V-notch Sharp-crested weir

V-notch Sharp-crested weir This type is used for small discharges. The weir has a V-notch as a control section.

The angle can take any value, the most common value is 90o. To design or evaluate the discharge, the following equation is used, 8 2.5 Q C e 2 g tan h1 15

2 The discharge coefficient is obtained from the following graph, 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.

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 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