Numerical modelling of urban stormwater management with grassed road divider as bioretention system

Abstract

Bioretention system is one of the best management practices for rainwater runoff redirecting and storing before discharge into existing stormwater system. On the other hand, road divider is designed for dividing the traffic flow for road safety. However, it may be a blockage for surface runoff on road and possibly created ponding during heavy rainfall event. This scenario could become a hazard for motorised vehicles. In this study, a grassed road divider in Broga Road, Semenyih, Malaysia, is modelled as bioretention system by EPA's Storm Water Management Model (SWMM) to investigate the performance of its application. A case of grassed road divider without bioretention cell was also modelled for comparison. A series of simulations were carried out for the ARI of 2, 5, and 10 years to further study the performance of grassed road divider as a bioretention system. Four different types of soil including sand, loamy sand, loam, and sandy loam are selected as filler soil in the bioretention cell. Results from the model simulations showed that the performances of grassed road divider as a bioretention system can reduce the surface runoff into the stormwater system up to 49.9% and 56.77% for different ARIs. The effect of this implication is more significant on the reduction as the ARI increased. Results also showed that the impact of soil types is insignificant. The findings show that a bioretention system in a grassed road divider may supplement conventional urban road drainage and provide an effective stormwater management.