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1. V-notch Sharp-crested weir

2. • This type is used for small discharges.

3. • The weir has a V-notch as a control
section.
• The angle Θ can take any value, the most
common value is 90o.
• To design or evaluate the discharge, the
following equation is used,
5
.
2
1
2
tan
2
15
8
h
g
C
Q e



4. • The discharge coefficient is obtained from
the following graph,

5. • To design the weir, a similar procedure to
the one explained in the previous weir is
used.
• However in this case, the value of h1 is
assumed and then obtained from the
equation until convergence is obtained.
• Also, if the characteristics of the weir are
known, the discharge can be evaluated
from the equation.

6. • Example:
Design a V-notch sharp crested weir
according to the following data;
Q= 0.25 m3/sec, B=1 m, d= 0.8 m
• Sol.
Assume p1 = 0.4 m … h1=0.4 m
h1/p1 = 1 …. b1/B = 0.4
From graph Ce= 0.598
Apply the equation ….. h1= 0.5 m

7. p1= 0.8 – 0.5 = 0.3 m
h1/p1 = 1.67 …. b1/B = 0.3
From graph Ce= 0.614
Apply the equation ….. h1= 0.495 m
close …. P1 = 0.3 m