Inverted Siphon For Storm Pipe

[Dredger01]

I've got a project where the outflow storm line (24") is draining a 2 acre commercial site. The contractors uncovered an existing water main that is conflict with the storm drain.

The City will not allow this waterline to be adjusted around the storm pipe. Unfortunately there is not another viable option for the site storm connection.

My thought is to install an inverted siphon under the water main. Basically have the 24-inch pipe duck under the existing waterline, then connect into the City curb inlet(discharge point).

Has anyone designed one of these before. I plan on installing an access MH just upstream of the waterline crossing. I'm not sure what hydraulic losses I might consider for such a system. The HGL of the site system should create enough pressure get through the siphon and into the point of connection.

I thought it might also be practical to install a second bypass line over the waterline for good measure.

Understandably that when the storm surge is over, there will be some residual water left in the pipe, like a grease trap in a house. In this part of the country, the soils are mostly clay, so infiltration of residual water might not work to well. In other words, we might have to live with that portion of the siphon holding some water.

Any thoughts or ideas? Much appreciated.

 

[cvg]

try a conflict structure

there are numerous examples online such as these:

http://www.cityofchesapeake.net/Ass...+Detail+Showing+Utilities+Passing+Through.pdf

http://hrregconstds.org/RCS_5thEdition/Standard Details/DS_02_1.pdf

http://www.pcbgov.com/home/showdocument?id=1278

 

[beej67]

I've done what you describe before Dredger. It's especially common in Florida where everything is flat anyway. But CVG is right, your first option should be to go with a conflict structure, and it sounds like your situation is perfect for one.

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[cvg]

inverted siphons are a maintenance nightmare for storm drains. almost guaranteed, they will fill up with sediment at the worst possible time. most agencies will not allow them. if you do it, make sure the velocity through a siphon is high enough to move the sand and gravel through. a conflict manhole may collect some debris, but unlikely to fill with sediment.

 

[77JQX]

In our jurisdiction, a conflict structure would not be allowed for a storm drain crossing a potable water main.