Hydrological modeling and field validation of a bioretention basin

An emerging green infrastructure, the bioretention basin, has been deployed world-wide to reduce peak flows, encourage infiltration, and treat pollutants. However, inadequate design of a basin impairs its treatment potential and necessitates the development and validation of a suitable hydrological model for design and analysis of bioretention basins. In this study, an existing numerical model, RECHARGE, has been adopted to simulate hydrological performance of a basin in the tropical climate of Singapore over a half year that included 80 storm events. Comparison of the model predictions with field observations shows that RECHARGE successfully simulates the basin hydrology of 80 events of varying rainfall characteristics with mass balance error of 5.1 +/- 7.5% per event and 0.3% overall. Using the verified model, we develop new design curves that predict bioretention basin performance as a function of three basin design parameters: detention depth; ratio of drainage basin area to bioretention area; and saturated hydraulic conductivity of the basin soil media. We evaluate basin performance in terms of the percentage of water that infiltrates and is treated in the subsurface portion of the basin and define an infiltration index to measure the change in infiltrated percentage caused by unit change in the basin design parameters. The marginal improvement in basin performance drops significantly when the basin depth (h(d)) is increased above 40 cm, when the ratio of drainage area to bioretention area (R) is decreased below 20, or when the saturated hydraulic conductivity (K-s) is increased above 10 cm/h.