20. Inverted Siphon

This flow monitor is installed in a sewer just upstream from an inverted siphon comprised of two 8-inch barrels.  The incoming sewer has a design capacity of 2.7 MGD.  The scattergraph shown here indicates that the first barrel has a capacity of 1.3 MGD.  Additional flow is conveyed to the second barrel by a side weir located in the inlet structure.  The pipe handles additional flow up to the design capacity of the incoming sewer.  At the observed capacities of 1.3 MGD and 1.4 MGD, the two pipes within the inverted siphon have a flow velocity of 5.76 and 6.20 ft/s, respectively – well within generally accepted guidelines for self-cleansing velocities.