1D, 2D & 3D hydrodynamic modeling of a Dyked Coastal River in the Bay of Fundy

The Town of Truro is an urban development in Nova Scotia situated on the floodplain of the Salmon River near its outlet to the Cobequid Bay. The Town and its adjacent communities are protected by a large network of dykes that were originally built by the Acadians in the 1600’s and are currently maintained by the Nova Scotia Department of Agriculture Land Protection Section. High water levels in the Salmon River frequently overtop the dykes and cause widespread flooding of roads, residences, schools, senior homes, offices, commercial areas, industrial facilities and agricultural land. These high water levels are a result of the complex interaction between large river flows, the highest tides in the world, mudflat sedimentation and ice jamming. A comprehensive flood risk study of the Salmon River was undertaken to quantify the flooding that results from the frequent dyke overtopping and to evaluate the impact and viability of potential flood mitigation solutions. This paper describes the details of the extensive hydrodynamic modelling that was carried out on the Salmon River using the latest in 1D, 2D and 3D modelling software. An integrated 1D-2D PCSWMM model was used to simulate the dynamic interaction between river and tidal flows, dyke breaching and urban floodplain hydraulics, a MIKE3 model was used to simulate the tidal damping between the Bay of Fundy and the Town, and a HEC-RAS model was used to simulate ice jamming. Together these models were used to quantify the flood extents of the Salmon River and evaluate the impacts of over 40 potential flood mitigation solutions.