weirs

[docmartin]

Hello all;

My question for today is this:
I am putting a rectangular weir into a u drain to measure the amount of fluid flowing in the drain. The water flows very, very quickly without the weir, so is a velocity approach correction needed for the speed of the water once the weir is put in?
Thanks for your help

 

[ArtR]

Cameron Hydraulic Data, 18th Ed (1995), page 2-10 has a table on Discharge From Rectangular Weir with End Contractions.

If the length of the weir opening is 4 to 8 times the weir height, and the height measurement is made 6 ft back from the weir, you can just read the table.