Question

The head of water over a rectangular weir is 28 cm. The length of the crest of the weir end contraction suppressed is 1.27 m. Find the discharge using the Francis formula.

(a) 0.346 m^3/s

(b) 0.556 m^3/s

(c) 0.788 m^3/s

(d) 0.225 m^3/s

The question was posed to me in a national level competition.

This is a very interesting question from Time Required to Empty a Reservoir with  Weirs or Notches topic in division Orifices, Mouthpieces, Notches and Weirs of Fluid Mechanics

Answer 1

The correct option is (a) 0.346 m^3/s

Explanation: Q = m * L * (2*g)^0.5 * H^1.5

                     m = ⅔ * Cd

                         = 0.405 + 0.003/H

                         = 0.405 + 0.003/0.28

                     Q = 0.346 m^3/s.