These weirs have greater control under low flow conditions. This weir is either a sharp or broad crested vee shaped weir. The angle of the vee can vary from greater than zero degrees to 180 degrees. It cannot be zero or 180 degrees.
The following are design limits (Casey) for practical applications of sharp crested V-Notch weirs:
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H/p1 <= 1.2
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H/B <= 0.4 and B >= 0.6m
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0.60 >= H >= 0.05 m
-
p1 >= 0.10 m
-
100 deg >= theta >= 25 deg
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Tail water level >= 0.05 m below the vertex of the V-Notch.
|
V-Notch sharp crested weir coefficients |
|
Notch angle (degrees) |
20 |
40 |
60 |
80 |
100 |
|
Ce |
0.595 |
0.581 |
0.577 |
0.577 |
0.580 |
|
Kh(mm) |
2.8 |
1.8 |
1.2 |
0.85 |
0.80 |
Figure 11: Triangular or Vee Weir
Kindsvater and Carter (1957) proposed that the discharge coefficient is a function of the notch angle and effective head (he) on the weir. The effective head is the head on the weir corrected by a correction factor kh such that he = h1 + Kh
This program uses the simplified formula:
Where
-
c is the orifice coefficient
-
q is the weir angle
-
H is the stage above the crest elevation (ft
Values of c are computed at runtime based on the following graph:
Figure 12: Vee Weir Coefficients