Short Sewer Sideweir

Abstract

Sideweirs for combined sewers in converging U-shaped channels are analyzed. The results are applicable for storm sewers. Based on extended model observations and a hydraulic approach, the characteristics of sideweir flow are determined. These include the surface profile, the discharge distribution, the end depth ratio, and the energy losses due to lateral outflow. All results are presented in terms of approach conditions, and it is demonstrated that the approach Froude number is the significant flow parameter. For sideweirs with a relatively small weir height, the flow may become unstable and set up a surging phenomenon in the approach pipe. After careful experimentation, the instability was effectively removed with a so-called end plate. This device is positioned at the end wall of the sideweir and is able to stabilize the vorticity interface between the bottom and the surface vortices. The end plate can simply be added to existing designs.