Storm Sewer Inverted Siphon 2

[jgailla]

We are working on a project in north Florida where an existing 18" storm pipe has to be diverted about 10' to go underneath a proposed pedestrian tunnel.
The standard approach of using a two or more smaller pipes to carry flow does not seem to apply, as there will be many days or weeks during the year when there will be no flow.
Therefore suspended solids will drop out of the stagnant stormwater in the siphon during periods of no rain.
Our present approach is to provide one 18" storm pipe, drop at 45 degrees to another manhole to help mitigate erosion caused by a 10 foot straight drop, run the pipe at 2 percent to get solids moving even under very low flow events, and provide a 1 foot deep sump on the downstream end to catch solids.
We would specify the sump to be pumped out each year in October and March, just before and just after the rainy season.
Does anyone have any alternate ideas?
Are there problems with this approach?

 

[bimr]

Have you thought about going horizontally around instead of under? Go several blocks over and then turn 90 degrees if you have to keep moving in the same direction. Change the direction of the stormwater flow.

 

[dicksewerrat]

first of all, the sump won't be pumped. Maybe flushed but i wouldn't count on it. Change the grade of the Ped Tunnel would be the easiest.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[jgailla]

Thanks for the responses. Unfortunately, we cannot move the tunnel and we don't have any way to divert the pipes around. This is an urbanized area and we're stuck with the inverted siphon approach.

dicksewerrat, do you mean maintenance won't bother to pump the sump or that it shouldn't be pumped?

 

[dicksewerrat]

Maintenance won't pump it out unless they are specifically told when and how to do it. And set the schedule and observe. You will need a jet-vac truck to clean this out at a minumum. And it needs to be done after every rain event, no matter how small.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com