Managing stormwater with low impact development in highly urbanized areas

Abstract

Low impact development (LID) implements small-scale hydrologic controls throughout a catchment to replicate the pre-development hydrologic regimes or in other terms control stormwater as close to the source as possible. Examples of such controls include green roofs, bioretention swales, rain gardens, porous pavements. This project evaluates the effectiveness of large-scale LID implementation in Singapore and Hong Kong. We examine the hydrologic impacts, namely peak discharge mitigation and baseflow restoration, under different land uses, rainfall conditions and LID strategies. For further comparison, we adopt an integrated distributed hydrological model for Singapore and a lumped hydraulic model for Hong Kong. Studies of both Singapore and Hong Kong suggest that LID is effective if there is substantial level of infrastructures (e.g., covering 5 to 10% of catchment area). LID is more efficient in reducing/delaying peak discharge and restoring baseflow on an average long term basis. However, its performance, particularly in peak discharge mitigation, diminishes during design storms (e.g., ARI of 5 years). In terms of modeling techniques, integrated distributed hydrologic models require extensive parameterization but can accurately simulate some important processes (e.g., increase of infiltration and restoration of baseflow) that are simplified in lumped hydraulic models. Overall, large-scale LID potentially provides more sustainable stormwater management but its success depends on factors such as design objectives, existing land uses and drainage networks. We should therefore further research to increase the feasibility of large-scale LID in highly urbanized areas such as Singapore and Hong Kong.