Hydraulic Design of Self-Cleaning Sewage Tunnels

A description of the different factors affecting the hydraulic design of self-cleaning sewage tunnels with a free water surface is presented. It is found that the two most important problems involved are related to shear stress distribution and critical shear stress to secure self-cleaning. Based on a shear stress distribution normally assumed for open channels, a trapezoidal bottom shape is suggested. A value for critical shear stress to prevent settlement of sand in a mixture of wastewater is recommended, but design data are also included for alternative values of critical shear stress. Curves for determining shape, slope, and size of tunnels with known minimum and maximum rate of flow are given.