As a part of City of Edmonton's commitment to reduce the environmental impact of combined sewer overflows (CSO) on the North Saskatchewan River (NSR), modifications of the CSO chambers to decrease discharge of overflows to NSR have been proposed. The Highland CSO chamber, one of the CSO chambers in City of Edmonton, has a sharp bend inlet section and two inverted siphons diverting the flow to the downstream wastewater treatment plant. A side overflow weir in the chamber spills flow during the wet weather to the CSO chamber which discharges directly to NSR. Using a three-dimensional (3D) finite-volume model with a renormalized group (RNG) k-e model and the volume of fluid (VOF) model for water surface representation, five options of chamber modification are investigated including: (1) existing chamber geometry for model calibration, (2) increase of CSO weir height; (3) removal of the dividing wall in the middle of the Chamber; (4) removal of the inner wall of the inlet bend and realigning it with the Chamber; and (5) removal of the hanging walls at the outlet of the chamber. The predicted flow characteristics in the CSO chamber are highly three-dimensional due to the existence of the inlet sharp bend and hydraulic jumps in the siphons. The simulation results show that the increase of CSO weir height will reduce the overflow volumes. Removing the dividing wall and relocating the inner wall of the inlet pipe will induce a large flow separation zone in the chamber, but the flow distribution and balance in two siphons will be improved.
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