BOTTOM OUTLET FOR SEWERS

The bottom opening is a standard structure in storm sewers, provided t he approach Bow is supercritical. Based on extended experimentation an d by using the governing flow equations, the hydraulic characteristics of bottom openings were derived. These include the approach reach, th e end depth ratio, the average discharge coefficient, the tailwater de pth, and the hydraulic loss across the outlet. Further, velocity distr ibutions in the outlet zone are discussed. The results of this study r eveal that the approach Froude number has a significant effect on the flow mechanism. General expressions are derived for the lower and uppe r nappes of the flow across the bottom opening, and a hydraulic design procedure is described. A generalized streamwise coordinate is also i ntroduced that allows description of supercritical sewer flow. It is d emonstrated that the excess discharge to the treatment station under d esign discharge is within the requirements of European standards.