Overview
The Don River watershed in Toronto has undergone rapid urbanization over recent decades, shifting the watershed’s hydrologic cycle toward lower infiltration and higher runoff. Metals sourced from roads, landfills, industrial effluents, and wastewater treatment plants are a particularly damaging component of the system. This research developed a 1D numerical model of the lower Don River — extending 9.81 km from Taylor Creek South to the river mouth at Keating Channel — to advance understanding of sediment and metals transport.
Model Setup
Two commercially available modeling packages were linked. The urban watershed model PCSWMM, calibrated by the Toronto and Region Conservation Authority, was upgraded and extended to provide pollutant loads from subcatchments for May to August 2010. A representative 1D hydrodynamic, sediment transport, and metals transport model was then developed in EFDC Explorer, which can simulate instream processes — erosion, deposition, resuspension, and the diffusion and sorption of metals to sediments — that PCSWMM cannot. A MATLAB tool, the SWMM to EFDC Model Setup tool (STEMS), was developed to create grid and boundary condition files linking the two models.
Key Findings
The EFDC model better predicted measured suspended sediment and metals loads than the PCSWMM model alone. While the hydraulic results of the two models were similar and highly correlated, the sediment and metal results clearly differed — underscoring the importance of simulating instream physical processes rather than adopting simplifying assumptions. Baseflow levels suggested metals are deposited with sediments during low flow and resuspended during high flow events, and resulting sediment bed metal concentrations at the river mouth agreed with observed trends, verifying the model as a representative predictive tool.