Online Rectangular Weir Calculator 131028 The program online_rectangular_weir calculates the discharge through a rectangular weir (Fig. 1). To produce full contraction, the crest and sides of the weir plate are placed sufficiently far enough from the bottom and sides of the approach channel. The computation procedure follows Section 6 of Chapter 7 of the USBR Water Measurement Manual. Fig. 1 Rectangular weir schematic.
The KindsvaterCarter formula for a rectangular weir, in U.S. Customary units, is:
in which C_{e} = effective coefficient of discharge; L = length of the weir crest, in ft, k_{b} = a correction factor to obtain effective weir length, in ft; H = head measured above the weir crest, in ft; and Q = discharge, in cfs. The value B is the average width of the approach channel.
The correction factor k_{b} is a function of the ratio
L/B, as shown in Fig. 2.
Fig. 2 Correction factor k_{b} to obtain effective weir length.
The effective coefficient of discharge C_{e} includes effects of relative depth and relative width
of the approach channel. It is a function of H/P
and L/B, as shown in Fig. 3.
Fig. 3 Values of C_{e} as a function of H/P and L/B. Given H, L, B and P, and the ratios H/P and L/B, the computation proceeds with the following steps:
The rectangular weir equation (Eq. 1) is subject to the following restrictions:

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