Broadcrested Weir This is the simplest device for

Broad-crested Weir

• This is the simplest device for flow measurement. • It is more suitable for large discharges. • The width of the weir is taken as the width of the waterway. • The following equations is used:

• The discharge coefficient Cd equals 0. 89. • To design the weir, h 1 is the only unknown and can be calculated from the equation. • If the characteristics of the weir are known, the discharge can be evaluated from the equation.

• Example: Design a broad crested weir for a maximum discharge of 3 m 3/sec, where the channel width is 2. 5 m and the depth is 1. 4 m. • Sol. B = 2. 5 m Apply the equation get h 1 = 0. 86 m

Ogee type Weir

Ogee Type weir • Ogee type weir is used as spillway for dams. • The shape of the weir is selected such that the water flow is always in contact with the face of the weir. • The shape of the weir face follows this equation:

• Where x and y are the coordinates and h 1 is the head of water above the crest level. • The discharge can be evaluated using the following equation: Where Ce is the discharge coefficient (1. 3) and bc is the crest width.

• Example: Design an Ogee type weir to pass a discharge of 100 m 3/sec. The crest width is 30 m and the weir height is 10 m. • Sol. Apply the equation … get h 1 = 1. 3 m Calculate the coordinates of the weir’s shape

Y X 0 0 2 4 6 8 10 2. 3 3. 1 3. 8 4. 4 4. 8