Monitoring singapore's first bioretention system: Rain garden at balam estate

Active, Beautiful and Clean Waters, (ABC Waters) Programme is a long term strategic programme by PUB that aims to transform utilitarian canals, drains and reservoirs in Singapore into clean flowing rivers, lakes and streams that blend naturally into the urban environment. A key strategy of the programme is to adopt "ABC Waters Management" which entails detaining and treating stormwater runoff closer to source using green features to achieve sustainable stormwater management. In respect to this, PUB has implemented several pilot projects to demonstrate the efficacy of ABC Waters design features like bioretention systems, constructed wetlands in tropical climate. The first bioretention system built in Singapore in 2008 is a 240m ² rain garden retrofitted in a residential estate to capture and treat runoff from the adjacent area. The rain garden has since gained popularity in Singapore. Upon completion of the project, a detailed hydrological and water quality monitoring was undertaken to test the performance of this system. The monitoring results indicate that the Balam Rain garden operates well within its design capability. The anoxic layer of the rain garden has found to enhance nitrogen removal. This paper presents the details, inferences and results of the monitoring study of this bioretention system.