The programs ≤ 0.4.H/BFig. 1 V-notch weir schematic.
The program Fully contracted vs partially contracted weir flow
Contraction refers to the size of the weir flow area as compared to the size of the
approach channel flow area. Depending on size and design,
a weir may be subject to
For V-notch weirs, full contraction is produced
when the distance . For a 90° V-notch weir,
the flow width at head level is equal to 2H. Therefore, the weir may be considered to be
fully contracted when the ratio 2H > 6, i.e., when B/H < 0.167.H/B < 0.194.H/B ≤ 0.2.H/B
A weir not satisfying the above criterion is partially contracted, i.e., the approach channel width .
In USBR practice, the practical criterion for a partially contracted V-notch weir is: H ≤ 0.4.H/BOnline V-notch calculator --- fully contracted
The fully contracted V-notch weir formula, due to Kindsvater and Shen (USBR Water Manual), is:
In Eq. 1, the discharge and angle Hθ.
The discharge coefficient C is a function of _{e}θ.
The head correction coefficient k is a funtion of θ.
The width of the approach channel is used to check to see if the weir is fully
contracted: B ≤ 0.2. Otherwise, the partially contracted weir calculator
is recommended.
H/B
The formula (polinomial fit) for θ in degrees, is:
θθ^{2}
The formula (polinomial fit) for
The formula for the fully contracted V-notch weir is restricted to the following conditions: - Head
< 1.25 ft (38 cm).*H* - Width
> 3 ft (91 cm).*B* - Height
> 1.5 ft (46 cm).*P* - Ratio
≥ 2.0.*b/H* - Head/width ratio
≤ 0.2.*H/B*
Online 90° V-notch calculator --- partially contracted
For the partially contracted 90° V-notch weir, the Kindsvater and Shen formula (Eq. 1) reduces to the following, in U.S. Customary units ( in ft):
H
The discharge coefficient and
H/P, as shown in Fig. 2.
P/B
C as a function of _{e} and H/P.
P/B
In The formula for the partially contracted 90° V-notch weir is subject to the following restrictions: - Head
< 2 ft (61 cm).*H* - Width
> 2 ft (61 cm).*B* - Height
> 0.33 ft (10 cm).*P* - Head/width ratio
≤ 0.4.*H/B*
Fig. 1 V-notch weir schematic. |

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