AECOM - MUSIC case study
Tapping into Singapore’s urban stormwater
The project to turn Singapore’s fully urbanised environment into a water supply catchment has attracted attention from around the globe. Singapore’s Public Utilities Board (PUB) has converted Marina Bay, in the heart of the city, into a freshwater reservoir fed by stormwater runoff from a third of the metropolis.
Professor Tony Wong and colleagues at Design + Planning at AECOM advised PUB on the implementation framework for water sensitive urban design (WSUD) in the catchment. The latest science from the Facility for Advancing Water Biofiltration (FAWB) at Monash University and eWater's MUSIC software have assisted in its development.
As part of Singapore’s Active Beautiful and Clean (ABC) Waters initiative, the PUB has conducted a number of design and MUSIC training courses to build local capacity for WSUD. In addition, two pilot projects have been completed. One project is a 240m2 ‘rain garden’ designed to collect and filter runoff from a 6000m2 residential estate. The other is a vegetated bioretention swale (bioswale), 180m long, beside a new arterial road. The installation occupies two sides of Sengkang West Way, and for experimental purposes each side is different. Finished in September 2008, testing of the systems is underway, and results will allow the most effective design to be adopted for larger scale use.
The rain garden was retrofitted into the Balam residential estate in 2007. It consists of a sandy loam filter layer 400–500mm thick which sits on top of a 400mm submerged zone; at the bottom is a gravel drainage layer intersected by perforated pipes which take the water away. The rain garden is planted with a wide range of vigorous and hardy plants whose root systems keep the filter material open. They also help remove nutrients.
The submerged zone – or saturated anoxic zone (SAZ) – has a special configuration designed by FAWB to turn NOx into nitrogen gas. It does this through a series of nitrification and denitrification steps involving anaerobic microbes. Coarse wood chips are added (about a third by volume) to provide the microbes with the necessary source of carbon.
The bioswale works in a similar, if simpler, way. It is designed as a linear structure beside the road without a submerged zone. It collects the water from the pavement and filters it through a medium before draining away. Again, suitable vegetation adds to the effectiveness and attractiveness of the system.
The testing of the systems is a key element of the project. The preliminary results from Balam Estate have been impressive, indicating that total dissolved solids could be reduced by 98% and total nitrogen by 85%.
PUB is also working on other pilot projects, including bioretention planter boxes for a multistorey carpark, a wetland beside a drainage canal, and similar installations along major existing waterways and reservoirs.
Professor Wong is confident that the work, associated design guidelines and upskilling in the use of software tools, including MUSIC, will lay the foundations for water sensitive urban design throughout Singapore. He is expects that the PUB efforts will be a forerunner of clean and healthy urban environments in neighbouring jurisdictions. PUB's engagment with other government agencies, and the involvement of the private sector is also a promising aspect.