Working with Combined Sewers: Geometric and Hydraulic Elements of Egg-Shaped Sewers

Wastewater professionals working with combined sewers often encounter a variety of non-circular sewer cross sections, including egg-shaped sewers. Equations are developed here to calculate the wetted area, wetted perimeter, and surface width for egg-shaped sewers flowing partially full and support a variety of hydraulic calculations. These equations supplant traditional graphical approaches using geometric and hydraulic element curves in favor of equations better suited to Smart Sewer applications. The equations are validated and provided a concise reference for those working with egg-shaped sewers in combined sewer systems.