Question

The height of water on upstream and downstream side of a submerged weir of 4 m length are 24 cm and 13 cm. If Cd for free and drowned portions are .62 and .78 respectively, find the discharge over the weir.

(a) .85 m^3/s

(b) 1.35 m^3/s

(c) 3.2 m^3/s

(d) .55 m^3/s

This question was posed to me in an interview for internship.

My doubt stems from Discharge Over different type of weirs topic in chapter Orifices, Mouthpieces, Notches and Weirs of Fluid Mechanics

Answer 1

Right option is (a) .85 m^3/s

Explanation: Q = 0.67 * Cd1 * L * √2g * H^1.5 +.  Cd2 * L * h * √2g(H – h)

                        = .67 * .6 * 3 * √2g * (.24 – .13)^1.5  + .8 * 3 * .13 √2g(.24 – .13)

                        = .85 m^3/s.