10 May 2011
Richard Ashley presents a joint post with Tony Wong, Centre for Water Sensitive Cities, Monash University, Melbourne.
We can now see some action in England and Wales regarding urban drainage after the flooding in 2007 that finally prompted new legislation. Within this, the preference for SUDS ‘sustainable drainage systems’ is encouraged for new developments, although the majority of the challenges lie with existing urban area drainage.
It is expected that the forthcoming standards for SUDS will focus on managing higher flows of urban runoff and to some extent environmental impacts by improving the discharge quality. These initiatives will lay the foundation for further community benefits accrued from the SUDS approach to managing urban stormwater for the potential multi-value that natural drainage systems can provide at a range of spatial scales. At the regional scale, ‘living with water’ is a rediscovered way of managing water in urban areas and examples of this include the Dutch Room for the river programme that incorporates some 34 schemes ranging in scale to provide greater conveyance to the rivers passing through the country. Providing more space for water in existing dense urban areas at the urban drainage scale is less straightforward.
In UK cities the natural watercourses have mostly been culverted and built over and even major rivers such as the Don in Sheffield, are not made best use of; with it being subordinate to and cut off by the road network. Yet there is a growing recognition of the multi-value benefits of managing water in urban areas in a more natural way. Stormwater runoff is generated across distributed areas and source-control measures typically provide the best opportunities to capture and use urban stormwater, and to establish ecological landscapes that provide a range of services to even the densest built environment.
Clearly there needs to be more space for any extreme flows using an interconnected exceedance flow blue-green corridor network. The original definition of green infrastructure by Benedict and MacMahon (2006) suggested the need for interconnectedness of the green areas via corridors and hubs for the movement of fauna through urban landscapes. Natural areas replaced by highly developed urban surfaces originally comprised vegetated surfaces, mostly forested in the UK, which drained naturally to networks of small and gradually larger watercourses downstream in catchments. We have the opportunity to restore elements of this natural system to create a network of blue and green open spaces and corridors within our urban environment to serve as an integral element of the drainage infrastructure and floodway for flood conveyance during rare (low probability) storm occurrences. Such initiatives help tackle current and future problems of flooding and environmental degradation of water bodies. Although the density and layouts of existing urban areas make this a challenge, the imperative to provide a higher level of flood protection to our communities has created a raft of new opportunities.
It is becoming widely recognised internationally that the way we manage urban water influences almost every aspect of our urban environment and quality of life. Future needs for livable urban areas to accommodate a growing population require design and planning innovation that simultaneously provide safe, secure and attractive places to live and work. Recent initiatives in the UK, Australia, Singapore and USA regarding the synergistic management of urban runoff with green infrastructure shows how multi-value benefits can be achieved that can simultaneously address social needs in terms of water supply, flood risk management, environmental protection and liveability of urban spaces. Examples include the promotion of evapotranspiration from trees to reduce heat stress, the harvesting of rainfall and urban runoff to tackle water shortages and the creation and maintenance of green spaces to provide flood storage and recreational areas at the same time. Natural systems also sequester carbon and reduce the need for energy for cooling in the summer.
Let us hope that the very small step that we believe is now being taken in England and Wales is actually much larger than we expect and the true value of water, not as a commodity handled by private enterprise, but as a multi-faceted benefit to our communities is properly recognised and taken advantage of as it is in so many other parts of the world.
Photo courtesy of Illman Young Landscape Design