The program online_cipolletti calculates the discharge through a Cipolletti weir. A standard Cipolletti weir is trapezoidal in shape (Fig. 1). The crest and sides of the weir plate are placed far enough from the bottom and sides of the approach channel to produce full contraction. The sides incline outwardly at a slope of 1 horizontal to 4 vertical. The computation procedure follows Section 12 of Chapter 7 of the USBR Water Measurement Manual.

Fig. 1  Definition sketch for a Cipolletti weir.

The formula for the Cipolletti weir, in U.S. Customary units, is:

Q = 3.367 L H3/2

[1]

in which L = length of the weir crest, in ft, and H = head on the weir crest, in ft.

The accuracy of measurements obtained by Eq. 1 is considerably less than that obtainable with V-notch weirs. The accuracy of the discharge coefficient is ± 5 percent.

The Cipolletti weir is subject to the following restrictions:

1. The head H ≥ 0.2 ft (6.1 cm).

2. The ratio P/H ≥ 2.

3. The ratio b/H ≥ 2.

The head H is measured at a distance of at least 4H upstream from the crest.