GATE 2021 CE (CE1) – Question 58
An unlined regime canal has silt factor 1 and flow width 71.25 m. Treating it as a wide channel, find average depth in m to two decimals.
Practise this question in The GATE Grind →
Show answer and explanation
Correct answer: 2.80 to 2.95
Explanation
For Lacey regime flow, wetted perimeter $P=4.75\sqrt Q$. With a wide channel P≈B=71.25 m, Q=225 m³/s. The regime hydraulic radius is $R=0.47(Q/f)^{1/3}=0.47(225)^{1/3}=2.85863$ m. Since a wide channel has R≈depth, the answer is **2.86 m**.