Hydraulic Design for Combined Sewer Diversion

The City of Richmond is building two diversion structures that will join two existing sewers to a retention basin where combined sewage and storm runoff will be stored for later treatment. This scheme will minimize the discharge of combined sewage to the James River. Levels in the sewers and diversion structures vary with flow, river level, and interaction between the connected diversion structures. In order to accurately predict and minimize levels in the sewers upstream of the diversion structures, a 1:18 hydraulic model was tested. The model showed that levels could be reduced in both the flow to the river mode and diversion mode by streamlining various elements of the diversion structures. A flow distribution device reduced unacceptably high velocities at the trash screens.