Inverted Siphon (Depressed Sewer) Design Calculation
LMNO Engineering, Research, and Software, Ltd.
Inverted siphons (also called depressed sewers) allow stormwater or wastewater sewers to pass under obstructions such as rivers. Our calculation allows up to five parallel siphons to go under the river. Unlike the main sewer pipe, the siphon pipes flow under pressure and must have flow velocities greater than 3 ft/s (0.9 m/s) to keep material suspended; therefore, several siphons having smaller diameters than the main sewer may be required. Our calculation computes the siphon diameters, velocities, and inlet chamber wall heights and siphon invert elevations.