Author(s)

J. Wang, L. Chua, P. Shanahan

Abstract

Bioretention basins or rain gardens are constructed green infrastructure in developed areas that retain and treat stormwater runoff. This study evaluates whether a tropical basin in Singapore that is built according to design guidelines from temperate countries has sufficient storage and infiltration capacity to handle tropical storms. Flow measurements from 80 storm events which varied in rainfall depth (2.6–71.8 mm), event duration (10 min–2.8 hr), and antecedent dry period (ADP) (0.25–9.08 days) were recorded for half a year. Hydrological performance in terms of surface and subsurface storage for each storm event has been analyzed. Results show that the basin storage capacity is inadequate since in about 50% of the events, more than 50% of the runoff overflows the basin without soil treatment. In a storm event, the subsurface storage space remains fully saturated throughout the ponding period and the infiltration rate estimated based on the aggregate statistics of 59 events with extended surface infiltration is 1.7 cm/hr. This is within the same order of magnitude as that found by direct field measurement using a double-ring infiltrometer (4.4 cm/hr) but is lower than a recommended rate of  > 10 cm/hr. The information drawn from this study could be of use to stormwater managers for sustainable planning and development. For instance, this study suggests that in order to meet pollutant removal rate targets, a tropical basin should be sized to retain a critical water quality volume (WQV) in the range of 10 to 30 mm.

Keywords

low impact development, best management practices, stormwater management, bioretention basin, rain garden, hydrology, water quality volume, urban catchment, tropics, infiltration