Sewer Sideweir with Throttling Pipe

Abstract

Sewer sideweirs in a combined sewer system are used for diversion of excess discharge during rainfalls. Their hydraulic performance depends significantly on the approach Froude number, the relative weir height, and the overflow length. The throttling pipe is a simple device to limit the discharge to treatment facilities. An experimental work was conducted to establish the main flow features of the converging sewer sideweir. The effect of the throttling pipe was determined. It was concluded that Abwassertechnische Vereinigung of Germany or the European regulations for side overflows can only be satisfied if the weir height is larger than about 70% of the approach diameter. Also, the approach Froude number should be smaller than about 0.7. Using the energy equation, relations for the free surface profile were developed that agree with experimental observations. Further results include the spatial discharge and velocity distributions, the lateral outflow characteristics, the excess overflow, the end depth, and equations for the discharge in the throttling pipe. Previous results of Gisonni and Hager for the short sewer sideweir without throttling pipe are confirmed, and photographs illustrate the complex spatial flow patterns.