I'm curious if anyone knows how to properly size siphon piping and if they could share that info. I'll share the methodology I've been using but the results I'm getting just don't seem right.

Based on topo maps I'm looking at just under 12 acres of watershed. I rounded up to 12.

Based on historical data the max rainfall we've gotten in my town in a single day was about 9.5". I rounded up to 10".

I calculated that if we had another 10" day and 100% of that reached my pond at a steady rate throughout the day I'd be looking at 2,263 gal/min. I used this calculator and also made a model in solidworks to use for dimensions.

What I'm seeing is that a 6" pipe should be able to handle this volumetric flow rate no problem. Again that's with no absorption of rainfall into the ground in the watershed and we live in a fairly sandy area.

What confuses/concerns me is the velocity of the water at discharge. I've been seeing that you want something below 10ft/s whereas I'm seeing more than 30 with this calculator. That makes me question the rest of my math. Certainly velocities that high would be downright dangerous and I'm not sure the piping would even stay together.

Please see the attached spreadsheet for more details. I just want to make sure I'm not overlooking anything and not making any dangerous assumptions. I'm working with a pretty good pond guy but I want to do my own research to make sure what he recommends makes sense.

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