City of Fredericton flood risk assessment using PCSWMM

Naomi Vaset, Oliver Olberg and Alex Mason


The City of Fredericton, the capital of New Brunswick, is situated in the west-central portion of theprovince along the Saint John River, which flows west to east as it bisects the City. This study evaluatedthe current and future flooding risk of watercourse and the major & minor drainage system within theCity. Surface water inundation mapping has also been developed accordingly.

The PCSWMM software was used for modelling the tributary watersheds discharging into the St. JohnRiver and overlaying the main river water levels as flood boundary conditions to dictate the tributarydischarge conditions. The model was large scale and covered the entire City including over 162 culvertsthat provide flow restrictions and generate storage areas or flood plains. Simulation scenarios for the 2-year through 100-year storms were run in combination with different main river water levels thatrepresent low water or spring freshet conditions with a tidal influence. Climate change scenarios for the2050 – 2100 planning horizon were added to the scenarios. A decision matrix was developed to screenout culverts that require upgrades, either based on hydraulic needs or asset condition. The studycontained recommendations to reduce flooding, future developments guidance as well as larger floodprevention strategy recommendations such as building berms or dykes in combination with largebackflow prevention systems and pumps in high value urban centers.

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