Question

What is the size of the tile at an outlet of a 12 hectare drainage system, if the D.C is 2 cm and the tile grade is 0.5%. Assume the rugosity coefficient as 0.015 for the tile drain material.

(a) 10 cm

(b) 20 cm

(c) 15 cm

(d) 25 cm

This question was addressed to me in a dream while sleeping

Query is from Water Logged Reclamation in section Water Logged Reclamation and Saline Soils for Agricultural Purposes of Irrigation Engineering

Answer 1

The correct choice is (b) 20 cm

Easiest explanation: Volume of water passing the drain in one day = (1/100 x 12 x 10^4) = 1200 m^3/day

Volume of water passing the drain in one second = (1200/24 x 3600) = 1/72 m^3/sec

Q = 1/72 m^3/sec

Q = 1/n x A x R^2/3 x S^1/2

A = πD^2/4, P = πD, R = A/P = D/4

1/72 = (1/0.015) x (πD^2/4) x (D/4) x (0.5/100)

On solving the value of D = 17.4 cm

Use D = 20 cm.