Assessing the Performance of Low Impact Development (LID) Measures During Large Rainfall Events in the Humber River Watershed, Ontario, Canada

This research used an EPA SWMM model of the Humber River watershed and simulated the 2 to 100 year rainfall event to assess peak flow attenuation for LID measures. The EPA SWMM model used a semi-distributed modelling approach to test three configurations of LID measures. The LID measures were implemented on 39 subcatchments grouped into four categories. Two design storm distributions (Chicago and AES) and a continuous simulation from 1976 to 1997 were input as rainfall into the model. The continuous simulation was compared to the design storm results by converting maximum annual peak flows using the extreme value distribution to 2 to 100 year peak flows. The design storm and continuous simulation modelling demonstrated that LID measures offer minimal reduction to the peak flow for large rainfall events and provide inconclusive conclusions for smaller rainfall events suggesting design storm modelling can be inaccurate in determining peak flow.