• # Thread: Bottom Drain Flow-rates

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## Bottom Drain Flow-rates

I've been working on a pond design where there will be three bottom drains of lengths approximately 9, 7.5 and 6.5 meters between the bottom drain inlet and a head tank before an RDF. 4" nominal heavy PVC pipe. Flow-rates in the pipe can be calculated using Poiseuille's Equation or the Hazen-Williams Equation. I've put both equations in a spreadsheet. You can enter your own data in cells B2 to B6 and the corresponding flowrate will be calculated. Results show Poiseuilles Eqn a bit higher than Hazen-Williams, but pretty close. Also in xls is a calc of the 'average' between the two equations. Hope it's of some use!!

Dan
Last edited by danbo; 1 Week Ago at 12:37 AM.

2. This is awesome! I'm still in the draft phase but am looking forward to applying this towards my design and better understanding the flow through my bottom drain into thefilter system.

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Originally Posted by Sk1er
This is awesome! I'm still in the draft phase but am looking forward to applying this towards my design and better understanding the flow through my bottom drain into thefilter system.
Thanks for comment. I put this spreadsheet together fairly quickly and surprised myself at how reasonably close the Poiseuille and Hazen-Williams calcs agreed. (all the work was in getting the units correct!). The Poiseulle Eqn is for laminar flow. Not 100% sure, but think the H-W is for turbulent flow. Some more research needed. Next step is to build in a calculation of Reynolds Number into the spreadsheet and make a better judgement on the flow. Reynolds Number less than 2000 the flow should be laminar, over 4000 should be turbulent. In between is so called critical region. Maybe apply a fudge factor in averaging the flows if Reynolds No. is between 2000 and 4000. Obviously it is also easy enough to calculate the velocity in the pipe. Next: Find a guideline on pipe velocity to ensure all the sh!t is swept along the pipe. Cheers!
Last edited by danbo; 1 Week Ago at 11:29 PM.

4. In a 4" (110mm) pipe if you get the flow rate near 5,000gph....no worries about that pipe becoming a settlement chamber.

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