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Broad CrestedWeir Profile for Level Spreader

Broad CrestedWeir Profile for Level Spreader

Broad CrestedWeir Profile for Level Spreader

Hi everyone,

In HydroCAD, I'd like to model my typical level spreader as a pond with insignificant storage.
My preferred level spreader design incorporates a level "lip" that is usually 10 to 20 feet long, with a height of 1 foot.
My preferred profile is 1:1 on the upstream side, and 4:1 on the downstream side.

The closest Broad Crested profile Id is "#29," which is defined as a 1:1 on the upstream, and 3:1 on the downstream.

real question is: from what text did those Profile ID's come from, since I would like to compute my own Head coefficients to use my 1:1 flowing to 1 4:1 profile.

Thanks very much

Craig Bailey
Hudson, NH

Craig T. Bailey, PE

RE: Broad CrestedWeir Profile for Level Spreader

As stated in Appendix D2 of they HydroCAD Owner's Manual, the profiles and coefficients are from PRACTICAL HYDRAULICS 1982 by Andrew L Simon.

HOWEVER, with a zero-storage pond your're always going to get Qout=Qin, so the details of the weir calculations are generally of little concern. The only thing you're going to learn from the zero-storage routing is the amount of head that will develop over the weir. And a sharp-crested weir (with a constant coefficient) should be entirely adequate for that purpose.

The Broad-Crested option is only needed for pond routings that are highly sensitive to the stage-discharge relationship, and even then I've never seen a need for custom coefficients. For details please see http://www.hydrocad.net/weir1.htm

Peter Smart
HydroCAD Software

RE: Broad CrestedWeir Profile for Level Spreader

I should add: The coefficients in Appendix D are obtained from actual field studies. I'm not aware of any procedure for calculating these coefficients.

Peter Smart
HydroCAD Software

RE: Broad CrestedWeir Profile for Level Spreader

Thank you Peter.

I understand fully. The head that may model was developing over the level lip was precisely why I asked... was not sure if the broad crested weir coefficients would make any difference.

I'll be modeling my Level Spreaders as sharp crests from now on.

Thank you very much.


Craig T. Bailey, PE, LLS

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