Sewer conduits are hydraulically designed to operate primarily as open channels under gravity flow conditions, except when lifting stations force flow through pressurized mains. Unlike water supply pipes that operate full under pressure, sewers carry suspended organic and inorganic solids. Consequently, the minimum flow velocity must be sufficient to prevent solids deposition, grease buildup, and anaerobic septic conditions, while maximum velocity must be capped to prevent abrasive invert scour. Flow velocity and discharge through circular sewer sections are evaluated using Manning's Equation : $$v = \frac{1}{n} \cdot R^{2/3} \cdot S^{1/2}$$ $$Q = A \cdot v = \frac{1}{n} \cdot A \cdot R^{2/3} \cdot S^{1/2}$$ Where $v$ is flow velocity ($\text{m/s}$), $n$ is Manning’s roughness coefficient, $R$ is hydraulic radius ($\frac{A}{P}$, where $A$ is wetted cross-sectional area and $P$ is wetted perimeter), and $S$ is the slope of the hydraulic grade line. When a sewer runs partia...