T Notches Weirs + Coefficients
T Notches Weirs + Coefficients
(OP)
I am designing a pond outlet control structures (OCS) in georgia. I am getting confused on what coefficient to use when modeling (we use pond pack) a T notch weir. Specifically, the 'notch' part to the "T" (said another way, the 'stem' to the letter T). The weir will be submerged at the higher end storms 50 yr, 100 yr. I think i should use something like a 0.6 coefficient. (this happens to be what we use for circular orifice flows)Then for my emergency spillway, a traditional longer length weir (located at the top of the T Notch, I would use something like 3.1.





RE: T Notches Weirs + Coefficients
Example: the 'stem' is 1' wide and 2'below the main part of the 'T', the top is 5' wide. You could do two weirs, 1' and 4', with different elevations. Or you can do a 5' weir at the 'T' elevation, and a 1'x2' orifice at the lower elevation.
RE: T Notches Weirs + Coefficients
RE: T Notches Weirs + Coefficients
As for my Main Part to the "T", I am using a Weir with (your example, 5' length)set at the invert elevation of the Main Part (or top horizontal segment to the "T").
RE: T Notches Weirs + Coefficients
But from what you're describing, it sounds like you're on the right path. If you're using orifice flow, 0.6 is probably the correct coefficient to use, and 3.1 for the weir computation. The length and elevation would be as you say.
I've done comparisons of both ways (dual weirs vs. orifice and weir) and they really come out with almost exactly the same results. So your model should work either way.
Make sure your software knows the shape of your orifice. A 1'wide by 2' high orifice will have different flow characteristics than a 2'wide by 1'high one.