Compound Urban Flood Risk Assessment for the City of Charlottetown

The frequent extreme wet weather events, sea level rise (SLR) and seawater intrusion (SWI) resulting from climate change are impacting the stormwater drainage infrastructure (SWDI) in coastal urban settings such as Charlottetown. The co-occurrence of rainstorms, high tides (HT) and continuous SLR increases the susceptibility of urban flooding and SWDI degradation in low-lying coastal environments. This study provides a comprehensive methodology for compound flood risk assessment modeling to map and determine the vulnerability of coastal stormwater systems resulting from the combined impacts of rainstorms (current and future), SLR, historic HT events, and SWI. Several scenarios are modeled in PCSWMM to assess the compound risk of flooding to the city of Charlottetown from all possible flooding drivers.

The seawater inundation with a 2.0m sea level rise shows that 6% of the city area will be underwater by 2100. However, in the base scenario with 10 years of design rainfall and tide level events, existing groundwater depth shows around 8% of the existing system under capacity. It is increased to 21% by 2100 with future projected datasets. The increased groundwater infiltration due to network age and SWI will also undermine the capacity of the existing stormwater system. The hydrologic and hydraulic modeling simulations of the stormwater system performance for existing and future scenarios indicate that flood events will be more damaging in coming years due to the compound impacts of frequent rainstorms, HTs, SLR and groundwater infiltration resulting from SWI.