7. V-Notch Weirs of Any Angle

The Kindsvater-Shen relationship can be used for fully contracted notches of any angle between 25 degrees and 100 degrees (Kulin and Compton, 1975). The equation which includes the angle theta as a variable is written as:

equation  (7-3)


The head correction factor, kh, is a function of theta (figure 7-6a). However, for fully contracted traditional 90-degree V-notch weirs, equation 7-6 and the rating table discussed later produce comparable accuracy.

Figure 7-6a -- Head correction factor, kh, for V-notches of any angle (courtesy of National Bureau of Standards, Kulin et al. [1975])..

Figure 7-6b -- Effective coefficient, Ce, for fully contracted V-notches of any angle (courtesy of National Bureau of Standards, Kulin et al. [1975])..

For fully contracted V-notch weirs, the value of kh is related to theta as given on figure 7-6a, and values of Ce are read from figure 7-6b. Partially contracted 90-degree V-notches only can be rated using figure 7-7 to obtain Ce values. The calibration relationships were developed with rectangular approach flow and head measurement sections for these weirs. For applications with other flow section shapes, the average width of the flow section for each h1 is used as B to determine coefficients.

Figure 7-7 -- Effective coefficient, Ce, for partially contracted 90-degree V-notches (courtesy of National Bureau of Standards, Kulin et al. [1975])..

Bos (1989) and International Organization for Standardization (1983) explain and define limits basic to the use of these figures. Precautions and restrictions concerning the use of V-notch weirs are as follows: