Broad CrestedWeir Profile for Level Spreader

[ctbailey]

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

http://www.bailey-associates.com

 

[psmart]

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

http://www.hydrocad.net

 

[psmart]

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

http://www.hydrocad.net

 

[ctbailey]

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.

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Craig T. Bailey, PE, LLS

http://www.bailey-associates.com