Question

A 2 m diameter sluiceway at RL 300 m is provided through a concrete overflow dam section to release water to the downstream where tail water level is not more than 275 m. The discharge through this outlet when the water level in the reservoir is at FRL of 330 m is of the order of_________________

(a) 20 cumecs

(b) 40 cumecs

(c) 50 cumecs

(d) 80 cumecs

The question was posed to me during a job interview.

This key question is from Dam Outlet in chapter Pressure Conduits, Outlet Works through Dams and Rivers of Irrigation Engineering

Answer 1

Right answer is (c) 50 cumecs

Explanation: The discharge passing through the dam outlet is given by using the equation-

Q = Cd. A. (2gHL)^1/2 where Cd is the coefficient of discharge = 0.62 for free over-fall, H = Water head over centre line of sluice = 330 – 300 = 30 m and A = π/4 x 4 = 3.14 m^2

Q = 0.62 x 3.14 x (2 x 9.81 x 30)^1/2 = 47.23 cumecs.