Question

What is Lacey’s equation for fixing the approximate value of the required waterway for the drain?

(a) P = 4.75 Q

(b) P = 4.57 Q

(c) P = 4.75 Q^1/2

(d) P = 4.57 Q^1/2

I have been asked this question at a job interview.

My question is taken from Cross Drainage Work Design in division Cross Drainage Work of Irrigation Engineering

Answer 1

The correct answer is (c) P = 4.75 Q^1/2

For explanation: The correct equation for fixing the waterway requirement for Aqueduct and Syphon-Aqueducts is given by P = 4.75 Q^1/2 where P is the wetted perimeter in meters and Q is the total discharge in cumecs. The wetted perimeter may be taken equal to the width of the drain and equal to the waterway required in case of wide drains.