Open Channel Flow and headloss in bends

[mae1133]

I'm designing a system for a treatment plant consisting of a number of open rectangular channels and partial full circular pipes. I am using software to determine the hydraulic grade line, but when it comes to changes in direction in the channels, I can't seem to find any information on how to calculate the losses in bends for open channels. There are many software programs for straight runs, but in the real world, there are lots of bends. Does anyone know of software or the methodology to calculate this?

 

[FrankHW]

Well usually in treatment plants the flow velocities in the open channels are slow enough and the total length of the open channels are short enough the headloss accumulated in theses channels can be safely ignored, considering you will be conservative everywhere else. If you have a baffled basin like a chlorine contact basin where the flow makes 180 turns many times, you can use the minor loss equation H = KV^2/2g where K is in the 2 to 3.5 range according to Design Municipal Wastewater Treatment Plant by WEF. If you need to deal with step up, step down, contraction, hydraulic jump etc., you can use the energy equation assuming the energy will be conserved.

 

[cvg]

bend losses are discussed in the LA County Hydraulics Manual. See conduits not flowing full. Superelevation is also discussed.

https://dpw.lacounty.gov/wrd/publication/engineering/design_manual.pdf