Investigating the effectiveness and optimal spatial arrangement of low-impact development facilities

This study employed SWMM for simulations to elucidate physical mechanisms of LID components in site, as well as coupled Genetic Algorithm with hydrological simulation to determine the optimal spatial configuration of LIDs in a watershed. Using main campus of NTU as a case study, the results shows that the effectiveness of LID depends on storage capacity in delaying and attenuating discharge prior to the onset of peak inflow. With enough surcharge storage control the discharge at the beginning of the rising limb, the benefits of the LID s increased with the rainfall recurrence intervals. A reversal of effect of peak reduction is observed when the surface storage space has been exhausted. At the watershed scale, the optimization results revealed that a higher ratio of LID installations in midstream subcatchments than in upstream and in downstream subcatchments. Hydrograph analysis also explained that installing LID facilities in subcatchments that make their primary contribution to outflow roughly simultaneously with the onset of peak flow is preferable in reducing peak flow at a watershed outlet. The finding of this study could be useful to formulate watershed guidelines or strategies for the installation of decentralized flood reduction facilities.