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I'm trying to write a technical report and one part involves calculating the rate of flow of water through a straight horizontal weir. Searching on the web has led me to the Francis formula, which seems to be pretty straightforward. The problem I have is that my specific application has a much lower head (height of water) then used in any of the sample problems and on the net with the Francis formula. In addition, the Francis formula seems to apply to water flowing over a weir, in almost waterfall like fashion. For my purposes, the water will cascade down a surface... I don't know if this will affect the flow rate, or if I can use the formula in my situation.

So basically, I want to know if there is a threshold that is "safe", in which I would be okay using the formula (getting reasonable values). I would really appreciate all the information I could get on the Francis formula (and any other ones that apply).

Thanks,

Preet

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# Fluid Dynamics and the Francis Formula

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