damage to the environments through which it travels.

Independent studies on landscape amenities values have been carried out on small raingardens at 41 Sydney intersections, involving 4000 properties. Within 50 metres properties became 6% more valuable, within 100 metres 4% more valuable. This translated to an average increase in property value at any given intersection at $1.5 million. If raingardens can be made attractive to developers, profitable in nature, then the expansion and development of this system, this way of thinking, has endless possibilities.

During this 2-year project Kefeng will be tailoring Australian biofiltration technologies to Chinese conditions. Using a variety of media to suit local ecologies, these raingardens can vary in size from a single tree pit, to the 4.5 square metre systems being piloted in Jiangsu Province, to huge 200 square metre systems that will be developed in the future. WRC is hoping to support this expansion by developing more green technology laboratory testing facilities.

The Sino-Australian Centre on Sponge City is about a globalised approach to environmental problems. It is about the sharing and flow of information. It is about discussion and co-operation. It is about hope.

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