Modeling an Inverted Siphon

Applies To 
Product(s): SewerGEMS, CivilStorm, StormCAD, SewerCAD
Version(s): V8i, CONNECT Edition
Area:  Modeling
Original Author: Scott Kampa, Bentley Technical Support Group


How to you model an inverted siphon? (sometimes known as an inverse siphon)

Problem ID#: 82436


An inverted siphon consists of two or more gravity pipes (depending on changes of slope) that will be surcharged. To model this create conduits sloping downward and upward connected at a central junction, such as a junction chamber, bolted manhole or a transition. The central nodes/structures on the siphon (which may not be exist in the actual system) are used to model the change in slope. They need to be bolted or extend above the ground so the hydraulic grade line can be above the top of the pipe (surcharge condition) If you do not have a vertical structure extending above the HGL then it is best to use a bolted manhole ("Bolted Cover" = "True") or a transition node element. 

The calculation engines are robust enough to handle adverse slopes. You can apply any bend losses to the central node as a standard headloss. If you feel that friction losses are the predominant loss you can assume no headloss at the central junction. 

If the siphon has multiple barrels in parallel, such that one takes the low flow and others come on line as flow increases, then it may be necessary to create a different physical alternative for each possible number of pipes and replace the siphon by the equivalent pipe size in each alternative.

Example Model

Note: the above model is for example purposes only. It can be opened in version and above.