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Craig,
A wall which is provided at the crest weir in an effective manner for increasing the Spillway discharge capacity of the dam.
It is considered as one of the renovation projects.
The essentiality of such type of project is very high because of an increase in expected flood inflow to the reservoir of an existing dam.
Trapezoidal weir is also called Cipolletti weir, used for measuring medium discharge & is a combination of ▭ular & △ular weirs. The slope of the sides, inclined outwardly from the crest, should be 1 horizontal : 4 vertical (1H : 4V). The selected length of the notch (L) should be at least 3H & preferably 4H or longer.
Q = ⅔ Cd L √2g H3/2 + 8/15 Cd tan θ/2 √2g H5/2
If Q is lps, H in cm & L in cm.
Q = 0.0186L H3/2
