Abstract: Besides frictional head losses in an urban drainage system, its minor head losses are significant under certain conditions and cannot be ignored in the design. Based on the model experiment of a sewer pipe system and its manhole, the minor loss coefficient of the manhole has been calculated for different working conditions, and an analysis of the calculated results is also presented. These results show that the flow ratio of the main pipe to branch pipe is a major factor that has a great effect on minor loss coefficients, and that with an increasing flow ratio, the increase in these coefficients can reach up to 1.2. The manhole shape and the angle between the main and branch pipes ranks second, two minor factors causing a minor loss coefficient change of less than 0.2 each. The downstream water depth and discharge of the outlet pipe has little impact on the coefficients; a comparative analysis of our experimental data with previous studies shows installing symmetric branch pipes reduces the minor losses. The results help an in-depth understanding of the variations in the manhole minor losses for optimizing urban drainage system design and improving practical urban flood management.

Key words: manhole, minor head losses, drainage system, urban waterlogging, physical model