Using Detailed 2d Urban Floodplain Modelling to Inform Development Planning in Mississauga, On

The city of Mississauga has recently identified strategic growth areas where investments will be targeted for redevelopment and intensification projects. One of the growth areas has a history of flooding during major storm events. In order to redevelop this area, businesses and land owners need to prepare development proposals ensuring that appropriate flood proofing requirements have been achieved and emergency management plans have been prepared. Although the area had previously been included in an update to the regulatory floodplain mapping, the one-dimensional (1D) model that was used to map the floodplain was not capable of representing the complex overland flow within the study area. Therefore, the Toronto Region Conservation Authority determined that a more detailed two-dimensional (2D) hydraulic model was required to refine the floodplain mapping for this area. MIKE FLOOD was selected for the modelling because it couples a 1D channel flow model (MIKE 11) with a 2D overland flow model (MIKE 21). This approach was advantageous because it could leverage the existing 1D HEC-RAS model to prepare a MIKE 11 model for the 1D channel flow in Little Etobicoke Creek and then model the overland flooding using the 2D MIKE 21 model. This approach provided the ability to accurately represent the depths and velocities of flooding in the streets, on properties, and around buildings. The resultant model was used to run different storm events such as 5-year, 50-year, 350-year and regional flow for the existing condition where a flood wall and flood protection berm were included in the model. Similar models were also run for 350-year and regional flow events for the condition without flood wall and the berm in order to determine the current level of flood protection being provided, and to meet regulatory floodplain mapping requirements. The model is also being used to evaluate the effectiveness of the proposed flood proofing and flood mitigation plans. The updated flood constraint mapping will also provide guidance to local, regional and provincial government agencies as well as private sectors in managing and planning existing and future developments throughout the study area.