V-notch Sharp-crested weir

This type is used for small discharges. This type is used for small discharges.

The weir has a V-notch as a control section. The weir has a V-notch as a control section. The angle Θ can take any value, the most common value is 90 o. The angle Θ can take any value, the most common value is 90 o. To design or evaluate the discharge, the following equation is used, To design or evaluate the discharge, the following equation is used,

The discharge coefficient is obtained from the following graph, 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. To design the weir, a similar procedure to the one explained in the previous weir is used. However in this case, the value of h 1 is assumed and then obtained from the equation until convergence is obtained. However in this case, the value of h 1 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. Also, if the characteristics of the weir are known, the discharge can be evaluated from the equation.

Example: Example: Design a V-notch sharp crested weir according to the following data; Q= 0.25 m 3 /sec, B=1 m, d= 0.8 m Sol. Sol. Assume p 1 = 0.4 m … h 1 =0.4 m h 1 /p1 = 1 …. b 1 /B = 0.4 From graph C e = Apply the equation ….. h 1 = 0.5 m

p1= 0.8 – 0.5 = 0.3 m h 1 /p1 = 1.67 …. b 1 /B = 0.3 h 1 /p1 = 1.67 …. b 1 /B = 0.3 From graph C e = Apply the equation ….. h 1 = m close …. P 1 = 0.3 m