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Outlet pipe from detention basin will have tailwater....what to do?

Outlet pipe from detention basin will have tailwater....what to do?

(OP)
Hello everyone,
The detention basin has an outlet structure of a 3' x 3' box, with a V-notch weir on the entrance side and a 12" RCP stubbed into the opposite wall. I work with HEC-HMS. The pipe has a very flat slope (0.26%); it has tailwater. How would I figure the discharge going through the V-notch weir and over the top of the box - all before flowing into the pipe? Will HMS work? Or would you rather I use some other software or do hand calculations?

Thank you,
Bills Sis

RE: Outlet pipe from detention basin will have tailwater....what to do?

go for pond pack or Bentley sewergems, I thick HMS will not provide result with tialwater conditions

RE: Outlet pipe from detention basin will have tailwater....what to do?

HMS does handle tail-water - for pipes and channels

for a spillway or weir, it might be easiest to input an elevation-discharge curve
if you have tail-water on your v-notch, suggest that this is not the best design. v-notch's should be designed without tail-water. Unlikely that you will be able to predict the discharge coefficient for a v-notch weir with submerged nappe.

RE: Outlet pipe from detention basin will have tailwater....what to do?

(OP)
Thank you everyone, for your response. Tailwater will only occur if there is higher flows; fortunately, discharges will not get that high, so the pipe is operating with much less tailwater. I'm going to charge forward using the v-notch weir, now that I won't have to worry about tailwater.

Thanks again!

RE: Outlet pipe from detention basin will have tailwater....what to do?

There is an approach to evaluating submerged weirs, just google it. Many options come up. You would have to analyze it external of HMS and code a rating curve as cvg stated. You may want to evaluate your options to see if there is a better design.

Found this one: http://www.fs.fed.us/biology/nsaec/fishxing/fplibr...

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