Inverted Stormwater Drainage Siphon

[jdpowell]

I'm in the process of recommending an inverted siphon to cross under a row of pipelines. My pipe(s) length will be approximately 350' and the elevation difference between the inlet and outlet could be as much as 2.65 feet. I'm using an HDPE pipe with a mannings n of around 0.010. I need to convey about 83 cfs from on side of the pipeline row to the other.

What would be an ideal velocity for this type of siphon? I've been told that 6fps is a good number to use, but I'd like a 'second opinion' (or more).

Thanks

 

[cvg]

really no different than typical drain design. between about 2 fps to 8 fps. Not too low, or sediment may not be conveyed through the system. Not to high, or energy grade line gets too high and energy loss in the manholes becomes too high.

 

[glennd]

You may want to ensure there is some slop in the inverted syphon so that any rubbish that enters the pipe ends up at one end or the other for maintenance.

You may want to lower the invert of the pit at the inlet to the syphon so that there is room for settling material to collect in one point for removal. This will also reduce the risk of potential blocks in the pipe.